The potential invasiveness of an aquatic macrophyte reflects founder effects from native niche

Abstract

Biological invasions are important drivers of biodiversity loss. Hence, predicting invasion risks considering the invasion history of a species might help drive meaningful conservation strategies. We investigated the niche dynamics occurring during the invasion of Hydrilla verticillata in North and South America. Because of founder effects, we hypothesised that occupied invaded area niches across North and South American are a subset of the occupied niche in the native range. Moreover, according to the invasion history, we expected that the South American niche is more similar to the North American one than the native niche. We built ecological niche models to predict the potential distribution of hydrilla from native and invaded occurrence records, as well as analysing niche overlap, equivalency, and similarity between the native and two invaded areas. Although the models predicted spatially congruent suitable sites, the ones based on native occurrence records predicted larger geographical ranges for hydrilla across South America than those based on the records of its North American invasions. The environmental conditions the species occupied in both invaded areas are modestly overlapped with the native area (Schoener’s D < 0.6), with native and South American niches showing the highest overlap and significant equivalency. Contrary to our prediction, the invaded North and South American niches presented the smallest niche overlap. Our findings suggest that founder effects triggered deep shifts in hydrilla’s occupation abilities across invaded areas, but do not support successive invasion events. Hydrilla’s Grinnellian niche was maintained throughout the invaded areas, and its potential invasion across South America is massive, regardless of its origin.