and detailed geological record of how past ecosystems responded to environmental change at a variety of timescales. Together they provide the basic knowledge needed to predict and manage the response of the biosphere to likely change in the future.

1. The Geologic Record as an Ecological Laboratory. The geological record comprises an immense array of natural laboratories for studying how ecological systems operate under diverse conditions and at broad timescales. Using these laboratories to answer fundamental questions about biological diversity and biogeochemical processes is both possible and urgently needed. Ecological and evolutionary processes at timescales beyond direct human observation have influenced biodiversity and biogeochemistry at all scales (see examples described below). Currently, most ecological theory is based on short-term observations and mechanics, which are then extrapolated to longer timescales. Ecological studies using geohistorical records are needed to characterize ecological processes that occur over longer timescales; identify patterns and mechanisms that are masked by the short timespans of direct observation; and recognize those aspects of modern ecological systems that are contingent on past events. The geologic record also contains a series of “alternative worlds” suitable for testing the universality of ecological theory.

2. Ecological Responses to Past Climate Change. The geologic record contains information on how ecological systems—from individual species to biomes—have responded to a wide array of climate changes in the past. Just as paleoclimatological studies have revealed sensitivities and vulnerabilities in the global climate system that could not have been identified from analysis of modern systems alone (NRC, 2002a), so too are paleoecological studies revealing ecological responses to past climate changes that could not have been predicted solely from modern ecological investigations and theory (see examples described below). Studies that link paleobiological and paleoclimatic records are urgently needed to assess the ecological consequences of ongoing and future climate changes. The past two centuries have experienced only a fraction of the potential variability within the global climate system. Therefore, direct observations of biotic responses to climate variability and change provide only a limited view of the full range of possible changes and responses. Parallel to the call for “extending the record of [climate] observations” using the geological record (NRC, 2001c), a concerted effort is needed to use geohistorical records to gather critical information on how ecosystems will respond to future change. Specific time intervals can also serve as model systems for understanding effects of climate changes of particular magnitude, rate, extent, and duration.



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