Larval niche differences between the sibling species, Drosophila montana and D. littoralis (Diptera) in northern Finland

Abstract

Differences in larval substrate, or in the spatial and temporal occurrence of larvae between two closely related and ecologically similar Drosophila species were investigated. Vials containing homogenised tissue of water lily stems or birch phloem wetted with sap were exposed for oviposition in two habitats during two time periods. A logit analysis of the field emergence data suggested significant niche differences between the species. The logit model best explaining the species composition among emerging adults included an interaction between habitat and substrate, and also an interaction between habitat and exposure period. The differences between the species were, however, small and the species overlapped broadly with respect to each of the studied niche dimensions. The distribution of emerging flies among the yellow water lily vials appeared to fulfill the assumptions of a theoretical model for aggregation-mediated coexistence, i.e. the distribution of flies was aggregated among vials in both species, and there was no interspecific correlation in the numbers of flies emerging from the vials.