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Coevolution in mutualistic communities
Plan
ts
Animals
Network structure for a plant-frugivore community in southeastern Spain. Bascompte and Jordano, 2007
Scott L. Nuismer
What is coevolution?
"Thus I can understand how a flower and a bee might slowly become, either simultaneously or one after the other, modified and adapted to each other in the most perfect manner, by the continued preservation of all the individuals which presented slight deviations of structure mutually favourable to each other." — Charles Darwin, The Origin of Species
Coevolution: Reciprocal evolutionary change in interacting species (Janzen, 1980)
Species 1
Species 2
For interacting pairs of species, coevolution:
• Generates diversity both within and among species– Levels of genetic polymorphism– Phenotypic diversification among populations
• Drives major evolutionary transitions– Sexual vs. Asexual reproduction– Ploidy level
• Modulates epidemiological dynamics– Incidence and severity of disease
Coevolution matters for pairs of interacting species
Plan
tsAnim
als
Network structure for a plant-frugivore community in southeastern Spain.
But most species interact with many others
Bascompte and Jordano, 2007
What role does coevolution play in these complex communities?
Quantifying the impact of coevolution
We can answer these questions by developing a simple model…
Does coevolution alter trait distributions?
Does coevolution alter community function?
Does coevolution alter network structure?
Question 1:
Question 2:
Question 3:
A simple model of mutualistic communities
• • •
• • •
Animals
Plants
1x
Each species is defined by a phenotype distribution and abundance
1,AN2x
2,AN
3x
3,AN
nx
nAN ,
1y
1,PN2y
2,PN
3y
3,PN
ny
nPN ,
Traits determine interaction probability
Phenotypic matching
e.g., Phenology
1 .0 0 .5 0 .0 0 .5 1 .0
0 .2
0 .4
0 .6
0 .8
1 .0
1 .0 0 .5 0 .0 0 .5 1 .0
0 .2
0 .4
0 .6
0 .8
1 .0
P[I
nte
ract
]
x - y
P[I
nte
ract
]
Phenotypic differences (threshold)
e.g., Corolla depth – proboscis length, Fruit size – beak size
x - y
• Consider two different functional forms of interaction
• • •
• • •
Animals
Plants
1y 2y 3y ny
1x 2x 3x nx
• Assumes mutualistic communities are organized by single “key” traits
Abundance + Traits + P[Interact] = Network structure
We want to predict how this network structure evolves
Predicting trait (co)evolution
Let’s start by defining individual fitness:
),()()( yxWxWxW BAT
Abiotic environment:
WA
Species interactions:
Phenotype, z
Optimal phenotype, • Assume all interactions are benefical
• Assume random encounters
• Focus on only inter-guild interactions
• Consider interactions mediated by either “matching” or “differences”
Predicting coevolution and community structure:
Two complementary approaches
Analytical approximation
Strong selectionEvolving G
Fitness
Individual based simulation
i
i
iii z
W
WGz
1
Does coevolution alter network structure?
Does coevolution alter community function?
Answering the questions using the model
Does coevolution alter trait distributions?
Question 1:
Question 2:
Question 3:
• Coevolution causes trait distributions to converge among guilds
• Coevolution causes trait values to converge within guilds
Weak coevolution Moderate coevolution
Species mean trait value
Frequency within
community
Species mean trait value
Frequency within
community
PlantsAnimals
PlantsAnimals
Does coevolution alter trait distributions?Case I: Phenotype matching
• Coevolution causes animal trait values to increase and plant trait values to decrease (or vice versa)
Weak coevolution Moderate coevolution
Species mean trait value
Frequency within
community
Species mean trait value
Frequency within
community
PlantsAnimals
PlantsAnimals
Does coevolution alter trait distributions?Case II: Phenotype differences
Does coevolution alter trait distributions?
• Yes! But the details depend on the functional relationship between plant and animal traits
Phenotypic matching
e.g., Phenology
1 .0 0 .5 0 .0 0 .5 1 .0
0 .2
0 .4
0 .6
0 .8
1 .0
1 .0 0 .5 0 .0 0 .5 1 .0
0 .2
0 .4
0 .6
0 .8
1 .0
P[I
nte
ract
]
x - y
P[I
nte
ract
]
Phenotypic differences (threshold)
e.g., Corolla depth – proboscis length, Fruit size – beak size
x - y
Does coevolution alter network structure?
Does coevolution alter trait distributions?
Does coevolution alter community function?
Question 1:
Question 2:
Question 3:
Answering the questions using the model
• Study how coevolution influences interaction rate and connectance
Low interaction rateand connectance
High interaction rateand connectance
Does coevolution alter community function?
Phenotype matching
Phenotype differences
Coevolution increases the rate of interaction within communities. Why?
Average fitness consequences to plants
Average fitness consequences to plants
Avera
ge fi
tness
co
nse
quence
s to
anim
als
Avera
ge fi
tness
co
nse
quence
s to
anim
als
Does coevolution alter community function?
Interaction rate Interaction rate
Why does coevolution increase interaction rates?
Species mean trait value
Frequency within
community
Species mean trait value
Frequency within
community
Proportion Successful
interactions
Proportion Successful
interactions
Proportion Unsuccessful interactions
Proportion Unsuccessful interactions
PlantsAnimals
PlantsAnimals
Trait Evolution: Matching Interaction rate: Matching
Trait Evolution: Differences Interaction rate: Differences
Yes. In all cases, mutualistic coevolution increases the
rate of interaction and network connectance
Low interaction rateand connectance
High interaction rateand connectance
Coevolution
Does coevolution alter community function?
Does coevolution alter community function?
Does coevolution alter trait distributions?
Does coevolution alter network structure?
Question 1:
Question 2:
Question 3:
Answering the questions using the model
• Study how coevolution influences the nestedness of mutualistic communities
Low nestedness High nestedness
Does coevolution alter network structure?
Matching Differences
Strength of Coevolution
What explains these patterns?
Strength of Coevolution
Nestedness(Plant)
Nestedness(Animal)
Does coevolution alter network structure?
Does coevolution alter network structure?Case I: Phenotype matching
A.
Trait distributions Network structureN
umbe
r of s
peci
es
B.
PlantsAnimals
PlantsAnimals
Mean phenotype
Num
ber o
f spe
cies
IE = 0.134NA = -28.00NP = -25.41
IE = 0.061NA = -8.16NP = -6.59
Before coevolution
After coevolution
Does coevolution alter network structure?Case II: Phenotype differences
A.
B.
Trait distributions Network structure
PlantsAnimals
PlantsAnimals
Mean phenotype
Num
ber o
f spe
cies
Num
ber o
f spe
cies
IE = 0.90NA = -9.08NP = -16.44
IE = 0.52NA = 31.42NP = 32.20Before
coevolution
After coevolution
Does coevolution alter network structure?
YES! Anti-nestedness &Reciprocal specializationRandom community
Coevolution(phenotype matching)
Coevolution(phenotype differences)
Low nestedness &GeneralizationRandom community
Conclusions I
• Mutualistic coevolution drives rapid shifts in trait distributions
Species mean trait value
Frequency within
community
PlantsAnimals
Conclusions II
• Mutualistic coevolution increases rates of interaction and the connectance of networks
Low interaction rate High interaction rate
Coevolution
Conclusions III
• Coevolution drives rapid changes in network structure
Before coevoluti
on
After coevoluti
on
500 Generations
Acknowledgements
Collaborators
Funding
National Science Foundation
Jordi Bascompte Pedro Jordano