PerspectiveEcology

Antarctic Biodiversity

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Science  28 Sep 2007:
Vol. 317, Issue 5846, pp. 1877-1878
DOI: 10.1126/science.1147261

Only about 0.3% of Antarctica is free of ice. The terrestrial and freshwater ecosystems in this tiny fraction are generally small and isolated, and are populated by small invertebrates, lower plants, and microbes (see the figure). Recent studies have shown that these biota are of ancient origin and have persisted in isolation for tens of millions of years. However, ice sheet modeling of the Last Glacial Maximum (~20,000 years ago) and previous ice maxima in the Miocene (23 to 5 million years ago), along with reconstructions of previous glacial extent, suggest that most or all currently ice-free low-altitude surfaces would have been covered with ice during previous glacial maxima (1, 2). These models leave no ice-free refuges for most terrestrial biota, and they require recolonization after each glacial maximum.

The latter view has been reinforced by the discovery of fossils that were referred to as the last surviving relicts from preglacial Antarctica (3, 4). The fossils describe a community assemblage, including tundra vegetation and terrestrial and freshwater faunas, that survived the formation of the ice sheets initiated more than 30 million years ago but became extinct between 12 and 1.8 million years ago. The implication is that the terrestrial biota we see today consist of species that have become established since the Last Glacial Maximum.

A different picture emerges from early biological studies and some recent geological work. Baseline entomological research carried out in Antarctica as early as the 1960s (5-7) documented much of the arthropod biodiversity, particularly from the Transantarctic Mountains and the Antarctic Peninsula (see the figure). These authors recognized that at least a proportion of these biota could not easily be explained as recent colonists. Furthermore, in some isolated parts of continental Antarctica, reconstructions of previous glacial extent (2) do support the existence of ice-free biological refuges at least from 1.8 million to 10,000 years ago. Evidence preserved from volcanic eruptions below the ice now also allows for the possibility of low-altitude ice-free land at glacial maxima (1, 8).

Ancient origins. Many organisms have persisted in Antarctica since well before the Last Glacial Maximum.

PHOTO CREDIT: K. NEWSHAM (NEMATODE), R. LEE (DIPTERA), B. O'BRIEN (SPRINGTAIL), BRITISH ANTARCTIC SURVEY (ALL OTHERS)

More recent biological studies also point to much of the terrestrial biota having a long, continuous but isolated, history on the continent. Biogeographical analyses of freshwater copepods and nunatak-inhabiting mites (9, 10) have identified distribution patterns consistent with evolutionary persistence in Antarctica over time scales between the Last Glacial Maximum and the final stages of Gondwana breakup (~40 to 60 million years ago), when Antarctica became isolated from South America and Australia. Other studies describe communities as having developed over the past 1.8 million years (5, 7, 11, 12).

Recent molecular studies provide evidence for the persistence of several species on multimillion-year time scales (even back to pre-Gondwana breakup). For example, closely related chironomid midges endemic to tectonically distinct parts of the Antarctic Peninsula and Scotia Arc persisted for about 50 million years (13), revealing a biological signal of the separation of Antarctica and South America (14). Likewise, ancient divergences between endemic springtails from East Antarctica suggest radiation from a fauna dating from at least 21 to 11 million years ago (15). Even nematodes, which are capable of long-distance dispersal and gene flow (16), are endemic species isolated within the confines of continental Antarctica (17). Collectively, these studies provide evidence that terrestrial biota persisted in both the Antarctic Peninsula and East Antarctica, suggesting separate and ancient origins for these biota (18).

Thus, reexamination of the existing literature provides robust support for ancient origins of Antarctic terrestrial biota across most parts of the continent and involving most extant higher taxa (see the figure). Understanding the evolution and biogeographical history of the Antarctic terrestrial biota—especially in coastal areas—requires a more detailed multidisciplinary study of the persistence of terrestrial habitats than the current generation of ice sheet models permits. Terrestrial biological evidence could help researchers to improve glaciological reconstruction modeling and to gain further understanding of the evolution of the Antarctic continent.

Mountains in the Antarctic Peninsula. Terrestrial and freshwater biota have survived through glacial cycles in parts of the Peninsula.

PHOTO CREDIT: DARRELL GULIN/CORBIS

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