Similar Physical, Geographic, and Historical Factors Shape Fish Species Richness in Lakes Across Ontario and Northern and Western Europe

Aim Species diversity patterns and their drivers are critical pieces of ecological knowledge needed to mitigate the threats faced by freshwater ecosystems globally. We used information on lake glacial history and environmental conditions to identify factors driving fish biodiversity patterns in Ontario and European lakes. Location 9350 lakes across Ontario; 1824 lakes across northern and western Europe. Methods Log–log linear mixed‐effects models (LMM) and generalised linear mixed‐effects models (GLMM) with a Poisson distribution were used to identify associations between fish species richness and climatic, geographic, physical, and historical variables. Local variation in fish diversity patterns was identified by applying beta diversity analysis and nested ‘temperature’ analysis to local richness data defined by sub‐basins identified in the global watershed database HydroBASINS. Results Lake area was the most important predictor of species richness in both regions. Other drivers evident in both regions were: local and regional measures of lake elevation, lake morphometry, lake age, and longitude. Results from our LMM models were similar to those from our GLMM models. In both Ontario and Europe, the error structure of these models was shaped by the HydroBASINS watershed sub‐basin structure defined for each landscape. At all spatial scales, beta diversity was > 0.9, with species turnover being more important than nestedness. Nestedness contributed no more than 22% to total beta diversity. Matrix ‘temperature’ covered a similar range on both continents (~4° to ~40°). Main Conclusions Similar physical, geographic, and historical predictors influenced lake fish species richness in Ontario and northern and western Europe. The spatial structure of the watershed sub‐basins in each region played a similar role in shaping the optimal error structure included in our richness models. By identifying variables that influence biodiversity generally and by mapping local variation in biodiversity in both regions, we provide new information that can inform landscape level conservation management strategies for lakes in both Ontario and Europe.