the ecological and evolutionary impacts of altered
DESCRIPTION
A talk I gave at the Marine Biological Laboratory in December 2011. It is all based on my dissertation work.TRANSCRIPT
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