Ecological niche dynamics of three invasive marine species under the conservatism and shift niche hypotheses

Marine bioinvasions are one of the main threats to biodiversity. According to assumptions based on ecological niche models, the conservatism and equilibrium of species with the environment are vital to understanding the bioinvasion process. However, these assumptions have been evaluated primarily for terrestrial species, with few examples in marine environments. We tested the niche conservatism and niche shift hypotheses in native and invaded environments and evaluated the niche dynamics and invasion stages on three invasive marine species: the algae Asparagopsis armata and Codium fragile , and the ascidian Asterocarpa humilis . We applied the identity and background similarity tests to assess the conservatism, the principal component analysis to evaluate the niche dynamics, the Gallien et al. approach to evaluate the invasion stages, and an ensemble of model to estimate potential distribution. Findings showed that the niche equivalence hypothesis was not rejected for any of the species, indicating equivalent ecological niches. Niche similarity demonstrated that niches in native and invaded ranges were not similar as expected by chance for A. humilis and C. fragile . However, for A. armata , the populations in the native and invaded areas had a very similar environmental niche. In addition, high niche stability is evident in the niche dynamics, and so as the stabilization phase of the invasion phases of the three species; thus, studying the three species supported the hypothesis of niche conservatism. These results indicated that all three species have dispersed and are in biogeographic equilibrium within their invaded regions.