Climatic niche differentiation between native and non-native ranges is widespread in Ponto-Caspian amphipods

Niche conservatism posits that a species’ non-native populations establish in areas that match the native environmental conditions. Although the Ponto-Caspian region is a major source of inland aquatic alien species, the extent to which their climatic niches diverged between the invasive and native ranges remains poorly understood. Using an n-dimensional hypervolume approach, we quantified climatic niche overlap and inferred patterns of niche differentiation (shift, contraction, or expansion) among native and invaded ranges for 12 widespread Ponto-Caspian amphipod species (six genera in three families). Our results show that all investigated species experience substantially different climatic conditions in the invaded range. The invasive niche either contracted (five species), shifted (four species), expanded and shifted (two species), or shifted and contracted (one species) relative to the native niche. We conclude that although the focal taxa share a common geographic origin and evolutionary history, they exhibit disparate patterns of climatic niche change outside the native range. The niche conservatism hypothesis receives mixed support given that half of the studied species underwent niche shifts/expansion. Furthermore, congeners exhibited both identical and contrasting patterns of niche differentiation, suggesting a limited phylogenetic effect. The uncovered diversity of niche dynamics among closely related species indicates that each has a unique potential for invasiveness and long-term persistence. This has important implications for predicting invasion risk and refining management strategies.