Amphidromous lives, divergent niches: The important role of biotic factors in understanding niche dynamics and geographic distributions.

Research Highlight: Ramírez-Álvarez, R., Peterson, A.T., Contreras, S., Górski, K. (2025). Effects of biotic interactions on ecological niche dynamics: low niche equivalence among amphidromous fish life-history strategies. Journal of Animal Ecology, https://doi.org/10.1111/1365-2656.70079. Understanding how biotic interactions shape ecological niches and geographic distributions at distinct geographical scales and hierarchical levels remains challenging in ecology, evolution and biogeography. While abiotic variables have traditionally been considered the main drivers at broad spatial scales, growing evidence highlights the important role of biotic interactions across these same scales. In this context, Ramírez-Álvarez et al. (2025) address this issue by an innovative approach that integrates biotic and abiotic dimensions to investigate niche dynamics in Galaxias maculatus, a facultatively amphidromous fish with distinct life-history strategies. The study compares marine-estuarine migratory (amphidromous) and freshwater-resident populations across several river basins in Chile. Using correlative niche models, the authors assessed both the existing fundamental niches, based exclusively on abiotic predictors and the realized niches, incorporating an isotopic niche breadth variable. The results revealed substantial overlap in environmental space, with 98% of the freshwater residents' niche included within that of amphidromous populations. Conversely, no overlap was found in isotopic (realized) niche space, evidencing the important role of biotic interactions in niche differentiation between the two life-history strategies. Moreover, models that included the biotic variable showed notable contractions in predicted suitable areas and limited ability to predict the distribution of the alternative population type, indicating a lack of equivalence in realized niches. We emphasize the importance of the approach developed by Ramírez-Álvarez et al. (2025) and reinforce the need to deepen our understanding of species' biotic interactions and life-history traits, as well as to better integrate this knowledge within established methods for evaluating the role of abiotic factors. Such progress is essential for addressing complex questions in ecological and evolutionary research.