Niche expansion of the invasive plant species Ageratina adenophora despite evolutionary constraints

Abstract

AbstractAimEcological inferences drawn from studies on niche dynamics of invasive species are often limited due to difficulties in disentangling evolutionary adaptations of the fundamental niche from demographic and interspecific processes shaping the realized niche. We used Ageratina adenophora, an invasive plant with restricted evolutionary potential to investigate shifts in the realized climatic niche independent of potential evolutionary adaptations.LocationNative Mexican range; exotic ranges in Asia, the USA, the Canary Islands and Australia.TaxonInvasive Asteraceae A. adenophora (Spreng.) R.M.King & H.Rob. Commonly known as Crofton weed.MethodsWe compiled a robust occurrence dataset of A. adenophora for its native Mexican range and four exotic ranges (Asia, USA, Canary Islands, and Australia) and quantified pairwise niche overlap (Schoener's D) and niche dynamic (stable, unfilling and expansion) indices between the native and exotic ranges in reduced climatic space using smoothed occurrence densities. Niche shift was statistically tested using niche equivalency tests.ResultsThe value of niche overlap (Schoener's D) differed considerably, ranging from relatively high between Mexico and Asia to low between Mexico and Australia. The niche dynamic indices indicated highest level of niche stability in Asia while highest degree of unstable niche was detected in Australia due to both niche expansion and unfilling. The niche similarity tests indicated that the native niche is more similar to the exotic niche than any randomly sampled niche from the exotic range. However, the niche equivalency tests showed evidence of niche differentiation as the observed niche overlap was lower than expected by chance for all pairwise comparisons. Jointly these tests indicate that despite the similarity, the native niche is not perfectly identical to any of the exotic niches.Main conclusionsThe current study has direct implications for understanding range expansion of invasive species even in the absence of evolutionary adaptation. Our study indicates that invasive species can occupy different, non‐consistent realized climatic niches in different parts of the world, thus limiting the transferability of species distribution models and corresponding risk assessments or future projections.