Abstract
Background: The sub-Antarctic Prince Edward Islands (PEIs), South Africa’s southernmost territories have high conservation value. Despite their isolation, several alien species have established and become invasive on the PEIs. Objectives: Here we review the invasion ecology of the PEIs. Methods: We summarise what is known about the introduction of alien species, what influences their ability to establish and spread, and review their impacts. Results: Approximately 48 alien species are currently established on the PEIs, of which 26 are known to be invasive. Introduction pathways for the PEIs are fairly well understood – species have mainly been introduced with ship cargo and building material. Less is known about establishment, spread and impact of aliens. It has been estimated that less than 5% of the PEIs is covered by invasive plants, but invasive plants have attained circuminsular distributions on both PEIs. Studies on impact have primarily focussed on the effects of vertebrate invaders, of which the house mouse, which is restricted to Marion Island, probably has the greatest impact on the biodiversity of the islands. Because of the risk of alien introductions, strict biosecurity regulations govern activities at the PEIs. These are particularly aimed at stemming the introduction of alien species, and are likely to have reduced the rates of new introductions. In addition, some effort is currently being made to eradicate selected range-restricted species. However, only one species that had established and spread on the PEIs, the cat, has been successfully eradicated from the islands. Conclusion: Given the ongoing threat of introductions, and the impacts of invaders, it is essential that future invasions to the PEIs are minimised, that the islands’ management policies deal with all stages of the invasion process and that a better understanding of the risks and impacts of invasions is obtained.
Highlights
While a number of reviews about invasions to the greater sub-Antarctic region have been written (e.g. Convey et al 2006; Frenot et al 2005; Hughes & Convey 2010; Shaw 2013), we aim to review the state of knowledge of invasions for the Prince Edward Islands (PEIs)
It is likely that some introductions of alien species to Prince Edward Island have been the result of secondary transport of alien propagules by natural vectors, such as wind or birds, from Marion to Prince Edward Island (Gremmen & Smith 1999; Ryan, Smith & Gremmen 2003)
The first record of S. procumbens L. on Prince Edward Island was in an area of high seal and bird activity, some distance from where scientists usually land on their expeditions to the island, making it unlikely that humans were responsible for the introduction (Gremmen & Smith 1999)
Summary
Vagility influences the nestedness of the different alien taxa of the sub-Antarctic Islands (Greve et al 2005); in other words, assemblages of groups that are most mobile are more nested than those of less mobile groups This suggests that organisms with better vagility are more likely to reach more subAntarctic Islands, whereas the arrival of species with lower vagility on the islands may be more haphazard (Greve et al 2005; Shaw et al 2010). The sub-Antarctic Prince Edward Islands (PEIs), South Africa’s southernmost territories have high conservation value Despite their isolation, several alien species have established and become invasive on the PEIs
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