The Geological Record of Ecological Dynamics Understanding the Biotic Effects of Future Environmental Change (2005) / Chapter Skim
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3 Research Opportunities
3 Research Opportunities
Pages 75-130
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From page 75... ...
A full understanding of current patterns and processes, therefore, requires geohistorical analysis to supplement knowledge based on shorter-term observations, experiments, and modeling. The geological record provides the rich source of information that is essential for developing an understanding of the origin and controls of biological diversity, the controls and dynamics of biogeochemical cycling, the ecological impacts of climate change and variability, and the extent and consequences of habitat alteration.
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From page 76... ...
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.
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From page 77... ...
The geologic record contains a rich store of information on ecological changes occurring during periods of past societal activity. The relative timing and nature of these correlations provide abundant material for evaluating direct and indirect causation -- such records are important for gauging the extent to which our modern world has already been altered by human activities (see examples described below)
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From page 78... ...
So far, the considerable potential of the geologic record has not been fully exploited by ecologists. Furthermore, although ecological rules identified from modern observation and theory are generally treated as universal, they may be contingent on the modern environment and biota.
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From page 79... ...
terminated, as a consequence of cli matic, tectonic, macroevolutionary, and other events. The controls on slow processes and the long-term effects of rare events can be understood only by using the geologic record.
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From page 80... ...
But this must be accompanied by integrated studies aimed at addressing the central questions of ecology across a range of timescales. For example, use of the geologic record is vital to addressing national ecological research priorities in the areas of biodiversity and biogeochemical cycles.
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From page 81... ...
Although the formation, invasion, migration, substitution, and even extinction of species can potentially be inferred from phylogenetic structure, the fossil record is a direct and rich source of data needed to discover the biological principles underlying the origin, maintenance, collapse, recovery, and extinction of species. Paleobiological time series leading to the present day, together with time series embedded entirely in the geologic record provide opportunities to identify and test fundamental ecological principles underlying biodiversity (see Box 3.2)
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From page 82... ...
The shapes of the distributions of the lower two intervals differ signifi cantly from those of the upper two intervals, and these differences are attributed to restrictions in population size, decreased isolation, and decreased chances of immigration resulting from lower sea levels in the upper two intervals. Accordingly, the geologic record of Permian fossils in this area preserves the results of a natural experiment on how environ mental change affects ecological community structure over long time periods.
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From page 83... ...
RESEARCH OPPORTUNITIES 83 species migrations and community turnover actually occur, will contribute significantly to our understanding of individual species behavior and the net outcomes for biodiversity and community structure in habitat fragments -- an understanding that has obvious practical implications for management of natural systems in the face of human activities and impacts.
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From page 84... ...
Although molecular data can provide information on the age of taxa, their mutual readjustments can only be documented using morphological and paleobiogeographic data from geohistorical records (e.g., Labandeira, 2002)
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From page 85... ...
Paleobiological records indicate that terrestrial and temperate marine communities did not migrate as cohesive, integrated units in response to Quaternary environmental changes. Instead, species shifted their geographic ranges individualistically, producing species associations that do not occur today (Box 3.3)
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From page 86... ...
A critical question for both ecology and conservation biology is how these singular communities arise. Their existence in the past indicates that animal and plant species have responded individualistically to environ mental changes of the late Quaternary, and that communities may be ephemeral at timescales beyond a few thousand years.
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From page 87... ...
Again, the past may serve as a guide. Analyses of high-resolution lacustrine records suggest that plant communi ties responded to past abrupt climate changes with lag times less than a century (Birks and Ammann, 2000; Tinner and Lotter, 2001; Williams et al., 2002)
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From page 88... ...
88 THE GEOLOGICAL RECORD OF ECOLOGICAL DYNAMICS BOX 3.3 Continued Rows 1 and 2 are plant associations over time for (row 1) spruce, sedge, and birch and (row 2)
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From page 89... ...
. These examples underscore that only paleobiological analysis can reveal the behavior of species over the timescales -- and through the repeated natural experiments -- that permit assessment of the relative importance of the different environmental and biological factors affecting biotic recovery.
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From page 90... ...
Geohistorical records can address fundamental biogeochemical questions at spatial scales ranging from local to global, and temporal scales ranging from the recent past to the entirety of geobiological history. Biogeochemical Fluxes and Controls: Retrospective Experiments and Chronosequences.
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From page 91... ...
. Biogeochemical cycles have evolved together with the biota of the planet, and the evolution of these cycles has involved reciprocal effects of biogeochemical and environmental changes on the biota.
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From page 92... ...
The unstocked lake -- Harrison Lake -- shows little change in algal productivity during recent decades. Bighorn Lake, with fish populations since 1965, shows a steady increase in productivity following the original stocking.
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From page 93... ...
e att m 5 c ani 0 org -1 g 100 selo Snowflake mn( 80 Lake 60 1965 tion ra ent 40 oncc 20 0 Pigment 800 Harrison 600 Lake 1965 400 200 0 15 10 5 0 Depth (cm) The stratigraphic profiles of algal-pigment biomarkers in sediments of three lakes in the Canadian Rockies with differing fish introduction histories demonstrate how net primary productivity is influenced by fish populations as a result of their effects on nutrient cycling.
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From page 94... ...
The latter can range from anaerobic, prokaryotic systems of the Proterozoic, to the modern biota of the late Quaternary. For the Phanerozoic, periods in which correlations of events or time series between marine and terrestrial domains should be emphasized.
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From page 95... ...
Geohistorical records of past invasions induced by climate change, dispersal, and continental drift provide a series of natural experiments that can help assess future community and ecosystem consequences of biotic invasions. For example, the past biotic interchanges from North Pacific to North Atlantic, between North America and South America, and between eastern Asia and western North America, recognized on the basis of phylogenetic and biogeographic analyses of pre- and post-interchange biotas, are rich in insights into the asymmetry seen in most biotic interchanges, the differential invasive properties of species, phylads,2 and functional groups, and the contrasting regional biotic histories of donor and recipient areas (Vermeij, 1991; Jablonski and Sepkoski, 1996)
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From page 96... ...
The "Final Recovery" of 13C may reflect the evolution of larger species of phytoplankton and their grazers in the post-K/T ocean, and the consequent recovery of ecological mechanisms for the delivery of organic matter to the deep sea. The end Cretaceous extinctions affected not only the composition of the earth's biotas but also its ecological dynamics and carbon cycling -- the ecological legacy of this mass extinction lingered in the oceans for millions of years.
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From page 97... ...
RESEARCH OPPORTUNITIES 97 BOX 3.5 Continued 13 C -0.5 0.5 1.5 2.5 3.5 85 sf mb 95 Final y Recovery arti erT 105 yl Early Recovery Ear K-T etaceousr 115 C Cretaceous-Tertiary 13C records from DSDP Site 577 in the Central Pacific Ocean, with red circles showing the difference between 13C values from bulk carbonate and benthic foraminfers. "mbsf" = meters below sea floor.
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From page 98... ...
in the face of ongoing and future climate change must be informed by knowledge of how such systems have responded to climatic variations in the past. Understanding how ecological systems have responded to past climatic and other environmental changes is necessary because the geologic record of ecological dynamics includes a vastly greater range of climatic conditions than are present today, or that are recorded in the instrumental and archival records of the past two centuries.
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From page 99... ...
Integrated studies of paleoclimate, paleoenvironment, and paleobiology are not practical for every interval of Earth history. With limited resources and in light of variation in the quality of the geologic record at different time periods, efforts should be targeted at selected intervals in Earth history that: 1.
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From page 100... ...
. In the figure below, postglacial pollen percentages of several important forest trees are plotted for a pond in the Berkshires of western Massachu setts, together with independently derived estimates of paleoclimate from lake levels (paleohydrology)
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From page 101... ...
indicate moisture balance. Changing pollen percentages indicate changing composition of regional forests in western Massachu setts (Whitehead and Crisman, 1978)
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From page 102... ...
However, earlier intervals in the geologic record also provide important opportunities for studying biotic responses to climatic changes of different magnitude, quality, and duration. The pre-Quaternary record is a rich source of information on how biological diversity and biogeochemical cycling responded to changes in climate at different scales (e.g., transitions from greenhouse to icehouse worlds)
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From page 103... ...
Geohistorical records provide abundant opportunities for learning about how the physical environment, particularly climate, constrains or determines features of the biosphere at scales ranging from genomic to global biogeochemistry and about how biotic systems affect climate. Following are select examples of how geohistorical approaches are contributing to fundamental understanding of ecological systems in the context of climate change and variability.
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From page 104... ...
A central goal of global change biology is to develop capacity to predict how climate change will affect -- both directly and indirectly -- such ecosystem properties and services as primary productivity, carbon storage, biogeochemical cycles, disturbance regimes, atmospheric feedbacks, and soil stability. Climate exerts direct control on many of these properties for terrestrial systems, and influences physical properties of vegetation and composition of the biota, which influence other ecosystem functions.
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From page 105... ...
Such slow changes are difficult to fully understand in the absence of geohistorical records, and changes of the past century or two are confounded by direct human impacts (e.g., land clearance, damming/diversions, pollutants)
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From page 106... ...
Studies of DNA from fossil material, although apparently limited to a handful of paleontological settings in the late Quaternary, can reveal spatiotemporal patterns of genetic and evolutionary responses to environmental change (Poinar et al., 1998, 2001, 2003; Kuch et al., 2002; Hofreiter et al., 2003; Willerslev et al., 2003; Hadly et al., 2004)
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From page 107... ...
(2001) examined insect damage on fossil leaves during the Paleocene-Eocene episode of global warming, approximately 56 Ma ago.
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From page 108... ...
have arisen entirely from paleoclimate records which indicate that such changes and responses are intrinsic features of the earth system. The rich geologic record of biotic responses to past climate changes is an essential component of ecological forecasting.
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From page 109... ...
. These syntheses and applications are important because they allow identification of the relative impacts of climate variability and human impacts (e.g., harvesting, fire suppression)
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From page 110... ...
These geohistorical records are providing information on the natural variability and climatic controls of marine fisheries. In the Santa Barbara Basin off the California coast, sardine and anchovy production has fluctuated tenfold during the past 1,700 years, with rapid increases and equally rapid declines (see figure below)
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From page 111... ...
from a biomarker proxy provide an independent baseline for environmental change. The record indicates an abrupt shift in mean and variance of SSTs around 1,000 years ago.
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From page 112... ...
. Integrated studies of individual cores can provide rich records of pelagic fish communities, primary productivity, and environmental variability.
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From page 113... ...
Ecological consequences of abrupt climate changes have received comparatively little attention, even though such changes were first identified from paleontological records (Younger Dryas interval) and tree ring studies (late Holocene droughts)
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From page 114... ...
. Abrupt changes in the Holocene are also suitable model systems for studying how climatic changes of smaller magnitude and shorter dura
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From page 115... ...
Habitat fragmentation may inhibit dispersal of native species to suitable habitats, and climate change may interact with wildfire, exotic invasions, and pathogen or disease outbreaks in creating stress on species, populations, and communities. The species living on Earth today have obviously been subjected to the effects of climate change repeatedly in the late Quaternary, and past climate changes have been accompanied by disturbances, invasions, and other stresses.
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From page 116... ...
An important lesson from paleoecological studies of the late Quaternary is that most terrestrial communities and ecosystems have developed within the past 800 to 8,000 years, and that most species have attained their modern distributions within that same period. Thus, the geographic ranges of species, the composition of ecological communities, and the properties of ecosystems (including diversity, productivity, and disturbance regimes)
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From page 117... ...
Restoration ecology, conservation biology, and ecosystem management all rely on these baselines, which often include estimates of past natural variability. However, geohistorical records are providing abundant evidence of widespread human impacts on populations, communities, and ecosystems, even in places long thought to be relatively unaffected by human activities (Douglas et al., 2004; Willis et al., 2004)
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From page 118... ...
(2004) examined the sedimentary and fossil record of a high Arctic lake adjacent to an AD ~1200-1600 Thule Inuit whaling settlement on Somerset Island, Canada.
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From page 119... ...
which ecological systems have been altered by human activities can lead to confusion and error in ecological theory and application. The pioneers of ecology often overlooked the fact that systems they studied were far from pristine, leading them to misattribute patterns arising from human disturbance to processes such as succession (e.g., S.T.
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From page 120... ...
The geologic record can and must play a critical role in assessing such legacies. In nearly all cases, geohistorical records provide the only source of information on ecological history that extends to pre-human (i.e., true baseline)
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From page 121... ...
First, ecological processes occur across a wide range of timescales, so one component of a system may change rapidly in response to distur bance or environmental change while another may change very slowly. For instance, a crown fire kills most trees and burns most fine fuels in a forest stand within minutes, while coarse woody debris and soil carbon can persist for decades after the fire (Foster et al., 1998)
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From page 122... ...
are only available in the geologic record. Fortunately, as described earlier, the quality of environmental and biotic information in the record often allows the reconstruction of environmental variation with seasonal and annual resolution.
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From page 123... ...
( 80 engthl 60 cod 40 Mean 20 0 6 5 4 10 10 10 1000 100 10 1 Years before present FIGURE 3.2 Time series of mean body length of Atlantic cod from kelp forests in the coastal Gulf of Maine. The earlier five data points are derived from archaeological records, whereas the last three points are from fisheries data.
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From page 124... ...
Human land use and habitat alteration have left signatures on the landscape and in geohistorical records dating in many cases to the first human colonizations. Sedimentary charcoal indicates increased incidence and extent of wildfires upon colonization of Australia by aboriginal hunter-gatherers ~40,000 years ago.
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From page 125... ...
Some possibly general patterns of the consequences of human activities have been identified, but require considerable further examination in a wide variety of settings: · the loss or ecological extinction of megafauna; · shortening of food webs; · distortion of biogeochemical cycles; · shifts from heterogeneous to homogeneous biogeographic distri butions due to invasive species; · general loss of biodiversity; and · replacement of eukaryotes in the oceans by bacteria and archaea. As pointed out by Margalef (1968)
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From page 126... ...
. Native species of crabs, marine mollusks, land snails, and birds that survived the Polynesian invasion were exterminated during the 19th century (see figures below)
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From page 127... ...
Note apparent extinctions of at least five native species during the Polynesian period, extinction of six species since European and Euro-American colonization, survival of three native species, and introduction of one exotic species. SOURCE: Burney et al.
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From page 128... ...
128 THE GEOLOGICAL RECORD OF ECOLOGICAL DYNAMICS BOX 3.12 Continued STRATIGRAPHIC UNIT Occurrence of vertebrate bones in sediments of the Mahaulepu Sinkhole, Kauai. Note the severe loss of native bird species (11 species portrayed are extinct on the island, as are other species not on this diagram)
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From page 129... ...
One of the greatest values of historical data describing ecological conditions before substantial human impacts is the formulation of goals for ecological restoration. This is particularly important in the case of habitats and ecosystems that were not described or monitored before human disturbance.
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From page 130... ...
In basic research, the integration and cross-calibration of observational, documentary, and proxy ecological data provides both a nearcontinuous and long-term ecological record as well as the opportunity to develop confidence limits for proxy indicators farther back in the geologic record. In applied research, the approaches of historical ecology demand close collaboration among biologists, geologists, and archaeologists engaged in ecosystem management and restoration -- practical issues that are an increasingly important focus of the U.S.
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