Effects of Recruitment and Post-recruitment Processes on Abundance of Stream Insects: a Comparative Approach

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ABSTRACTDEB 0089863PI: Barbara L. PeckarskyEffects of recruitment and post-recruitment processes on abundance of stream insects: a comparative approachThis study will help us understand how multiple factors interact to affect the abundance of plants and animals in nature. The goal of this proposal is to explain patterns of abundance of stream insect populations by conducting observations and experiments under realistic field conditions. Experiments in natural streams will test whether the abundance of larvae of two mayfly species is determined by the number of eggs laid by adults or the amount of food or predators in the larval habitat. The two mayfly species differ in egg-laying behavior, vulnerability to trout predation and behavior when faced with the risk predation and low levels of food (algae). First, in collaboration with Dr. Stephen Ellner we will use simulation models to predict how recruitment (egg-laying), presence of predators, and amount of food should affect the relative abundance of each mayfly species. Second, we will measure egg-laying, larval dispersal behavior (drift) and mayfly abundance in natural fish and fishless streams with different levels of food (algae). Third, in large-scale field experiments we will add or remove rocks and logs used by one of the mayfly species for egg-laying to test directly whether abundance of larvae is a function of recruitment. Fourth, we will drip water from containers with trout into fishless streams to determine whether drift of mayflies in response to trout chemicals can explain patterns of abundance in fish and fishless streams. Finally, we will manipulate multiple factors in experiments carried out in stream-side, flow-through chambers to determine whether drift of mayflies in response food and predators can explain larval abundance. Specifically, we hope to determine whether interactions with predators and resources override recruitment to explain the abundance of mayfly larvae in streams. This research can be generalized to apply to populations of other organisms that live in open systems and have one or more highly mobile life stages.