different in rate or magnitude than the declines that took place in the absence of any human influence? Are the effects of declines in ecological diversity today likely to have the same effects as those in the past?

The answers to all these questions—whether targeting site-specific problems or exploring general principles of ecological dynamics—require detailed, reliable information on past species abundances and environmental conditions from time intervals predating the last century of direct observation by scientists. Although the past decade has seen major advances in understanding the global climate system by a combination of real-time observations, modeling, and paleoclimate records, predicting and planning for the future depends upon our ability to understand not only how and why environments change but also how and why biological systems react. We also need to understand how biological systems themselves mediate important elements of environmental change ranging from key climatic parameters to biogeochemical cycles. Ecological dynamics (see Box 1.1), whether at the single-species, community, or global scale, generally have been studied by biologists over relatively brief timescales (one to two decades at most) and almost always in systems already highly altered by human activities.

There is thus a growing realization that only geohistorical data—the organic remains, biogeochemical signals, and associated sediments of the geological record—can provide a time perspective sufficiently long to establish the full range of natural variability of complex biological systems, and to discriminate human perturbations from natural cycles (e.g., Jablonski and Sepkoski, 1996; Swetnam et al., 1999; Lawton, 1999; McDonald and Chure, 2001; Woodruff, 2001; Hubbell, 2001; Barnosky et al., 2004). Such data are crucial for acquiring the necessary long-term perspective on modern systems and, by sampling past environmental states both like and unlike those of the present day, for providing the empirical framework needed to discover the general principles of biosphere behavior that would permit prediction and management of future change. This time perspective, which is outside the reach of conventional ecological monitoring (e.g., Long Term Ecological Research [LTER] sites; see Chapter 4), is readily accessible through geohistorical records. The rigorous evaluation of such records by earth scientists over the last few decades has shown that both the character and the rate of biotic response to environmental change can be determined with confidence. Advances in the development of proxy environmental indicators, the reconstruction of species ecologies, and sophisticated dating methods, are changing the way biologists view the world and have prompted a series of workshops on how to best capitalize upon the unique opportunities that geohistorical records afford for direct analysis and modeling of biological systems (e.g., Cohen et al., 1998; Aubry et al., 2000; Flessa, 2000; Myers and Knoll, 2001). Indeed,

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