Global variation in zooplankton niche divergence: Evidence of environmental and trait signals for calanoid copepods

Ocean warming has led to significant changes for marine zooplankton. Modelling responses to climate change assume that zooplankton respond uniformly with little adaptation (niche conservatism). Oceanic barriers, local adaptation and genetic variation in cosmopolitan species could drive niche divergence between same species populations. We assess niche divergence among 325 globally distributed species across the five main ocean basins. There were 487 diverged niches out of 1124 ocean basin comparisons. The proportion of diverged niches varied both across and within phyla. Calanoida (133 of 325 species) were used to test the likelihood of niche divergence between same species population across environmental gradients. Niche divergence was more likely to occur in species that occupy colder waters and in shallower depths. Niche divergence was more likely for larger ominivore-herbivores than smaller sized carnivores. This study demonstrates adaptive potential across environmental-niche gradients, which must be considered when modelling population responses to climate change.