Conservationists invest heavily in the restoration of animal populations. However, the mechanisms regulating their size are still poorly understood. Density is hypothesized to be a chief regulator of population abundance through a potential impact on individual growth and survival in the juvenile stage of many species of insects, mammals, birds, reptiles, amphibians and fish. Nevertheless, the extent to which density influences individual growth, survival and behavior is uncertain. Similarly, the mechanisms by which density-dependence operates are uncertain, and the variability in responses to density between distinct populations has received very limited empirical investigation.
In this light, we are investigating the effects of density on individual growth and survival across populations and habitat types (streams and ponds), and the mechanisms by which they operate. To do so, we are conducting a series of field experiments in which we manipulate the density of young-of-the-year brook trout (Salvelinus fontinalis) in natural streams at Cape Race, Newfoundland. More specifically, we are testing the predictions that: (1) density-dependent growth and survival have different relationships between populations; (2) density-dependence operates through both prey depletion and an increase in energy-taxing behaviours; and (3) density-dependent growth and survival operate differently between streams and ponds, due to different habitat constraints. Through this research, we will gain better understanding of the effect of density on juvenile salmonid ecology, which is a critical for ongoing conservation efforts.