What Drives the Abundance of Littoral and Pelagic Brook Charr in Canadian Shield Lakes?

Resource polymorphism is more common among vertebrates than we first thought. This phenomenon occurs when individuals of the same species exhibit distinct phenotypes associated with differential resource use. Some native brook charr (Salvelinus fontinalis) populations exhibit a subtle resource polymorphism in Canadian Shield lakes, where a littoral form feeds mostly on benthic prey in shallow water and a pelagic form feeds mainly on zooplankton in open water. However, the few lake populations studied so far revealed important resource polymorphism variations among populations. These results highlight the importance of biotic and/or abiotic determinants on resource polymorphism expression. Therefore, the main objective of this study is to identify the influence of intra- and interspecific competition as well as environmental factors on brook charr resource polymorphism over a broad scale. We addressed the main determinants of brook charr abundance in the littoral and pelagic habitats of 28 Canadian Shield Lakes. Our preliminary results suggest that strong interspecific competition in the littoral zone has an important impact on brook charr abundance in both habitats. More results will be presented at the meeting.