Nicho abiótico e efeitos do aquecimento global em Riorajini (Rajiformes, Arhynchobatidae), raias do Atlântico Sudoeste

Abstract

The abiotic niche of species tells part of their ecological and evolutionary history, as well as helps to identify groups that are more susceptible to extinction in a context of a rapidly changing climate. Marine species from temperate regions are among the most vulnerable taxa because habitat loss as a consequence of thermal stress and other cascading impacts can constrain the availability of suitable area of occurrence, or result in distribution shift towards higher latitudes. The tribe Riorajini comprises four species of neotropical skates that are evaluated by IUCN as vulnerable or endangered, and cooccur in the subtropical Atlantic Ocean: Atlantoraja castelnaui, A. cyclophora, A. platana and Rioraja agassizii. The present dissertation is divided into two chapters and uses this group as a model for eco-evolutionary studies. In the first chapter, phylogenetic niche conservatism is questioned for a clade of sympatric and competitive sister-species. Low niche overlap was expected to reduce interspecific competition between closely-related species. The second chapter assessed the impacts of climate change on the current geographical distribution of the tribe Riorajini. First, the phylogeny of the tribe was reconstructed. Then, ecological niche models for each species of the group were developed under current and future (2100, for the most extreme scenario) geophysical and climatic conditions of the marine environment. Environmental data and species occurrence data were compiled from public databases and literature. Niche shift and overlap were measured within and between species. Results indicate phylogenetic niche conservatism in which shallow waters, proximity to the coast, and low nitrate concentration are the most important variables for the occurrence of these species. Under the future climatic scenario projected, the areas of higher environmental suitability for the occurrence of each species analysed increases up to 20% towards deeper areas, suggesting that this clade will resist the thermal stress resulting from global warming. Nevertheless, future studies should consider the combined effects of an increase in temperature in the time of hatching of egg-capsules and the early development of juveniles, as well as the impact of other factors potentially determining the coexistence of these species, such as prey availability.