Ecological niche dynamics across continents for aquatic plants native to South America and invasive aliens elsewhere

Understanding the niche dynamics of invasive non-native aquatic plants is limited by the insufficiency of freshwater-specific climatic environmental information. Specifically, non-native species are frequently not in equilibrium with environmental conditions in the introduced areas, allowing them to colonize environments absent from their native range. We investigated the niche dynamics of five South American aquatic non-native plants (Egeria densa, Myriophyllum aquaticum, Pistia stratiotes, Pontederia crassipes, and Salvinia molesta) considered invasive worldwide. The differences between the native and invaded niches were assessed using niche overlap, equivalence, and similarity indices. The dynamics of invasive niches were quantified by indices describing unfilled, stable, and expansion of niches. In general, the plants showed a moderate overlap, except for S. molesta (low overlap). North America showed the highest overlap values, while niche stability was high (mean = 0.726), but with potential expansion and unfilled, especially in Europe and Africa. Niche equivalency was mostly rejected, indicating significant climatic differences between native and invaded niches. This study showed species and continent-specific niche shifts, while niche expansion and unfilling were evident, most shifts occurred within the boundaries of the native niche. The findings highlight limited niche conservatism, suggesting that dispersal events and introduction pathways facilitate invasions into novel conditions.