Causes and consequences of population cycles in a highly size- and stage-structured population

High elevation populations of tiger salamanders (Ambystoma tigrinum nebulosum) are composed of multiple year classes of larvae because short-growing seasons and cold temperatures in the ponds lead to a protracted period of larval development. The purpose of this talk is to describe how this population size structure 1) leads to the development of long-term cycles in salamander abundance, 2) determines how those cycles affect the underlying prey community, and 3) influences the polyphenic development of metamorphic and paedomorphic adult salamanders. Fluctuations in salamander population size at our study site appear to be driven intrinsically by inter-cohort cannibalism. The abundance of paedomorphic adults in the population is negatively correlated with recruitment of new cohorts, and experimental data suggest cannibalism on young-of-the-year larvae by paedomorphs in dominant cohorts can lead to extended periods in which there is little or no recruitment. This decline phase in the observed cycles ends when dominant cohorts senesce, resulting in a "recruitment boom" and the establishment of the next dominant cohort. These large amplitude fluctuations in salamander abundance are negatively coupled with fluctuations in prey biomass. However, because of the presence of multiple size classes of salamander larvae foraging at different trophic levels, counteracting impacts on the prey community preclude a classic top-down trophic cascade. Finally, we present evidence that inter-pond and inter-cohort differences in the relative abundance of size classes influences the  developmental fate of individual larvae, and hence the maintenance of the developmental polyphenism that leads to the coexistence of paedomorphic and metamorphic adults. We conclude that nearly all aspects of the population and community ecology of the subalpine ponds at our study sites is influenced directly or indirectly by how population structure determines the outcome of intra- and interspecific interactions.