Subantarctic flowering plants: pre‐glacial survivors or post‐glacial immigrants?

Abstract

Aim The aim here was to assess whether the present-day assemblage of subantarctic flowering plants is the result of a rapid post-Last Glacial Maximum (LGM) colonization or whether subantarctic flowering plants survived on the islands in glacial refugia throughout the LGM. Location The circumpolar subantarctic region, comprising six remote islands and island groups between latitudes 46° and 55° S, including South Georgia in the South Atlantic Ocean, the Prince Edward Islands, Îles Crozet, Îles Kerguelen, the Heard Island group in the South Indian Ocean and Macquarie Island in the South Pacific Ocean. Methods Floristic affinities between the subantarctic islands were assessed by cluster analysis applied to an up-to-date dataset of the phanerogamic flora in order to test for the existence of provincialism within the subantarctic. A review of the primary literature on the palaeobotany, geology and glacial history of the subantarctic islands was carried out and supplemented with additional palaeobotanical data and new field observations from South Georgia, Île de la Possession (Îles Crozet) and Îles Kerguelen. Results First, a strong regionalism was observed, with different floras characterizing the islands in each of the ocean basins, and endemic species being present in the South Indian Ocean and South Pacific Ocean provinces. Second, the majority of the plant species were present at the onset of accumulation of post-glacial organic sediment and there is no evidence for the natural arrival of new immigrants during the subsequent period. Third, a review of geomorphological data suggested that the ice cover was incomplete during the LGM on the majority of the islands, and ice-free biological refugia were probably present even on the most glaciated islands. Main conclusions Several independent lines of evidence favour the survival of a native subantarctic phanerogamic flora in local refugia during the LGM rather than a post-LGM colonization from more distant temperate landmasses in the Southern Hemisphere

Changes in Holocene climate and the intensity of Southern Hemisphere Westerly Winds based on a high-resolution palynological record from sub-Antarctic South Georgia

“…High Acaena percentages in Holocene pollen records have also been used on the Kerguelen Islands and Marion Island to identify warmer and drier climates, respectively (Scott and Hall, 1983;Young and Schofield, 1973). Despite these previous studies, we still treat the interpretation of Acaena and Poaceae with caution because in the South Indian Ocean sector, Van der Putten et al (2010) could not demonstrate a relationship between the occurrence of A. magellanica and warmer climates. We therefore consider other proxies such as organic carbon and sedimentological evidence in addition to Acaena and Poaceae to support our palaeoclimate interpretations.…”

“…For example, while the flowering plants, Juncus (Juncus inconspicuous, Juncus scheuchzerioides) and Rostkovia magellanica are two of the most common native species (Greene, 1969;Van der Putten et al, 2010), the pollen are not preserved in fossil assemblages (Van der Putten et al, 2004).…”

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

“…In addition, the Kerguelen Islands are not situated along major commerce routes, are inhabited by a limited number of non-permanent people each year (at most 100), do not have any industry and have very limited means of terrestrial transportation that would facilitate quick and regular exchanges between geographically distant points for an alien species. Overall, the Kerguelen Islands are characterized by low species diversity, supporting just 23 native insect species (Schermann-Legionnet et al 2007) and 22 native flowering plant species (Van der Putten et al 2010). It is therefore reasonably straightforward to detect the arrival and establishment of alien insect species.…”

King penguin demography since the last glaciation inferred from genome-wide data

“…Highly dispersive species negatively affected by glacial conditions could have moved northwards to more suitable ice-free breeding habitats during the LGM, while low-dispersive ones may have been strongly reduced in population size or may even have gone extinct [9]. Therefore, post-glacial warming and the subsequent retreat of glaciers and sea ice, probably favoured the re-colonization of Antarctic and sub-Antarctic territories by dispersive species dependent on ice-free breeding sites [5,6,10].…”