Effects of biotic interactions on ecological niche dynamics: Low niche equivalence among amphidromous fish life-history strategies

Although key biotic interactions can shape species distributions across large geographic areas, the specific roles and spatial scales of these interactions are not well understood. Correlational models, often used in ecological studies, assume niche equivalence among populations of a species. However, this assumption overlooks how different factors can affect defined ranges and the reliability of predictions. In this study, we evaluate ecological niche equivalence among populations of the facultative amphidromous fish Galaxias maculatus, which includes both migratory amphidromous and freshwater resident populations. We identify sources of niche variation across hierarchical levels of biological organization (individuals, populations, species) and operational niche definitions (existing fundamental niche, realized niche). Our findings reveal structural niche differences based on population movement ranges and the operational niche definition used. Notably, no overlap exists in realized niches between amphidromous and freshwater resident populations, with isotopic niche breadth driving this differentiation. This niche difference resulted in models that poorly predicted distributions of populations with different life-history strategies, indicating low niche equivalence between these groups when considering biotic factors. Our results suggest that differing life-history strategies are key drivers of G. maculatus distribution. Habitat selectivity based on freshwater recruitment conditions and loss of diadromy through local adaptation may also contribute to niche divergence. We emphasize the importance of assessing niche breadth changes across hierarchical levels to understand species' distributional patterns better, particularly in species with complex life-history strategies. Las interacciones bi & oacute;ticas pueden modelar la distribuci & oacute;n de las especies a gran escala geogr & aacute;fica, pero sus mecanismos y escalas espec & iacute;ficas de acci & oacute;n siguen siendo poco comprendidos. Los modelos correlativos com & uacute;nmente utilizados en ecolog & iacute;a suelen asumir equivalencia de nicho entre poblaciones de una misma especie, omitiendo fuentes relevantes de variaci & oacute;n y comprometiendo la solidez de las predicciones. En este estudio evaluamos la equivalencia del nicho ecol & oacute;gico entre poblaciones del pez anf & iacute;dromo facultativo Galaxias maculatus, que incluye formas migratorias y residentes dulceacu & iacute;colas. Identificamos fuentes de variaci & oacute;n del nicho a diferentes niveles jer & aacute;rquicos de organizaci & oacute;n biol & oacute;gica (individuos, poblaciones, especie) y bajo definiciones operativas distintas (nicho fundamental existente y nicho realizado). Nuestros resultados revelan diferencias estructurales en el nicho seg & uacute;n el rango de movimiento poblacional y la definici & oacute;n operativa utilizada. En particular, no se observ & oacute; solapamiento entre los nichos realizados de las poblaciones migratorias y residentes, siendo la amplitud del nicho isot & oacute;pico el principal eje de diferenciaci & oacute;n. Esta divergencia conllev & oacute; a una baja capacidad predictiva de los modelos entre estrategias de vida, indicando una reducida equivalencia de nicho al considerar factores bi & oacute;ticos. Concluimos que las estrategias de historia de vida, la selectividad del h & aacute;bitat y la p & eacute;rdida de anf & iacute;drom & iacute;a por adaptaci & oacute;n local son impulsores clave en la configuraci & oacute;n del nicho de esta especie. Recalcamos la importancia de evaluar la din & aacute;mica del nicho a lo largo de niveles jer & aacute;rquicos para mejorar la comprensi & oacute;n de los patrones de distribuci & oacute;n en especies con historias de vida complejas.