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Map of the biogeographic region referred to as the Southern Ocean Islands, between 37°S and 55°S
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Isolation and climate have protected Southern Ocean Islands from non-native species. Relatively recent introductions have had wide-ranging, sometimes devastating, impacts across a range of species and ecosystems, including invertebrates, which are the main terrestrial fauna. In our comprehensive review, we found that despite the high abundance of n...
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The ice-associated copepods Stephos longipes, Paralabidocera antarctica, and Drescheriella glacialis are the dominant species inhabiting Antarctic sea ice. They influence the pelagic ecosystem after being released into the water column when the ice melts from spring to summer in the marginal ice zone (MIZ), although less is known about those in the...
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... Lastly, the presence of predator control targeting stoats, rats and or cats had no significant effect on invertebrate community composition, abundance, or body size. At lower elevations, there is strong international evidence that mice influence invertebrate abundance, body size and community composition (Marris 2000;Angel et al. 2009;St Clair 2011;Houghton et al. 2019). For example, comparisons of invertebrates on sub-Antarctic Marion Island with those on nearby mouse-free Prince Island suggest the presence of mice influenced invertebrate community composition, causing a decrease in the body size of medium to large-bodied invertebrates (Crafford and Scholtz 1987;Crafford 1990;Chown and Smith 1993). ...
Invasive mammalian predators are a key threat to native fauna globally. Island ecosystems that developed in isolation from mammals are particularly threatened by introduced mammalian predators. This is the case in New Zealand, where introduced mammalian predators have caused the decline of native birds, lizards, and invertebrates. In alpine areas of New Zealand, predator control targets stoats, rats, and cats as they are recognised as the key threats to native birds. Mice, which are known predators of invertebrates at lower elevations, are not actively controlled. As a result, alpine invertebrates in New Zealand represent an ideal focus for a natural experiment to understand the effects of predator control efforts and invasive mice on native invertebrates that evolved in isolation from mammals. In the Fiordland region of New Zealand, we assessed the large-bodied alpine invertebrate community at eight different sites that vary in their occurrence of mice and control of higher-order predators. We found that the recent presence of mice influenced the invertebrate community: wētā (a group of native orthopterans) were less common at sites where mice were present, and the mean body size of invertebrates collected in pitfall traps was larger at sites where mice were absent compared to sites where they were present. Control of other predators (specifically rats and mustelids) did not influence invertebrate body size, abundance, or community composition. Our findings suggest that, as in lowland environments, mice are an important predator of large-bodied invertebrates in the alpine zone and should be incorporated into future predator management programmes.
... Despite its geographical isolation and relatively harsh sub-Antarctic climate, South Georgia currently hosts species of plants and invertebrates that were introduced by sealing -and later shore-based whaling -industries between the late 18 th and mid-20 th centuries (Convey and Lebouvier 2009;Convey et al. 2011;Black 2022) with new introductions occurring up to the present day (Convey et al. 2010;Tichit et al. 2023). Some introduced species have negative impacts on native communities (Ernsting et al. 1995;Houghton et al. 2019) and the island's terrestrial ecosystems may be particularly vulnerable to introductions due to the presence of vacant niches that are readily available to new competitive invasive taxa (Convey and Lebouvier 2009;Houghton et al. 2019). To tackle this issue, the Government of South Georgia & the South Sandwich Islands (GSGSSI) has implemented rigorous biosecurity measures and invasive mammals have been successfully eradicated from the Island (GSGSSI 2013; Martin and Richardson 2019). ...
... Despite its geographical isolation and relatively harsh sub-Antarctic climate, South Georgia currently hosts species of plants and invertebrates that were introduced by sealing -and later shore-based whaling -industries between the late 18 th and mid-20 th centuries (Convey and Lebouvier 2009;Convey et al. 2011;Black 2022) with new introductions occurring up to the present day (Convey et al. 2010;Tichit et al. 2023). Some introduced species have negative impacts on native communities (Ernsting et al. 1995;Houghton et al. 2019) and the island's terrestrial ecosystems may be particularly vulnerable to introductions due to the presence of vacant niches that are readily available to new competitive invasive taxa (Convey and Lebouvier 2009;Houghton et al. 2019). To tackle this issue, the Government of South Georgia & the South Sandwich Islands (GSGSSI) has implemented rigorous biosecurity measures and invasive mammals have been successfully eradicated from the Island (GSGSSI 2013; Martin and Richardson 2019). ...
... Introduced invertebrates may also have impacts on the terrestrial ecosystems of sub-Antarctic islands (Convey et al. 2010;Houghton et al. 2019). In our study, they were restricted to coastal sites, suggesting that inland sites might provide refuges for native taxa (but see Lebouvier et al. (2020) who note that M. soledadinus is now invading inland and higher altitude locations on the Kerguelen Islands). ...
Biological invasions are one of the main drivers of global biodiversity decline. At the same time, glacial retreat induced by climate warming is occurring at an alarming rate across the globe, threatening unique taxa and ecosystems. However, we know little about how introduced species contribute to the dynamics of colonisation in newly-deglaciated forelands. To answer this question, detailed inventories of plant and invertebrate communities were undertaken during two summer field seasons in the forelands of three tidewater and three inland glaciers that are retreating on the sub-Antarctic Island of South Georgia. The vascular plant communities present included a large proportion of South Georgia’s native flora. As expected, plant richness and cover increased with time since deglaciation along a deglaciation chronosequence. Introduced plants were well represented in the study sites and two species ( Poa annua and Cerastium fontanum ) were amongst the earliest and most frequent colonisers of recently-deglaciated areas (occurring on more than 75% of transects surveyed). Introduced arthropods were also present around tidewater glaciers, including an important predatory species ( Merizodus soledadinus ) with known detrimental impacts on native invertebrate communities. Our study provides a rare and detailed picture of developing novel communities along a deglaciation chronosequence in the sub-Antarctic. Introduced species are able to track glacial retreat on South Georgia, indicating that further local colonisation and spread are inevitable as the region’s climate continues to warm.
... Climatic conditions on the islands are changing rapidly in step with global climate change, with temperatures having increased by 1.2degC and precipitation decreased by 25% since the 1960s (le McGeoch, 2008, Smith, 2002). Additionally, invasion by some plant and animal species is transforming some of these islands' landscapes, especially on the more heavily impacted Marion Island , McGeoch et al., 2015, Houghton et al., 2019. Biologically, the PEIs constitute a fairly simple system, with few vascular plant species (around 22 native and 6 persistent invasive aliens) (Chau et al., 2020, Greve et al., 2017. ...
Environmental and biotic factors drive species richness patterns, but the nature of this relationship can vary with sampling grain. Understanding the scale-dependent effects of these factors is crucial for interpreting species richness patterns in ecosystems experiencing rapid environmental change. We investigated the effects of local environmental drivers on plant species richness at small (1 x 1 m) and large (3 x 3 m) sampling grains, and the factors correlated with differences in richness between the two grains, on a sub-Antarctic island. Broadly, richness was higher in warmer (i.e., lower altitude, north-facing) and wetter (i.e., higher topographic wetness index, lower distance from drainage line) sites, and in more topographically heterogenous (i.e., steeper slopes) sites. Additionally, there was some evidence of competition with a keystone plant limiting species richness, though this was only evident at low elevations. However, the effects of several drivers on richness depended on spatial grain. Differences in species richness between large and small grain sizes were more pronounced at low elevations, indicating that there is more compositional heterogeneity at low altitudes at both grains. Richness was positively related to northness at large grain size but not at small grain size, suggesting that higher northness increases local turnover at a grain size > 1 m2. On the other hand, TWI boosted richness at small but not large grains, implying that competition limited coexistence at low TWI, and that higher TWI only resulted in more species coexisting at a grain of 1 m2, while having no effect on richness at large grains. Our study therefore highlights that drivers of plant species richness can vary with sampling grain, suggesting that environmental effects on local species turnover affect richness patterns at different grains. Assessing how the influence of such drivers differ with grain size provides insight into local patterns of species assemblage.
... These sub-Antarctic islands are highly vulnerable to biological invasions (Convey, 2007;Frenot et al., 2005), potentially because (1) native communities contain vacant niches as a result of geographical isolation and may thus have low resistance to invasion, (2) there has been an increase in human activities (e.g. tourism, scientific expeditions) likely associated with a higher propagule pressure of non-native species, and (3) contemporary climate change may both destabilise native ecosystems and facilitate the establishment and spread of introduced species (Bergstrom & Chown, 1999;Convey & Lebouvier, 2009;Houghton et al., 2019;Hughes et al., 2019). Successful biosecurity measures are key to counteracting the growing challenge of biological invasions on sub-Antarctic islands, by preventing introductions and managing species already present in a given area. ...
Biological invasions represent a growing threat to islands and their biodiversity across the world. The isolated sub‐Antarctic island of South Georgia in the South Atlantic Ocean is a highly protected area that relies on effective biosecurity including prevention, surveillance and eradication to limit the risk of biological invasions. Based on an opportunistic field discovery, we provide the first report of an introduced ladybird beetle on South Georgia. All specimens discovered belong to the Eurasian species Coccinella undecimpunctata Linnaeus (1758) (Coleoptera: Coccinellidae). Tens of individuals of both sexes were discovered at a single location, indicating that the species may already be established on South Georgia. Transport connectivity with this site suggests that the species most likely arrived recently from the Falkland Islands as a stowaway on a ship. We discuss the implications of our discovery for the continued development of South Atlantic biosecurity.
... These native communities are often species poor, and characterized by a high degree of endemism, making non-native species a high risk to biodiversity conservation in the absence of trophically-analogous species 17 . Insular cold areas also have lower functional diversity, hence displaying vacant niches that can be readily exploited by non-native species 18,19 , and in some cases even lack predatory species 17 . Consequently, native communities from cold regions are naive to predators, as evidenced, for example, by the fact that many native insect species are flightless; an obvious disadvantage in the face of non-native predators [20][21][22][23] . ...
Biological invasions represent a major threat to biodiversity, especially in cold insular environments characterized by high levels of endemism and low species diversity which are heavily impacted by global warming. Terrestrial invertebrates are very responsive to environmental changes, and native terrestrial invertebrates from cold islands tend to be naive to novel predators. Therefore, understanding the relationships between predators and prey in the context of global changes is essential for the management of these areas, particularly in the case of non-native predators. Merizodus soledadinus (Guérin-Méneville, 1830) is an invasive non-native insect species present on two subantarctic archipelagos, where it has extensive distribution and increasing impacts. While the biology of M. soledadinus has recently received attention, its trophic interactions have been less examined. We investigated how characteristics of M. soledadinus, its density, as well as prey density influence its predation rate on the Kerguelen Islands where the temporal evolution of its geographic distribution is precisely known. Our results show that M. soledadinus can have high ecological impacts on insect communities when present in high densities regardless of its residence time, consistent with the observed decline of the native fauna of the Kerguelen Islands in other studies. Special attention should be paid to limiting factors enhancing its dispersal and improving biosecurity for invasive insect species.
... Despite being present on Macquarie Island for over a century, P. patersoni has shown limited range expansion and remains confined to a narrow area (Figure 1; see also Houghton et al. 2022), even though suitable habitats are available outside and adjacent to its current distribution range (Richardson and Jackson 1995) and identifiable barriers to dispersal are absent (Houghton et al. 2022). Additionally, the removal of invasive rodents from the island, which are known to preferentially prey on amphipods on sub-Antarctic Islands (Houghton et al. 2019), does not appear to have led to recent population changes in P. patersoni (Houghton et al. 2022). Our analysis of mtDNA data also suggests a small population with limited genetic diversity and the absence of population expansion on Macquarie Island. ...
The terrestrial amphipod Puhuruhuru patersoni (Amphipoda: Talitridae) was discovered on sub-Antarctic Macquarie Island in 1992. The species is only known to naturally occur on New Zealand’s South Island and some associated offshore islands. The possible routes by which the species was introduced to Macquarie Island have previously been considered based on morphology and historic activities between New Zealand and Macquarie Island. Here, we sampled across the known range for P. patersoni and generated mtDNA COI data for these specimens to investigate the likely origin of the Macquarie Island incursion. Our results showed high genetic diversity across the native range and substantially lower genetic diversity on Macquarie Island. Additionally, our phylogenetic reconstructions suggested that the source of the introduction to Macquarie Island is likely to have been from the southern region of New Zealand’s South Island.
... There is widespread documentation of the consumption of plant matter and macroinvertebrates by mice on Southern Ocean islands (e.g. Angel et al. 2009;Houghton et al. 2019;Russell et al. 2020). Over the last decade evidence of significant negative impacts of mice on avian species, including predation on large live seabirds, has emerged from Southern Ocean islands (Wanless et al. 2012;Dilley et al. 2015). ...
House mice (Mus musculus) are an invasive species on Auckland Island in the New Zealand subantarctic and planning for their eradication is underway. Mast seeding events cause rodent populations to irrupt, though little is known about this phenomenon in snow tussock grass (Chionochloa spp.) systems on Southern Ocean islands. The aim of this study was to understand population fluctuations of mouse abundance on Auckland Island for the 2 years following a mast event, and with which tools to monitor abundance, to inform planning of bait application for eradication. Mouse populations were studied using kill and live trapping at two sites on Auckland Island, and mouse density was estimated using spatially explicit capture-recapture models. Mouse population density was highest during summer mast seeding of Chionochloa antarctica and then declined the following winter and subsequently remained low for the following year. Breeding remained seasonal, with a pulse in early summer and a very low level continuing through winter in both years, regardless of mast conditions. These results are similar to those from other cool temperate Southern Ocean islands where seasonal resource availability appears to drive breeding. Throughout the study the capture probability of mice was generally higher when population density was lower, which highlights that conclusions about population trends could be misleading if abundance indices are not calibrated to measures of population density. Mouse eradication should preferentially take place outside of a mast event but would likely still succeed during and following a mast event. Our work fills a key knowledge gap about rodent population trends during mast events for Southern Ocean islands, which is particularly important where eradications are planned.
... There is widespread documentation of the consumption of plant matter and macroinvertebrates by mice on Southern Ocean islands (e.g. Angel et al. 2009;Houghton et al. 2019;Russell et al. 2020). Over the last decade evidence of significant negative impacts of mice on avian species, including predation on large live seabirds, has emerged from Southern Ocean islands (Wanless et al. 2012;Dilley et al. 2015). ...
... This is especially so for sub-Antarctic ecosystems which are characteristically simple and lack representatives of many functional groups (Vernon et al. 1998;Chown and Convey 2016;. Consequently, in sub-Antarctic ecosystems not only do invasive mammalian predators have particularly devastating consequences (Courchamp et al. 2003;Frenot et al. 2005;Angel et al. 2009), but so can invasive invertebrate predators, pollinators, herbivores, and macro-detritivores (Jones et al. 2003;Smith 2007;Chown et al. 2008;Greenslade et al. 2007Greenslade et al. , 2008Convey et al. 2010;Lebouvier et al. 2020), although more research into the extent of such impacts is required (Houghton et al. 2019a). ...
... As macro-detritivores, non-native isopods can have considerable impacts on Southern Ocean Island ecosystems (Jones et al. 2003). Neither native nor non-native isopod species are preferred rodent food according to several rodent diet studies on Southern Ocean Islands where they are present (Houghton et al. 2019a). However, they are potentially sensitive to habitat changes, such as vegetation recovery following the cessation of grazing and burrowing since the removal of rabbits during MIPEP (Shaw et al. 2011;Whinam et al. 2014;Fitzgerald 2020). ...
... Factors limiting their spread therefore remain unclear. Furthermore, the removal of invasive rodents from the island, which are known on sub-Antarctic islands to preferentially prey on amphipods (Houghton et al. 2019a), has not influenced amphipod numbers. Although in 2018 we detected singletons of S. otakensis at sites outside their 2004 range, given the animal's tendency to mass in high numbers where present (Houghton, pers. ...
Spanning the Southern Ocean high latitudes, Sub-Antarctic islands are protected areas with high conservation values. Despite the remoteness of these islands, non-native species threaten native species and ecosystem function. The most ubiquitous and speciose group of non-native species in the region are invertebrates. Due to their cryptic habits and ambiguous establishment history, the impacts of non-native invertebrates on native species and ecosystems in the region remains largely unknown. Understanding how non-native invertebrate species are transported, disperse, establish and colonise new habitats is key to understanding their existing and future impacts. This research is fundamental to improving biosecurity practise and informing future management of Southern Ocean islands. We undertook invertebrate surveys on Macquarie Island to determine the current status of four non-native macro-invertebrates—Kontikia andersoni and Arthurdendyus vegrandis (Platyhelminthes: Geoplanidae), Styloniscus otakensis (Isopoda: Styloniscidae) and Puhuruhuru patersoni (Amphipoda: Talitridae). Arthurdendyus vergrandis was not intercepted in our surveys, while we found S. otakensis and P. patersoni had not expanded their range. In contrast, K. andersoni has more than doubled its previously mapped area and expanded at a rate of ~ 500 m-yr since 2004. We discuss the possible underlying mechanisms for the dramatic range expansion of K. andersoni and consider the implications for the future management of Macquarie Island.
... How arthropod communities reliant on native vegetation on sub-Antarctic islands, are impacted by non-native plants is yet to be tested (Houghton et al. 2019) and is difficult to predict. This is due to the absence or low richness of many insect groups (Gressit 1970;Vernon et al. 1998), and to the high interactions at play between native and non-native plants, native and non-native arthropods and between plants and arthropods (Houghton et al. 2019). ...
... How arthropod communities reliant on native vegetation on sub-Antarctic islands, are impacted by non-native plants is yet to be tested (Houghton et al. 2019) and is difficult to predict. This is due to the absence or low richness of many insect groups (Gressit 1970;Vernon et al. 1998), and to the high interactions at play between native and non-native plants, native and non-native arthropods and between plants and arthropods (Houghton et al. 2019). Trait-based approaches have been proposed as useful tools to study plant-arthropod interactions at the community level e.g., Deraison et al. 2015;Le Provost et al. 2017) and to understand community responses to biotic disturbance induced by nonnative species (Gross et al. 2013;Mouillot et al 2013). ...
... Dominant non-native taxa in our study were the aphids, which are sap-feeders and the thrips A. apteris, which feeds on the content of leaf cells (Karban and Strass 1994). By occupying previously vacant or unsaturated ecological niche (Russel et al. 2017;Houghton et al. 2019), they probably don't compete with native species. Since data is missing from locations on the Kerguelen Islands that do not host non-native invertebrates (Hullé and Vernon 2021) against which to compare the diversity and abundance observed in our surveys, it is difficult to conclude on this hypothesis. ...
Biological invasions are a major threat to the terrestrial ecosystems of the sub-Antarctic islands. While non-native plants generally have negative impacts on native arthropods, few studies have investigated how both native and non-native arthropods and plants interact in the sub-Antarctic islands. This was the aim of our study, which was conducted on three islands of the Kerguelen archipelago. The design was based on the spatial proximity of areas dominated by non-native or native plant species. Trait-based indices were calculated to characterize the functional structure of plant communities, considering plant stature and leaf traits. Native and non-native vegetation had contrasting functional composition but their functional diversity was similar. The effects of the type of vegetation, native or non-native, and plant functional diversity on arthropods were tested. Native macro-arthropod richness and abundance were similar or higher in non-native vegetation, and benefited from greater plant functional diversity. Abundances of macro-herbivores, macro-decomposers and macro-predators were also similar or higher in non-native vegetation. Conversely, the abundances of micro-arthropods, Symphypleona springtails and Oribatida mites, were higher in native vegetation but we also found that plant functional diversity had a negative effect on Symphypleona. Our results suggest that non-native plants can affect micro-arthropods directly or indirectly, likely through their effects on abiotic factors. By affecting macro-arthropod abundances across different trophic groups and by depleting micro-arthropods, non-native plants can alter trophic interactions, functional balances and the functioning of whole ecosystem.
