The ecological and evolutionary impacts of altered

trophic structure due to climate change in aquatic communities

@DistribEcology

Edmund M. Hart and Nicholas J. GotelliUniversity of Vermont

Talk outline

• Background on climate change

• Study system / Experimental design

• How will climate change alter community structure?o How climate change destabilizes trophic

structure• Using network analysis

o The Evolutionary impacts of climate change in a model organism

• Using a common garden experiment

Climate change

Models predict changes in both temperature and precipitation

Climate change

Lavergne et al 2010

Framework for understanding the impacts of climate change on species

Climate change

Lavergne et al 2010

Woodward et al 2010

Decre

asin

g a

ltitud

e (in

creasin

g te

mp

era

ture

)

Climate change

Lavergne et al 2010

Chlamydomonas

Collins and Bell 2004

Questions1. How will climate

change alter trophic structure in a model system?

2. Will altered trophic structure be an agent of selection?

Study system

Study system

Vernal pond foodweb

Detrital / bacterial food source

Experimental design

Food websQuestion:

How will climate change alter trophic structure in a model system?

Hypothesis:Increased warming and drought severity will create more variable habitat that destabilizes food web structure.

Food websSpecies

Link

Each pond has a food web for each week it was sampled. Each was characterized bytwo metrics links / species (L/S) and the proportion of links that are predators (P)

Food websWeb dynamics

Each pond can be characterized by a time series of network metrics

How can we quantify the differences between these two time series?

Food websWeb dynamics

Food websWeb dynamics

Use autoregressive model parameters to quantify temporal stability.

Food websWeb dynamics

Quantify the variance of first order difference of a time series.

Food websHierarchical mixed model results for L/S

Ponds with a smaller water loss rate have the most temporally stable networks.

Enhances network stability

Destabilizes network structure

Food websHierarchical model of stationary variance in P

Ponds with a smaller water loss rate have lower variability in the proportion of links that are predators

Food websWhy are dynamics different?

Less variable habitats have far fewer larval stage predators.

Food websPredator use of stable habitat

Stable networks have high numbers of larval predators

Food websPredator use of unstable habitat

Unstable networks are used transiently adult predators

Food websConclusions

• Water loss rate had a strong effect on trophic structure dynamics.o High water loss rates decreased temporal

stabilityo Increased the variance in the proportion of

predators

• Changes in dynamics most likely due to changes in larval stage habitat usageo Ponds with unstable web dynamics had few

larval predators

Natural selection

Leuning 1992

Spitze 1991

Question:Will altered trophic

structure be an agent of selection driving

evolutionary change?

Hypothesis:D. pulex has demonstrated

rapid microevolutionary responses to predators in laboratory studies. We

expect a similar response if climate change alters trophic structure by reducing predators.

• Daphnia pulex

Natural SelectionD. pulex life cycle

D. pulex is cyclically parthenogenic producing clonal daughters

Natural selection

A B

A1

A3

A2

C

B1

B3

B2 C1 C2 C3Clones

Mothers

Common garden design

D. pulex were collected in September of 2010 and raised in a growth chamber for 3 months prior to the start of the experiment.

Trait Type MethodFrequenc

y

Spine lengthMorphologic

alMeasured from

photoEvery other

day

Body lengthMorphologic

alMeasured from

photoEvery other

day

Total lengthMorphologic

alMeasured from

photoEvery other

day

Head widthMorphologic

alMeasured from

photoEvery other

day

Clutch size Life-historyCounted live born

youngEvery

occurrence

Clutch number Life-history Counted liveEvery

occurrence

Growth rate Life-historyCalculated from

photographsOnce per individual

Intrinsic population growth rate

(r)

Life-historyCalculated via life table analysis of

individuals

Once per pond

0.203 mm

0.568 mm

1st instar D. pulex

Natural selectionTraits measured

Natural selectionTrait results

Lower values of 1st instar spine length and r were selected for in the most unstable ponds

Natural selectionTrait results

Natural selectionPredators abundance

Predator abundance was greatest in the most stable ponds and lowest in the least stable.

Natural selection

R2 = 0.69

R2 = 0.76

Trait correlation with predator abundance

Predator abundance was tightly correlated with each trait value. Traits were not correlated with any other covariate

Natural selection

• 1st instar tail spine length and r show a genetically based change in trait means.

• More variable habitats have lower predator abundance.

• Trait response is due to climate change, but mediated through that reduction in predator pressure.

• Lab results from earlier selection experiments can be useful in making predictions

Conclusions

Bringing it all togetherHabitat variability gradient due to climate change

Decrease in food-web stability

Changes in trophic structure directly related to climate change

cause an indirect evolutionary response.

Decrease in predator abundance

AcknowledgementsFunding from Vermont EPSCoR and

the NSF

Nick Gotelli

Head field assistant Tuesday the dog

• Alison Brody

• DonTobi and the Jericho Research Forest

• Many undergrad field assistants through the years, especially Cyrus Mallon, Chris Graves, Rachel Brooks, Maria Donaldson,Collin Love, Erin Hayes-Pontius and Jordan Smith.

Allie Hart (my dad)

Questions?

• @DistribEcology