Why are there so many exotic Springtails in Australia? A review.

Native invertebrate assemblages in Australia are adversely impacted by invasive exotic plants because they are replaced by exotic, invasive invertebrates. The reasons have remained obscure. The different physical, chemical and biotic characteristics of the novel habitat seem to present hostile conditions for native species. This results in empty niches. It seems the different ecologies of exotic invertebrate species may be better adapted to colonise these novel empty niches than native invertebrates. Native faunas of other southern continents that possess a highly endemic fauna, such as South America, South Africa and New Zealand, may have suffered the same impacts from exotic species but insufficient survey data and unreliable and old taxonomy makes this uncertain. Here I attempt to discover what particular characteristics of these novel habitats are hostile to native invertebrates. I chose the Collembola as a target taxon. They are a suitable group because the Australian collembolan fauna consists of a high percentage of endemic taxa, but also exotic, non-native, species. Most exotic Collembola species in Australia appear to have originated from Europe, where they occur at low densities (Fjellberg 1997, 2007). Once in Australia many become invasive forming large populations. This occurs most frequently in exotic grasses and other weeds, but also even in native vegetation. I provide here species records from a number of sites that have been both invaded and colonised by exotic Collembola as well as those that still only carry native species, and document the differences between sites and faunas as far as is known. I suggest that a major factor is likely a change in microflora because of higher nutrient levels on invaded sites, particularly nitrogen and phosphorus from either fertilisers or rapid decomposition rates of exotic plants. The traits of exotic species, where known, tend to be r selected and so have a competitive advantage over the mainly K or A selected native species is another factor.