Space to invade? Comparative range infilling and potential range of invasive and native plants

Abstract

Aim: Our understanding of potential ranges for native and non-native species is often based on their current geographic distributions. Non-native species have had less time than co-occurring native species to expand their ranges following introduction, so non-native ranges may under-represent suitable conditions. Therefore it is often assumed that species distribution models will predict disproportionately smaller potential ranges for non-natives than natives. We compare the distributions of native, endemic, alien and invasive plants to determine how the different range attributes of these groups might influence ecological forecasting. Location: Continental USA. Methods: We compared the geographic ranges of 13,575 plant species (9402 native, 2397 endemic, 1201 alien and 755 invasive) using (1) US only and (2) global distribution data from herbarium records. We calculated US longitudinal and latitudinal range extents as potential indicators of range-limiting factors, modelled potential range based on climate using principal components analysis, and calculated occupancy of potential ranges (range infilling). Results: Contrary to expectations, modelled potential ranges were significantly larger for non-natives than natives, even for species with few occurrences. Distributions of native species, not invasive species, appeared strongly limited longitudinally. However, invasive plants occupied substantially less area within their climatically suitable ranges than native plants (lower range infilling). Main conclusions: Invasive plant distributions were consistently broader, both climatically and geographically, than comparable native species. This suggests that invasive plant distribution models at regional scales are not underpredicting potential ranges relative to models for native species. In contrast, the comparatively limited longitudinal ranges of native species suggest a high degree of non-climatic limitation, which is likely to cause distribution models to underpredict the potential ranges of native species. Invasive plants have not achieved the degree of range infilling expected relative to natives. Thus, plants introduced to the US still have plenty of space to invade.