The Contribution of Population, Spatial and Temporal Structure to Persistence in the Development of Stream Community
Ecologically similar species frequently occur together, but theory places restrictions on the conditions that allow for the coexistence of these species. This gap between predicted and observed distributions has proven particularly large for species with intraguild predation relationships that mix competitive and predatory interactions. A variety of ecological mechanisms have been proposed to explain this pattern, but these explanations fail to consider the role of evolution in species persistence. My dissertation explores the joint contributions of ecological and evolutionary factors to the persistence of killifish, which co-occur with guppies, an intraguild predator of killifish. I exploit variation in the duration of killifish-guppy interactions and the resulting evolution to assess how population, spatial and temporal structure influence killifish persistence as the community develops.
In chapter one, I show that killifish persist across a range of intra- and interspecific population densities and size structures in a killifish-guppy community, although the long-term dynamics of the killifish population depends upon guppy predation on neonate killifish, intraspecific density-dependence and the population size structure of each species. In chapter two, I find that killifish population densities declined after guppy introduction into previously killifish-only streams and that guppies, but not killifish, used pools more than alternative habitats. This differential habitat use correlated with an increase in the mean of the killifish size distribution and a decrease in killifish recruitment, but not differences in individual growth rates, in pools with abundant guppies. In chapter three, I demonstrate that killifish habitat use and spawning site selection depends upon evolutionary experience with guppies, although diel activity patterns remain consistent as killifish-guppy communities age. As a whole, these results suggest that size- and stage-structured interactions among killifish and guppies vary in intensity across habitats and times of day, and contribute to the persistence of killifish in the presence of intraguild predator guppies. However, the contributions of each of these mechanisms to killifish dynamics fluctuate with the adaptation of killifish and guppies to the evolving ecology of the community. Species persistence may rely on a dynamic interplay among multiple ecological and evolutionary mechanisms.