Trophic Niche Partitioning Between Lake Whitefish and Cisco: Post-glacial Patterns and Response to Anthropogenic Cisco Introductions

We estimated isotopic niche size and trophic position of native lake whitefish (Coregonus clupeaformis (Mitchill, 1818)) decades after cisco (Coregonus artedi Lesueur, 1818) introduction into two lakes of Algonquin Park, Ontario, Canada. Lake whitefish residing in a set of neighboring lakes without native cisco were used for comparison. We found lake whitefish isotopic niche size was larger and trophic position higher in lakes with abundant introduced cisco compared to a lake with a low density of introduced cisco, consistent with findings for European coregonines. At sufficient densities, planktivorous coregonines introduced into lake food webs will shift the niche space of native coregonines. We then compared isotopic niche size and trophic position for native pairings of lake whitefish and cisco to assess if isotopic niche and trophic patterns resulting from cisco introductions are features of native parings of cisco and lake whitefish that have co-existed post-glacially for thousands of years. Introductions of cisco match to some degree niche partitioning and niche size between lake whitefish and cisco co-existing since glacial retreat. The range of trophic niche size and partitioning was large in native pairings indicating niche expansion, compression and divergence characterize lake whitefish coexisting with cisco for thousands of years.