PAPER Latitudinal diversity relationships of fiddler crabs: biogeographic differences united by temperature

Aim To investigate whether latitudinal diversity gradients differ among biogeographic realms for members of a closely related clade and to examine whether differences can be explained by environmental differences such as the temperature gradient. Location Indo-Pacific, eastern Pacific and western Atlantic temperate to tropical coastal intertidal. Methods We digitized the ranges of fiddler crabs (Decapoda, Ocypodidae, genus Uca) and calculated standing diversity as a function of latitude in the Indowest-Pacific, eastern-Pacific Americas and western Atlantic regions. We examined correlations between diversity and summer sea surface temperature, water column primary productivity, and also investigated the contribution of spatial autocorrelation. Results There was a latitudinal diversity gradient with a peak in the tropics or subtropics, but richness as a function of latitude differed by region. The western Atlantic had a broad zone of equal diversity with a peak that corresponds to the Gulf of Mexico‐Caribbean Basin. The eastern Pacific had a distinct peak of diversity at about 10° N latitude corresponding to Panama. The Indo-west-Pacific had a broad relatively flat upper level of diversity, reaching a peak at about 20° S latitude corresponding to the north coast of Australia. In both the eastern Pacific and western Atlantic, Northern Hemisphere diversity was greater than Southern Hemisphere. Species richness of the three regions was positively and strongly correlated with air and sea surface temperature at the start of summer. In contrast, diversities were weakly and inconsistently correlated with productivity. Main conclusions This paper shows that a physical factor is more important in explaining latitude distributions than regional cladal structure or presumed dispersal patterns. While observed diversity‐latitude functions are region specific, the feature seen across regions to most strongly explaining the pattern is temperature.