File - Dr. Julius A. Ellrich

Trait-Mediated Indirect Interactions
in Intertidal Food Chains
Julius A. Ellrich
BREMEN
UNIVERSITY
Consumptive & Nonconsumptive Effects (NCEs)
nonconsumptive effects
consumptive effects
direct
effects
predation
predator
predator
chemical cue
killing
prey
changes in prey traits:
(risk effects)
predation risk
• behaviour, activity
• morphology, physiology
• habitat shift, life-history
Direct & Indirect Interactions
consumptive effects
direct
effects
predation
nonconsumptive effects
predator
predator
chemical cue
killing
density
mediated
indirect
effects
(DMIIs)
predation risk
consumer
basal species / ressource
trait
mediated
(TMIIs)
Indirect Interactions
-
density-mediated
(DMII)
X
-
+
trait-mediated
(TMII)
-
X
+
TMIIs: Positive Indirect Effect on Basal Species
Basal species response
- Towards Generality -
Control Consumer
Control Consumer
Predation risk
1st Example : Green Crab – Periwinkle – Fucus
a
a
a
b
Field Experiment, Maine, USA, several months
 STRONG positive indirect effect!
Trussell et al. 2002, Ecology Letters
2nd Example: Green Crab – Dogwhelk – Barnacle
13%
28.8%
dogwhelks
Lab Experiment, Maine, USA
 positive indirect effect!
Trussell et al. 2003, Ecology
North East Atlantic
Denmark
North Sea
Helgoland
Germany
Helgoland, North Sea
http://www.google.de/imgres?imgurl=http://upload.wikimedia.org/wikipedia/commons/d/d0/Helgoland_Vogelperspektive_sx.jpg&imgrefurl=http://de.wikipedia
.org/wiki/Hafengesellschaft_Helgoland&h=2380&w=3500&tbnid=ejqXTr9UBLVXlM:&zoom=1&tbnh=90&tbnw=132&usg=__sHfDrutDOYnfLRfIxNHwRpLWK5U=&d
ocid=uhgKxoiRE2cqKM
Nordostwatt, Helgoland
Picture: Paolo-Film, taken from ZDF Abenteuer Wissen: "Algenfischer - Im Regenwald der Meere" (German TV broadcast)
Collection of Organims
Crab Trap
Periwinkles
Crabs
Seaweeds
Upbringing of Seaweed Recruits
Seaweed recruits (12 x magnification)
Recruit Sampling
Fucus Survivorship (%) = Final Recruit Density/Initial Recruit Density *100
1st Experiment
-Laboratory-
Factorial Design
Independent variables:
predation risk
consumption
Dependent Variable: Fucus Recruits Survivorship (%)
Lab: Basic Experimental Unit
Crab compartment
Mesh divider
Periwinkle & seaweed
compartment
unidirectional
water flow
Lab 1: Green Crab - Periwinkle - Seaweeds
10 replicates, summers 2009
Lab: Summer 2009
Results: Summer 2009
120
A
B
Fucus Survivors (%)
100
a
a
b
(32 %)
80
b
60
40
20
0
(mean±sem)
 STRONG positive indirect effect!
Ellrich 2010
2nd Experiment
-Field-
Field: Summer 2008
Picture: Markus Molis, 2008
Open Plot Setup
No Risk
Risk
Fucus Survivorship (%)
Field: Summer 2008
Early Summer
Late Summer
 NO positive indirect effect!
Molis et al. 2011,
Journal of Ecology
Field: Summer 2008
Picture: Markus Molis, 2008
Study Site
Fucus
barren
mean: 150 periwinkles/m2
Picture: Andreas Wagner, 2008
Patchiness in Periwinkles
max.: 829 periwinkles / m2
3rd Experiment
-Lab: Periwinkle Density-
Basal Species Response
TMIIs: Effects of Consumer Conspecific Density?
increasing consumer density
increasing consumer density
Predation Risk
Lab 2: Periwinkle Density
10 replicates, May 2009
Lab 2: Periwinkle Density
A
Periwinkle Effect Size (%)
140
B
120
100
80
60
40
20
0
 STRONG positive indirect effect!
Ellrich. 2010
4th Experiment
-Wild Crab Exclusion-
Field: Summer 2008
Picture: Markus Molis, 2008
Crab Activity
mean: 12 Green Crabs / day
Predation Risk Arenas
No Risk
Risk
5 replicated plots, Jul 2009
(drawings: green crab (Gruber 1993), periwinkle (Götting 1974)
Arenas
Study Site: Summer 2008
Field: Summer 2008
120
A
B
100
Fucus Survivorship [%]
a
a
80
b
60
34 %
40
c
20
0
1
1
(mean±sem)
 MEDIUM positive indirect effect!
Molis et al. 2011, Journal of Ecology
Conclusions
TMIIs have positive effect basal species:
•
similar patterns found…
in two different food chains
in NW & NE Atlantic systems
in two different years
in lab & field experiments
•
but:
local factors (e.g. wild green crabs) may differ and therefore affect pattern
“NCE strenght” may differ between study sites (~75% NW Atlantic VS 34 % NE Atlantic)
Basic general pattern?
 literature review, field observations, experiments
 include other systems (freshwater, terrestrial etc.)
Nonconsumptive Effects - Habitat Shift
Littoraria irrorata
on marshgrass
Panopeus obesus
1http://science.kennesaw.edu/~jdirnber/Bio2108/Lecture/LecBiodiversity/BioDivFungi.html
2http://www.flickriver.com/photos/alan_cressler/sets/72157604854442016/
Data: Griffin et al. 2011 Biology Letters
3rd Example: Crab – Periwinkle - Marshgrass
Study Site
Experimental Unit
Pictures: Griffin et al. 2011, Biology Letters
TMIIs: Negative Effect on Basal Species
Griffin et al. 2011 Biology Letters
TMIIs: Positve & Negative Effects on Basal Species
-
+
Trussel et al. 2002, Ecology Letters
Trussel et al. 2003, Ecology
Molis et al. 2011, Journal of Ecology
-
-
Griffin et al. 2011, Biology Letters
Summary
• Two types of indirect interactions (DMIIs & TMIIs) in food chains
• DMIIs occur in food chains (tri-trophic interactions), when predators kill
consumers und thereby alter basal species responses
• TMIIs occur, when predator non-consumptive effects (NCEs) cause trait changes in
prey and thereby alter basal species responses
• Indirect effects caused by DMIIs and TMIIs can occur at the same time (one single
predation event)
• TMIIs may often be stronger than DMIIs, as the NCE of one predation event can
affect multiple consumers simultaneously
• TMIIs can have positive or negative effects on basal species
Thank You!
References
Ellrich, J. A. 2010. Effects of Crab Predation Risk on Periwinkle Grazing
Activity. MSc Thesis, Marburg University, Germany
Griffin, J. N., J. Butler, N. N. Soomdat, K. E. Brun, Z. A. Chejanovski, and B. R.
Silliman. 2011. Top predators suppress rather than facilitate plants in a traitmediated tri-trophic cascade. Biology Letters 7:710-713.
Molis, M., I. Preuss, A. Firmenich, and J. Ellrich. 2011. Predation risk indirectly
enhances survival of seaweed recruits but not intraspecific competition in an
intermediate herbivore species. Journal of Ecology 99:807–817.
Trussell, G. C., P. J. Ewanchuk, and M. D. Bertness. 2002. Field evidence of
trait-mediated indirect interactions in a rocky intertidal food web. Ecology
Letters 5(2):241-245.
Trussell, G. C., P. J. Ewanchuk, and M. D. Bertness. 2003. Trait-mediated
effects in rocky intertidal food chains: predator risk cues alter prey feeding
rates. Ecology 84:629–640.