Biotic responses to rapid climatic changes during the Late Glacial: High-resolution biostratigraphies and biological processes

Abstract

Organisms can respond to rapid climatic changes in three ways: (1) adaptation (by evolution, affecting physiology and morphology), (2) migration and population dynamics (including biogeographical changes) and (3) extinction (local or global). Here, the focus is on examples of the second type. Organisms, whether algae, trees, or animals, find their ecological niches in a multi-dimensional space of gradients such as temperature (winter, summer, means or extremes), humidity (soil or air), pH, various nutrients, light. Presence or absence of taxa (species, genera, families) can be related to such gradients. With training sets based on current gradients, they can also be related to environmental changes of the past (e.g. summer mean temperatures or pH). The relationships between the occurrence of taxa and environmental variables can also be used to examine the biotic response to changes based on other proxies, for example, changes in temperature inferred from oxygen-isotope ratios in carbonates or from the content in organic matter of lake sediments. The groups of organisms referred to here are plants (pollen), insects (chironomids) and other aquatic invertebrates. The three Tate Glacial periods with very high rates of change in temperature estimates are the transition from the Oldest Dryas to the Billing (from GS-2 to GI-1 in the Tate Glacial, ca. 14 670 cal yr BP), and the beginning and the end of the Younger Dryas (ca. 12 600 cal yr BP, 11 500 cal yr BP respectively). The « classical » hypothesis was that trees represented in pollen diagrams) respond more slowly to climatic change than invertebrates aquatic or terrestrial) because of differences in life cycles. But it is shown here that terrestrial vegetation) and aquatic invertebrate) ecosystems may respond synchronously. Three major biological processes are involved in the responses to climatic change: 1) Migration can be slow if, for example, a longliving tree migrated back from a southern refugium. 2) Buildup of populations intermediate velocity, for the process needs time depending on the life cycles of the organisms. 3) Productivity can change rapidly, within a year or a few years e. g. pollen productivity, tree rings). The first two of these processes occur on the organisational level of populations, the last one on the level of the individual. These processes develop also in various combinations. © Author(s) 2008. This work is distributed.