Abstract
Invasive alien species pose a serious threat to the integrity and function of natural ecosystems. Understanding how these invaders alter natural communities is therefore an important aspect in predicting the likely future outcomes of biological invasions. Many studies have documented the consequences of invasive alien species on native community structure, through the displacement and local extinction of native species. However, sampling methods and intensities are rarely standardised across such studies, meaning that it is not clear whether differences in response among native communities to the same invader species are due to biological differences between the invaded regions, or differences in the methodologies used. Here we use a matched sampling methodology to compare the effects of the Argentine ant (Linepithema humile Mayr) on native ant community assemblages in two distinct biogeographical regions that share similar ecologies: Girona (Spain) and Jonkershoek Nature Reserve (South Africa). We found a strong negative association between L. humile presence and native ant species richness within both geographic regions. However, the effects differed between the two study regions: in Girona, a single native ant species (Plagiolepis pygmaea) persisted in invaded sites; by contrast, substantially more native ant species persisted at invaded sites in Jonkershoek Nature Reserve. In addition, in Jonkershoek Nature Reserve, the abundance of certain native species appeared to increase in the presence of L. humile. This study therefore demonstrates the potential variable effects of an invasive species in contrasting locations within different biogeographical regions. Future work should explore the causes of this differential resistance among communities and expand standardised sampling approaches to more invaded zones to further explore how local biotic or abiotic conditions of a region determine the nature and extent of impact of L. humile invasion on native ant communities.
Highlights
Invasive alien species (IAS) pose a serious threat to the structure and function of native communities
In Jonkershoek Nature Reserve (South Africa), 9,166 ants were collected in the 220 pitfall traps across 11 sites, belonging to 41 species, from 22 genera (Table 2)
By using an identical sampling methodology, how the impact of L. humile on native ant community composition can vary across two distinct regions
Summary
Invasive alien species (IAS) pose a serious threat to the structure and function of native communities. The presence of an IAS within a region is often associated with a number of negative impacts on resident communities, such as the reduction in the abundance and diversity of native species Cascading effects on the structure, function and resilience of native communities and ecosystems (Sanders et al 2003; Sax and Gaines 2008) following IAS introductions can, in turn, have severe negative impacts on the economy and human health (Essl et al 2011; Carpenter et al 2013; Bradshaw et al 2016). Understanding, predicting, and mitigating the impact of invasive species on biodiversity and human livelihoods remains a key priority for the global community. In order to prioritise when and where an intervention is applied, one needs a clear understanding of which ecosystems are more vulnerable to invasion
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