PARENT SESSION
Oral Session #9: Theoretical Ecology -- Populations, interactions.
Presiding: D. Srivastava
Monday, August 5. 8:00 AM to 11:30 AM. Grand Ballroom Central, Radisson.

Competition and coexistence in multiple life history stages.

Moll, Jason^*,1, Brown, Joel¹, ¹ University of Illinois at Chicago, Chicago, IL

ABSTRACT- To investigate the interplay of mechanisms of coexistence and complex life histories, we have developed a population dynamic model of life histories with tradeoffs both within and between life history stages. In this Lotka-Volterra variant of the Ricker equation with multiple life history stages, the parameters of the model can be manipulated in order to change the effects of density dependence. Collapsing the model to a single life history stage creates dynamics similar to a Lotka-Volterra model of competition. Coexistence occurs when interspecific effects are weaker than intraspecific effects, while stronger interspecific effects result in either a single-species equilibrium or multiple stable states (where the winner depends on who is more common). When both life history stages are considered, the population dynamics of all life history stages of both species are intimately tied together. Weak density dependence in either life history stage for one species can create a buffer against strong interspecific interactions in the other stage, expanding the regions of the parameter space where the species can coexist. Similarly, if there are strong interactions in a given stage, it can exacerbate strong effects in the other stage, increasing both regions of single species equilibria and regions of multiple stable states. The model shows that coexistence most likely results from the interplay of both stages, therefore studying only one life history stage will give an incomplete picture.

KEY WORDS: competition, complex life cycles, ontogenetic niche shifts