Transcript ppt
Spring 2014 Community Ecology Symposium Sharon P. Lawler UC Davis Department of Entomology and Nematology Professor of Aquatic Entomology and Community Ecology Sarah Bolinger Community Ecology April 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 Publications 1993 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 individualbased 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: 245271. 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 Lawler and Morin 1993 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 Experimental Setup Detritus-based food webs Bacterivorous ciliates Tetrahymena pyriformis Colpidium striatum Facultatively omnivorous ciliate Blepharisma americanum 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? 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. 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? 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.