PARENT SESSION
Oral Session # 95: Predator - Prey Ecology III: Aquatic Systems.
Presiding: J Vonesh
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 201.
Inducible morphological defense and community dynamics in protists.
Altwegg, Res*,1, Marchinko, Kerry B.1, Anholt, Bradley R.1, 1 University of Victoria, Victoria, BC, Canada
ABSTRACT- Inducible defenses are expressed according to current risk situation and incur a fitness cost that may decrease competitive ability. Thus, predators affect food webs both directly, through consumption, and indirectly by changing the interaction strength between their prey and other community members. Depending on which of these effects prevail, the dynamics of communities are predicted to be quite different. In response to live or dead predators, the hypotrich ciliate Euplotes aediculatus develops lateral projections that effectively protect it from being eaten by the gape limited predator Stenostomum sphagnetorum, at the cost of slower reproduction. Paramecium aurelia shares resources with Euplotes, but does not alter its morphology in response to predators. In an attempt to disentangle direct from indirect effects, we exposed Euplotes, alone or together with Paramecium, to either live, dead or no predators and followed the dynamics for twenty generations. The morphological defense of Euplotes varied over time and loosely tracked predator density. Simple models predict destabilizing lagged effects on population dynamics for such systems. However, population dynamics of Euplotes, characterized by the coefficient of variation in population size, was not affected by the predator treatment in any detectable way. Paramecium depressed the population growth rate of Euplotes, and the effect was stronger when Euplotes expressed defenses in response to dead predators. Thus, we present a system in which inducible morphological defenses affect community processes. Its experimental tractability and the short generation time may make this system an important tool to bridge the gap between theory and empirical evidence and significantly improve our understanding of community dynamics.
Key words: population dynamics, predation, food web, competition