Macroecology meets invasion ecology : linking the native distributions of Australian acacias to invasiveness

Abstract

AIM : Species' native ranges reflect the net outcome of interactions between life-history strategies and biotic and abiotic influences over evolutionary timescales. Differences in native ranges might be indicative both of relative historical performance, and adaptability to new conditions. Consequently, the native ranges of successful invaders might have distinctive biogeographical characteristics. We test this hypothesis by (i) quantifying macroecological patterns of the entire assemblage of native taxa in Acacia subgenus Phyllodineae in Australia, (ii) testing whether highly invasive taxa represent random samples from the patterns observed for the assemblage as a whole, and (iii) exploring the link between native geographic range and the position of species along the introduction-naturalisation-invasion continuum. LOCATION : Australia and worldwide. METHODS : Three distributional metrics representing particular biogeographical characteristics of species' native ranges—the logarithms of range size; percolation intercept; and percolation exponent—were calculated by fitting a revised alpha-hull to records from Australia’s Virtual Herbarium. Randomization and cascaded tests were used to compare these metrics for species at different stages of invasion. RESULTS : The macroecological patterns of the three distributional metrics displayed lognormallike frequency distributions. Most invasive species had significantly lower percolation exponents and larger native ranges than expected from random draws from the entire assemblage of Australian acacias, but percolation intercepts were not significantly different. This can be explained by a selection bias at the early stages of invasion. MAIN CONCLUSIONS : The outcome of the natural experiment of transplanting many Australian acacias into novel environments is not random. While invasive species have a particular macroecological pattern, this can be explained by the observation that species with large native ranges and low percolation exponents (i.e. high population increase rate) are most likely to have been introduced and naturalised. Whether this pattern is an artefact of human selection or reflects a human bias towards selecting invasive species remains to be seen.