Global Variation in Zooplankton Niche Divergence Across Ocean Basins

Modelling responses to climate change assumes zooplankton populations remain similar over time with little adaptation (niche conservatism). Oceanic barriers, genetic, phenotypic variation and species interactions in cosmopolitan species could drive niche divergence within species. We assess niche divergence among 223 globally distributed species across the seven main ocean basins. There were 357 diverged niches out of 828 ocean basin comparisons. The proportion of diverged niches varied both across and within phyla. Copepoda (156 of 223 species) were used to test for niche divergence between same-species populations across different environmental gradients. Global niche divergence was found to be more likely for species in colder temperatures and nearshore environments. Opposing temperature responses were found for four comparisons, which may relate to the different connectivity patterns between them. This study demonstrates adaptive potential across environmental-niche gradients, which must be considered when modelling population responses to climate change.