Understanding the causes and consequences of species invasion is essential to managing ecosystems in the Anthropocene. Ecologist often couch invasive species questions in existing ecological theory to test if and how exotic species differ from native species. One such approach is to compare species-area relationships (SARs) between native and exotic species. Based on the assumption that exotic species are adept at spreading and establishing, it is predicted that the SAR exponent (z) from the power-law SAR should be lower for exotic species. However, a recent meta-analysis found little support for differences in z values between native and exotic species. One potential reason is that exotic species can be further divided into invasive and non-native species. Invasive species are those exotics that spread aggressively and have definite ecological and economic impacts while non-natives simply identify species found outside of their range. Given these definitions, we hypothesize that invasive SARs should have lower SAR exponent than both native and non-native species. We test this hypothesis with plant data from 243 parks in South Florida, USA. This data set consists of 1429 native, 743 non-native, and 137 invasive species with species designated as invasive by the Florida Exotic Pest Plant Council (FLEPPC).
Results/Conclusions
We analyzed species-area relationships for 243 parks is south Florida ranging in size from 6,102 km2 (Everglades National Park) to 0.003 km2 (John Kunkel Small Pineland) using the power-law SAR. As expected, the exponent of the SAR for invasive species (z = 0.058) was significantly lower (p < 0.05) than that of native species (z =0.128), but not significantly lower than the z value of the non-native SAR (z = 0.084). Our results indicate that invasive species, which are often designated based on their ability to spread and impact ecosystems, had lower z values than both native and non-native species, but were not significantly lower than non-natives. Thus, sampling efforts are less likely to pick up a new invasive species as area increases relative to native species, because invasive species are so common and widespread. In other words, most invasives are present in smaller areas (i.e., parks). Considering differences between native, non-native, and invasive species in the context of SARs has the potential to elucidate how invasive species can alter biodiversity relationships across scales.
