Environmental filtering and niche differentiation across global hermit crab lineages

Environmental niche structure across large spatial scales provides insight into the processes that shape species distributions in marine systems. Hermit crabs (Paguroidea) are widely distributed benthic crustaceans that occupy a broad range of habitats, from shallow coastal environments to the deep sea. In this study, we analyzed global patterns of habitat suitability and partial environmental niche differentiation among representative hermit crab genera from the families Diogenidae, Paguridae, and Parapaguridae. We obtained occurrence records from the Global Biodiversity Information Facility and aggregated them at the genus level. Genus level species distribution models were calibrated using correlative approaches and sea bottom environmental predictors, including bathymetry, temperature, salinity, pH, current velocity, and dissolved oxygen. We assessed environmental niche differentiation using a PCA framework and pairwise niche overlap metrics, while habitat suitability was evaluated using genus level species distribution models. Ensemble models showed high predictive performance across genera, and habitat suitability patterns were strongly structured by bathymetry and temperature. Hermit crab genera showed substantial environmental niche overlap, particularly among several Diogenidae genera and between the parapagurids. Notably, parapagurid genera were associated with deeper, colder, and lower pH benthic environments, whereas several Diogenidae genera occupied comparatively shallower and warmer environmental space. Pagurus showed comparatively greater environmental heterogeneity than most other genera. These differences may suggest differential sensitivity to future ocean conditions, with specialized taxa potentially more vulnerable than environmentally flexible genera. Integrating macroecological patterns with physiological constraints will be critical for anticipating how climate change may reorganize hermit crab assemblages.