Niche conservation in copepods between ocean basins

Niche conservatism is the hypothesis that a species' niche remains stable in space and time. This concept is central to understanding phenomena ranging from the role of climate change impacts on species biogeography to community dynamics. Marine zooplankton have been used as indicators of global change in the ocean, and niche conservatism is usually assumed for these organisms due to their high dispersal capacity, which may limit the development of local adaptations. However, recent evidence suggests that several zooplankton species with a circumglobal distribution are comprised of several cryptic species complexes, but it is unknown if the niches of cryptic species complexes have remained conserved or if they have diverged. Habitat management based on niche modelling would be strengthened by better understanding patterns of niche conservation or divergence, as the usual assumption that species have fixed environmental niches may be misleading. We assess the niche differences for 15 copepod species with populations in the North Atlantic, Southern Ocean and Australia. Pairwise differences in the realised niches were computed for each species using two complementary analyses. Our analysis indicates that global‐scale niche modelling of zooplankton cannot assume niche conservatism across all lineages and future studies should look to incorporate phylogenetic information to improve future niche estimates.