Effects of individual variation in size on growth and development of larval salamanders

Theoretical population models suggest that variation among individuals can affect population-level properties like stability and equilibrial density. Few studies, however, have tested the importance of individual variation to factors affecting population dynamics (e.g., average individual growth rates, developmental rates, survivorship, etc.) using natural populations. We conducted a field experiment designed to test effects of larval density and individual variability in body size on growth and development of larval tiger salamanders (Ambystoma tigrinum nebulosum). We performed our experiment in a natural sinkhole lake in central Arizona; experimental populations differing in density and initial variability in body size were held in nylon mesh enclosures. Effects of individual variability in size were examined independently of any effects due to mean body size of the population or total population biomass. Density affected growth rates and development to metamorphosis of experimental larvae in a manner consistent with other studies. Initial variability in body size did not affect larval growth rates or diets but did interact with density to affect survivorship and development: experimental larvae held with similarly sized individuals experienced lower survivorship and were metamorphosing earlier than experimental larvae held with variably sized individuals. These effects did not appear to be mediated by size-specific competitive abilities but may have been mediated by individual behavioral responses to size structure. This study underscores the importance of incorporating information about interindividual variability into our understanding of processes affecting population dynamics.