Invasive species impacts on sub-Antarctic Collembola support the Antarctic climate-diversity-invasion hypothesis

The Antarctic climate-diversity-invasion hypothesis (ACDI) predicts that in Antarctic soil systems, climate change should lead to increases in the abundance and diversity of indigenous assemblages. Where biological invasions have occurred, however, invasive alien species should have negative effects on indigenous faunal assemblages. To assess these predictions, we provide the first systematic ecological survey of the Collembola assemblages of pristine, sub-Antarctic Heard Island (53.1°S, 73.5°E) and compare the results to similarly conducted surveys of three other sub-Antarctic islands (Marion, Prince Edward, and Macquarie), characterised by assemblages including invasive Collembola. In particular, we examine differences in densities of three indigenous species (Cryptopygus antarcticus, Mucrosomia caeca, Tullbergia bisetosa) shared between the invaded islands and Heard Island. On average, density of these species was four or more-fold significantly lower on the invaded islands than on uninvaded Heard Island. Yet mean assemblage densities of springtails, accounting for variation among vegetation communities, did not differ substantially or significantly among the islands, suggesting that compensatory dynamics may be a feature of these systems. The invasion impact prediction of the ACDI is therefore supported. On Heard Island, indigenous assemblage variation is strongly related to vegetation community and less so to elevation, in keeping with investigations of Collembola assemblage variation elsewhere across the Antarctic. These findings, in the context of field experimental and physiological data on Collembola from the region, suggest that the climate-diversity predictions of the ACDI will play out in different ways across the Antarctic, depending on whether precipitation increases or decreases as climates change.