Spatial scale and the ecological determinants of the distribution and diversity of fishes in Ontario lakes

Data on the occurrence of freshwater fishes in Ontario lakes were used to evaluate the scale of the processes that are primarily responsible for shaping their distributions and patterns of diversity. In Chapter 2 it is shown that, regardless of the scale of analysis, the most important factors structuring their distributions are climatic measures of energy, suggesting that species tend to be able to survive heterogeneous conditions falling within large areas encompassing their climatic affinities. In Chapter 3 it is shown that the relationship between species richness and energy (annual potential evapotranspiration) changes according to the scale on which it is measured. The species-energy relationship is weak at the local scale and stronger and steeper at increasing regional scales. This scale dependence is due to the ability of high energy regions to accommodate relatively large numbers of rare or infrequent species, and reflects the regional scale at which species respond to environmental gradients, particularly those related to energy. In Chapter 4 the relationship between local and regional species richness is examined. It is found that mean richness of lakes is linearly related to the species richness of the watersheds in which they reside. Together, the results point to the importance of processes that are regional in scale for shaping species' distributions and patterns of diversity