Negative effects of habitat drying and prior exploitation on the detritus resource in an ephemeral aquatic habitat

Ephemeral aquatic habitats are characterized by cycles of drying and subsequent inundation, and by production of sequential non-overlapping cohorts of organisms. Both processes may alter the quantity or quality of resources, and may therefore affect survival and development of cohorts that subsequently colonize ephemeral habitats. We examined these effects of habitat drying and non-overlapping cohorts on experimental cohorts of the tree hole mosquito Aedes triseriatus, testing specifically whether the value of leaf litter as a food resource is altered by cycles of inundation and drying, or by exploitation by a prior non-overlapping cohort. We created four treatments of leaf litter: (1) no prior cohort, continuously wet; (2) no prior cohort, one␣wet/dry cycle; (3) prior cohort, continuously wet, and (4) prior cohort, one wet/dry cycle, and tested for effects on individual fitness components (survivorship, mean dry mass at, and median days to eclosion) and on population growth (estimated finite rate of increase –λ′). Both resource drying and the presence of a prior cohort negatively affected individual fitness components in tires, increasing days to eclosion, and decreasing mean dry mass at eclosion for both sexes. Resource drying also negatively affected estimated rates of increase (λ′) in tree holes. A prior cohort had no significant effects on λ′. These results indicate that intraspecific interactions among mosquito larvae may include amensalistic effects of earlier, non-overlapping cohorts, and that resource drying reduces resource quality. The latter effect indicates that enhanced production of A. triseriatus from recently filled containers is not due to resource drying per se, and may result from more complex community-level effects of habitat drying. Extreme cycles of drying and inundation seem likely to increase intraspecific resource competition among drought-adapted species like A. triseriatus. Received: 5 May 1997 / Accepted: 20 January 1998