A study of trophic niche partitioning between larval populations of reproductively isolated whitefish (Coregonus sp.) ecotypes

The abundance, spatio-temporal distribution, and feeding of larvae were compared from two reproductively isolated dwarf and normal ecotypes of whitefish (Coregonus sp.) to test the hypothesis that larval ecotypes should reduce competition by using different resources. Contrary to a priori expectations, trophic niche partitioning between larval populations was much less pronounced than previously reported for the adult stages of fish ecotypes, presumably due to the lack of competition acting at this stage, and related to non-limiting food resources. Because this study was conducted in a single year and a single lake, we cannot however, strictly rule out the possibility that resource-based competition and resulting niche partitioning may occur at the larval stage in these species complexes. Nevertheless, this suggests for the first time, that resource-based selection at the larval stage may be relatively unimportant compared to that occurring at older life-history stages in driving the divergence and the development of reproductive isolation in sympatric fish ecotypes.