Consistent spatial patterns across biogeographic gradients in temperate reef fishes

Abstract

Biogeographic gradients may facilitate divergent evolution between populations of the same species, leading to geographic variation and possibly reproductive isolation. Previous work has shown that New Zealand triplefin species (family Tripterygiidae) have diversified in habitat use, however, knowledge about the consistency of this pattern throughout their geographic range is lacking. Here we examine the spatial habitat associations of 15 New Zealand triplefin species at nine locations on a latitudinal gradient from 35°50'S to 46°70'S to establish whether distant populations differ in habitat use. Triplefin diversity and density varied between locations, as did habitat variables such as percentage cover of the substratum, onshore-offshore location, microposition, depth and exposure. Canonical discriminant analysis identified specific species-habitat combinations, and when habitat was statistically partialled from location, most species exhibited consistent habitat associations throughout their range. However, the density of a few species at some locations was lower or higher than expected given the habitat availability. This indicates that the habitat variables recorded were not the sole predictors of assemblage structure, and it is likely that factors influencing larval dispersal (e.g. the low salinity layer in Fiordland and geographic isolation of the Three Kings Islands) play an additional role in structuring assemblage composition. Together these results suggest that New Zealand triplefin species show strong and consistent habitat use across potential biogeographical barriers, but this pattern appears to be modified by variation in larval supply and survival. This indicates that species with broad geographic distributions do not necessarily show phenotypic variation between populations.