Yves Frenot

Biological invasions in the Antarctic: extent, impacts and implications

Alien microbes, fungi, plants and animals occur on most of the sub‐Antarctic islands and some parts of the Antarctic continent. These have arrived over approximately the last two centuries, coincident with human activity in the region. Introduction routes have varied, but are largely associated with movement of people and cargo in connection with industrial, national scientific program and tourist operations. The large majority of aliens are European in origin. They have both direct and indirect impacts on the functioning of species‐poor Antarctic ecosystems, in particular including substantial loss of local biodiversity and changes to ecosystem processes. With rapid climate change occurring in some parts of Antarctica, elevated numbers of introductions and enhanced success of colonization by aliens are likely, with consequent increases in impacts on ecosystems. Mitigation measures that will substantially reduce the risk of introductions to Antarctica and the sub‐Antarctic must focus on reducing propagule loads on humans, and their food, cargo, and transport vessels.

Continent-wide risk assessment for the establishment of nonindigenous species in Antarctica

Invasive alien species are among the primary causes of biodiversity change globally, with the risks thereof broadly understood for most regions of the world. They are similarly thought to be among the most significant conservation threats to Antarctica, especially as climate change proceeds in the region. However, no comprehensive, continent-wide evaluation of the risks to Antarctica posed by such species has been undertaken. Here we do so by sampling, identifying, and mapping the vascular plant propagules carried by all categories of visitors to Antarctica during the International Polar Years first season (2007–2008) and assessing propagule establishment likelihood based on their identity and origins and on spatial variation in Antarcticas climate. For an evaluation of the situation in 2100, we use modeled climates based on the Intergovernmental Panel on Climate Changes Special Report on Emissions Scenarios Scenario A1B [Nakićenović N, Swart R, eds (2000) Special Report on Emissions Scenarios: A Special Report of Working Group III of the Intergovernmental Panel on Climate Change (Cambridge University Press, Cambridge, UK)]. Visitors carrying seeds average 9.5 seeds per person, although as vectors, scientists carry greater propagule loads than tourists. Annual tourist numbers (∼33,054) are higher than those of scientists (∼7,085), thus tempering these differences in propagule load. Alien species establishment is currently most likely for the Western Antarctic Peninsula. Recent founder populations of several alien species in this area corroborate these findings. With climate change, risks will grow in the Antarctic Peninsula, Ross Sea, and East Antarctic coastal regions. Our evidence-based assessment demonstrates which parts of Antarctica are at growing risk from alien species that may become invasive and provides the means to mitigate this threat now and into the future as the continents climate changes.

Human activities, ecosystem disturbance and plant invasions in subantarctic Crozet, Kerguelen and Amsterdam Islands

Abstract Recent floristic surveys of the French islands of the southern Indian Ocean (Ile de la Possession, in the Crozet archipelago, Iles Kerguelen and Ile Amsterdam) allow a comparison of the status of the alien vascular plant species in contrasted environmental and historical situations. Four points are established: (1) the current numbers of alien plant species are almost the same on Amsterdam (56) and La Possession (58), slightly higher on Kerguelen (68); (2) some of these species are common to two or three islands but a high number of them are confined to only one island (18, 28 and 28 on La Possession, Kerguelen and Amsterdam, respectively); (3) all the alien plant species are very common species in the temperate regions of the northern hemisphere and belong to the European flora; and (4) a high proportion of the introduced species are present on the research stations or their surroundings (100, 72 and 84% on La Possession, Kerguelen and Amsterdam, respectively). These results are discussed in term of propagule pressure (mainly attributed to ships visiting these islands), invasibility of such ecosystems (in relation to climatic conditions and degree of disturbance by previous or current human activities such as sheep farming or waste deposits) and invasion potential of alien plant species.

Challenges to the Future Conservation of the Antarctic

Changing environments and resource demands present challenges to Antarctic conservation. The Antarctic Treaty System, acknowledged as a successful model of cooperative regulation of one of the globes largest commons (1), is under substantial pressure. Concerns have been raised about increased stress on Antarctic systems from global environmental change and growing interest in the regions resources (2, 3). Although policy-makers may recognize these challenges, failure to respond in a timely way can have substantial negative consequences. We provide a horizon scan, a systematic means for identifying emerging trends and assisting decision-makers in identifying policies that address future challenges (2, 3). Previous analyses of conservation threats in the Antarctic have been restricted to matters for which available evidence is compelling (4). We reconsider these concerns because they might escalate quickly, judging from recent rapid environmental change in parts of Antarctica and increasing human interest in the region (see the map). We then focus on a more distant time horizon.

Recovery of native plant communities after eradication of rabbits from the subantarctic Kerguelen Islands, and influence of climate change

The introduction of rabbits in 1874 into the Kerguelen archipelago had a significant impact on plant communities: the most sensitive species Pringlea antiscorbutica and Azorella selago disappeared and Acaena magellanica became dominant in most of the coastal areas. To study the recovery of native plant communities, rabbits were eradicated by poisoning on two islands. This produced a significant increase in species richness on both islands with a decline in the cover of some native species (primarily A. magellanica) and an increase in the abundance of alien species (especially Taraxacum officinale). Other native species showed signs of increased abundance but overall responses were slow. These trends are obviously due to the removal of grazing, but recent changes in climatic conditions (warming and drought) may also be responsible for the decline or slow recovery of native species, and for the success of introduced species. Owing to the effects of present climate changes on plant communities, eradication of alien herbivores may not be always appropriate for the conservation of native biota in the subantarctic islands, and regulation of populations should be explored.

The significance of the sub-Antarctic Kerguelen Islands for the assessment of the vulnerability of native communities to climate change, alien insect invasions and plant viruses

The suite of environments and anthropogenic modifications of sub-Antarctic islands provide key opportunities to improve our understanding of the potential consequences of climate change and biological species invasions on terrestrial ecosystems. The profound impact of human introduced invasive species on indigenous biota, and the facilitation of establishment as a result of changing thermal conditions, has been well documented on the French sub-Antarctic Kerguelen Islands (South Indian Ocean). The present study provides an overview of the vulnerability of sub-Antarctic terrestrial communities with respect to two interacting factors, namely climate change and alien insects. We present datasets assimilated by our teams on the Kerguelen Islands since 1974, coupled with a review of the literature, to evaluate the mechanism and impact of biological invasions in this region. First, we consider recent climatic trends of the Antarctic region, and its potential influence on the establishment, distribution and abundance of alien insects, using as examples one fly and one beetle species. Second, we consider to what extent limited gene pools may restrict alien species’ colonisations. Finally, we consider the vulnerability of native communities to aliens using the examples of one beetle, one fly, and five aphid species taking into consideration their additional impact as plant virus vectors. We conclude that the evidence assimilated from the sub-Antarctic islands can be applied to more complex temperate continental systems as well as further developing international guidelines to minimise the impact of alien species.

Diet of the house mouse (Mus musculus) on Guillou island, Kerguelen archipelago, Subantarctic

Abstract. The diet of the house mouse (Mus musculus domesticus), introduced to the Kerguelen archipelago in the 1800s, was studied at monthly intervals from August 1997 to July 1998 in the closed communities of Acaena magellanica, the main habitat of mice on Guillou Island. The analysis of 291 stomach contents showed that this opportunistic rodent included a variety of items in its diet: earthworms (Dendrodrilus rubidus tenuis, Microscolex kerguelensis), caterpillars of a flightless moth (Pringleophaga kerguelensis), weevil adults and larvae (Ectemnorrhinus spp.), seeds of Acaena magellanica, and floral parts of dandelion (Taraxacum officinale). The animal prey were dominant in its diet all year round, except in summer. Based on the presence of chaetae in the stomach contents, our results show that earthworms are an important prey for the house mouse at Kerguelen. The consequences of these food habits for the invertebrate communities of the subantarctic islands are discussed.

Contribution of alien and indigenous species to plant-community assemblages near penguin rookeries at Crozet archipelago

The influence of seabird colonies on a remote insular flora was investigated through the analysis of plant community patterns at the boundaries of three colonies of king penguins (Aptenodytes patagonicus) on the subantarctic Île de la Possession. This study revealed that the physical and chemical impacts of these seabirds greatly influence plant assemblages (community composition, alien and native species abundance and richness). Plant richness appears to be maximum for a moderate disturbance intensity, on areas slightly influenced by penguin activities. The abundance of alien species near penguin rookeries may be due to their ability to withstand animal-induced disturbances and to efficiently colonise the stripped areas. In addition, the diversity and abundance of alien species recorded in study plots depend on the location of the colony. The closer the colony is to the permanent scientific station, the higher the number and abundance of aliens recorded.

Environmental modifications of a subantarctic peat-bog by the Wandering Albatross (Diomedea exulans): A preliminary study

SummaryOn Ile de la Possession, as on all the subantarctic islands, major compounds of organic nutrients are provided by avifauna. The presence of Wandering Albatrosses (Diomedea exulans) induces great perturbations in the environment at the site of their nest building activities: physical and chemical modifications of the soil (by removal of litter material for nest building, trampling and accumulated organic deposits) as well as microbiological, botanical and faunal changes. These perturbations are very localized in extent. The pedological changes have been described in terms of morphological modifications. The influence of Wandering Albatrosses on the vegetation and the invertebrate fauna has been assessed and shows a decrease in the number of plant species and an increase in the number of invertebrate species. The role of some of these as indicator species is discussed.

Reproductive performance of native and alien colonizing phanerogams on a glacier foreland, Iles Kerguelen

The retreat of the Ampère Glacier, on Kerguelen, has left wide ice-free areas where five native and two alien vascular plant species are involved in primary colonization. The number of seeds produced by individual fertile plants has been determined for each species and germination capacity has been tested under different temperature and light conditions. Colobanthus kerguelensis and Cerastium fontanum produced the highest number of seeds per plant. No dormancy mechanism occurred in either species and they appeared to be the most successful colonizers during the early stages following the deglaciation. No seeds of Azorella selago and Agrostis magellanica had germinated after 2 months. Dormancy was demonstrated only in Poa kerguelensis. Festuca contracta was the only species which exhibited a negative photo-sensitivity. Germination of indigenous seeds required relatively high temperatures, whereas the optimum temperature for germination in the introduced Poa annua was 10°C. These results are compared with the few data available in the subantarctic literature and ecological implications are discussed.