Accurate forecasts of biological invasions are crucial for managing invasion risk but are hampered by niche shifts resulting from evolved environmental tolerances (fundamental niche shifts) or the presence of novel biotic and abiotic conditions in the invaded range (realized niche shifts). Distinguishing between these kinds of niche shifts is impossible with traditional, correlative approaches to invasion forecasts, which exclusively consider the realized niche. Here we overcome this challenge by combining a physiologically mechanistic model of the fundamental niche with correlative models based on the realized niche to study the global invasion of the cane toad Rhinella marina. We find strong evidence that the success of R. marina in Australia reflects a shift in the species’ realized niche, as opposed to evolutionary shifts in range-limiting traits. Our results demonstrate that R. marina does not fill its fundamental niche in its native South American range and that areas of niche unfilling coincide with the presence of a closely related species with which R. marina hybridizes. Conversely, in Australia, where coevolved taxa are absent, R. marina largely fills its fundamental niche in areas behind the invasion front. The general approach taken here of contrasting fundamental and realized niche models provides key insights into the role of biotic interactions in shaping range limits and can inform effective management strategies not only for invasive species but also for assisted colonization under climate change. Significance Species’ distributions result from dispersal and physiological constraints, interactions with other species, and ultimately, evolution. Biological invasions result from the deliberate or accidental movement of species between regions they would not reach through natural dispersal and can cause major conservation, economic, and human health issues. However, invasions also provide fascinating insights into species’ distribution limits. We investigate the invasion of the cane toad from South America to Australia by comparing the results of two modeling approaches: one considering physiological constraints and the other considering the joint influences of physiology, dispersal, and biotic interactions. Our findings demonstrate that the cane toad is limited in its native distribution by biotic interactions but, in Australia, is free to fill its climatic potential.

Diversification of Amazon birds led by climate stability: lineages originated in the wetter west and dispersed into the drier east.

The classical perspective that interspecific hybridization in animals is rare has been changing due to a growing list of empirical examples showing the occurrence of gene flow between closely related species. Using sequence data from cyt b mitochondrial gene and three intron nuclear genes (RPL9, c-myc, and RPL3) we investigated patterns of nucleotide polymorphism and divergence between two closely related toad species R. marina and R. schneideri. By comparing levels of differentiation at nuclear and mtDNA levels we were able to describe patterns of introgression and infer the history of hybridization between these species.