Data from: Similar physical, geographic, and historical factors shape fish species richness in lakes across Ontario and Northern and Western Europe

Species diversity patterns and their drivers are essential for
understanding and mitigating threats to freshwater ecosystems worldwide.
We examined limnetic fish biodiversity across 9350 lakes in Ontario and
1824 lakes in northern and western Europe, using data on lake glacial
history and environmental conditions to identify the main factors
influencing species richness. We applied log-log linear mixed-effects
models (LMM) and generalized linear mixed-effects models (GLMM) with a
Poisson distribution to assess relationships between fish species richness
and climatic, geographic, physical, and historical variables. Local
variation in diversity was further explored using beta diversity and
nested ‘temperature’ analyses based on sub-basins defined by the
HydroBASINS database. Across both regions, lake area emerged as the
strongest predictor of species richness, with additional influences from
lake elevation, morphometry, age, and longitude. LMM and GLMM results were
broadly consistent, and model error structures were shaped by the
sub-basin organization in each landscape. Beta diversity was consistently
high (>0.9), with species turnover driving most variation and
nestedness contributing no more than 22%. Matrix ‘temperature’ values were
similar between continents (~4° to ~40°). Overall, physical, geographic,
and historical factors similarly affected fish richness in Ontario and
Europe, and sub-basin spatial structure played a key role in shaping model
error. These findings highlight variables that generally influence
biodiversity and reveal local diversity patterns, providing insights for
landscape-level conservation planning for lakes in both regions.