The role of phenotypic plasticity and indirect interactions on the structure of ecological communities.

摘要

I investigated the influence of phenotypic plasticity on species interactions, and the consequences to the structure of ecological communities. Predictions generated with mathematical models were tested experimentally using an aquatic community composed of predatory larval dragonflies (Anax spp.), tadpoles (Rana spp.), and algal resources. Dragonflies have two principal direct effects on tadpoles; they reduce their density through predation, and they induce changes in phenotype that are associated with reduced tadpole foraging. A model predicted that such predator-induced modifications in prey phenotype could significantly affect other species in the community. This prediction was supported experimentally; a dragonfly-induced change in tadpole phenotype led to a five-fold increase in the indirect effect of the predator on the growth rate of a tadpole competitor.;I examined the mechanistic causes of this result by investigating the influence of relative species densities and system productivity. I showed that predator-induced changes in prey phenotype (1) have a negligible effect on prey growth rate at high prey density, precisely where indirect effects on competitor growth rate are greatest, and (2) have opposing effects on prey growth rate, the net effect of which depends on resource growth parameters. The corroboration between experimental results and model predictions strengthened the validity of the proposed underlying mechanism, namely the effect of predator-induced changes in prey phenotype on the nature and magnitude of species interactions.;These results have far-reaching implications for the study of ecological communities. In current ecological theory, species pair interactions are depicted as independent 'building-blocks' that are combined to describe the community as a whole. But I found that the magnitudes of species interactions are a strong function of other species: the tadpole-resource interaction was strongly dependent on predator density. The typical theoretical representation is therefore not applicable to this aquatic system. Because the magnitude of the phenotypic modifications observed in my experiments is representative of those exhibited by many species from disparate taxonomic groups, this result is likely general in diverse ecological communities. This result therefore challenges managers of ecosystems, empiricists, and theorists alike to consider the influence of phenotypic plasticity on the structure of ecological communities.