Species richness and phylogenetic diversity of native and non-native species respond differently to area and environmental factors

Aim: To test whether native and non-native species have similar diversity-area relationships (species-area relationships [SARs] and phylogenetic diversity-area relationships [PDARs]) and whether they respond similarly to environmental variables. Location: United States. Methods: Using lists of native and non-native species as well as environmental variables for > 250 US national parks, we compared SARs and PDARs of native and non-native species to test whether they respond similarly to environmental conditions. We then used multiple regressions involving climate, land cover and anthropogenic variables to further explore underlying predictors of diversity for plants and birds in US national parks. Results: Native and non-native species had different slopes for SARs and PDARs, with significantly higher slopes for native species. Corroborating this pattern, multiple regressions showed that native and non-native diversity of plants and birds responded differently to a greater number of environmental variables than expected by chance. For native species richness, park area and longitude were the most important variables while the number of park visitors, temperature and the percentage of natural area were among the most important ones for non-native species richness. Interestingly, the most important predictor of native and non-native plant phylogenetic diversity, temperature, had positive effects on non-native plants but negative effects on natives. Main conclusions: SARs, PDARs and multiple regressions all suggest that native and non-native plants and birds responded differently to environmental factors that influence their diversity. The agreement between diversity-area relationships and multiple regressions with environmental variables suggests that SARs and PDARs can be both used as quick proxies of overall responses of species to environmental conditions. However, more importantly, our results suggest that global change will have different effects on native and non-native species, making it inappropriate to apply the large body of knowledge on native species to understand patterns of community assembly of non-native species.