Spatial and environmental correlates of fish community structure in Canadian Shield lakes

We used data on fish species biomass from 38 lakes of the Canadian Shield (Quebec) to determine the contribution of environmental (lake and watershed morphometry) and spatial (e.g., hydrographic connectivity and geographic coordinates) variables on fish community structure. By using a combination of multivariate analyses, we show that nearly half of the variation in the fish community structure is explained by the independent contributions of spatial and environmental factors. Walleye (Sander vitreus) and lake whitefish (Coregonus clupeaformis) were significantly associated with the absence of beaver (Castor canadensis) dams, whereas northern pike (Esox lucius) was positively correlated with beaver dam presence. Altitude and longitude, but not current patterns in lake connectivity, were the main explanatory spatial variables accounting for the observed pattern in fish community structure. Large piscivorous fish were associated with a reduced richness and biomass of small prey, suggesting that predation is a structuring factor in these lakes. By showing that geographic coordinates and altitude are better descriptors of fish community structure than hydrographic connections, our study suggests that past colonization routes are relatively more important than current ones in structuring fish communities at the landscape level. This interpretation is supported by recently published genetic data.