Post on 15-Apr-2017
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Cascading effects of spatial structure across trophic levelsRachel M. GermainKillam/Biodiversity Postdoctoral Fellow
Main collaborators: Natalie Jones, Tess Grainger, Ben Gilbert, Andrew MacDougall
Community ecologist: species coexistence and metacommunities
Schematic modified from Velland 2016
Botany seminar Oct. 11th @12:30pm
env gradient
Collaborators
Tess Grainger Natalie Jones Ben Gilbert
Biological communities rarely exist in isolation
‘metacommunity’
biotic/abiotic environment
Predictions of island biogeography/metapopulation theories
species richness/site occupancy larger, less isolated patches
species richness/site occupancy smaller, more isolated patches
MacArthur & Wilson 1967; Hanski 1994
Predictions of island biogeography/metapopulation theories
species richness/site occupancy larger, less isolated patches
species richness/site occupancy smaller, more isolated patches
MacArthur & Wilson 1967; Hanski 1994
Spatial constraints likely vary among species
sessile vs. motile, dispersal ability, cognitive function → behavior (habitat selection, territory, predator avoidance), body size, matrix sensitivity, etc.
P
C2
C1
C3
Cascading spatial dynamics among trophic levels
patchisolation
patchsize
spatial patterns
spatial patterns
Multi-trophic extensions of island biogeography and metacommunity theories
Trophic dependency: predators can only establish in patches that already contain their prey• prey must outpace their predators• predator distributions should be a subset of prey distributions• IBT patterns should be stronger at higher trophic levels
Holt 2002 EcoRes; Leibold et al. 2004 EcoLett; Harvey & MacDougall 2014 Ecology
Assumes that predators: are specialists, are bound to same habitat patches as their prey, and experiencethe world at the same spatial scales as their prey
What are the consequences for diversity in systems where spatial constraints differ within and among trophic levels?
aspen-understory plantsJones, Germain, et al. 2015 JEcology
tall-grass prairie plantsGermain et al. 2013 AmNat
milkweed insect specialistsGrainger, Germain, et al.
in review Ecology
What are the consequences for diversity in systems where spatial constraints differ within and among trophic levels?
aspen-understory plantsJones, Germain, et al. 2015 JEcology
tall-grass prairie plantsGermain et al. 2013 AmNat
milkweed insect specialistsGrainger, Germain, et al.
in review Ecology
Tall-grass prairie restoration efforts in SW Ontario
System: tall-grass prairie plant communities
System: tall-grass prairie plant communities
How does risk avoidance behavior by small mammals affect spatial patterns in plant communities?
predationrisk
cognition
yes
yes
no
rangesize
Predation risk increases with distance from old-field edge
pre-prairie
more removal less removal
old-field
Prediction:
Closedold-field Pre-prairie
-30 -10 10 30 50 70 90+
Distance from edge (m)
Prop
. see
ds re
mov
ed
F1,84 = 150.9, P < 0.0001*
Seed removal was strongest in the old-field, and decreased with distance from the edge
Consequences of small mammals for plant diversity depends on foraging selectivity
Cafeteria trial w/ 8 plant species from 3 functional groups
B. kalmii H. divaricatus R. blanda
H. annus
H. dive
ricatus
L. capita
ta
R. blanda
S. trifo
lia
S. cryp
tandrus
B. inerm
is
B. kalm
ii0
2
4
6
8
10
Seed species
Seed
s rem
aini
ng
Forb seeds were consumed significantly more than shrub and grass seeds
Functional group: F2,23 = 29.97, P < 0.001*Species: F5,23 = 0.35, P = 0.876
Forbs Shrubs Grasses
P = 0.012*F1,48 = 12.82, P <0.001*
β-di
vers
ity (J
acca
rd’s
diss
imila
rity)
α-di
vers
ity (s
peci
es p
er p
lot) α β
Distance from edge (m) Distance from edge (m)
What does this all mean for plant community distributions?
What does this all mean for plant community distributions?
P = 0.012*F1,48 = 12.82, P <0.001*
β-di
vers
ity (J
acca
rd’s
diss
imila
rity)
α-di
vers
ity (s
peci
es p
er p
lot) α β
Distance from edge (m) Distance from edge (m)
oldfield
increasingβ-diversity
decreasing seed
predation
prairie interior
Net effect: emergent patterns in plant diversity that reflect risk environment
What are the consequences for diversity in systems where spatial constraints differ within and among trophic levels?
aspen-understory plantsJones, Germain, et al. 2015 JEcology
tall-grass prairie plantsGermain et al. 2013 AmNat
milkweed insect specialistsGrainger, Germain, et al.
in review Ecology
System: milkweed insect specialistshabitat use
generalist
milkweedspecialist
Milkweed specialists differ in susceptibility to predators and dispersal ability
Constrained by predation1:
yes
1Duffey & Scutter 1972, Zalucki & Kitching 1982, Smith et al. 2008 2Jones & Parella 1986, St Pierre & Hendrix 2003, McCauley et al. 1981
no
yes no
Constrained by size/isolation2:
<100 m >1000 m
Predictive framework for island biogeography informed by natural history
P, S, I
S, Inone
P
Patc
h oc
cupa
ncy
Patch size/isolation
P = predator, S = size, I = isolation
Do constraints of patch size/isolation vary among species, and are they altered by predation?
Field surveys of milkweed patches
Patch isolation
Patch size (m2)
𝐼 𝑖=1−∑𝑗 ≠𝑖
𝑛
𝐴 𝑗𝑒(−𝑑 𝑖𝑗 /𝛼 )
Hanski 1994 TREE
Presence/absence data Predator abundances
occupancy ~ patch size x patch isolation x predator abundances
Predictive framework for island biogeography informed by natural history
none
P
N.S.
Patch isolation
Occ
upan
cy
P, S, I
S, I
P = predator, S = size, I = isolation
Predictive framework for island biogeography informed by natural history
none
PP = predator, S = size, I = isolation
P, S, I
S, I
Predictive framework for island biogeography informed by natural history
none
PP = predator, S = size, I = isolation
P, S, I
S, I
Zalucki & Kitching 1982a JZoology, Zalucki & Kitching 1982b Oecologia
“More eggs were laid per plant on single isolated plants than on plants within a patch”
“The trend was for increasing [mortality] with increasing patch size” → predation
Predictive framework for island biogeography informed by natural history
none
PP = predator, S = size, I = isolation
P, S, I
S, I
Tying it all together…
Dispersal-limited species were directly affected by spatial constraints
Predation affected palatable species indirectly through interactions with spatial drivers
Incorporating predator-avoidance tactics (refuge seeking and crypsis) can help refine predictions
Biogeographic constraints highly variable among species in this community – but fairly predictable
Matrix-dwelling predators can weaken or modify the effects of spatial drivers
What are the consequences for diversity in systems where spatial constraints differ within and among trophic levels?
aspen-understory plantsJones, Germain, et al. 2015 JEcology
tall-grass prairie plantsGermain et al. 2013 AmNat
milkweed insect specialistsGrainger, Germain, et al.
in review Ecology
System: Aspen understory plant communities
Do effects of stand size and isolation on species distributions vary with dispersal mode?
cognition
yes
no
rangesize
Field surveys of aspen stands
𝐼 𝑖=1−∑𝑗 ≠𝑖
𝑛
𝐴 𝑗𝑒(−𝑑 𝑖𝑗 /𝛼 )
Hanski 1994 TREE
Stand characteristics
size (m2) isolation
stand age
Presence/absence data Dispersal mode
No aid
Wind
Animal
Aspen stand
Adjacent grassland
Predicted effects of stand size and isolation for different dispersal modes
No aid Wind-dispersed Animal-dispersed
Observed effects of stand size and isolation for different dispersal modes
No aid Wind-dispersed Animal-dispersed
competition among dispersal modes?
ruderal species and disturbance?
Paired plot design to identify aspen specialists vs. generalists or grassland specialists
Quantifying species affinity for aspen stands
all species includedoccurs in aspen stands ≥50% of the timeoccurs in aspen stands ≥ 66% of the timeoccurs in aspen stands ≥75% of the time
cut-off is not always clear in “diffuse” metacommunities
Cook et al. 2002 EcoLett; Leibold et al. 2004 EcoLett
metacommunity = species that occur in favourable habitat patches imbedded in a matrix of unfavourable habitat
The results are insensitive to cut-off, except when all species are included
SR ~ stand size
Matrix-associated species can obscure metacommunity processes – paired plot design is one day to discount their effects
IBT patterns are somewhat consistent with our initial predictions, but …There are three complicating factors:• dispersal mode• unexplained inconsistencies • grassland specialists + generalists
…and so, to summarize…
ability to persist in matrix habitat = modifications to biogeographic constraints in insect species that are sensitive to predators
greater habitat use by granivores in low risk areas = gradients in ecological filters that dictate plant species distributions
habitat selection by animals = non-IBT patterns for animal-dispersedplant species
“patch area and isolation are surprisingly poor predictors of occupancy for most species”
data from 1,015 bird, mammal, reptile, amphibian, and invertebrate population networks
metapopulation metacommunity∑ =
Island biogeography in non-island systems
suitable habitat unsuitable habitat
Island biogeography in non-island systems
suitable habitat unsuitable habitat
Are patch size and isolation unimportant compared to/in combination with local factors? How do spatial dynamics cascade across trophic levels? How do spatial dynamics change with species additions or losses at different trophic levels? Should conservationists only be focusing on patch size/isolation?
AcknowledgementsCo-authorsNatalie JonesTess GraingerBen GilbertAaron HallLynn BaldwinAndrew MacDougallKarl CottenieLaura JohnsonElizabeth Gillis
Webpage: rgermain.wordpress.com Email: rgermain@zoology.ubc.caOffice: BIODIV245
Monarch caterpillar mortality as a function of stand size
PCoA testing turnover in proportion of species belong to each dispersal modes