EMPIRICAL EVIDENCE FOR NONSELECTIVE RECRUITMENT AND A SOURCE–SINK DYNAMIC IN A MAYFLY METAPOPULATION

Abstract

Dispersal among spatially subdivided populations and variability in local habitat patch quality can strongly affect local and regional population dynamics. A metapopulation of mayflies (Callibaetis ferrugineus hageni) was studied in which larvae developed in beaver ponds and emerged to the terrestrial habitat as adults; adult females had the potential to disperse among ponds before oviposition. Ponds (patches) differed in the presence or absence of trout. Densities of late instar larvae were more than an order of magnitude greater in fishless ponds. Estimates of adult production, migration, and oviposition rate were used to determine whether the difference in larval abundance between pond types was more consistent with a source–sink or balanced dispersal model. Patch quality among ponds (estimated by the emergence rate of adults) varied from 0 to ∼3900 individuals·m−2·yr−1, and was significantly lower in ponds with trout. Survivorship of adult females in the regional terrestrial habitat was low (1.7%). Consistent with the predictions of source–sink theory, local recruitment to the next generation was not related to local emergence. Moreover, comparison of emergence and recruitment revealed that some ponds were net exporters of females (sources) and others were net importers (sinks). Ovipositing females did not avoid ovipositing in ponds with trout. Overall, the data were consistent with a source–sink dynamic because patches differed in quality, and because there was net migration of individuals from sources to sinks. The results support the hypothesis that local and regional population dynamics are influenced by spatial variation in patch quality, and by the ability of individuals to both disperse among and assess the quality of habitat patches.