The Geological Record of Ecological Dynamics: Understanding the Biotic Effects of Future Environmental Change (2005)

Earth’s environment is in constant flux. Driven by physical processes, biological processes (now including the effects of human activity), and their interactions, incessant changes occur at virtually all temporal and spatial scales. Recent research has greatly increased scientific understanding of the nature and pace of current and past physical environmental changes, and is now also yielding information on the complex ways biological systems contribute to and react to environmental change. Given the diverse roles played by biota in Earth’s environmental system, as well as the direct importance of wild and managed biological resources to human welfare, a deeper understanding of the ecological dynamics of environmental change constitutes a critical scientific priority.

Longer-term historical perspectives are essential for answering a host of questions about the ecological dynamics of present day environmental systems and about feedbacks between biotic systems and environmental change, including climate change. The geologic record—the organic remains, biogeochemical signals, and associated sediments of the geological record—provides unique access to environmental and ecological history in regions lacking monitoring data and for periods predating human impacts. It also provides information about a broader range of global environmental conditions than exist today, as well as insights into biological processes and consequences that are expressed only over longer time intervals and the opportunity to discover general principles of ecological organization. Understanding how ecological processes scale up from short-term to evolutionary time frames is critical to a full understanding of the biotic response to environmental change, and thus to

developing sound policies to guide future management. Advances during the past 10-20 years have transformed the ability of earth scientists to extract critical biological and environmental information from the geologic record. These advances at the interface of earth and biological sciences—combined with a greatly improved capacity for accurate dating of past events, the development of high-resolution timescales, and new techniques for correlation—set the stage for this assessment of research priorities in geohistorical analysis of biotic systems (see Box ES.1).

The committee recommends a major, decadal-scale scientific commitment to improving our ability to predict the biotic dynamics of environmental change through geohistorical analysis. Given the inherent complexity of biological systems and the increasing footprint of human activities over the last several millennia and centuries, it is critical that geohistorical analysis informs modeling and analysis of present day systems. Such a major effort will require an explicit commitment to innovative and genuinely multidisciplinary research both by agencies and by individuals. It will also require investments in the infrastructure needed to support collaboration between earth scientists and biologists, and new educational opportunities for earth scientists and biologists early in their careers that encourage them to bridge traditional disciplines.

The committee sees three directions as most promising for significant advances and identifies these as initiatives with the highest scientific and policy value: (1) using the geologic record as a natural laboratory to explore biotic response under a range of past conditions and thereby revealing basic principles of biological organization and behavior; (2) using the record to enhance our ability to predict the response of biological systems to climate change in particular; and (3) exploiting the relatively young geologic record to evaluate the effects of anthropogenic and non-anthropogenic factors in the variability of biotic systems.

Most ecological theories are derived from short-term observations and models. Yet we know that past events, and ecological and evolutionary processes operating at timescales beyond direct human observation, affect present day biodiversity and biogeochemical cycling on local, regional, and global scales. The geologic record provides empirical data from longer timescales. This broader perspective both obviates the need to extrapolate ecological behaviors and principles from short-term observations and creates the opportunity to understand the effects of environmental change over an expanded range of temporal and spatial scales. For example, the geologic record is the only source of empirical information on the long-term effects of a broad range of CO₂ concentrations on biotas and climate systems.

Geohistorical analyses are essential to (1) characterize ecological processes and trends that unfold over longer timescales; (2) identify patterns and mechanisms that are masked by the variability inherent in direct, short-term observation; and (3) recognize which aspects of modern ecological systems are contingent on past events. The geologic record of past ecosystems establishes the extent to which conclusions based on modern systems can be extrapolated through time and also permits ecological analysis under global environmental conditions different from those of today. Geohistorical analyses thus permit tests of ecological theories and their underlying assumptions. The geologic record provides access to a wide range of past “alternative worlds” from which truly general principles can be derived. Ecological principles can be considered truly general only if they apply to ancient species and communities as well as to modern ones.

Society needs not only to predict but also to manage the biotic response to future environmental change. Such management can occur only if the principles of large-scale ecology are understood at a level of generality beyond the specifics of a particular time interval. Understanding these fundamental principles of ecological organization and behavior will require significantly increased collaboration across the earth and biological sciences to a degree that traditional funding and administrative structures do not currently encourage or support.

Climate exerts a dominating influence on the distribution and abundance of organisms, the nature and rates of biogeochemical fluxes, the structure and composition of ecological communities, and the frequency and intensity of ecological disturbances. Climate interacts with and mediates other global change processes, such as biological invasions, human land clearance, anthropogenic alterations of mineral cycles, and disease outbreaks. Because of the importance of climate in governing ecological patterns and processes, documentation of biotic responses to past climate changes is a critical step toward full understanding of ecology. Paleoclimatic studies indicate that Earth’s climate is capable of a wide variety of system states and modes of variability and that the past two centuries have experienced only a fraction of the potential variability within the climate system. Therefore, any comprehensive understanding of ecological dynamics requires that we understand how ecological systems have responded to climate change and variability in the past. Just as the instrumental record of the past two centuries provides an inadequate sample of the range and nature of climate variation, ecological studies based on direct observation in present day systems provide an inadequate sample of the array of biotic responses to climate change, and the potential consequences for biodiversity and biogeochemistry. Studies of biotic response to climate change must therefore include insights from geohistorical analysis.

Ecology is poised to make great advances by building on the improved understanding of past climate variation and change. In particular, the development of multiple, independent paleoclimate proxies is providing a rich understanding of past climates, while at the same time liberating paleoecological data from being the primary source of paleoclimate inference. Paleoecological data can now be compared to past climate change inferred from other proxies, allowing direct study of biotic responses to climate changes in the geological record. A more sophisticated understanding of the effects of climate change and variability on biodiversity, biogeochemistry, biogeography, community structure, disturbance regimes, and genetic structure of populations requires a concerted effort to link paleoecological and paleoclimatic records.

The profound effect of human activities on natural environments and ecosystems is clearly evident, but the consequences are less well understood. In effect, an unintentional global experiment is already in progress. However, the initial conditions of this far-reaching experiment are largely unknown, because the onset of human interactions with natural systems—both intentional and unintentional—predate scientific monitoring efforts, which largely extend back at most to the late 1800s. There is also no “control” in this experiment; completely natural habitats are no longer available either locally or globally to use as a benchmark for comparison with habitats that have been modified. The geohistorical record is thus the only source of information on (1) the natural range of environmental variability and ecosystem function before human impact; (2) how ecosystems functioned in the absence of human influence; (3) how ecosystems have responded to progressive human impacts; and (4) which aspects of present day environmental variability and ecosystems are legacies of past societal activity. Geohistorical records of the past provide an invaluable archive of the state of ecosystems before significant societal impact. They also show how ecosystems have been transformed by human activity.

Because human activity has already affected natural ecosystems in myriad ways, acquiring knowledge of pre-human baseline states and natural variability is essential for discriminating between anthropogenic and non-anthropogenic change in species, biotas, and ecosystems. Insights into such dynamics from geohistorical analysis are critical in developing strategies for conservation and restoration. In seeking to predict and manage the response of ecosystems to future societally driven perturbations, we must take advantage of the opportunity to understand how these activities have affected ecosystems in the past. Understanding the ecological impact of past human activities is also crucial for the recognition of persistent effects—legacies—that may continue to influence ecosystems long after the causative activities have ceased.

Research on the geologic record as an ecological laboratory, on the ecological responses to past climate change, and on the ecological legacies of societal activities will require additional funding. Current levels of support are inadequate for the increased activities that these three initiatives will generate. High-precision dating, sophisticated geochemical analyses, large numbers of samples, database development, collections maintenance, and the need for collaboration among investigators and students from multiple disciplines are all required, and all will cost money. Increases in funding have not kept pace with society’s increasing need to predict and manage future biotic change, or with the increased interest in this topic within the scientific community. The new kinds of research that are needed cannot be pursued without modifying the resource allocation to increase support.

Research on the geologic record of ecological dynamics should be structured to encourage and support the collaboration of professional biologists and geologists, as well as the training of an increasingly flexible new generation of scientists with the necessary multidisciplinary talents. We recommend establishing a postdoctoral program whereby a new Ph.D. in one discipline would undertake collaborative research with a mentor from the other discipline. This would engage scientists at an early stage in their careers with opportunities for innovation and would have a long period of positive downstream effects.

Substantial support for research in natural laboratories, and for actual or virtual collaborations and facilities, is needed to focus intellectual efforts and develop research tools for the three initiatives described above.

Long Term Ecological Research (LTER) sites have successfully lengthened the time-perspective of ecological studies, generating observations of natural (and in some instances experimentally manipulated) habitats over several to many decades. Nevertheless, LTER event timescales are short relative to many ecological process and environmental change timescales. Existing LTER projects represent a superb opportunity to leverage relatively unusual long-term ecological and environmental monitoring with observations from times before the instrumental record, in order to acquire information on both the character and rates of environmental change and the biotic components of that change. Geohistorical records from lakes, bogs, reefs, or estuaries near or adjacent to LTER sites would provide opportunities to integrate geohistorical data with observations and experiments from the LTER sites. Such integrated records would provide the temporal perspectives necessary to detect decadal and longer ecological trends, and to discriminate between natural and human-driven changes. Activities within the new National Ecological Observatory Network (NEON) program should also go beyond the monitoring, experimentation, and modeling of biotic systems in the present. Geohistorical analysis should be made an integral part of the NEON mandate. Incorporating retrospective data on past biotas and environmental variability is essential to efforts in ecological forecasting.

The development of Geologic Time Ecological Research (GTER) projects would be a promising platform for research on ecological dynamics. A GTER project would focus on a particular habitat type, critical region, (paleo)latitudinal belt, environmental gradient, or time interval as a natural laboratory for focused, collaborative study for a 5- to 10-year period. The availability of excellent geologic records might motivate the selection of a region for modern-day ecological analysis. For example, a long-lived modern lake basin would provide the opportunity to extend observations of current processes back in time using fossils and environmental data derived from cores to address all three of the initiatives identified here. Similarly, a region known to have experienced biotic invasions in the past (e.g., oceanic islands) would constitute a useful laboratory to examine the controls and consequences of biotic invasions.

Research collaborations are envisioned as actual or virtual forums for the analysis, synthesis, and modeling of existing data and for the general exchange of intellectual capital. These collaborations might take a form similar to the NCEAS (National Center for Ecological Analysis and Synthesis) model, by providing a setting for collaborative working groups to focus for short periods of time on integrative ecological problems that require synthesis of empirical and model-generated information. The former Pliocene Research, Interpretation, and Synoptic Mapping (PRISM) project of the U.S. Geological Survey (USGS), which targeted global paleoclimates of the Pliocene, demonstrates how federal agencies with intramural researchers can lead collaborative projects, although this particular project emphasized physical environmental reconstruction and improved age determination more than biotic response. This virtual collaboration demonstrated the value of targeting a past interval of geologic time—rather than a geographic site or region—to better understand natural systems with relevance to future change.

Both examples represent innovative ways to foster integrative work among biologists and paleobiologists (as well as other physical scientists), producing immediate scientific results as well as long-term benefits by associating individuals usually separated by administrative and disciplinary barriers.

Data are the currency of research in the geological and biological sciences. The maintenance and accessibility of data in either digital form (e.g., electronic databases) or physical form, including voucher materials (e.g., museum collections, cores, paper records), are essential for the effective and efficient conduct of research in ecological dynamics. The number and size of online databases have grown enormously in the past decade. This increase will continue, thereby providing for greater access to the results of publicly funded research. Previously collected data must be maintained, access must be provided, and repositories for newly collected data should be designated. The key disciplines are being overwhelmed with data even as they labor to find more information relevant to new questions. Enhanced federal support is critical for the expansion and coordination of community-wide database efforts, including the discovery and integration of metadata and the maintenance of key specimens and samples in museum collections. Community-wide databases provide a new research tool for the synthesis and analysis of data at scales that would have been impossible in the past.

Such efforts also add value by promoting the culture of collaboration essential for multidisciplinary research on the geologic record of ecological dynamics. These database efforts will require long-term commitments from agencies, institutions, and professional societies to ensure quality, continuity, and availability of the data and products. Previous recommendations that have focused on geoscience data and collections (NRC, 2002b), including museum collections, also apply to the broadly interdisciplinary data of both the geoscience and bioscience communities that will be needed to address the complex biosphere issues outlined above.

High-precision radiometric dates are expensive, time consuming, and frequently constitute the money-limiting or rate-limiting factor in paleobiological research. There is a clear need for support of low-cost, fast-

turnaround laboratories for radiometric dating and related chronostratigraphic analyses (e.g., radiocarbon, volcanic ash, geochemical markers). Support is also needed for chronostratigraphic databases and quantitative techniques to facilitate comparison and correlation among geohistorical records. Refining the precision and accuracy of temporal resolution will require improvements in radiometric dating, in our understanding of the temporal resolution of fossil assemblages themselves, and in methods to assign individual geohistorical records to a high-precision geologic timescale. As the resolution of the geologic timescale is progressively refined, there will be a continuing need to improve the accuracy of geochronologic techniques.

Proxy indicators (environmentally and biotically diagnostic physical, chemical, or biotic features of rocks or fossils) of past environments, biotas, and biotic interactions provide the essential evidence needed to assess the nature, rate, and magnitude of the biotic response to that change. Additional research is needed to develop proxy indicators that can be applied in older geohistorical records, to evaluate the preservation of geochemical and biogeochemical proxies, and to develop measures of short-term environmental variability. Reconstructing the range of natural variation in past environments is needed to detect environmental changes that exceed the natural background.

Proxy indicators are especially needed for determining the characteristics of past biotas that are not preserved as conventional fossils. Proxy indicators for ecological attributes such as abundance, trophic relationships, and growth rates are important for recognizing how ecosystem function changes in response to environmental change. Technological advances now permit the recognition of biotic elements from distinctive organic molecules and stable isotopes preserved in geohistorical records, but this research area is still in an early stage of development. There is enormous potential to use biomolecular and isotopic methods to recognize the presence, abundance, and biochemical significance of biotas that are not preserved as conventional fossils and as records of ecological functioning. Improved understanding of the diagenesis of biomarkers is essential for their application in deeper time.

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 natural perturbations in such systems from those induced or magnified by humans. Such data are crucial for acquiring the necessary long-term perspective on modern systems. Information from past environmental states, both like and unlike those of the present day, provide the empirical framework needed to discover the general principles of biosphere behavior necessary to predict future change and inform policy managers about the global environment.