Spring 2014 Community Ecology Symposium

Sharon P. LawlerUC Davis Department

of Entomology and Nematology

Professor of Aquatic Entomology and Community Ecology

Sarah BolingerCommunity EcologyApril 2014

Education

B.A., Lehigh University

M.S., Rutgers University

Ph.D., Rutgers University Worked with well-known community ecologist

Peter J. Morin on competition in aquatic systems between insects and vertebrates

Continued to work with him on studies of population dynamics in laboratory protist microcosms

Research Interests

Insect-vertebrate competition in aquatic systems

Food web architecture and population dynamics Diversity effects on ecosystem function Ecotoxicology – effects of toxics on stream

ecology Mosquito control

MODEL SYSTEMS

Laboratory protist microcosms to research population and metapopulation dynamics; food chain architecture

Ecotron research “Ecology in a Bottle”

Protist Microcosm Studies

Microcosms are small, bounded habitats containing the desired number of organisms

Used to study ecological interactions on a scale that is highly replicable and easily controlled

Some population dynamics scale well; others don't

Protist Microcosm Studies

KINGDOM PROTISTA

(may actually be 8 separate kingdoms)

Eukaryotes that don't fit into other kingdoms

Euglena Paramecium

Publications1993 Lawler, Sharon P,. Morin, Peter J. Food web architecture and population dynamics in laboratory microcosms of protists. The American Naturalist, 141(5): 675-686.

1993 Lawler, Sharon P. Species richness, species composition and population dynamics of protists in experimental microcosms. Journal of Animal Ecology, 62: 711-719.

1993 Lawler, Sharon P. Direct and indirect effects in microcosm communities of protists. Oecologia, 93: 184-190.

1995 Balciunas, Dalius and Sharon P. Lawler. Effects of Basal resources, predation, and alternative prey in microcosm food chains. Ecology, 76(4): 1327-1336.

1995 Morin, Peter J. and Sharon P. Lawler. Food web architecture and population dynamics: Theory and empirical evidence. Annual Review of Ecology and Systematics, 26: 505-529.

1996 Morin, Peter J. and Sharon P. Lawler. Effects of food chain length and omnivory on population dynamics in experimental food webs. Food Webs - Integration of Patterns & Dynamics, 218-230.

1996 Holyoak, Marcel and Sharon P. Lawler. The role of dispersal in predator- prey metapopulation dynamics. Journal of Animal Ecology, 65: 640-652.

2000 Holyoak, M., S.P. Lawler and P.H. Crowley. Predicting extinction: Progress with an individual-based model of protozoan predators and prey. Ecology, 81(12): 3312-3329.

2004 Orland, M.C. and S.P. Lawler. Resonance inflates carrying capacity in protist populations with periodic resource pulses. Ecology, 85(1): 150-157.

2005 Holyoak, M. H. and S. P. Lawler. The contribution of laboratory experiments on protists to understanding population and metapopulation dynamics. Advances in Ecological Research, 37: 245-271.

Food Web Architecture and Population Dynamics

In theory, food chain length and presence of omnivory are important to population dynamics

Food web theory was controversial because experimental evidence of the effects of food chain length and omnivory (and other food web characteristics) on population dynamics were relatively few at the time

Lawler and Morin 1993

Food web architecture and population dynamics in laboratory microcosms of protists.

Look at population dynamics in protist microcosms Do protist communities in longer food chains

experience more instability? Does the presence of omnivory by top predators

destabilize population dynamics? Complications: stability as evaluated in model

systems is harder to measure empirically

Look for parallels between model behavior and measurable dynamics in experimental populations (used as proxy for stability)

Dynamics used: persistence time temporal variability of population size return time

Lawler and Morin 1993

Detritus-based food webs

Bacterivorous ciliates

Tetrahymena pyriformis Colpidium striatum

Facultatively omnivorous ciliate

Blepharisma americanum

Experimental Setup

Experimental Setup, cont.

Testing effect of position in food web on stability of population of a species

Compare mean abundance and temporal variation in abundance in populations of bacterivores (T. pyriformis and C. striatum) when each is top predator (short food chain length) or penultimate predator (long food chain length)

Long food chains also differ in whether top predator is omnivore or nonomnivore

Experimental Setup, cont.

Testing effects of omnivory Two conditions for facultative omnivore B.

americanum: 1. feeds only as bacterivore 2. feeds as omnivore

Compare population dynamics between the two Also compare to population dynamics of a

nonomnivore top predator Lastly, compare effects on prey population stability by

looking at population dynamics in bacterivores preyed on by omnivores vs. nonomnivores

Do longer food chains and food chains containing omnivory show signs of unstable population dynamics?

Results and Conclusions

Results and Conclusions

Addition of top predator reduces abundance of bacterivores Blepharisma increases more rapidly and has higher mean

abundance when feeding as omnivore; max population was the same

Population dynamics of bacterivores vary more in longer food chains except in one case

Omnivore abundance varies less than that of nonomnivores at third trophic level

Blepharisma shows greater variation when restricted to bacteria, because of slower growth of these populations

Results and Conclusions

Tentatively support population fluctuation and extinction increase with increased chain length

Omnivore study seems to indicate that species feeding at multiple trophic levels better endure fluctuations in prey abundance

Generalization requires more research, but it's important that real communities of organisms display theoretical food web phenomena

Lawler and Morin 1995

How to find experimental evidence of issues within food web theory:

Factors limiting food chain length How length and complexity affect trophic

cascades How length and complexity affect population

dynamics

Experimental Evidence of Food Web Theory

Lots of theoretical work existed, but much less experimental work – why?

Hard to get from long-lived organisms in natural systems

Skepticism exists over whether food web models are accurate and even applicable to natural systems at all

Lawler and Morin: Theories are testable, especially in artificially constructed environments (ie microcosms)

Food Web Theory: Background

Elton: Food chains are short Hypotheses: energetic transfer efficiency;

dynamic instability Omnivory

Lotka-Volterra models destabilize with omnivory

Thought to be uncommon until recently

Food Web Complexity and Population Dynamics

Relationship between complexity and stability – positive or negative?

Empirical studies hard to interpret No studies vary connectance while holding

species richness constant

Testing Food Web Theory – Future Work

Show quantitatively that dynamics are similar between model and real system

Study food chains longer than 2 or 3 levels Increase species richness in studies More work needed in studies of:

Omnivory effect on population dynamics Effects of nutrient enrichment Effects of more complex food chains on

trophic cascades

Contributions of Laboratory Microcosm Studies

Holyoak, M., and S. P. Lawler 2005. The contribution of laboratory experiments on protists to understanding population and metapopulation dynamics. Advances in Ecological Research, Vol. 37: Population Dynamics and Laboratory Ecology 37:245-271.

Huge variety of protists useful in constructing communities

Many protists make good analogs of larger species with similar ecological strategies

Studying protists is convenient – short generation time, high replicability

Protist study has been historically important in verifying models, like Gause's studies of logistic growth and competitive exclusion

How useful are natural microcosms for study?

Whole ecosystem vs. laboratory microcosm studies: tractability vs realism in ecological study

Can natural microcosms help circumvent the conflict?

Potential for replication; natural boundaries; small size; short generation time of most organisms

Some questions well-suited to these systems:

How does diversity affect ecosystem function? How does the metacommunity affect species

richness? So why use natural? How good is the external validity,

actually?

Srivastava, D.S, Kolasa, J., Bengtsson, A. Gonzalez, Lawler, S.P., Miller, T.E., Munguia, T, Romanuk, Schneider, D.C., Trzcinski, M.K. 2004. Are natural microcosms useful model systems for ecology? Trends in Ecology & Evolution, 19(7): 379-384.

Ecotron

Climate-controlled facilities for ecological experiments

16 chambers

Uses of Ecotron

Create simplified communities to study in a lab

Real-life simplified model of nature

Because of climate control, experiments can be replicated across the chambers and statistical analysis is more robust

Species Diversity and Ecosystem Performance

Naeem, S. et al. 1995. Empirical evidence that declining species diversity may alter the performance of ecosystems. Philosophical Transactions of the Royal Society of London Series B, 347: 249-262.

Hector, A., J. Joshi, S.P. Lawler, E.M. Spehn, and A. Wilby. 2001. Conservation implications of the link between biodiversity and ecosystem functioning. Oecologia, 129: 624-628.

Ecotron Experiment

Direct manipulation of diversity Replication: 14 chambers; all

conditions held constant except diversity – high, med, low

Four trophic levels Keep at least one member of each

trophic group and functional group Look at effects on identified

ecosystem processes Community respiration, productivity,

decomposition, nutrient retention, water retention

Using Mesocosms to Study Effects of Diversity

Loss of a whole trophic level or functional group has clear impact, but what about part? As biodiversity declines, will ecosystem function change?

Know about causes of diversity, and about biogeochemical cycles and energy in ecosystems, but what about how diversity affects cycling and energy flow?

Four hypotheses at the time

Results and Conclusions

“Higher diversity systems had more dense, more complex canopies, higher numbers of earthworms and insect herbivores, greater rates of CO2 flux, greater productivity and greater accumulation of phosphorus and potassium.”

Doesn't appear to be an artifact of particular plant community used

Limitations

Some caveats when attempting to extrapolate results to natural systems, but it appears that affecting diversity can cause ecosystem function to change even if trophic structure is unmanipulated, but changes vary across functions. Also it appears that if loss of diversity affects canopy structure, CO2 and productivity are affected.

Other Research

Cascade frogs What are indirect effects of introduced trout on

Rana cascadae? Competition for prey appears to be limiting

populations of R. cascadae Mosquito control

Literature Cited

Lawler, Sharon P,. Morin, Peter J. 1993. Food web architecture and population dynamics in laboratory microcosms of protists. The American Naturalist, 141(5): 675-686.

Naeem, S. et al. 1995. Empirical evidence that declining species diversity may alter the performance of ecosystems. Philosophical Transactions of the Royal Society of London Series B, 347: 249-262.

Morin, Peter J. and Sharon P. Lawler. 1995. Food web architecture and population dynamics: Theory and empirical evidence. Annual Review of Ecology and Systematics, 26: 505-529.

Srivastava, D.S, Kolasa, J., Bengtsson, A. Gonzalez, Lawler, S.P., Miller, T.E., Munguia, T, Romanuk, Schneider, D.C., Trzcinski, M.K. 2004. Are natural microcosms useful model systems for ecology? Trends in Ecology & Evolution, 19(7): 379-384.

Holyoak, M., and S. P. Lawler 2005. The contribution of laboratory experiments on protists to understanding population and metapopulation dynamics. Advances in Ecological Research, Vol. 37: Population Dynamics and Laboratory Ecology 37:245-271.

Joseph, M., J. Piovia-Scott, S. Lawler and K. Pope. 2011. Indirect effects of introduced trout on Cascades frogs (Rana cascadae) via shared aquatic prey. Freshwater Biology, 56: 828-838.