Assessing the equilibrium between assemblage composition and climate: A directional distance‐decay approach

The variation of assemblage composition in space is characterised by the decrease similarity with spatial distance. Climatic constraint and dispersal limitation are major drivers distance-decay similarity. Distance-decay usually conceptualised modelled as an isotropic pattern, that is, assuming decays same rate all directions. Because climatic gradients markedly anisotropic, they have different strength directions, if species distributions were equilibrium climate, decay should be anisotropic direction gradient, faster turnover maximises gradient. Thus, deviations from between conditions would result differences anisotropy gradients. We assessed patterns marine plankton assemblages, terrestrial vertebrates European beetles, using two procedures: (a) measuring correlation residuals a model angle which pairs sites separated (b) computing separate models for each dataset, one only pairwise cases on North-South another East-West direction. also analysed whether degree related to ability (proportion wingless body size) ecological niche characteristics (main habitat trophic position) assessing these relationships among beetle taxonomic groups (n = 21). Anisotropy varied across realms biological groups. Despite being steeper than datasets, distance-decays tended most vertebrate but flatter amphibians depending their ability, proportion explained 60% variance difference slopes. Our results suggest decreases realms, beetles. This has profound implications expected track suitable climates, thus impact climate change biodiversity.