The population dynamics of rock-pool corixids living on supplementary food (Hemiptera, Corixidae)

Naturally established corixid populations living in four rock-pools were given frozen Chironomus larvae to supplement their diet. Initially the amount was 50—100 larvae/m2, and this was gradually increased to 300—400 larvae/m2. Supplementary feeding rapidly increased the egg production and, initially, the survival of corixid larvae. Population densities and the numbers of individuals completing development increased markedly. A net immigration of adults was detected during the first four weeks of the experiment. Later a strong emigration of adults occurred, and larval mortality increased, leading to the characteristic mid-season drop in total biomass. During late summer a comparable new cycle with corresponding high densities occurred. These results suggest that rock pool corixid populations are food-limited. The main regulating mechanisms are density-dependent changes in survival of small larvae and dispersal of mature adults. The balance between immigration and emigration will change with changing food availability and leads to concentration of adults in high resource patches.