Niche shift and resource supplementation facilitate an amphibian range expansion

CITATION: Davies, S. J., et al. 2019. Niche shift and resource supplementation facilitate an amphibian range expansion. Diversity and Distributions, 25(1):154-165, doi:10.1111/ddi.12841.The original publication is available at https://onlinelibrary.wiley.comAim: To determine whether recent range expansion of small- bodied arboreal frogs, Hyperolius marmoratus Rapp, is accompanied by changes in species–environment re- lationships and whether its historical range was constrained by climate, availability of water bodies or topographic variables. We test if artificial water bodies in the novel range have facilitated niche shift by increasing available habitats for frog establishment. Location: Western Cape Province, South Africa, with reference to the broader spe- cies range in southeastern Africa. Methods: We build species distribution models using occurrence data from the his- torical and novel ranges and reciprocally project them to highlight areas of putative niche change. We test for niche shift through ordination- based approaches to disen- tangle how species–environment relationships may have altered and whether climate or landscape features (artificial water bodies and topography) are more strongly as- sociated with the identified change. We further decompose niche change into areas of expansion and unfilling to quantify niche shift and describe potential future spread. Results: We observed niche expansion into novel environmental space, with 21% of niche space in the invaded range composed of environments that were not occupied in the native range. We also observed 16% niche unfilling, signifying range disequilib- rium and potential for further spread. Mean annual precipitation and proximity to water bodies were more influential in models constructed in the novel range than in historical or combined range models, suggesting that presence of artificial water bodies in the landscape ameliorates novel range conditions. Together, these metrics suggest that range expansion may be ongoing based on climate and water body availability. Main conclusions: Our analyses identify a realised niche shift that has allowed painted reed frogs to occupy drier and more thermally variable habitats in their novel (invaded) range. This shift may be mediated by artificial water bodies that provide additional buffered habitats, a key resource supplement for these small- bodied tropi- cal frogs.https://onlinelibrary.wiley.com/doi/10.1111/ddi.12841Publisher's versio