Dissecting Trends in the Latitudinal Diversity Gradient of Benthic Macroinvertebrates in Freshwater Lakes Across Scales

ABSTRACT The latitudinal diversity gradient is one of the most striking biogeographical patterns on Earth and typically reveals increases in species richness from the poles towards the tropics. However, the latitudinal diversity patterns vary among taxa, ecosystems and scales. In freshwater, the patterns are particularly obscure, partially owing to limited geographical and taxonomical scope, as well as unclear controls of sampling effort. Here, we compiled data from a diverse group of benthic macroinvertebrates derived from standardised offshore surveys of 485 shallow freshwater lakes spread across the northern hemisphere to elucidate how diversity patterns at multiple spatial scales vary with latitude. At each scale, we calculated multiple effort‐controlled measures emphasising different aspects of biodiversity. Contrary to our expectations, we found no evidence of a latitudinal gradient for any metric of diversity at small (local, α‐) or large (regional, γ‐) scales, nor any pattern of β‐diversity among the lakes. Our results therefore provide some of the broadest evidence to date of a lack of latitudinal diversity gradient in offshore benthic macroinvertebrates in freshwater shallow lakes. Understanding this null relationship, and its contrast with many terrestrial and marine patterns, will require a concerted effort towards data compilation and comparative analyses.