composition and floral resources of bees and butterflies in kaya

Transcription

Composition and Floral Resources of Bees and Butterflies in
Kaya Muhaka Forest and Surrounding Farmlands, Kwale
County, Kenya
By
David Odhiambo Chiawo (B.Ed. Science)
Reg. No. I56/5001/2003
Department of Zoological Sciences
Thesis submitted in partial fulfilment of the requirements for the award of
the degree of Master of Science (Animal Ecology) in the School of Pure and
Applied Sciences of Kenyatta University
November 2011
ii
DECLARATION
Candidate
This is my original work and has not been presented for the award of a degree in any
University or any other award.
David Odhiambo Chiawo
Signature........................................Date.........................................
Supervisors
We confirm that the candidate carried out this work under our supervision.
Prof. Callistus K.P.O. Ogol
Department of Zoological Sciences
Kenyatta University
Signature........................................Date.........................................
Dr. Mary W. Gikungu
Centre for Bee Biology and Pollination Ecology
Zoology Department
National Museums of Kenya
Signature........................................Date.........................................
Dr. Esther N. Kioko
Zoology Department
National Museums of Kenya
Signature........................................Date..........................................
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DEDICATION
I dedicate this work to my wife Verrah and daughter Mitchelle.
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ACKNOWLEDGEMENTS
I acknowledge the National Museums of Kenya (NMK) and the National Council for Science
and Technology (NCST) for the financial support of this study. I am grateful to Dr. Mary W.
Gikungu, Centre for Bee Biology and Pollination Ecology, Zoology Department, NMK for
facilitating this support. I acknowledge her for supervision and guidance throughout the study
period. I owe much thanks to Prof. Callistus K.P.O. Ogol, Department of Zoological
Sciences, Kenyatta University for supervising this work and his leading role in facilitating the
academic requirements of this study at Kenyatta University. I also owe the success of this
work to Dr. Esther N. Kioko of Zoology Department, NMK for supervision and guidance
throughout the study period. I thank the supervisors for their timely responses and being
ready to discuss with me the work at frequent intervals. I thank NMK management for
hosting me at Centre for Bee Biology and Pollination (CBBP) during the study period. The
CBBP supported my work with taxonomic skills, field materials and equipment; it also
provided working space and resources that were useful for the bee identification. I do thank
Mr. Joseph Mugambi of Invertebrate Zoology laboratory, NMK for assisting me during the
identification of butterfly samples. I owe thanks to Jane Macharia of Bee centre, NMK for
organising my samples at the centre and making available the requirements during the study.
I acknowledge the support of Kaya elders and Kaya Muhaka community. They allowed me to
access the forest and farms freely. I acknowledge the support of Abdalla Omari a residence of
the local community for field assistance. I also thank Teachers Service Commission for
granting me study leave during the period and Kenyatta University for accepting the study. I
thank Dr. Itambo Malombe, Botany department for organising with the staff of herbarium,
NMK to assist me infloral resources identification. I also thank the CFCU staff at Ukunda for
logistical assistance. I acknowledge the support of my family during the period. Above all, I
thank God for the opportunity, strength, and protection throughout the study period.
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TABLE OF CONTENTS
DECLARATION......................................................................................................................ii
DEDICATION........................................................................................................................ iii
ACKNOWLEDGEMENTS ................................................................................................... iv
TABLE OF CONTENTS ........................................................................................................ v
LIST OF TABLES ............................................................................................................... viii
LIST OF FIGURES ................................................................................................................ ix
LIST OF PLATES .................................................................................................................. xi
LIST OF APPENDICES .......................................................................................................xii
ABBREVIATIONS AND ACRONYMS ............................................................................ xiii
ABSTRACT ........................................................................................................................... xiv
CHAPTER ONE ...................................................................................................................... 1
INTRODUCTION.................................................................................................................... 1
1.1 Background .......................................................................................................................... 1
1.2 Statement of the problem ..................................................................................................... 2
1.3 Research questions ............................................................................................................... 4
1.4 Null hypotheses .................................................................................................................... 4
1.5 Objectives ............................................................................................................................ 4
1.5.1 General objective .............................................................................................................. 4
1.5.2 Specific objectives ............................................................................................................ 4
1.6 Justification of the study ...................................................................................................... 5
CHAPTER TWO ..................................................................................................................... 6
LITERATURE REVIEW ....................................................................................................... 6
2.1 Vulnerability of bee population to habitat change ............................................................... 6
2.2 Bee response to land use and habitat disturbance ................................................................ 6
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2.3 Butterfly response to land use and habitat disturbance ........................................................ 7
2.4 Ecological and economic significance of insect pollinators ................................................ 7
2.5 Pollination crisis and conservation concern ......................................................................... 9
2.6 Conservation value of remnant indigenous Kaya forests .................................................. 10
2.7 Butterfly taxa and habitat preference ................................................................................. 11
2.8 Edge effects and tropical forest invertebrates .................................................................... 12
2.9 Linking butterflies and bees to plant resources.................................................................. 13
CHAPTER THREE ............................................................................................................... 15
MATERIALS AND METHODS .......................................................................................... 15
3.1 Study area........................................................................................................................... 15
3.1.1 Biodiversity of the coastal forests ................................................................................... 16
3.1.2 Farmlands ........................................................................................................................ 16
3.2 Study design ....................................................................................................................... 16
3.2.1 Establishment of transects and sampling points ............................................................. 17
3.2.2 Data collection ................................................................................................................ 21
3.3 Data management and analysis .......................................................................................... 21
CHAPTER FOUR .................................................................................................................. 23
RESULTS ............................................................................................................................... 23
4.1 Bee species richness and abundance .................................................................................. 23
4.1.1 Effect of increasing distance from forest core on bee species richness .......................... 27
4.1.2 Effect of increasing distance from forest core on bee abundance .................................. 27
4.2 Cluster analysis of bee composition based on Bray-Curtis ecological distance ................ 28
4.3 Butterfly species richness .................................................................................................. 29
4.3.1 Effect of increasing distance from forest core on butterfly species richness .................. 31
4.3.2 Butterfly abundance ........................................................................................................ 32
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4.3.3 Effect of increasing distance from forest core on butterfly abundance .......................... 33
4.4 Cluster analysis of butterfly composition based on Bray-Curtis ecological distance ........ 34
4.5 Effect of habitat type on the diversity of bees and butterflies ........................................... 35
4.5.1 Effect of increasing distance from forest core on bee diversity...................................... 37
4.6 Bee relative abundance in the study habitats ..................................................................... 38
4.7 Butterfly relative abundance in the study habitats ............................................................. 40
4.8 Associated floral resources to bees and butterflies ............................................................ 41
4.8.1 Important floral resources in Muhaka area ..................................................................... 45
4.9 Effect of floral resources richness on bee and butterfly species richness .......................... 47
CHAPTER FIVE ................................................................................................................... 48
DISCUSSION, CONCLUSIONS AND RECOMMENDATIONS .................................... 48
5.1 Effect of habitat type on bee abundance ............................................................................ 48
5.2 Effect of habitat type on butterfly abundance .................................................................... 50
5.3 Effect of habitat type on bee and butterfly diversity.......................................................... 51
5.4 Effect of increasing distance from forest core on bees and butterflies .............................. 54
5.5 Effect of habitat type on bee and butterfly relative abundance ......................................... 55
5.6 Effect of floral resources on bees and butterflies............................................................... 56
5.7 Conclusions ........................................................................................................................ 58
5.8 Recommendations .............................................................................................................. 58
REFERENCES ....................................................................................................................... 59
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LIST OF TABLES
Table 1: GPS coordinates of sampling points .......................................................................... 20
Table 2: Bee species composition ............................................................................................ 23
Table 3: Butterfly species composition.................................................................................... 30
Table 4: P values for pair wise comparison of butterfly means ............................................... 36
Table 5: Butterfly diversity at varying distance from forest core ............................................ 37
Table 6: Bee floral resources ................................................................................................... 41
Table 7: Butterfly floral resources ........................................................................................... 43
Table 8: Bee species caught on flight ...................................................................................... 44
Table 9: Butterfly species caught on flight .............................................................................. 44
Table 10: Floral richness and corresponding bee and butterfly species richness .................... 47
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LIST OF FIGURES
Figure 1: Satelite map showing the location of study area and land use. ................................ 15
Figure 2: Location of main transects ....................................................................................... 18
Figure 3: Schematic illustration of belt transects and sampling points ................................... 18
Figure 4: Satelite map showing study area and sampling points ............................................. 19
Figure 5: Bee species accumulation curve ............................................................................... 23
Figure 6: Relative abundance of three families of bees ........................................................... 25
Figure 7: Total bee abundance per habitat ............................................................................... 25
Figure 8: Abundance of bee families per habitat ..................................................................... 26
Figure 9: Proportion of bee families in each habitat ................................................................ 26
Figure 10: Effect of distance away from forest core on bee species richness ......................... 27
Figure 11: Effect of distance away from forest core on total bee abundance .......................... 28
Figure 12: Dendrogram of cluster analysis of bee species composition .................................. 29
Figure 13: Butterfly species accumulation curve..................................................................... 29
Figure 14: Effect of distance from forest core on butterfly species richness ........................... 31
Figure 15: Relative abundance of butterfly families in KMF and surrounding farmlands ...... 32
Figure 16: Overall butterfly abundance per habitat ................................................................. 32
Figure 17: Butterfly families abundance per habitat................................................................ 33
Figure 18: Effect of distance away from forest core on butterfly abundance .......................... 34
Figure 19: Dendrogram of cluster analysis of butterfly species composition ......................... 34
Figure 20: Rényi diversity profiles for separate habitats of bee data set ................................. 35
Figure 21: Rényi diversity profiles for separate habitats for butterfly data set ....................... 36
Figure 22: Effect of distance from forest core on bee diversity .............................................. 37
Figure 23: Effect of increasing distance from forest core on butterfly diversity ..................... 38
Figure 24: Rényi evenness profiles of bee data set .................................................................. 39
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Figure 25: Overall rank-abundance curve showing the most abundant bee species................ 39
Figure 26: Rényi evenness profiles of butterfly data set ......................................................... 40
Figure 27: Overall rank-abundance curve showing the most abundant butterfly species ....... 41
Figure 28: Effect of floral resources richness on bee species richness .................................... 47
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LIST OF PLATES
Plate 1: Forest canopy cover at forest core (center) of KMF ................................................... 19
Plate 2: A site at forest edge of KMF ...................................................................................... 19
Plate 3: A site in crop fields ..................................................................................................... 20
Plate 4: A site in fallow farmland ............................................................................................ 20
Plate 5: A site in open fallow farmland ................................................................................... 20
Plate 6: Xylocopa caffra L. foraging on Agathisanthemum bojeri K. ..................................... 46
Plate 7: Cajanus cajan L., a bee pollinated local crop............................................................. 46
Plate 8: Jubernardia magnistipulata H., a forest tree pollinated by bees mainly Xlocopa sp. 46
Plate 9: Graphium angolanus G. foraging on Sida cordifolia L. ............................................ 46
Plate 10: Macrogalea candida S. foraging on Urena lobata L. .............................................. 46
Plate 11: Vigna unguiculata L., a common crop in the area that requires bee pollination. .... 46
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LIST OF APPENDICES
Appendix I: Checklist of bee species in KMF and surrounding farmlands ............................. 65
Appendix II: Checklist of butterfly species in KMF and surrounding farmlands ................... 66
Appendix III: General list of floral resources in KMF and surrounding farmlands ................ 68
Appendix IV: Floral resources preference by bee species ....................................................... 69
Appendix V: Distance matrix calculated using bray-curtis ..................................................... 70
Appendix VI: Some common bee species collected in Muhaka, Kwale Kenya ...................... 71
Appendix VII: Some forest dependent butterfly species in Kaya Muhaka forest ................... 72
Appendix VIII: Bee taxonomy certificate................................................................................ 73
xiii
ABBREVIATIONS AND ACRONYMS
ANOVA............................................................................Analysis of Variance
CEPF.................................................................................Critical Ecosystem Partnership Fund
CFCU................................................................................Coastal Forest Conservation Unit
GPS....................................................................................Global Positioning System
HSD...................................................................................Honest Significance Difference
IPI......................................................................................International Pollinators Initiative
KMF...................................................................................Kaya Muhaka forest
NMK..................................................................................National Museums of Kenya
TFCG.................................................................................Tanzania Forest Conservation Group
WWF-US..........................................................................World Wildlife Fund-United States
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ABSTRACT
The current global pollination crisis and the importance of insects in pollination service that
maintains the native plant populations, agricultural enterprise, ecosystem resilience and food
security do motivate the concern to conserve insect pollinators. Kaya forests are rich in
biodiversity and endemism; they are potential sites for conservation of these pollinators in the
coastal region of Kenya. However, they are threatened by illegal deforestation, charcoal
burning, settlement and farming causing conservation threat to the pollinators. Understanding
the composition of bee and butterfly communities and their response to the disturbance is
essential if their conservation is to be successful in the area. The main objective of the study
was to establish the composition of bees and butterflies along the disturbance gradient. The
study examined the diversity and abundance of these pollinators and their floral resources
along a disturbance gradient from the natural forest through the forest edge to farmlands. The
study was carried out between April 2010 to September 2010 and data analysed using R
software. Diversity, species richness, abundance and floral resources were examined in Kaya
Muhaka forest, forest edge, surrounding fallow farmlands and crop fields. The survey was
done at sampling points along two habitat zones in transition from the forest core to
farmlands. Sampling was done using sweep nets within three permanent 50 m x 2 m belt
transects at each sampling point. 36 belt transects were surveyed in 12 sampling points across
the habitats for six months. Floral resources were identified and linked to the associated bees
and butterflies. A total of 52 bee species and 66 butterfly species were recorded. The highest
bee diversity was recorded in fallow farmlands and lowest in forest core. The diversity of bee
species across the habitats was not statistically different. However, butterfly diversity was
significantly higher in forest edge than in crop fields (P = 0.021). The lowest butterfly
diversity was recorded in fallow farmlands. Both bees and butterflies were more abundant in
the farmlands. Crop fields and forest edge were closely similar in bee and butterfly
composition. Increasing distance from forest core had no significant effect on bee and
butterfly diversity and abundance. The effect of floral resources richness on bee species
richness was highly significant (P = 0.004). However, floral richness did not have significant
effect on butterfly richness. Bees and butterflies were not evenly distributed in the habitats.
These findings are important for understanding and management of insect pollinators in
changing landscapes.
1
CHAPTER ONE
INTRODUCTION
1.1 Background
Biodiversity conservation calls for identification of biodiversity hotspots where exceptional
concentrations of endemic species are undergoing continuous loss of their habitats; the sacred
coastal Kaya forests are no exception. Sacred forest sites throughout the world are important
for the preservation of plant and animal species useful to local people (Wadley and Colfer,
2004). However, more than 87% of the Earth‟s land surface is not currently protected
(Winfree et al., 2007). It is therefore pragmatic for conservation planning to consider species‟
use of anthropogenic habitats and to understand whether organisms that perform particularly
important ecosystem functions persist in human-dominated ecosystems (Kremen et al.,
2007). The evidence that pollinators are declining in some parts of the world (Kearns et al.,
1998; Kremen and Ricketts, 2000) has attracted public attention and research.
Ecosystem services are critical to human survival (Kremen et al., 2002), a powerful argument
for conserving the principal pollinators. However, it is important to note that conservation
areas are no longer sufficient due to human activities, leading to increased focus on managed
land for conservation (Tylianakis et al., 2005). In Africa and Madagascar, reliance on
conserved areas such as National Parks will not be sufficient to preserve pollinator diversity
in the face of increasing land use change (Eardley et al., 2009). Moreover, the community
structure of forest insect pollinators is related to their host plants (Potts et al., 2003), meaning
a strategic conservation plan should focus on both the insects and their associated floral
resources. Past studies have revealed positive relationships between bee abundance and floral
abundance, bee and floral diversity (Banaszak, 1996), butterfly diversity and floral abundance
(Potts et al.,2003). According to Pauw (2007) generalist pollinators are predicted to be
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sensitive to human-caused disruption, and their early loss will trigger a cascade of linked
declines among the multiple plant species that they pollinate. Kremen et al. (2007) explains
that pollination services are provided by varied wild, free-living organisms but chiefly bees
and also many butterflies and commercially managed bee species (primarily the honey bee,
Apis mellifera L.). Bees form keystone mutualisms with their host plants maintaining the
biodiversity of most terrestrial eco-systems (Stubbs et al., 1997).
In spite of the pollinators‟ ecological significance, land use has changed the landscape
structure in ecosystems influencing their temporal and spacial availability of food, nesting
and mating sites (Kremen et al., 2007). The recent large scale parallel decline of plants and
pollinators is a reinforcement to the concern that pollination as an ecosystem service is at risk
(Biesmeijer et al., 2006). The pollinator declines and losses of pollination services have been
identified in the context of habitat destruction and land use intensification (Steffan-Dewenter
and Westphal, 2008). Despite the ongoing concerns and controversy over a putative „global
pollination crisis‟ there is little information on the response of bees, the most important group
of pollinators, to land-use change (Brosi et al., 2008). Given the importance of bees for the
maintenance of native plant populations, human agricultural enterprise and attached
commercial value, it is vital that their complex responses to ongoing global changes,
particularly in the tropics be investigated (Brosi et al., 2008) in order to understand how their
diversity, distribution and community composition are affected. The study focuses on bees
and butterflies the predominant and most economically important pollinators in the region.
1.2 Statement of the problem
The decline in bee populations is now a worldwide phenomenon. In Africa and Kenya in
particular, a very large number of bee species are undescribed despite the increasing trend in
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habitat destruction and degradation. Bees and butterflies offer essential pollination service
linked to food production and ecosystem regeneration. Bees are also important in honey
production while butterflies promote eco-tourism and foreign exchange. The two insect
groups have potential commercial value and improved livelihoods for the Mijikenda
community living around the Kaya forests. Despite the high biodiversity and endemism of the
Kaya forests, they are threatened by illegal deforestation, settlement and farming causing a
conservation threat to these commercial insects. Kaya Muhaka forest (KMF) is outstanding
among the biodiversity reserves of the coastal forest remnants due to high diversity and
endemism of butterflies. Although this concept has strong resonance and logic, ecosystemwide studies on the commercial insects of the Eastern African Coast in general, and the
region in particular, is unfortunately limited, and yet the emerging picture is alarming, with
entire sets likely to disappear. No study has been done to link insect pollinators of this area to
their associated floral resources with bee data completely lacking.
Even though KMF is a protected area, human disturbance, habitat change and land use
contexts in the neighborhood may intensify the pollinator decline due to shrinking natural
habitat and food resources. Bees being more vulnerable to such changes due to their genetic
and demographic characteristics stand to be most affected. The problem to be addressed by
this study is lack of tangible baseline data on bees, butterflies and their floral resources in the
region. The study is motivated by the need for an inventory for these insects and their
associated floral resources in order to make a more informed, pragmatic and comprehensive
conservation plan. Regeneration, conservation, monitoring and sustainable utilization
programs for such species and their floral resources can then be developed, which is critically
crucial for the ecosystem resilience and livelihoods.
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1.3 Research questions
i.
What is the diversity of bees and butterflies in the forest core (center), forest edge,
fallow farmlands and crop fields?
ii.
What is the relative abundance of bees and butterflies in the habitats?
iii.
What is the relationship between species richness of the insects and floral resources
richness?
1.4 Hypotheses
i.
There is no significant difference in species diversity of bees and butterflies in the
forest core, forest edge, fallow farmlands and crop fields.
ii.
Bees and butterflies are evenly distributed among forest core, forest edge, fallow
farmlands and crop fields.
iii.
There is no correlation between species richness of the insects and richness of the
floral resources.
1.5 Objectives
1.5.1 General objective
To establish the composition and floral resources of bees and butterflies in Kaya Muhaka
Forest and surrounding farmlands in Kwale county, coastal Kenya for improved livelihoods
and biodiversity conservation.
1.5.2 Specific objectives
i.
To determine the diversity of bees and butterflies in the forest core, forest edge and
surrounding fallow farmlands and crop fields.
ii.
To determine the relative abundance and distribution of bees and butterflies in the
various KMF habitats.
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iii.
To identify the floral resources and determine the relationship between their richness
and richness of the insect pollinators.
1.6 Justification of the study
A global pollination crisis has been recognized (Allen-Wardell et al., 1998; Kearns et al.,
1998; Tylianakis and Tscharntke, 2005) and the international pollinator initiative (IPI) points
to a lack of baseline ecological data for plant-pollinator interactions on which to develop
strategies for integrated management of landscapes (Potts et al., 2003). The current
pollination crisis emphasizes the importance of understanding the fundamental determinants
of plant-pollinator community structure and the need to document their floral requirements
(Sāo Paulo declaration, 1999) to underpin any conservation efforts. Bees and butterflies
provide pollination service which is essential to human welfare; pollination provides
significant and measurable benefits to humanity (Kremen et al., 2002), this is a potential
economic argument for their conservation. Pollinators play a crucial role in ecosystem
processes and contribute to the maintenance of ecosystem function (Potts et al., 2003); they
are a functional group with high relevance for ensuring cross-pollination in wild plant
populations and yields in major crops. Data on their relative abundance and diversity gives an
indication of pollinator force (Kevan, 1999). It is important to note that Kaya Muhaka Forest
(KMF) is an isolated habitat, which may reduce species richness and abundance of pollinator
guilds, change the foraging behaviour of flower-visiting insects, disrupt plant-pollinator
interactions, and reduce seed set and gene-flow of isolated plant population (Didham et al.,
1996). The study will be useful in that it will develop an inventory of commercial insects and
associated flora for conservation and improvement of livelihoods in KMF.
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CHAPTER TWO
LITERATURE REVIEW
2.1 Vulnerability of bee population to habitat change
Human impacts have modified the landscape through fragmentation, degradation and
destruction of natural habitats and the creation of new anthropogenic habitats. The changes in
land use and landscape structure influence pollinators at individual, population and
community scales. Kremen et al. (2007) explains that at population level, genetic and
demographic characteristics may predispose bee populations to be particularly vulnerable to
habitat and landscape changes that reduce population size. Zayed and Packer (2005) reports
two reasons for their vulnerability. First, bees are haplodiploid, which reduces the effective
population size to at most 3/4 that of equivalently sized diploid populations with
approximately even sex ratios. Second, single-locus sex determination contributes to reduced
population size because homozygotes at the sex locus become sterile diploid males.
2.2 Bee response to land use and habitat disturbance
The effects of high quality habitats are likely to be more effective in enhancing pollinator
diversity and abundance, when ecological restoration sites are available in the close vicinity
(Steffan-Dewenter and Westphal, 2008). Activities associated with such high-intensity land
uses, such as pesticide application, tilling, other soil disturbance, and the clearing of native
habitat from local to landscape scales, may make it difficult for bees of nearly any guild to
persist (Kremen et al., 2007). However, bee communities appear to have some degree of
resilience to land-use change, as diverse bee faunas have persisted over decadal time scales in
agricultural landscapes in Poland (Banaszak, 1992). It is therefore possible that some
modified habitats may support more species than has been previously assumed (Driscoll,
2005). On the contrary, stingless bee abundance is dependent on the proportion of forested
7
area in the surrounding landscape (Brosi et al., 2008). Disturbed forests tend to have greater
absolute bee species richness (α-diversity) (Liow et al., 2001). They may attract more
“wanderer” bees (those that do not reside within the forest) with potentially large foraging
ranges like Amegilla and Xylocopa spp. However, undisturbed lowland primary and
secondary forests tend to have high absolute abundance of bees (Liow et al., 2001).
2.3 Butterfly response to land use and habitat disturbance
According to Davros et al. (2006) some butterfly species are disturbance-tolerant and can be
found in areas altered by humans and are effectively tolerant to removal of the native
vegetation. However, habitat-sensitive species have more specific requirements for habitat
and vegetation composition to suit the needs of other life stages and are often found only in
relatively natural areas with native vegetation. Studies by Steffan-Dewenter and Tscharntke
(1997) indicated that butterfly richness did not change with vegetation succession over time
but species composition was affected significantly.
2.4 Ecological and economic significance of insect pollinators
Estimates of the value of pollination done by bees have varied and are primarily based on. A.
mellifera. Bees also aerate soil by digging nesting burrows, consume honeydew, nectar, and
pollen; fertilize plants with their wastes; pollinate plants; and serve as food for other
organisms in numerous habitats (Sheffield et al., 2003). The value of crop pollination by the
most important managed pollinator, the honey bee A. mellifera, is estimated to be 5-14 billion
dollars per year in the United States alone (Kremen et al., 2002) and a global estimate of US$
65-70 billion (Hartmann, 2004). Recent reviews quantify that 35% of the crop production
volume and 70% of major global crops rely on animal pollination (Klein et al., 2007). In
agricultural regions, bees (Hymenoptera: Apoidea) have long been recognized as being vital
for successful fruit production (Sheffield et al., 2003). According to Potts et al. (2003) it is
8
estimated that 60-70% of flowering plant species are dependent upon insects for pollination
worldwide with bees being the principal pollinating group in most geographic regions and the
non-Apis species maintaining the integrity of many natural communities. Bees are more
effective pollinators for other crops including alfalfa, an important forage crop and cover crop
contributing to soil fertility, and many orchard crops (O'Toole, 1993).
In Ethiopia, the largest honey producer in Africa and the 10th largest honey producer in the
world; the total honey production is estimated up to 24 tonnes. About 80% of this goes into
preparation of a national drink“Tej” (honey wine). Ethiopia is the fourth largest producer of
beeswax in the world, which is exported mainly to Japan, Germany, Netherlands and the
USA (Hartmann, 2004). Further economically important honey products are propolis and
pollen, and others that are used in pharmacy, cosmetic and colour industry (Hartmann, 2004).
In xeric areas and Mediterranean scrub communities, bees are present in particularly high
diversity and are the principal pollinators, contributing to the preservation and reproduction
of the natural vegetation, which prevents erosion and provides the cover and food for native
wildlife (Neff and Simpson, 1993; Michener, 2000). In view of their effectiveness as
pollinators, bees are a prime example of “keystone mutualists", being essential for the
maintenance of ecosystem integrity and of angiosperm diversity (LaSalle and Gould, 1993).
On the other hand, butterfly taxa are used increasingly as habitat or environmental quality
indicators (Hamer et al.,1997; Hill, 1999; Fiedler and Schulze, 2004). Currently butterflies
have greater commercial returns to some Kenyan communities. Butterfly farming has
improved the livelihood of the local people in Taita Hills where farming of 14 species of
Taita Hills endemics Cymothoe teita van Someren and Papilio desmondi teita van Someren
earned them up to US$ 600 from the sale of 61 percent of 1052 pupae after six months of
rearing (TFCG, 2007).
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2.5 Pollination crisis and conservation concern
Pollination provided by wild bees is likely being reduced in many of the areas where they
could be contributing to crop production with pollination-related problems within natural and
agricultural ecosystems becoming more common (Buchmann and Nabhan, 1996).
Approaching such issues by documenting which species are involved is a key step to
facilitate their preservation and management (Danks, 1994). Moreover, numbers of
commerciallymanaged colonies of A. mellifera have also declined inmany parts of the world
(Kremen et al., 2007).
Torchio (1990) explains that out of the approximated 20,000 to 30,000 species of bees,only a
few species have been domesticated and are available commercially, e.g., A. mellifera, the
bumble bee Bombus impatiens Cresson, and the alfalfa leaf cutting bee, Megachile rotundata
Fabricus. These concerns about the loss of pollinators and the services they provide have
grown over the last decades (Kearns et al., 1998), but only a few studies have been published
for Kenya (Gikungu, 2002; Eardley et al., 2009). The concerns are warranted based on recent
evidence of pollinator declines (Biesmeijer et al., 2006). The decline may be aggravated at
the coastal Kenya due to habitat fragmentation, making threatened species within key sites
highly vulnerable to extinction. Agricultural encroachment, timber extraction and charcoal
burning are the greatest threats to habitat in this region, although weak management capacity
within government and communities is a serious issue (CEPF, 2005).
Bees are the most highly adapted of all flower visitors, making them most successful
pollinators. Owing to their high dependence on nectar, pollen, and oil from flower resources
for feeding and larval food, bees exhibit among the highest floral visitation rates in the world,
making them the single most important group of pollinators (Neff and Simpson, 1993).
10
However, the pollination success of insect-pollinated plant species is usually not dependent
on single, highly specialized pollinator species, but rather on a diverse community of
pollinators (Steffan-Dewenter and Westphal, 2008). This means the current evidence of
elevated pollinators extinction rates across all taxa (Kremen et al., 2007) puts pollination as
an ecosystem service at risk (Biesmeijer et al., 2006). According to Sheffield et al. (2003)
there is historic knowledge of the importance of bees in agricultural plant communities, but
only recently there has been an appreciation of the fragility of many plant-pollinator
relationships. Furthermore, very little is known about how stingless bees respond to forest
disturbance caused by human activities (Eltz et al., 2002).
To effectively conserve the pollinators in human dominated habitats, there is need for an
ecosystem approach to management of crop fields and semi-natural habitats in order to
sustain the availability of their floral resources in different seasons of the year. Floral
community composition, the quantity and quality of forage resources present, and the
geographic locality do organize bee communities at various levels and act in specific ways to
modulate the diversity of the local geographic species pool (Potts et al., 2003). Therefore, the
pollinator crisis exemplifies the intimate relationship existing between the welfare of natural
environments and their biodiversity and the needs of sustainable agriculture.
2.6 Conservation value of remnant indigenous Kaya forests
Remnant indigenous coastal forests are important conservation corridors which may attract
ecological interactions between plants and insects (Bullock and Samways, 2005). Despite the
relative small size of the Kaya forests, they have high rarity and conservation values
(Robertson and Luke, 1993). Majority of plant species in these forests are woody but there
are also endemic climbers, shrubs, herbs, grasses and sedges (Burgess et al., 2000). The
11
forests are also known for higher endemism of invertebrate groups such as millipedes,
molluscs and forest butterflies (Burgess et al., 2000). Kaya Muhaka forest which is one of the
sacred forests of the Mijikenda community in Kwale county is an isolated lowland coastal
forest classified as “Wetter mixed semi-deciduous forest” with a high Lepidoptera diversity
and endemism (Lehmann and Kioko, 2005). Lepidoptera diversity and endemism is high in
KMF including species with a western and central Africa distribution, as well as the Kenyan
endemic montane subspecies Charaxes acuminatus shimbanus van Someren (Lehmann and
Kioko, 2005).
2.7 Butterfly taxa and habitat preference
Within the family Nymphalidae, members of the subfamilies Satyrinae and Morphinae have
relatively broad wings, favouring slow agile flight, and are often encountered beneath the
canopy in dense unlogged forests. These species with greater shade preference have
significantly narrow geographical distributions. Open gaps in unlogged forests attract
widespread species of Nymphalinae and Charaxinae (Hamer et al., 2003). However, species
in the subfamilies Nymphalinae and Charaxinae with broad thoraces have rapid powerful
flight, and are often encountered in more open areas (Hill et al., 2001; Schulze et al., 2001).
Hamer et al. (2003) explains that selective logging in primary forests is associated with loss
of environmental heterogeneity, primarily affecting the relative abundance of species rather
than species richness; suggesting preservation of environmental heterogeneity as far as
possible in any conservation management. Butterflies with strong powers of flight and open
population structures such as the large white (Pieris brassicae L.), the brimstone (Gonepteryx
rhamni L.) and the small tortoise shell (Aglais urticae L.) are unlikely to be constrained by a
lack of shelter, allowing them to exploit resources effectively in areas inaccessible to other
less vagile species (Feber et al., 1996). Nonetheless, floristic heterogeneity within a habitat
12
has an influence on butterfly species composition and abundance (Namu, 2005) with
intermediate disturbance increasing species richness in tropical forests (Sheil and Burslem,
2003).
Butterfly taxa appear to be negatively impacted by fragmentation, exhibiting population
declines and even extinction (Shahabuddin and Terborgh, 1999). According to Foggo et al.
(2001) it is generally assumed that large species are more sensitive to fragmentation and
therefore need larger reserve sizes than small species. They are also thought to be more
sensitive to fragmentation because of greater space use and food requirements; this
assumption ignores the fact that large species may be able to use multiple patches because of
their higher mobility (Foggo et al., 2001). Evidence from experiments suggests that field
edges support breeding populations of most of the butterfly species rather than simply
attracting aggregations of mobile individuals (Feber et al., 1996). They are likely to be most
effective as supplements to, or replacements for, established plant species, where sources of
suitable colonists have been eliminated and the vegetation is impoverished or dominated by
annuals (Smith et al., 1994). Such wild flower mixtures will be most beneficial to adult
butterflies if they include early and late flowering species to provide nectar throughout the
seasons (Feber et al., 1996).
2.8 Edge effects and tropical forest invertebrates
Edge effects in landscape ecology are essentially the biotic and abiotic contrasts between
adjacent habitat types (Foggo et al., 2001). They are causal mechanisms influencing
behaviour, distribution, species abundance and other higher order assemblages. They may
therefore exert an influence that extends beyond the limits of the physical edge itself. In most
terrestrial ecosystems, edges can be defined as the physical boundaries between plant
13
community types (Samways, 1994), characterised by changes in factors such as floral
structure, composition, and microclimate (Foggo et al., 2001). Three mechanisms have been
cited most commonly to explain increased abundance of forest insects near edges; spill-over,
edges as enhanced habitat, and complementary resource distribution (Ries and Sisk, 2004).
According to Shmida and Wilson (1985) increased abundance near edges have often been
attributed simply to spill-over, which occur when individuals disperse into non-habitat by
crossing the boundary from their preferred habitat but are not likely to penetrate very deeply
into a patch of non-habitat.
2.9 Linking butterflies and bees to plant resources
Presence of appropriate plants is obviously important in determining the suitability of a given
habitat for a butterfly species (Sharp et al., 1974). According to Ehrlich and Gilbert (1973),
plant resource distribution may be of critical importance in butterfly population structure.
Contrary to this opinion; Sharp et al. (1974) found no relationship between butterfly
population structure and total plant diversity. However, according to Yamamoto et al. (2007)
both larval and adult stages of butterflies depend almost entirely on specific plants for their
dietary requirements and therefore supports that resource abundance explains the variation in
the abundance and species richness of herbivorous insects. The influence of plant
associations on butterfly distribution seems to be determined by the range of the animals, the
distribution of particular plants of critical importance to them and the predictability of their
environment. Studies conducted on both wide-ranging and rather sedentary butterflies where
food sources were locally distributed have shown strong associations between the distribution
of the butterflies and of the nectar sources (Sharp et al., 1974).
14
Competition theory for diversity regulation predicts that the diversity of consumers and
resources are positively correlated, as should consumer and resource abundance (MacArthur,
1972). In Mt. Carmel National reserve in Israel, the abundance A. mellifera was found to be
closely related to resource availability even though the family Apidae had no close linkage to
environmental variables. In contrast, the Megachilidae appeared to be organized by both
nectar and pollen resources; species richness was related to floral diversity. The diversity
within Andrenidae was positively associated with floral diversity (Potts et al., 2003). The
linkage between bee and flower diversity is accounted by the strong associations found
within the Andrenidae and Megachilidae, which appear to be absent from the Apidae (Potts et
al., 2003). This study explains further that the absolute diversity of bees is strongly related to
the diversity of flower species, especially annuals, and it is the variety of nectar foraging
resources that appears to be the defining factor. Nonetheless, the overall bee abundance is a
positive function of the abundance of flowers in a particular habitat. An understanding of the
underlying ecological interactions between plants and pollinators at a variety of spatial scales
is essential for the conservation and restorationof the threatened communities found
worldwide (Sāo Paulo Declaration, 1999). This understanding will be useful in conservation
planning for bees and their associated floral resources in KMF and surrounding farmlands.
15
CHAPTER THREE
MATERIALS AND METHODS
3.1 Study area
The study was conducted at the sacred Kaya Muhaka forest (KMF) situated on the coastal
plains of Kenya (East Africa) at a geographical location of 04° 18‟ S - 04° 38‟ S; 39° 33‟ E 39° 53‟ E and surrounding farmlands (Figure 1). KMF covers about 130-150 ha and is
located 32 km from Mombasa town at an altitude of 20 - 40 m ASL. Kaya forests are residual
patches of once extensive diverse lowland forest of Eastern Africa. It is a protected area and
managed by Coastal Forest Conservation Unit (CFCU) of National Museums of Kenya
(NMK) in conjunction with the local community.
Figure 1: Satelite map showing the location of study area and land use.
16
3.1.1 Biodiversity of the coastal forests
Coastal forests stretch from Kenya to Tanzania and Islands of Zanzibar and Pemba. The
forests host more than 4500 plant species and 1050 plant genera with around 3000 species
and 750 genera occurring in the forest. At least 400 plant species are endemic to the forest
patches and another 500 are endemic to the intervening habitats that make up 99 % of the
eco-region area (WWF-US, 2003).
3.1.2 Farmlands
The surrounding farmlands are characterised by small scale farming of subsistence crops such
as cassava, cowpea, maize and rice. Also found sparsely distributed in these farms is Cajanus
cajan. Major commercial crops include, coconut, citrus, cashewnut and mangoes. Fallow
farmland were characterised by a mix of open grasslands, shrubs, mango and cashew nut
trees. Farmlands close to settlements are dominated by coconut plantations.
3.2 Study design
The main focus of this study were bees, butterflies and their floral resources. Surveys were
conducted along two transects established from the forest core and tranversed through the
forest edge to the farmlands. Sampling points were located at an interval of 0.5 km along two
2.5 km transects (Figures 2 and 3) in the forest core (Plate 1), forest edge (Plate 2) and
farmlands. The farmland was categorised further into fallow farmlands and crop fields due to
their ecological differences (Plates 3, 4 and 15).
A set of 3 parallel 50 m x 2 m belt transects located 50 m apart were laid with one passing
through the center of the point and one on each side as shown in figure 3. Individual bees and
butterfly samples were coded to be able to associate them with their habitats and floral
resources. Belt transects are most effective active sampling methods for bees, as compared
17
with timed observations of quadrats or sweeping vegetation (Banaszak, 1996). Bee samples
were collected in vials containing cotton wool soaked with ethyl acetate to kill the bees. Bees
collected for each day were mounted every evening to avoid loss of taxonomic structures.
Butterflies were killed by gently pressing the thorax and placed in envelopes for transfer to
the laboratory at NMK. In the laboratory, they were relaxed, pinned and set in the setting
boards and placed in oven for 48 hours to ensure they were fully dry. They were then pinned
in insect storage boxes. Collections were first pooled according to sampling points then
habitats. Flower cutting and a small branch of plant species supplying the floral resources
were sampled and given the same code as that of the associated bee or butterfly to be able to
document insect-plant association correctly (Gikungu et al., 2011; Gikungu, 2006). It was
assumed that the samples collected did not affect the population of the insect species. Bee and
butterfly samples were identified to species level at the entomology section of the NMK.
Plant materials were pressed and taken for identification at NMK Herbarium.
3.2.1 Establishment of transects and sampling points
Two transects were established from the forest core through the forest edge to the farm lands.
The transects were established across four habitat types; forest core, forest edge, fallow
farmland and crop fields (Figure 2). Location of the two transects wasbased on vegetation
structure and land use types. Sampling points were located along the two main transects as
shown in figure 3. Six sampling points were located on each transect (Figure 4) at global
positioning system coordinates shown in table 1.
18
Figure 2: Location of main transects
The points were sampled in the same order in the six months of collection period for
uniformity. For each sampling day, the selection of sampling points were randomized along
the main transect as described by Winfree et al. (2007) to limit temporal effects. To
adequately sample species with different diurnal patterns, sampling was done between 8.30
a.m. – 12.30 a.m. and 2.00 p.m. – 4.00 p.m. during sunny and partly cloudy days when bees
and butterflies actively forage.
Figure 3: Schematic illustration of belt transects and sampling points
19
Figure 4: Satelite map showing study area and sampling points
Plate 1: Forest canopy cover at forest core
(center) of KMF
Plate 2: A site at forest edge of KMF
20
Plate 3: A site in crop fields
Plate 4: A site in fallow farmland
Plate 5: A site in open fallow farmland
Table 1: GPS coordinates of sampling points
A1
A2
A3
A4
A5
A6
4° 19' 72" S
4° 19' 68" S
4° 19' 65" S
4° 19' 57" S
4° 19' 48" S
4° 19' 40" S
GPS coordinates of sampling points
B1 4° 20' 16" S
39° 31' 59" E
°
B2 4° 20' 08" S
39 31' 41" E
B3 4° 20' 02" S
39° 31' 17" E
°
B4 4° 19' 97" S
39 30' 91" E
B5 4° 19' 93" S
39° 30' 64" E
°
B6 4° 19' 90" S
39 30' 36" E
39° 31' 44" E
39° 31' 30" E
39° 31' 02" E
39° 30' 75" E
39° 30' 45" E
39° 30' 18" E
21
3.2.2 Data collection
All foraging bees and butterflies encountered along the 50 m x 2 m belt transects were
collected using a sweep net (hand netting) within a standard 20 minutes sampling time per
belt for the diversity and abundance data as described by Potts et al. (2003) and Banaszak
(1996). Each belt transect was surveyed three times a month for 6 months for the purpose of
replication. Sampling was done from April 2010 to September 2010 covering the wet and dry
periods. The number of bees visiting collected at the sampling points during the sampling
period was considered an estimate of bee abundance at the points (Diego and Simberloff,
2002). Butterfly abundance was estimated in the same way. To assess floral resources
richness at each site, plant species with open flowers were counted and recorded at each
sampling point. Forest data including bees, butterflies and floral resources were from the
understory.
3.3 Data management and analysis
Diversity was determined based on species richness; α Shannon‟s diversity index. Evenness
index (J) was used to measure the relative abundance of bees and butterflies in the study area.
Renyi diversity and evenness profiles were used to compare the diversities and evenness of
the habitats. Renyi technique characterizes the diversity of a community by (a scaledependent) diversity profile rather than expressing it simply as a numerical value (Renyi,
1961). Therefore, it is robust and takes into account both rare and dominant species in the
diversity analysis (Renyi, 1961; Tothmeresz, 1998). Renyi diversity profiles of the separate
habitat types were used to order the habitats based on species richness. A habitat with
diversity profile starting at a higher level than others was considered richer. Profiles above
others along their range from start to end indicated higher diversity or evenness of the habitat
(Kindt and Coe, 2005). Cluster analysis was used to analyse the ecological distance among
22
the habitats to depict their similarity in species composition. One-way analysis of variance
(ANOVA) was used to compare the diversity and relative abundance of the insects among the
habitats. Tukey's honest-significance difference test (HSD test) was used in comparisons of
means. The relationship between species richness of insects and floral resources was tested
using linear regression analysis. Simple linear regression was also used to test the effect of
increasing distance from forest core along the disturbance gradient on species diversity,
richness and abundance. Species rank-abundance curves were used to identify the dominant
butterfly and bee species and to show the overall pattern of species evenness. Bee and
butterfly data sets were analyzed separately using R 2.12.1 program. Species abundance
distribution was presented in bar graphs with standard error bars. Numerical values of
Shannon-Wiener diversity index (H') and Evennes index (J) were calculated using the
formulas according to Krebs (1993). The Renyi diverisity formula as expressed by
(Tothmeresz, 1998) is shown below.
Renyi diversity formula;
H
= ln (∑Pi)/1-
Where; ln is the natural logarithm, ∑ Pi is the summation of the proportions of each species
and
- is the scale parameter whose values vary from 0 to infinity, excluding 1.
Shannon-Wiener diversity index (H') formula;
S
H' = -∑Pi ln Pi
i= 1
Where Pi is the proportion of species i and ln is the natural logarithm of the proportion with i
= 1, 2 .....S. S is the total number of species present.
Evennes (J) index formula;
J = H'/ log S
Where H' is the Shannon-Wiener diversity index and S is the species richness.
23
CHAPTER FOUR
RESULTS
4.1 Bee species richness and abundance
A total of 755 bees were collected in forest core, forest edge, fallow farmlands and crop
fields. Fifty two species were recorded (Figure 5).
Figure 5: Bee species accumulation curve
Bees collected were from Apidae, Halictidae and Megachilidae (Table 2).
Table 2: Bee species composition
Bee Family
Apidae
Bee species
Amegilla mimadvena Cockerell
Amegilla sp. 1
Amegilla sp.2
Amegilla sp.4
Amegilla sp. 6
Apis mellifera Linnaeus
Braunsapis sp.
Ceratina sp. 1
Ceratina sp. 2
Ceratina sp. 3
24
Ceratina sp. 4
Ceratina sp. 5
Ceratina sp. 6
Ceratina sp. 7
Dactylurina schmidti Stadelmann
Hypotrigona sp. 1
Hypotrigona sp. 2
Macrogalea candida Smith
Meliponula ferruginea Lepeletier
Pachymelus sp.
Thyreus sp.
Xylocopa caffra Linnaeus
Xylocopa flavicollis DeGeer
Xylocopa flavorufa DeGeer
Xylocopa hottentota Smith
Xylocopa nigrita Fabricius
Xylocopa scioensis Gibodo
Halictidae
Halictus sp.
Lasioglosum sp.
Lipotriches sp. 1
Lipotriches sp. 2
Lipotriches sp. 3
Lipotriches sp. 4
Nomia sp.
Pseudapis sp.
Pseudapis sp. 2
Sphecodes sp.
Steganomus sp.
Unidentified 1
Unidentified 2
Megachilidae
Euaspis sp.
Coelioxys sp.
Heriades sp.
Megachile discolour Smith
Megachile felina Gerstacker
Megachile sp. 2
Megachile sp. 3
Megachile sp. 5
Megachile sp. 7
Megachile sp. 8
Megachille sp. 6
Pachyanthidium sp.
25
Apidae family were most abundant with a much greater proportion of 76%, followed by
Halictidae at 14% and then Megachilidae at 10% (Figure 6).
Figure 6: Relative abundance of three families of bees
The highest overall bee abundance was recorded in fallow farmlands followed by crop fields
then the least number in forest core (Figure 7).
Figure 7: Total bee abundance per habitat
26
Halictidae was most abundant in fallow farmlands while Megachilidae were most abundant in
the crop fields. Forest core had the least abundance for the three bee families. The highest
abundance of Apidae was recorded in crop fieldsthen forest edge (Figure 8).
Figure 8: Abundance of bee families per habitat
Apidae had the largest proportion in all the habitats while Megachilidae had the least
proportion at the forest edge (Figure 9).
Figure 9: Proportion of bee families in each habitat
27
4.1.1 Effect of increasing distance from forest core on bee species richness
Forest edge recorded the highest bee species richness while the lowest was recorded at the
forest core. There was marked reduction in species richness with increasing distance from the
forest core especially from 1.5 km. Increasing distance from forest core had no significant
effect on bee species richness (F1, 4 = 0.001, P = 0.977, R2 = 0.00025, y = -0.1714x + 26.048)
(Figure 10).
Figure 10: Effect of distance away from forest core on bee species richness
4.1.2 Effect of increasing distance from forest core on bee abundance
The highest bee abundance was 215 individuals recorded at 1 km from the forest core along
the disturbance gradient to crop fields. There was apparent reduction in bee abundance from
215 to 60 individuals from 1 km to 2.5 km from the forest core. But Overall, increasing
distance from forest core had no significant effect on total bee abundance (F1, 4 = 0.389, P =
0.567, R2 = 0.089, y = -23.029x + 154.62) (Figure 11).
28
Figure 11: Effect of distance away from forest core on total bee abundance
4.2 Cluster analysis of bee composition based on Bray-Curtis ecological distance
Crop fields and forest edge had closely similar bee species composition. Fallow farmland
shared more species with crop fields and forest edge than forest core as shown by the clusters
in figure 12. Habitats which share most of their species have smaller ecological distance
between them while those with a few species in common have larger ecological distance
(Kindt and Coe, 2005). Therefore, crop fields and forest edge shared more species in
common.
29
Key: X1-Crop fields, X2-Fallowfarmland, X3-Forest core, X4-Forest edge
Figure 12: Dendrogram of cluster analysis of bee species composition
4.3 Butterfly species richness
A total of 545 butterflies representing 5 families, namely Papilionidae, Hesperiidae,
Nymphalidae, Lycaenidae and Pieridae were collected and 66 species identified (Figure13
and table 3).
Figure 13: Butterfly species accumulation curve
30
Table 3: Butterfly species composition
Butterfly Family
Hesperiidae
Lycaenidae
Butterfly Species
Spilia sp.
Anthene demarah Guerin-Meve
Anthene sp.
Azanus natalensis Trimen
Baliochila sp.
Leptotis pirithous Linnaeus
Spindasis homeyeri Dewitz
Spindasis victoriae Butler
Teriomima subpunctata Kirby
Nymphalidae
Acraea acrita Hewitson
Acraea braeasia Godman
Acraea eponina Cramer
Acraea natalica Boisduval
Acraea satis Ward
Amauris niavius Linnaeus
Amauris ochlea Boisduval
Bebearia chriemhilda Staudinger
Bicyclus safitza Hewitson
Bicyclus sp.
Byblia antavara Boisduval
Byblia ilithyia Drury
Chraxes contrarius Weymer
Coenyropsis carcassoni Kielland
Danaus chrysippus Linnaeus
Euphaedra neophron Hopffer
Euryphura achlys Hopffer
Eurytela dryope Cramer
Hypolimnas anthedon Douleday
Hypolimnas deceptor Trimen
Hypolimnas misippus Linnaeus
Hypolimnas usambara Ward
Nymphalidae
Junonia oenone Linnaeus
Junonia natalica Felder
Melanitis leda Linnaeus
Neptis goochi Trimen
Neptis kiriakoffi Overlaet
Neptis saclava Hopffer
Pardopsis puntatissima Rothschild
Phalanta phalantha Drury
Physcaeneura leda Drury
Salamis parhassus Bonte & Van Dyck
Tirumala petiverana Klug
Ypthima asterope Klug
Salamis cacta Fabricius
Pseudacraea lucretia Cramer
Papilionidae
Graphium angolanus Goeze
Graphium antheus Cramer
Graphium colona Ward
31
Graphium kirbyi Hewitson
Papilio demodocus Esper
Papilio dardanus Brown
Pieridae
Appias epaphia Boisduval
Appias lasti Grose-Smith
Belenois crawshayi Butler
Belenois creona Cramer
Belenois thysa Hopffer
Catopsilia florella Fabricius
Colotis antevippe Lucas
Colotis euippe Linnaeus
Colotis ione Godart
Colotis vesta Reiche
Eurema brigitta Stoll
Eurema hecabe Butler
Leptosia acesta Bernardi
Nepheronia argia Fabricius
Nepheronia thalassina Boisduval
4.3.1 Effect of increasing distance from forest core on butterfly species richness
The highest butterfly species richness was recorded at the forest edge, 0.5 km from the forest
core. Butterfly species richnes reduced with increasing distance into the crop fields.
However, this reduction was not statistically significant (F1, 4 = 7.165, P = 0.060, R2 = 0.642,
y = -9.714x + 35.476) (Figure 14).
Figure 14: Effect of distance from forest core on butterfly species richness
32
4.3.2 Butterfly abundance
The family Nympalidae was most abundant and dominant across all habitat types (Figure 15).
Figure 15: Relative abundance of butterfly families in KMF and surrounding farmlands
Crop fields had the highest abundance of butterfly species followed by fallow farmlands then
forest edge. Forest core recorded the least abundance of butterflies. There was a trend of
butterfly abundance from forest core to crop fields (Figure 16).
Figure 16: Overall butterfly abundance per habitat
33
The family Nymphalidae was dominant in all the study sites with peak abundance in crop
fields while Hesperiidae was only recorded at the forest edge. Pieridae was the second
dominant family across all the habitat types. Papilionidae was least abundant in crop fields
compared to other study sites. Hesperidae was the least abundant at forest edge (Figure 17).
Figure 17: Butterfly families abundance per habitat
4.3.3 Effect of increasing distance from forest core on butterfly abundance
There was reduction in butterfly abundance between 0.5 – 2 km from the forest core.
However beyond 2 km, the overall butterfly abundance increased remarkably. Increasing
distance from forest core to crop fields had no significant effect on butterfly abundance (F1, 4
= 0.439, P = 0.544, R² = 0.099, y = -11.143x + 104.76) (Figure 18).
34
Figure 18: Effect of distance away from forest core on butterfly abundance
4.4 Cluster analysis of butterfly composition based on Bray-Curtis ecological distance
Crop fields and forest edge shared most of the butterfly species in common compared to
fallow farmland and forest core. Butterfly composition in forest core was least similar to that
in the crop fields (Figure 19).
Key: X1 – crop field; X2 – Fallow farmland; X3 – forest core; X4 – Forest edge
Figure 19: Dendrogram of cluster analysis of butterfly species composition
35
4.5 Effect of habitat type on the diversity of bees and butterflies
Forest core had the lowest bee diversity (H' = 2.1304). The highest bee diversity was
recorded in fallow farmland (H' = 3.0341) then crop fields (H' = 2.9761) while diversity at
forest edge was H' = 2.8737 (Figure 20). These diversities were however not statistically
significant (F3, 8 = 2.0514, P = 0.1853, n =12). Butterfly diversity was highest at the forest
edge, H' = 3.1419. Unlike bee diversity which was lowest in the forest core, butterfly
diversity was second highest, H' = 2.7859, fallow farmland had the lowest butterfly diversity
where its profile is lowest in the entire range, H' = 2.3640. Crop fields had the second lowest
butterfly diversity, H' = 2.5534 (Figure 21).
Key: X1- Crop fields; X2 – Fallow farmland; X3 – Forest core; X4 – Forest edge
Figure 20: Rényi diversity profiles for separate habitats of bee data set
36
Key: X1- Crop fields; X2 – Fallow farmland; X3 – Forest core; X4 – Forest edge
Figure 21: Rényi diversity profiles for separate habitats for butterfly data set
The difference in butterfly diversity among the study habitats was statistically significant (F3,
8
= 6.329, P = 0.017). Tukey‟s HSD result showed significant difference in butterfly diversity
between one pair of the habitats, forest edge and crop fields (P = 0.021), the other pairs were
not statistically significant (Table 4).
Table 4: P values for pair wise comparison of butterfly means
(Tukey's HSD result at 0.05 level of significance)
Forest core
Forest edge
Fallow farmland
Crop fields
Forest core
Forest edge
Fallow farmland
Crop fields
1
0.781
0.239
0.104
1
0.057
0.021
1
0.962
1
37
4.5.1 Effect of increasing distance from forest core on bee diversity
Bee diversity was peak between 0.5 km and 1.5 km and reduced gently with increasing
distance to crop fields. The diversity was measured using Shannon‟s diversity index (H’). At
1 km, H‟ = 2.6726, at 1.5 from the forest core, H‟=2.6678, at 2 km, H = 2.2998 and 2.5 km,
H‟ = 1.883. The lowest diversity was recorded at 0 km (forest core) which was considered
undisturbed area, H‟ = 1.571. Distance away from forest core to crop fields had no significant
effect on bee diversity (F1, 4 = 0.0189, P > 0.05, R2 = 0.0047, y = 0.0341x + 2.243) (Figure
22).
Figure 22: Effect of distance from forest core on bee diversity
4.2.3Effect of increasing distance from forest core on butterfly diversity
Butterflies were more diverse at 0.5 km from the forest core. There was an overall reduction
in butterfly diversity with increasing distance from the forest core (Table 5).
Table 5: Butterfly diversity at varying distance from forest core
Distance from forest core (km)
0
0.5
1
1.5
2
2.5
Butterfly diversity (H’)
2.339913
2.665789
1.698388
1.514743
1.692551
1.548863
38
However, the reduction in butterfly diversity was not statistically significant (F1, 4 = 6.731, P
= 0.0604, R² = 0.6272, y = -0.4033x + 2.4142) upto 2.5 km from the forest core (Figure 23).
Figure 23: Effect of increasing distance from forest core on butterfly diversity
4.6 Bee relative abundance in the study habitats
Forest core was largely even than other habitats followed by fallow farmlands. Forest edge
and crop fields were largely uneven as indicated by their lowest profiles (Figure 24a).
Overall, there was uneven distribution of bee species in the survey area (Figure 24b). The
evenness index was J = 0.4271.
39
(a)
(b)
Key: X1-Crop fields, X2-Fallow farmland, X3-Forest core, X4-Forest edge
Figure 24: Rényi evenness profiles of bee data set
(a - Rényi profiles for separate habitats; b - overall rènyi profile for the study area)
The high abundance of Ceratina sp.3, Apis mellifera, Xlocopa flavicollis, Braunsapis sp. and
Lipotriches sp.1 largely affected the evenness of bee distribution (Figure 25).
Figure 25: Overall rank-abundance curve showing the most abundant bee species
40
4.7 Butterfly relative abundance in the study habitats
Forest edge and forest core had largely evenly distributed butterfly community than fallow
farmlands and crop fields (Figure 26a). However the overall distribution of butterfly in the
survey area was uneven (Figure 26b).
(a)
(b)
Key: X1-Crop fields, X2-Fallow farmland, X3-Forest core, X4-Forest edge
Figure 26: Rényi evenness profiles of butterfly data set
(a –Rényi profiles for separate habitats; b-Overall rènyi profile forthe study area)
41
The unevenness was influenced by high abundance of Acraea eponina, Eurema brigitta,
Catopsilia florella, Physcaeneura leda and Bicyclus safitza (Figure 27). The area had an
overall evenness index of J = 0.8053 for butterflies.
Figure 27: Overall rank-abundance curve showing the most abundant butterfly species
4.8 Associated floral resources to bees and butterflies
Fourty bee species were linked to their associated floral resources (Table 6).
Table 6: Bee floral resources
Bee species
Amegilla sp. 1
Braunsapis sp.
Floral resources
Hibiscus surattensis Linnaeus
Vernonia cinerea Less
Rhynchosia velutina Wight & Arn
Julbernardia magnistipulata Harms
Agathisanthemum bojeri Klotzsch
Nesaea radicans Guill. & Perr.
Abutilon zanzibaricum Bojer ex Mast
Tridax procumbens Linnaeus
Sorindeia madagascariensis DC.
Ludwigia sp.
Paulinia piñata Linnaeus
Hoslundia opposita Vahl.
Crotalaria emarginata Benth
Cocos nucifera Linnaeus
42
Ceratina sp. 1
Ceratina sp. 2
Ceratina sp. 3
Allophylus rubifolius Harms
Eriosema glomeratum Guill
Gossypioides kiekie Vahl.
Waltheria indica Linnaeus
Ceratina sp. 4
Ceratina sp. 5
Ceratina sp. 6
Ceratina sp. 7
Gaultheria indicia Linnaeus
Cajanus cajan Linnaeus
Urena lobata Linnaeus
Truimfetta rhomboidea Jacq.
Eriosema glomeratum Guill. & Perr.
Pupalia lappacea Linnaeus
Hewittia malabarica Linnaeus
Indigofera paniculata.Vahl. ex Pers.
Indigofera paniculata Vahl. ex Pers.
Tephrosia villosa Pers.
Hyptis suaveolens Poit
Euaspis sp.
Heriades sp.
Hypotrigona sp. 1
Hypotrigona sp. 2
Lasioglosum sp.
Lipotriches sp. 1
Lipotriches sp. 2
Lipotriches sp. 3
Lipotriches sp. 4
Megachile sp. 2
Megachile sp. 3
Megachile sp. 7
Megachile sp. 8
Megachille sp. 6
Philenoptera bussei Harms
Nomia sp.
Pachyanthidium sp.
Rhynchosia velutina Wight & Arn.
Pseudapis sp.
43
Pseudapis sp. 2
Steganomus sp.
Chamaecrista mimosoides Linnaeus
Abutilon zanzibaricum Bojer
Rhynchosia velutina Wight & Arn
Abutilon zanzibaricum Benth
Twenty butterfly species were linked to their floral resources. (Table 7).
Table 7: Butterfly floral resources
Butterfly species
Floral resources
Aspilia mossambiensis Oliv.
Emilia coccinea Sims
Tridax procumbens
Acraea satis Ward
Anthene sp.
Vernonia sp.
Bridelia cathartica Bertol
Bicyclus sp.
Agerotum conyzoides Linnaeus
Lobelia fervens Thunb
Sida cordifolia Linnaeus
Vernonia sp.
Pentas bussei Krause
44
Stylosanthes fruticosa Retz.
Papilio demodocus Brown
Pardopsis puntatissima Rothschild
Catunaregam nilotica Stapf
Kyllinga cartilaginea Schum
Asystasia gangetica Linnaeus
Most bee species were netted while foraging on flowers. However, bees of 10 genera were
caught on flight. Two other unidentified bee species were also caught while flying between
flowers (Table 8).
Table 8: Bee species caught on flight
Amegilla sp. 2
Amegilla sp. 4
Amegilla sp. 6
Coelioxys sp.
Halictus sp.
Megachile sp. 5
Pachymelus sp.
Thyreus sp.
Unidentified 1
Unidentified 2
Sphecodes sp.
Compared to bee species, most butterfly species were netted on flight (Table 9).
Table 9: Butterfly species caught on flight
Appias lasti Grose-Smith
Baliochila sp.
45
Colotis ione Godart
Junoia oenone Linnaeus
Leptotis pirithous
Spilia sp.
Spindasis victoriae Butler
4.8.1 Important floral resources in Muhaka area
Some floral resources were visited by many bee species and were considered important bee
flora in the area, e.g. Agathisanthemum bojeri (Plate 6), Crotalaria emarginata, Truimfetta
rhomboidea, Cajanus cajan (Plate 7), Rhynchosia velutina, Julbernardia magnistipulata
(Plate 8), Hyptis suaveolens., Eriosema glomeratum and Waltheria indica. However, A.
bojeri, Waltheria indica and Vernonia cinerea were important to both bees and butterflies.
Aspilia mossambiensis, Tridax procumbens and Sida cordifolia (Plate 9) were important
46
specifically to butterfly species.Urena lobata (Plate 10) and Vigna unguiculata (Plate 11)
were also important floral resources in the area.
Plate 6: Xylocopa caffra L. foraging on
Agathisanthemum bojeri K.
Plate 7: Cajanus cajan L., a bee pollinated local crop
Plate 8: Jubernardia magnistipulata H., a forest
tree pollinated by bees mainly Xlocopa sp.
Plate 9: Graphium angolanus G. foraging on Sida cordifolia L.
Plate 10: Macrogalea candida S. foraging on
Urena lobata L.
Plate 11: Vigna unguiculata L., a common crop in the area
that requires bee pollination.
47
4.9 Effect of floral resources richness on bee and butterfly species richness
Floral resources richness at sampling points equidistant from the forest core were summed to
give the floral resources richness at each distance from the forest core, forming 6 categories
of floral resources richness from the 12 sampling points (Table 10).
Table 10: Floral richness and corresponding bee and butterfly species richness
Distance from forest
core (km)
0
0.5
1
1.5
2
2.5
Bee species
richness
11
38
30
32
28
16
Butterfly Species
richness
30
43
22
16
15
14
Floral resources
richness
18
78
75
57
59
34
Floral resources richness had significant positive effect on bee species richness (F1,
4
=
36.6443, P = 0.004, R2 = 0.902, y = 0.611x + 1.1448) (Figure 28). However the richness of
butterflies was not significantly affected by floral resources richness (F 1,
0.638, R2 = 0.061, y= 0.1191x + 16.961).
Figure 28: Effect of floral resources richness on bee species richness
4
= 0.2577, P =
48
CHAPTER FIVE
DISCUSSION, CONCLUSIONS AND RECOMMENDATIONS
5.1 Effect of habitat type on bee abundance
The overall abundance of bees was high in fallow farmland. Fallow farmland was open with
high abundance of flowers. This finding agrees with that of Gikungu et al. (2011) and
Gikungu, 2002; where bee abundance was found to be high in open farmlands. According to
Banaszak (1996) and Potts et al. (2003), the overall bee abundance is a positive function of
abundance of flowers in a particular habitat. Agathisanthemum bojeri; a floral resource of
rank level 1 (visited by most bee species) was abundant in fallow farmland. In addition,
Waltheria indica which attracted more Ceratina sp. was also abundant.
The type of farming in the region is a non-intensive small scale agriculture where crop fields
supported abundant weedy flowering plants after crop harvesting. As a common practice by
farmers in the region, these weedy plants are not removed until the next planting season.
During this fallow period they produce flowers which attract bees. The fields are also
characterised by unmanaged hedgerows which appear advantageous in allowing the survival
of wild flowers which could be a major contributing factor to bee abundance. More open
habitats with abundant floral resources will attract abundant foraging bee species, such
habitats have greater possibilities for partitioning available resources (Potts et al., 2003),
limiting competition between and within species. Open habitats have favourable
environmental variables correlated with the abundance of bees including temperature, light
intensity and humidity (Liow et al., 2001). Therefore, low bee abundance in the forest could
also be caused by low temperatures, higher humidity and low light intensity due to closed
forest canopy. Furthermore, only the understory community was surveyed and few
understory plants or trees were observed flowering during the sampling period.
49
Halictidae were more abundant in fallow farmlands compared to other habitats. Possibly
fallow farmlands support both annual and perennial plants with high pollen availability
relative to nectar that is the crucial property of floral communities that determine the
composition of Halictidae (Potts et al., 2003). Stable habitat conditions with grass and shrubs
in this habitat could be providing favourable nesting sites for members of this family. Apidae
was the dominant bee family across all the study habitats. This compares with the study in
Mt. Carmel where Apidae were found to be dominant (Potts et al., 2003). Most of the
members of this family are long distance foragers with advanced foraging behaviour and
therefore explore diverse nectariferous flowers across different habitats. They extensively
forage for both nectar and pollen across the habitats. Megachilidae were abundant in crop
fields. Presence of Papilionaceae plants e.g Cajanus cajan and Crotalaria emarginata could
have contributed to its abundance. While Halictidae was linked to pollen rich sites and areas
providing good nesting opportunities, Megachilidae appeared to be organized by both nectar
and pollen resources. These findings concur with those of Potts et al. (2003) which reported
dependence of Megachilidae and Halictidae on pollen rich floral resources in Mt. Carmel.
The findings are evidence that different groups of bees show contrasting responses to land
use change, which is probably driven by differences in their foraging and nesting biology
(Brosi et al., 2008).
This study shows that crop fields surrounding KMF can offer supplementary conservation
sites for bee species while the forest acts as an ecological restoration site. Habitats are likely
to be more effective in enhancing pollinator diversity and abundance when ecological
restoration sites are available in the close vicinity (Steffan-Dewenter and Westphal, 2008).
Use of agrochemicals has been found to lower the pollinator diversity and abundance in crop
fields (Kremen et al., 2007). No observation was made on agrochemical use in the study area.
50
This could have contributed to high bee abundance in the crop fields. An ecosystem approach
with carefully designed wild flower and crop mixtures in crop fields can be successful in
supplying nectar and pollen resources to bee species in farmlands thereby supporting their
diversity and abundance in such habitats. Wild flower mixtures in active agricultural
landscapes are likely to be most effective supplements or replacements where sources of
suitable plant colonists have been eliminated and the vegetation impoverished (Smith et al.,
1994).
5.2 Effect of habitat type on butterfly abundance
Overall butterfly abundance was high in the crop fields followed by fallow farmlands. This
could be due to the openness of these habitats. Generalists butterfly species which were
netted in relatively higher numbers majorly from the family Nymphalidae could have
contributed to the overall abundance in the crop fields. This concurs with Hill et al. (2001)
and Schulze et al. (2001) who reported high Nymphalidae abundance in open farmlands.
Farmlands in Kaya Muhaka are characterised by many and scattered cashewnut and mango
trees around which are herbaceous plants, seasonal, annual flowering plants and grasslands.
Some parts of the fallow farmland were characterised by open grasslands with stable stands
of the highly preferred A. bojeri. Abundant weedy plants after crop harvesting provided floral
resources to butterflies in crop fields and fallow farmlands. Despite the fact that these
generalists could be less richer than the forest specialists in this region, their numbers could
be higher than the forest dependents. This may have lead to the higher abundance in the crop
fields. The finding on butterfly abundance also agrees with that of Namu (2005) in which a
high butterfly abundance in Kakamega was recorded in a more open habitats compared to the
primary forest. It is possible that some modified habitats may support more species of
pollinators (Driscoll, 2005).
51
Two main categories of butterflies in this region are noticed, forest dependent and forest
independent. Forest dependent species are contributing to the abundance at the forest and
forest edge and forest independent contributing to the abundance in the crop fields and fallow
farmlands. According to the findings of this study, 45% of butterfly species recorded in KMF
and surrounding farmlands were forest dependent. Some of the forest dependent species
recorded were, Hypolimnas usambara, Hypolimnas deceptor, Graphium antheus, Salamis
cacta, Neptis goochi, Neptis saclava, Chraxes contrarius, Amauris niavius and Graphium
kirbyi. However, Danaus chrysippus, Bicyclus safitza, Catopsilia florella, Acraea eponina,
Eurema hecabe and Eurema brigitta are among the species that showed independence to the
forest and high resilience in farmlands.
5.3 Effect of habitat type on bee and butterfly diversity
High bee diversity was recorded in fallow farmlands and crop fields. This was attributed to
the richness and abundance of important floral resources in the two habitats. The key floral
resources in fallow farmlands and crop fields were largely annuals which supported high bee
diversity in the habitats. It is known that bee diversity has a strong positive association with
the species richness of annuals (Potts et al., 2003) and overall floral diversity (Banaszak,
1996). Apart from the floral resources richness, fallow farmland showed stable habitat
heterogeneity consisting of woody and herbaceous plants which could offer the variety of
habitat requirements, including nesting and feeding for diverse bee species. The
heterogeneous mix of large cashew nut trees, mango trees and associated woody shrubs,
annual flowering plants and grassland patches was probably able to support diverse bee
species with diverse foraging behaviour. Crop fields had greater absolute bee species
richness. This could be explained by the abundance of floral resources enabling the fields to
attract more“wanderer” bee species and those with long foraging ranges, such as Amegilla
52
and Xylocopa sp.. Liow et al. (2001) explains that bees with long foraging ranges are
associated to disturbed habitats. The high floral resources richness recorded in fallow
farmlands was dominated by more annuals than perennial floral species. The data showed
that the difference in bee diversity was not significant among the various habitats. This can be
explained by the fact that the habitats were close to each other with a high overlap and
probably allowed free movement of bee species. Extensive fallow corridors within the
farmlands could have contributed to greater habitat overlap leading to the closeness in bee
species diversity among the habitats. However, bee species composition at the forest edge
was closely similar to that in crop fields. This can be explained by a possible similarity in
floral resource composition and richness between the two habitats.
High butterfly diversity and absolute species richness were recorded at forest edge and forest
core. The habitat heterogeneity at the forest edge could be effective in offering habitat
requirements for both adult butterflies and their developmental stages. High floral resources
abundance in this habitat could have also contributed to the high butterfly diversity. A
positive reletionship is known to exist between butterfly diversity and floral abundance
(Steffan-Dewenter and Tscharntke, 1997). Butterfly diversity was significantly higher at the
forest edge than crop fields. This shows that a greater proportion of butterfly species of Kaya
Muhaka could be restricted to the forest and forest edge with limited foraging ranges between
the two habitats. Probably, the forest and forest edge provide specific habitat requirements for
diverse butterfly species in the area. Butterflies are known to exhibit specific habitat
requirements, namely adequate numbers of a single or a few host-plants for oviposition,
nectar-source plants, or even more cryptic resources ranging from mutualistic dependencies
to pools of standing water for critical minerals (Baz and Antonio, 1995). Many of these
butterflies in the forest could be specialised to inhabit the forest understorey and feed on
53
other food sources other than flowers. The food resources could be restricted in the forest and
within the narrow range of forest core and forest edge. This concept highlights the
significance of the forest in the conservation of butterflies.
Maybe some species can only thrive within the microclimate provided by closed canopies of
the forest. It could be justified to acertain that the presence of this forest is key to support of
diverse butterfly species in the area. Crop fields had the lowest butterfly diversity compared
to the other habitats. This could mean that the area consists of few generalist butterfly species
which have long foraging ranges and are associated with disturbed habitats, habitat
disturbance favours generalist butterfly species irrespective of habitat distinctiveness
(Spintzer et al., 1993) and can be found in areas altered by humans (Davros et al., 2006). The
close similarity in butterfly species composition between forest edge and crop fields could
mean that most butterfly species found at the forest edge had long foraging ranges and were
able to utilize floral resources in crop fields and forest edge. It could also mean that the two
habitats had closely similar habitat composition leading to inhabitation by closely similar
butterfly species. Forest core showed least similarity in butterfly composition to crop fields.
This can be explained by the presence of two categories of butterflies in the area, forest
dependent and forest independent. Forest indipendents inhabited majorly open farmlands
with some having extensive foraging ranges from forest edge to crop fields. The forest
dependents were restricted to KMF and its edge. Forest dependents are habitat sensitive and
have more specific requirements for habitat and vegetation composition to suit the needs of
their developmental life stages and are often found only in relatively natural areas with native
vegetation (Steffan-Dewenter and Tscharntke, 1997) like in the case of KMF. This highlights
further the need to conserve the forest.
54
5.4 Effect of increasing distance from forest core on bees and butterflies
Distance away from the forest core had no significant effect on overall butterfly abundance
and diversity. Increasing distance from forest core also had no significant effect on bee
species richness, diversity and abundance. The findings conform to the pattern found by
Klein et al. (2007) and Banaszak (1992) which reported no change in bee diversity or
abundance with distance from the forest. It also agrees with the findings of a similar research
done at Las Cruces forest in southern Costa Rica in which overall bee abundance, species
richness, and diversity did not vary significantly with distance from a large forest fragment
(Brosi et al., 2007). Bee communities appear to have some degree of resilience to land use
change. Bee and butterfly species showed resilience to human settlement, unplanned multiple
access routes and continuous vegetation clearance around settlements for perpetual
monocroping and related activities. The levels of these activities were not intense in the
region. This could have contributed to the persistence of bee and butterfly populations even
in points away from the forest. There is need to control these activities to avoid reaching
threat levels. The overall bee abundance, absolute species richness and diversity did not vary
significantly with distance from the forest. This implies that most bees are rather dependent
on habitat quality than proximity to primary forests.
The Kaya forest and forest edge probably acts as abuffers for the conservation of bees and
butterflies where they seek refuge for nesting and foraging when the farmlands are
extensively impoverished and indiscriminately disturbed. A. bojeri, a priority floral resource
to both bee and butterflies was dominant upto 1 km from the forest. This could have also
contributed to the reduction of abundance and diversity of the bee species. Though the level
of habitat heterogeneity in the habitats was not the same, it was realised across all the
habitats. This could have been the most important factor that influenced the diversity and
55
abundance of bees. Regional habitat heterogeneity could be more important factor than
farming practice in influencing the diversity and abundance of pollinators in agricultural
landscapes (Brosi et al., 2008). However, there was significant reduction in diversity of
butterflies with increasing distance from forest core. This implies a high butterfly diversity in
forest edge and forest core while farmlands (Crop fields and fallow farmland) recorded a low
butterfly diversity. Forest specialists are sensitive to habitat disturbance highlighting further
the role of Kaya forest in the conservation of butterflies in the region. The loss of this primary
forest would mean loss of these forest specialists. Butterfly families, Nymphalidae and
Pieridae were more resilient to habitat disturbance and distance from the forest. The two
families have strong powers of flight and open population structures such that they are
unlikely to be constrained by a lack of shelter, thus allowing them to exploit resources
inaccessible to other less vagile species (Dover, 1996) like those of family Hesperiidae. It is
possible that most members of the two butterfly families are generalist species which are able
to utilize a wide range of floral resources across the habitats including disturbed areas. The
opportunist butterflies with wide geographic distribution, most of them migrants, are
associated with disturbed habitat (Spitzer et al., 1993).
5.5 Effect of habitat type on bee and butterfly relative abundance
All the habitats recorded low relative abundance for both bees and butterflies. The relative
abundance of pollinators in a habitat is dependent on the distribution and abundance of floral
resources. This could mean that floral resources in the study area were patchily distributed,
less diverse and were not in abundance throughout the habitats to support high proportions of
individual bee and butterfly populations. The low abundance of some bee species especially
solitary bees could be attributed to low numbers or absence of their preferred host plants.
Probably the sampling period did not coincide with the emergence of some bee species as
56
well as the blooming time of their floral resources. Therefore, the associated bee species were
recorded in relatively low numbers leading to the low relative abundance. According to
Minckley et al. (2000) the emergence of certain solitary bees is governed by the blooming time
of their host plants and the distribution of their host plants directly influence their distribution.
The principal determinants of relative abundance of pollinator species is closely linked to
quality of forage resources, habitat heterogeneity, impact of natural enemies and plant
structural diversity (Potts et al., 2003).
Bees and butterfly utilization of these resources in the area could be a matter of chance. It
could also mean that the floral resources were restricted to certain parts of the habitats
restricting high densities of these pollinators in such areas during the flowering season. It is
known that the niche space of butterflies (i.e., the amount of their resources) strongly
influences the abundance of butterflies and consequently butterfly biodiversity patterns
(Yamamoto et al., 2007) and relative abundance. On the other hand bees are completely
dependent on flowers for food, their distribution pattern is therefore closely linked to the
distribution pattern of their floral resources. This finding points to a possible limitation of
floral resources to the local bees and butterflies. The findings also imply that while some
butterfly and bee species are abundant in Kaya Muhaka some could be rare.
5.6 Effect of floral resources on bees and butterflies
Most of the bee species were generalized feeders and visited many of the floral resources.
The bee species visited more than one plant species. This finding agrees with that of Waser et
al. (1996) in which plant-pollinator interactions was found to be generalized. They found that in
many cases a single plant species was visited by more than one bee species and one bee species
visited more than one plant species. There was a positive correlation between floral resources
57
richness and bee species richness. A similar result was found by Potts et al. (2003) and Banaszak
(2000). It was possible to link most of the bee species collected to their associated floral resources
unlike butterfly species. This is because most bees were collected as they were foraging except
afew, while most butterflies were collected on flight. This shows that bees unlike butterflies are
completely dependent on flowers for their food requirements (Neff and Simpson, 1993) and
their diversity within a habitat is linked to the diversity of flowering plants (Banaszak, 2000).
Their population structure is highly dependent on the composition of the plant community that
provide the resources. This is emphasized by Samways and Wright (1998) in which gall-insect
species richness was found to be highly dependent on plant richness.
The general pattern of floral resources utilization by bees and butterflies and habitat selection
with respect to suitable flowers seems to be that of opportunistic use of what is available
through the season, which is certainly advantageous under unpredictable conditions. The
observed lack of correlation between butterfly species richness and floral richness of the
study area conforms to the observation that overall butterfly diversity at a site is more
influenced by the diversity of nearby vegetation types than by the local plant diversity of the
site itself (Sharp et al., 1974). Most butterflies in this region could also be depending on other
food resources other than flowers and only a few are over-dependent on flowers. The
influence of plant associations on butterfly distribution seems to be one of scale. The range of
the animals, the distribution of particular plants of critical importance to them, and the
predictability of their environment all play a part in determining what the pattern of habitat
selection will be for each butterfly population (Sharp et al., 1974).
58
5.7 Conclusions
i.
Habitat heterogeneity could be a more important factor influencing the diversity and
abundance of bees and butterflies. Sites with high heterogeneity have the highest
capacity to satisfy the diverse ecological requirements of insect pollinators including
shelter, foraging, mating and breeding sites. Heterogenous habitats support high bee
diversity and an overall pollinator abundance.
ii.
Forest core, forest edge, fallow farmlands and crop fields are all important in the
conservation of bees and butterflies and complement each other in the conservation of
the species. However, some butterfly species are forest dependents. At least 45% of
butterfly species recorded during the study were seen to have preference to forest and
forest edge, pointing towards the need to conserve the forest.
5.8 Recommendations
i.
There is need to focus on conservation of insect pollinators in the coastal region
through an integrated approach e.g. community based projects on bee keeping and
butterfly farming.
ii.
Ecosystem approach to farming and careful planning of farmlands with wildflowers
and crop mixtures to improve habitat quality and heterogeneity to sustain bee and
butterfly populations.
iii.
There is need for further studies on habitat preference, species rarity and spatial
distribution of bee and butterfly communities in the study area and other coastal
forests.
59
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65
Appendix I: Checklist of bee species in KMF and surrounding farmlands
Bee species Sampling points
Amegilla sp. 1
Amegilla sp. 2
Amegilla sp. 4
Amegilla sp. 6
Braunsapis sp.
Ceratina sp. 1
Ceratina sp. 2
Ceratina sp. 3
Ceratina sp. 4
Ceratina sp. 5
Ceratina sp. 6
Ceratina sp. 7
Coelioxys sp.
Euaspis sp.
Halictus sp.
Heriades sp.
Hypotrigona sp. 1
Hypotrigona sp. 2
Lasioglosum sp.
Lipotriches sp. 1
Lipotriches sp. 2
Lipotriches sp. 3
Lipotriches sp. 4
Megachile feline Gerstacker
Megachile sp. 2
Megachile sp. 3
Megachile sp. 5
Megachile sp. 7
Megachile sp. 8
Megachille sp. 6
Nomia sp.
Pachyanthidium sp.
Pachymelus sp.
Pseudapis sp.
Pseudapis sp. 2
Sphecodes sp.
Steganomus sp.
Thyreus sp.
Unidentified 1
Unidentified 2
A1
0
0
0
0
0
0
0
0
0

0
0
0
0
0
0
0
0

0
0
0
0
0
0
0
0
0
0
0
0
0

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

0
0
A2
0

0








0
0

0
0

0
0
0
0
0



0

0
0


0
0

0
0


0




0
0
0


0



A3


0
0



0
0

0
0
0
0
0
0
0
0

0
0
0


0


0
0

0
0
0
0
0

0
0
0

0
0
0
0
0
0


0
0
0

A4
0

0
0
0

0






0
0

0
0
0

0
0

0

0
0

0


0

0
0
0
0
0
0

0
0
0
0
0
0

0
0
0
0
0
A5


0
0
0


0
0


0
0

0

0
0


0
0

0
0
0

0


0

0
0
0
0
0
0


0
0
0

0



0
0
0
0
A6
0


0
0

0

0


0
0

0
0
0
0
0
0
0
0

0
0
0

0
0

0
0
0
0
0
0
0

0
0
0
0
0
0

0
0
0
0
0
0

B1
0

0
0
0

0

0

0
0
0
0
0
0
0
0
0
0
0

0
0
0
0
0
0
0

0
0
0
0
0
0

0
0

0
0
0
0
0
0
0
0
0

0
0
B2
0

0
0
0



0


0


0
0
0
0





0
0
0

0
0
0
0
0
0
0

0
0
0
0

0
0
0
0




0


0
B3
0
0
0
0
0



0

0
0


0

0
0


0


0







0
0

0

0
0
0


0

0
0
0


0
0
0

B4
0

0

0


0


0
0
0
0


0



0
0

0

0

0



0
0

0

0
0
0


0

0
0
0

0

0


B5

0

0
0
0
0

0


0
0

0
0
0
0
0
0
0
0
0
0

0

0
0

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

0
0

0

B6
0
0
0
0
0

0
0



0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

0
0
0
0
0
0
0

0
0
0
0
66
Appendix II: Checklist of butterfly species in KMF and surrounding farmlands
Butterfly species
Acraea satis Ward
Anthene sp.
Appis lasti Grose-Smith
Baliochila sp.
Belenois creona Cramer
Bicyclus sp.
Colotis ione Godart
Hypolimnas deceptor Trimen
Junonia oenone Linnaeus
Leptotes pirithous Linnaeus
A1
0
0

0


0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

0
0


0


0
0
0

0
0
0
0

0

A2
0


0
0
0

0

0
0
0
0
0
0
0
0

0
0
0
0
0
0
0
0
0

0


0
0
0



0
0
0
0
0


0

0
0
0
0

0
A3
0

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

0
0
0

0
0
0

0
0
0
0
0
0
0

0
0
0
0
0
0
0
0
0
Sampling points
A4 A5 A6

0
0
0
0
0
  
 0
0
0
0
0
0
0
0
 0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
 0
0
0
0
0
 0
0
0
0
0
0
0
0

0
0
 0
0
0
0
0
 0
0
0
0
0
0
0
0

0
0

0
0
0
0
0
0
0
0
 0
0
0
0
0

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
B1 B2 B3 B4 B5 B6
 0
0
0
0
0
0
0
0
0
0
0
  0
0
0
0
  0
0
0
0
 0
0
0
0
0
  0
0
0
0
 0

0
0
0
 0
0
0
0
0
0
0
0
0
0
0
 0
0
0
0
0
 0
0
0
0
0
 0
0
0
0
0
 0
0
0
0
0
0
0
0
0
0
0
 0
 0
0
0
0
0
0
0
0
0
 0
  0
0
  0
 
0
0
0
0
0
0
0
 0
0
0
0
0
 0
0
0
0
0
 0
 0

0
 0
0
0
0
0
 0
0
0
0
0
 0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
 0
0
0
0
0
  0

0
0
  0
 0
0
 0

0
0
0
  0
0
0
0

0
0
0
0
0
  0
0
0
0
0
0
0
0
0
0
 0
0
0
0
0
0
0
0
0
0
0
 0
0
0
0
0
0
0
0
0
0
0
   0
0
0
 0
0
0
0
0
 0
0
0
0
0
  
0
0
0
 0
0
0
0
0
 0
0
0
0
0
 0
0
0
0
0
 0
0
0
0
0
 0
0
0
0
0
 0
0
0
0
0
 0
0
0
0
0
 0
0
0
0
0
67
Papilio demodocus Esper
Pardopsis puntatissiman Rothschild
Pseudacraea lucretia Cramer
Salamis cacti Fabricus
Spilia sp.
Spindasis victoria Butler
0
0
0

0
0
0
0
0
0
0
0
0
0
0

0


0
0
0
0
0
0
0
0
0
0
0
0
0

0
0
0
0

0
0
0

0
0
0


0
0

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

0
0
0
0
0
0
0

0
0
0
0
0
0
0


0
0
0
0
0
0
0
0
0




0

0
0
0
0

0

0
0

0
0
0
0
0

0
0
0
0


0
0
0
0
0
0
0
0
0

0

0
0
0
0
0
0
0
0
0
0

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
68
Appendix III: General list of floral resources in KMF and surrounding farmlands
Family
Papilionaceae
Rubiaceae
Compositae
Sapindaceae
Compositae
Acanthaceae
Euphorbiaceae
Papilionaceae
Rubiaceae
Caesalpiniaceae
Palmae
Papilionaceae
Compositae
Papilionaceae
Malvaceae
Convolvulaceae
Malvaceae
Labiatae
Labiatae
Papilionaceae
Caesalpiniaceae
Cyperaceae
Lobeliacea
Onagraceae
Lythraceae
Sapindaceae
Rubiaceae
Fabaceae
Amaranthaceae
Papilionaceae
Malvaceae
Anacardiaceae
Papilionaceae
Papilionaceae
Compositae
Tiliceae
Malvaceae
Compositae
Compositae
Sterculiaceae
Floral resources
Abutilon zanzibaricum Bojer ex Mast.
Ageratum conyzoides Linnaeus
Aspilia mossambiensis Oliv.
Asystasia gangetica Linnaeus
Bridelia cathartica Bertol
Catunaregam nilotica Stapf
Emilia coccinea Sims
Gossypioides kirkii Vahl.
Indigofera paniculata Poit
Kyllinga cartilaginea Schum
Lobelia fervens Thunb
Ludwigia sp.
Pentas bussei Krause
Philenoptera bussei (Harms) Schrire
Stylosanthes fruticosa Retz.
Tephrosia villosa Linnaeus
Urena lobata Linnaeus
Vernonia cinerea Less.
Vernonia sp.
69
Appendix IV: Floral resources preference by bee species
Floral resource
Abutilon zanzibaricum Bojer ex Mast.
Hoslundia opposite Vahl.
Chamaecrista mimosoides Trimen
Gossypioides kirkii Vahl.
Indigofera paniculata Poit
Ludwigia sp.
Philenoptera bussei Harms
Tephrosia villosa Linnaeus
Number of visiting
bee species
14
7
7
6
5
5
5
5
4
4
4
3
3
3
3
2
2
2
1
1
1
1
1
1
1
1
1
70
Appendix V: Distance matrix calculated using bray-curtis
Distance matrix for butterfly data set
X2
X3
X4
X1
0.6908517
0.8704453
0.5816993
X2
X3
0.9230769
0.6382253
0.8116592
Distance matrix for bee data set
X2
X3
X4
X1
0.4000000
0.7132616
0.3545455
X2
X3
0.7396825
0.4243697
0.6679245
Key: X1- Crop fields, X2 - Fallow farmland, X3 - Forest core, X4 - Forest edge
71
Appendix VI: Some common bee species collected in Muhaka, Kwale Kenya
Amegilla sp.
Ceratina sp.
Megachile sp.
Megachile discolor Smith
72
Appendix VII: Some forest dependent butterfly species in Kaya Muhaka forest
(Back side)
(Under side)
73
Appendix VIII: Bee taxonomy certificate

composition and floral resources of bees and butterflies in kaya

Transcription

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