Biological responses to climate change
- This page is part of the topic Antarctic climate and environment history in the pre-instrumental period
This section reviews the evolutionary and biogeographical factors that have shaped the contemporary terrestrial and marine biota of the Antarctic continent. It includes descriptions of some of the physiological adaptations in the marine realm that have led to the distinctive marine fauna seen today. This section also highlights some of the reorganisations in terrestrial and marine species distributions that have occurred during the relatively minor natural climate changes of the Holocene that are being used to inform our understanding of the climate and biological changes that might be anticipated in the near future (Chapter 5).
The fossil record, stretching back over 500 million years, provides a broad outline of evolutionary history of the continent and its biota. The first signs of temperate biotas, marine and terrestrial, were in the middle Devonian (ca. 375 Ma). During the Cretaceous, the highly seasonal, then warm, high-CO2 climate and unstable landscape of high-latitude Gondwana may have been the centre of origin for gymnosperm and angiosperm taxa that subsequently spread northward, providing sources for temperate southern hemisphere floras. Environmental change, including climatic change, in Antarctica and its surrounding waters has been dramatic since separation of the other southern hemisphere continents from Antarctica during the Cretaceous and Tertiary. It is possible that some elements of the living marine biotas can be traced back to the Early Cretaceous period (130 Ma). The earliest cold climate marine faunas are thought to be latest Eocene-Oligocene (ca. 35 Ma) in age. Conditions on land fluctuated greatly between cold and warm during the Tertiary, and terrestrial floras changed accordingly. There is local high diversity of invertebrates on the deeper shelf, where environmental conditions are relatively homogenous so that distributional limits of species assemblages cannot be explained only by ecological demands. The “climate diversity pump”, a variation of the refugio-survival model, is based on surges of the Antarctic ice cap to the coast and sometimes as far as the shelf break. These episodes are first documented from the Late Eocene (40 Ma) and have continued into the Pleistocene. It is possible that they have acted as a barrier for genetic exchange. During such periods of the separation of populations these continued to evolve and mixed again when the ice retreated but interbreeding was not possible anymore. As a consequence, more species with broadly overlapping ecological niches can be expected after the exposure to large scale disturbances. This might be especially relevant for filter feeders among which competition is not highly effective to reduce the number of species and diversity. Our knowledge of the relevance of the “climate diversity pump” can only improve when glaciological and sedimentological findings are combined with those of ecological surveys using statistics and genetics and a sampling design adapted to this specific question.
