Abstract

--- - Ecological processes that are behind distributions of species that inhabit isolated localities, complex disjunct distributions, remain poorly understood. Traditionally, vicariance and dispersion have been proposed as explanatory mechanisms that drive such distributions. However, to date, our understanding of the ecological processes driving evolution of ecological niches associated with disjunct distributions remains rudimentary. Here, we propose a framework to deconstruct drivers of such distribution using World's most widespread freshwater fish Galaxias maculatus as a model and integrating marine and freshwater environments where its life cycle may occur. Specifically, we assessed ecological and historical factors (Gondwanan vicariance, marine dispersion) and potential dispersion (niche-tracking) that explain its distribution in the Southern Hemisphere. Estimated distribution was consistent with previously reported distribution and mainly driven by temperature and topography in freshwater environments and by primary productivity and nitrate in marine environments. Niche dynamics of G. maculatus provided evidence of synergy between vicariance and marine dispersion as explanatory mechanisms of its disjunct distribution, suggesting that its ecological niche was conserved since approximately 30 Ma ago. This integrated assessment of ecological niche in marine and freshwater environments serves as a generic framework that may be applied to understand processes underpinning complex distributions of diadromous species. - Los procesos ecologicos que subyacen a las distribuciones de especies que habitan en localidades aisladas, distribuciones disjuntas complejas, siguen siendo poco conocidos. Tradicionalmente, se han propuesto la dispersion y la vicarianza como mecanismos explicativos de tales distribuciones. Sin embargo, hasta la fecha, nuestra comprension de los procesos ecologicos que impulsan la evolucion de los nichos ecologicos de distribuciones disjuntas sigue siendo rudimentaria. Aqui proponemos un marco para de-construir los factores que impulsan dicha distribucion, utilizando como modelo el pez de agua dulce con distribucion mas extendida del mundo, Galaxias maculatus, e integrando los entornos marinos y dulceacuicolas en los que se desarrolla su ciclo vital. En concreto, evaluamos los factores ecologicos e historicos (vicarianza gondwanica, dispersion marina) que explican su distribucion en el hemisferio sur. La distribucion estimada coincide con la descrita anteriormente para la especie y esta determinada principalmente por la temperatura y la topografia en ambientes dulceacuicolas, y la productividad primaria y el nitrato en ambientes marinos. La dinamica de nicho de G. maculatus aporto pruebas de la sinergia entre vicarianza y dispersion marina como mecanismos explicativos de su distribucion disjunta, lo que sugiere que su nicho ecologico se conservo desde hace aproximadamente 30 Ma. Esta evaluacion integrada del nicho ecologico en ambientes marinos y dulceacuicolas puede aplicarse para comprender los procesos que subyacen a las distribuciones complejas de especies diadromas. - This study decomposes ecological niche of facultative amphidromous species to elucidate ecological processes behind the widest disjunct freshwater fish distribution in the world and advance understanding of differentiation of the ecological niche at population level. It combines analyses of environmental variables (freshwater and marine), biogeographic mechanisms and dispersion capacity.image