Why Are There So Many Exotic Springtails in Australia? a Review

90 (3) · December 2018 pp. 141–156 Why are there so many exotic Springtails in Australia? A review. Penelope Greenslade1, 2 1 Environmental Management, School of School of Health and Life Sciences, Federation University, Ballarat, Victoria 3353, Australia 2 Department of Biology, Australian National University, GPO Box, Australian Capital Territory 0200, Australia E-mail: [email protected] Received 17 October 2018 | Accepted 23 November 2018 Published online at www.soil-organisms.de 1 December 2018 | Printed version 15 December 2018 DOI 10.25674/y9tz-1d49 Abstract 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. Keywords invasion biology | decomposition | soil nutrients | exotic plants | competitive traits 1. Introduction poisoning, biofouling, herbivory, chemical, physical or structural impact or by causing impacts by interacting The threats exotic (= non-native) invertebrate species with other alien species. More specifically, the invasion pose to native faunas have been highlighted in recent and establishment of an exotic species into an ecosystem publications, showing that they frequently outcompete has the potential to modify interactions between species native species and even cause extinctions (Gurevitch & at all trophic levels. This phenomenon is described as Padilla 2004 and included references). McGeoch et al a trophic cascade (French & Major 2001, Le Maitre et (2015) list ten ways in which invasive insects can impact al. 2011, Marchante et al. 2015, Walsh et al. 2016). In on native insects. They are by competition, predation, addition, exotic species present economic threats by hybridisation, transmission of disease, parasitism, loss of crops, and the magnitude of their effects varies © Senckenberg Museum of Natural History Görlitz · 2018 ISSN 1864-6417 (print) · ISSN 2509-9523 (digital) 142 Penelope Greenslade not only with climatic factors but also with soil nutrient identify species, but molecular sequence data can be availability as they can monopolise resources and, with practical if recorded already online (Porco et al. 2012, different physiologies, can alter mineral composition Cicconardi et al. 2017). of soils (Tabassum & Leishman 2016). The cost in lost There exists a considerable body of relevant information ecosystem services that invasive species can pose in on Collembola faunas from surveys carried out throughout native environments has been estimated, in one fresh Australia in many different types of ecosystems and water environment, to be in the millions of dollars (Walsh vegetation types documented over fifty years. Firstly, I et al. 2016). summarise this work by documenting existing data on Exotic invertebrates are a particular threat in the characteristics of habitats that are have been invaded Australia because of the high endemism of the native by exotic species and those that are not. Secondly, I fauna, in particular, to short-range endemic species by document native habitats that are not or unlikely to be outcompeting them. Intuitively, native species should be invaded as well as noting any exotic Collembola that protected, not only because of the ecosystem services are not invasive although present in Australia. Their that they and their habitats provide, but also because ecologies and traits where known are noted as well as these species are a store of information on the origins those of the invaded on non-invaded habitats. Finally, I and evolution of Australian fauna and flora and their summarise this information and develop hypotheses on biogeographical relationships. the characteristics of both invaded communities and It is important therefore to investigate what habitat invasive species based on this information. characteristics permit colonisation by exotic species so their impacts can be assessed, contained and even, where possible, eliminated. I use as focus group a common soil arthropod taxon, the 2. Examples of invaded habitats Collembola. This is because the Australian collembolan fauna is large and the total number of species is nearly What factors facilitate invasion of exotic Collembola 350 described native and endemics with a further 700 not into exotic vegetation and prevent retention of natives? yet described (Greenslade 2018). This number includes eighty-five proven and probable exotic Collembola species identified for Australia, increased from the number of 35 2.1 Wheat crops recorded by Greenslade & Ireson (1986) (Tab. 1). Of the total number of exotic species recorded from Australia, i) The soil and surface fauna of a tillage trial on sixty species are confirmed, another 20 species are broad-acre arable land in central New South Wales with probables and five possibly misidentified (Tab. 1). The seasonally dry summers and cool winters was sampled native collembolan fauna of Australia is highly endemic eight times over 20 years and all Collembola identified. at species and generic level and is a proven measure of Fertilisers and pesticides had been applied to the soil disturbance (Greenslade 1994, 1997, 2007). annually since 1990 when the trial began. Twenty-four Several publications within and outside Australia species, mainly exotics, were found (Longstaff et al. have shown that species compositions rather than taxa 1997) and did not change significantly in composition abundances are impacted by exotic plants (Greenslade et between years but abundance varied with season and al. 2014; Coyle et al. 2017; Rusterholz et al. 2014). Much weather. In the early 1990s, there were a maximum of earlier work evaluating the deleterious effects of exotic eight native species but, by 2017, only two native species, collembolan species has identified fauna to higher levels in very low numbers, were found, neither present in the but not to species (see Coyle et al. 2017), so obscuring their 1990´s samples. The eight species lost were all epigaeic species-specific habitat preferences. This is particularly a Symphypleona and Entomobryidae. (Greenslade & Nash problem in understanding processes following invasions in prep.) The differential effect on ecological types over of Collembola to Australia where there is a clear time may be the result of an increased regime of spraying distinction between native species and non-native species for aphids. in their habitats and ecologies. Specimens collected must ii) The effect of herbicides on surface-active fauna was therefore be identified to species and counted rather investigated in another tillage trial in broad-acre wheat than only counts of genera, families or higher taxa. In paddocks also in central New South Wales in a locality Australia, identification of exotic species is straight with a similar climate. The fauna consisted of the same forward as many have originated from the Northern suite of exotic species of Collembola as the trial reported Hemisphere where the fauna is well known (Greenslade above and with the same four species of Symphypleona, & Convey 2012). Normally morphology is sufficient to one of which was native. Four exotic species were SOIL ORGANISMS 90 (3) 2018 Invasive Collembola in Australia Table 1. List of assumed exotic species of Collembola in Australia and their habitats in the country based on Greenslade & Ireson (1986) and later references by Greenslade 1987 to 2018. Species names in bold – abundant & widespread. Superfamily Family Species Definite Probable Misidentified Habitat requirements Coecobrya communis (Chen & Christiansen, disturbed land, caves, cattle grazed mound Entomobryomorpha Entomobryidae 1997) D springs, logs, worm farms Entomobryomorpha

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