Latitudinal gradient in niche breadth of brachyuran crabs

AIM: Niche breadth has long been hypothesized to decrease at low latitudes and contribute to global patterns of species diversity. Range size, phylogenetic relatedness and body size also have hypothesized relationships with both latitude and niche breadth, which may further affect niche breadth patterns. Existing terrestrial data are inconclusive and few data exist on latitudinal gradients in niche breadth in the marine realm. We tested the latitude–niche breadth relationship in a marine system while exploring the correlations of both variables with range size, and accounting for relatedness and body size. LOCATION: Global. METHODS: We compiled a global dataset on the dietary niche breadth of 39 brachyuran crab species from existing studies and additional analyses on species collected in Connecticut and Florida, USA and Bocas del Toro, Panama. Estimates of latitude, range size, clade and body size were obtained for each species. We then tested for correlations among focal variables and examined the strength of their relationships with diet breadth. RESULTS: Latitude was the strongest predictor of niche breadth in temperate species, and the latitude–niche breadth relationship was stronger in larger‐bodied species. The strongest predictor of the niche breadth of tropical species was clade, with the newest clade having the narrowest diet. Niche breadth was related to range size for both temperate and tropical species. Tropical species had larger ranges on average than temperate species. MAIN CONCLUSIONS: We found an interesting division in the niche breadth relationships of temperate and tropical species; diets of temperate species were positively correlated with latitude, range size and body size, and diets of tropical species were related to range size and clade. Therefore, only temperate species demonstrated the predicted positive relationship between niche breadth and latitude, while evolutionary history was a stronger predictor of niche breadth in tropical species.