Deer and Diversity in Garry oak ecosystems

Deer and Diversity in
Garry oak ecosystems
Emily Gonzales, Ph.D. Candidate
Centre for Applied Conservation Research
University of British Columbia, Canada
with thanks to the Canon National Park Science Scholars
Program, Parks Canada, Friends of Ecological Reserves
and Dr. Peter Arcese
Native Ecosystem Restoration
Efficient, effective restoration
depends on understanding
ecosystem function and species
relationships
Non-native species a challenge for
restoration
But ecosystems can be like a mystery
novel
Ecological detective work
The Mystery: What
happened to native
plants in Garry oak
ecosystems?
The Victims
Native plants in grasslands
• land conversion
• grazing
• invasion of non-native species
Complex – difficult to restore
Garry oak ecosystems in
top 3 most endangered
80% are gone
< 5% dominated by native
species
Saturna Island
98% biomass = non-native
The Suspects
Non-native grasses
Herbivores (native black-tailed deer,
introduced sheep and goats)
Three hypotheses
1.“Bottom-Up” hypothesis (e.g., Tilman)
Plants compete with each other for resources
2.“Top-Down” hypothesis
(Hairston, Smith & Slobodkin)
Herbivores
Plants regulated
are regulated
by herbivores
by predators
3. Enemy of my Enemy hypothesis (e.g., Colautti)
Herbivores eat certain plants which helps less
palatable plants by removing competitors
(e.g., insect biocontrol)
Experimental
Plants
2 x 2 Factorial Experiment
Plant native plants in experimental plots
2 crossed “states” = 4 treatments
Competition – Uncut or Cut extant
plants, spade around plots
Herbivory - No fence or Fence from deer
Monitored
5 Lilies
No fence/ No fence/
Uncut
Cut
Fence/
Uncut
Fence/
Cut
Camas Bulbs
5
4
Native plants
Change in mass(g)
6
Predictions
Bottom-up
Top-down
Enemy
3
2
1
0
No fence/
Uncut/No
Uncut
Fence
No fence/
Cut/No
Cut Fence
Fence/
Uncut/Fence
Uncut
Fence/
Cut/Fence
Cut
Seablush
500
Uncut/No fence
400
# Plants
Cut/No fence
300
Uncut/Fence
Cut/Fence
200
100
0
Start
2003
2004
2005
2006
Pattern consistent on landscape scale
100
Abundance
75
50
Native
Non-native
25
0
None
Med
High
Herbivory
200 plots in the Southern Gulf & San Juan Islands
Dastardly deer!
Sidney Island
D’Arcy Island
Many deer
Low native
richness,
abundance,
and biomass
Sallas Rocks
Little D’Arcy Islet
Few deer
High native
richness,
abundance,
and biomass
American Midwest
Comparison of vegetation plots between
1950 and 2000: 18% loss of diversity
unpalatable, generalist & non-native
plants (abundance non-natives low & not
correlated with decline)
(Rooney et al. 2004)
12% natives in unprotected areas
>50%
loss natives in protected areas
Presence of hunting, not actual deer
killed, benefits native species
(Brown et al. 1999, Martin and Baltzinger 2002)
Fencing & Cutting for Restoration
350
Biomass (g)
300
250
200
150
No Fence/Uncut
(sheep maybe not so baaaaad)
No Fence/Cut
Fence/Uncut
Fence/Cut
100
50
0
native
non-native
Conclusion
Restoration: 1. reduce deer, 2.
augment native plants, and 3.
remove non-native grasses
Barriers to restoration:
Knowledge gaps, funding,
unexpected results
Doing restoration in a research
framework = efficient
Acknowledgements
Funders: Canon National Parks Science Scholars Program NSERC
Parks Canada James Robert Thompson Fellowship Friends of
Ecological Reserves Hugh Robert Duncan Chisholm Scholarship
University Graduate Fellowship University of British Columbia
Islands Trust
Property Owners: Trinity Western University Salt Spring Island
Conservancy Dr. John Peirce Jim Campbell Peter Pearse & James
Kok Phil & Mary Middleton Ava Brumbaum Melissa Franks Ilsa
Leader Jacky Booth Jim Macdonald Galiano Conservancy
Association
Drs. Judy Myers & Jamie Smith
Staff & Volunteers: Rob Landucci Geri Poisson Melissa Flint
Rebecca Best Nicole Tunbridge Jennifer Mundy Sara Lebedoff
Liza Baer Steve Symes Brandi Roberts David Blasby Isaac
McEachern Greg Robertson Crow’s Nest Volunteers
Academics: Dr. Peter Arcese Dr. Roy Turkington Dr. Sarah Gergel
Dr. David Clements Dr. Andrew MacDougall Dr. Mark Vellend
The Suspects
Eastern grey squirrels introduced to
Stanley Park in 1909, Metchosin in 1967
Active spread in 80’s & 90’s
Introduced to cities around world
Replace Eurasian red squirrels in Europe
Sciurus vulgaris
The Victims
Douglas Squirrel
Tamiasciurus douglasii
Red squirrel
T. hudsonicus
Squirrel War in the Woods
Or is there another culprit?
Test of 2 hypotheses:
1. Displacement: Are EGS
competitively displacing native
squirrels?
2. Habitat: Does habitat selection
determine the distribution of
squirrels?
Gonzales et al. submitted
Number of Squirrels
500
400
300
Squirrel abundance data from shelters
Eastern grey
Douglas
Northern flying
200
100
0
1985
1988
1991
1994
1997
2000
2003
Year
Are EGS competitively displacing native squirrels? - No
Gonzales 2005
Habitat Selection for Squirrels in Greater Victoria
1.00
Gonzales 2005
Land type
Proportion
0.80
Grey squirrels
Red squirrels
0.60
0.40
0.20
0.00
Agriculture
Parks
Residential
Schools
Commercial
Open
Does habitat selection determine distribution? - Yes
Douglas squirrels
isolated in fragments
of conifer forest
No dispersal
Small population
effects
Native squirrels may
decline independent
of EGS
Gonzales et al. in review