The Geological Record of Ecological Dynamics Understanding the Biotic Effects of Future Environmental Change (2005) / Chapter Skim
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2 The Nature and Value of Geohistorical Information
2 The Nature and Value of Geohistorical Information
Pages 30-74
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From page 30... ...
In the study of climate and ocean dynamics, geohistorical records -- including ice cores, sediment cores, tree rings, and coral skeletons -- have provided the first evidence for the existence of many important phenomena, including climate flickers and other abrupt climate change, the reorganization of deepwater circulation patterns, and Milankovitch oscillations in temperature and atmospheric composition. Geohistorical records also have provided the impetus and an essential empirical framework for modeling and experiments (see Box 2.1)
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From page 31... ...
Until recently, geohistorical data have not been used extensively by biologists. BOX 2.1 CO2 Through Geologic Time: Observations, Models, and Geohistorical Data Royer et al.
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From page 32... ...
A Individual proxy indicators (paleosols = fossil soil 13C; phytoplankton = 13C of phytoplankton remains; Stomata = density of stomatal pores in leaves of plants; Boron = 11B in remains of planktonic foraminifera.
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From page 33... ...
COMPLETENESS OF THE GEOLOGIC RECORD Taken as a whole, the geological record is incomplete -- not every individual or species that ever lived is preserved, all the environmental conditions for every part of the globe are not recorded in the sediments, and deposition of rocks has not been continuous everywhere on the face of the earth and throughout geologic time. This heterogeneity in the quality of geohistorical data is a fundamental property of the geologic record, just as completeness and bias in written documents and instrumental records are properties that must be considered in the analysis of human cultural history and instrument-based environmental histories.
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From page 34... ...
. Similarly, biotic response to events in the deeper past can be analyzed in the absence of complete time series by using geohistorical records that are appropriately positioned in time or space, for example by comparing samples from before and after mass extinctions (e.g., Raup and Jablonski, 1993; Jablonski and Raup, 1995; Jablonski, 1995; Erwin, 1996; Foote, 2003)
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From page 35... ...
High-quality geohistorical records are present throughout the ~4 billion year record of Earth, although the total quantity of records decreases with increasing age. Geohistorical records from the relatively recent past contain a wider variety of extractable information (e.g., ancient DNA is more likely to be preserved, and isotopic signatures are less likely
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From page 36... ...
As a consequence, some systems are not as well explored as others despite the likely existence of materials (living communities, geohistorical records) that could yield valuable insights.
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From page 37... ...
INFERRING ENVIRONMENTAL CONDITIONS- RESOLUTION AND CONFIDENCE Various elements of the geologic record capture environmental information in indirect, or "proxy," form. For example, variations in air temperature and rainfall affect the width of tree rings and, accordingly, variations in the widths of tree rings are proxy indicators of variation in temperature and moisture.
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From page 38... ...
, the recognition of semi-quantitative depth categories in the geologic record is sufficient in most instances. In the terrestrial fossil record, geologists can similarly discriminate among the fluvial sub-habitats of main channel, channel bar, levee, and flood plain by using sedimentary features (e.g., grain size distribution, sediment color, presence and type of root traces)
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From page 39... ...
THE NATURE AND VALUE OF GEOHISTORICAL INFORMATION 39 TABLE 2.1 Examples of Proxy Indicators and Their Interpretation Source Proxy Type of Information Individual Number and variation of Seasonality, growth rates, growth fossils growth rings/bands, size conditions, generation times, biomass, age, and season of death Fire scars in tree rings Fire intensity and frequency Stomatal density in leaves Atmospheric CO2 Herbivore or predator Intensity of herbivory or predation, damage herbivore or predator preferences, evolution of herbivore feeding strategies and plant responses Leaf shape and size Mean annual temperature, elevation Overgrowth relationships in Competitive relationships encrusters Larval shell type Mode of dispersal, mode of development, evolutionary history Body size Body size, biomass, size frequency distribution Density Individuals per unit area, biomass Location Habitat, dispersal history, geographic distribution Tooth wear Diet in mammals Preservational condition Exposure, hydraulic energy, sedimentation rate Fossil DNA (generally limited Presence of species not otherwise to deposits <130 Ka) preserved, evolutionary relationships and rates Composition Taxonomic composition Taxa present, guild structure, and structure environmental tolerances, diverse of fossil climatological, hydrological, and assemblages other environmental variables continued
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From page 40... ...
40 THE GEOLOGICAL RECORD OF ECOLOGICAL DYNAMICS TABLE 2.1 Continued Source Proxy Type of Information Composition Presence/absence and relative Physical structure of vegetation-and structure abundance of plant functional albedo, surface roughness, of fossil types evapo-transpiration assemblages (continued) Species richness, diversity, and Species richness, diversity, and evenness evenness Relative abundance of taxa Relative abundance of taxa, dominance, shape of abundance frequency distribution Geographic distribution Geographic distribution, climate Presence/absence and relative Sediment consistency, suspended abundance of animal guilds food supply, presence and structure of vegetation Geochemical Strontium isotopes Source and amount of freshwater, and isotopic migration histories, home range composition of skeletal Oxygen isotopes Temperature range and variability, hard parts salinity, ice volume, source of moisture Carbon isotopes Source of food, vegetation type, productivity, atmospheric CO2, humidity, temperature Nitrogen isotopes Source of food, trophic level Boron isotopes pCO2 concentrations Hydrogen isotopes Temperature, source of moisture Multi-isotope systematics Climate, hydrologic conditions, source of organic compounds, biogeochemical cycling Ba/Ca ratios Productivity Mg/Ca ratios Temperature Sr/N ratios Trophic level in mammals Sr/Ca ratios Temperature range and variability
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From page 41... ...
THE NATURE AND VALUE OF GEOHISTORICAL INFORMATION 41 TABLE 2.1 Continued Source Proxy Type of Information Biogeochemical Biomarkers and other Presence of species, trophic groups, and geochemical molecular fossils or guilds not otherwise preserved evidence in sediments Chlorophyll levels in Productivity, sedimentation rate sediments Nitrogen and carbon isotopes Source and level of productivity in organic compounds Anthropogenic heavy metals Human disturbance and toxins Evaporite minerals Evaporation rates Authigenic minerals such as Productivity phosphorites and glauconites Mn, Fe, Mo, U, V, and Cr Redox conditions trace elements Sulphur isotopes Redox conditions, atmospheric oxygen, microbial activity Lithologic Sediment grain size and Hydraulic energy, storm/bottom evidence sedimentary structures disturbance, current direction, substrate character Paleosols Soil development and climate Peats and coals Wetlands hydrology Trace fossils Behavior, surface stability, sediment reworking rates, presence of biota not otherwise preserved, water table position The abundance of fossil species whose living representatives are restricted to particular environmental conditions often has been used as a proxy for those same conditions in the geologic past. For example, the relative abundance in sedimentary cores of warm- versus cool-water species of planktic foraminifera was used through the 1970s to infer water temperatures using factor analysis, integrating knowledge of these
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From page 42... ...
, fueling a generation of climate and ocean modeling. The diversity and sophistication of non-biotic, primarily geochemical proxy indicators that are now available for use is increasingly liberating
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From page 43... ...
The historical record provided by the observations of early explorers, museum collections, or the natural accumulations of resistant remains can now be used to provide a bench mark to measure the effects of human activity. paleoenvironmental analysis from the potential circular reasoning of using fossils both to indicate environmental change and to measure biotic response to that change.
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From page 44... ...
This study illustrates the influence of climate change on forest composition and disturbance regime, and the power of using independent paleoclimate proxies together with paleoecological data. BIOLOGICAL INSIGHTS CONTAINED IN THE GEOLOGIC RECORD The geologic record contains information on past biotas in many forms, including fossils (the remains of individual bodies)
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From page 45... ...
combined information from these diverse sources is known as the fossil record of life on Earth. The fossil record is widely appreciated as a source of valuable, and in many ways unique, information on the evolutionary relationships and dynamics of taxa.
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From page 46... ...
These are the biological insights that are the primary focus of this report on the nature and value of geohistorical records. Many of the biotic variables that are widely analyzed in biology are commonly captured by body fossils in the geologic record, especially for the higher (multicellular)
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From page 47... ...
In addition, some kinds of data used in biological analysis are at present rarely extracted from geologic records, with DNA being perhaps the most notable example (see Box 2.4)
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From page 48... ...
These and other recent studies clearly show that fossil DNA, far from being a mere curiosity, can provide important information on past biotic communities, environments, animal diets, and species occurrences, and can be used to develop and test specific hypotheses on the evolutionary responses of plant and animal populations to environmental change (see also Poinar et al., 2003; Hadly et al., 2004; Willerslev et al., 2003)
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From page 49... ...
This information is possibly knowable, but at present can be estimated only by extrapolation from living analogs, and deserves much more vigorous investigation. The application of new technologies from outside paleobiology has already greatly enhanced the power and sophistication of biological information that can be extracted from geohistorical records.
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From page 50... ...
Salmon carcasses are an important source of nutrients to these Alaskan lakes, and a natural positive feedback exists between salmon abundance and lake productivity. Analysis of lake sediments indicates that the abun dance of diatom and zooplankton remains -- proxy indicators of lake pro ductivity -- fluctuate with 15N.
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From page 51... ...
In marine benthic systems, actualistic studies indicate that 75-100 percent of living marine macrobenthic invertebrate species that have biomineralized hard parts (e.g., shelled invertebrates such as most mollusks, sea urchins, barnacles, and corals as well as mineral-secreting algae and various unicellular benthos) are present as dead skeletal material in immediately surrounding sediments, and a similar proportion of living genera have known fossil records (Schopf, 1978; Valentine, 1989; Kidwell and Flessa, 1995; Kidwell, 2002a)
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From page 52... ...
. Although generally only sparsely fossiliferous in terms of numbers or density of specimens, they can be invaluable sources of novel morphologic, ecologic (e.g., preserved gut contents, pollen on fur)
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From page 53... ...
; and among the preserved fraction, how faithful are quantitative data to that portion of the original source community? Studies in modern depositional environments comparing local death assemblages with surrounding live communities indicate that among the intrinsically preservable taxa, the original proportions of taxa -- and thus many aspects of community structure -- are surprisingly well recorded, even by the time-averaged death assemblages that dominate the fossil record of many groups (Kidwell and Flessa, 1995; Kidwell, 2001a; 2002a; see Box 2.6)
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From page 54... ...
54 THE GEOLOGICAL RECORD OF ECOLOGICAL DYNAMICS BOX 2.6 Ecological Information from Time-Averaged Death Assemblages The fidelity of the taxonomic composition, spatial distribution, and abundance of taxa in fossil assemblages relative to the source living popu lations is particularly problematic in assemblages of the well-mineralized taxa that dominate the fossil record. Such taxa have generally high preser vation potential, but their hard parts are consequently also likely to survive postmortem transport and -- whether transported or not -- accumulate in time-averaged death assemblages where the number and relative abun dance of taxa might be distorted by their differing rates of mortality and relative postmortem fragility (Vermeij and Herbert, 2004)
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From page 55... ...
These results are very encouraging, both for using dead remains for rapid biodiversity assessment in modern environ ments, and for building prehistoric time series using sedimentary records.
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From page 56... ...
Studies of modern communities and environments have been critical to quantifying these values, and despite the complexities the results are encouraging. For example, radiocarbon dating and other chronologic methods indicate that individual cm-scale samples in Quaternary lake records represent only approximately one decade of time-averaging of pollen input from the local community; in many instances, annual resolution is possible, but as in modern monitoring time series, it is often easier to analyze trends when annual data are blurred into decadal time-windows (running averages)
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From page 57... ...
THE NATURE AND VALUE OF GEOHISTORICAL INFORMATION 57 BOX 2.7 How Much Time Is Represented in Accumulations of Shells in Modern Marine Environments? Flessa and Kowalewski (1994)
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From page 58... ...
These issues have been examined aggressively over the last 15 years by a combination of statistical analysis of large empirical datasets and model simulations that use increasingly realistic assumptions for biases in geohistorical records (Marshall, 1990, 1997; Holland, 1995, 2000, 2003; Foote, 2003)
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From page 59... ...
. Microbial organisms still dominate primary productivity on Earth today (that is, photosynthetic and other autotrophic means of synthesizing organic matter from inorganic compounds)
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From page 60... ...
Understanding the functioning of microbial communities, especially in systems that include multicellular life, is an important aspect of understanding ecological dynamics. A major direction of research lies in the development of techniques to identify, from geohistorical records, the presence and role of microorganisms in ecosystems.
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From page 61... ...
Biomarkers are proving to be increasingly valuable in reconstructing the input of organic matter and microbial dynamics of ecosystem change in Quaternary environments, especially in lakes and coastal estuaries of high societal and economic value (e.g., Boon et al., 1979; Laureillard and Saliot, 1993; Canuel et al., 1995; Mudge and Norris, 1997)
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From page 62... ...
Isotopic signatures can be preserved in organic molecules from geohistorical records that range from decades to billions of years in age. For those signatures that are biological in origin, the magnitude of the isotopic fractionation potentially can discriminate among a variety of candidate organisms.
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From page 63... ...
Corals are largely limited to tropical, shallow marine habitats, with individual sclerochronologies able to be taken as far back as a few centuries, and older time series able to be developed using radiometric dating. Decadal-, centennial-, and millennial-scale modalities generally can be recognized from these annual records.
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From page 64... ...
of some dating techniques commonly used to date geologic materials. The numbers below each technique indicate 2 variation expressed as a percent of calculated age; horizontal scale bars below each expanding triangle express the 2 variation in millions of years.
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From page 65... ...
as an alternative means of assessing isotopic composition of carbon samples helps circumvent some of these problems. Much smaller quantities of carbon are required (as little as 10 µg)
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From page 66... ...
Amino acid racemization dating is also valuable beyond the range of the radiocarbon technique, although precision is lower. Electron spin resonance can also be applied directly to fossil materials, such as shell and enamel, but the method requires further calibration and dates are rarely as precise as those produced by radiocarbon dating (Blackwell, 1996)
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From page 67... ...
SHRIMP studies are particularly powerful for Archean and Proterozoic rocks, although they are also useful through much of the Phanerozoic. Where dates are not available for every level in a local sedimentary sequence, it is generally possible to develop an age model to estimate the ages of intervening levels, especially when the record is from depositional systems that have generally uniform sedimentation rates (most notably lake and deep marine sediments)
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From page 68... ...
quantitative biostratigraphy. These approaches are especially valuable tools because they permit correlation between marine and terrestrial sequences, resolve the ordering of events, and greatly improve the fidelity of correlation over standard zonations.
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From page 69... ...
The most recent geologic timescale (see Figure 2.3; Gradstein and Ogg, 2004; Gradstein et al., 2004) integrates currently available geochronologic and stratigraphic information and represents perhaps a two-fold increase in refinement over the timescale available 20 years ago.
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From page 70... ...
.y 850 542 Str Stage names Age 1996, (ICS) edv base national yb Each atig Statoil ages their and Ma yb a are raph and is , Global and the unit GSSP of an y GSSA FIGURE 2.3 The geologic timescale of Gradstein and Ogg (2004)
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From page 71... ...
The addition of web-based technologies for rapid data transfer and communication has greatly improved scientific communication and dramatically improved the dissemination of research results. Databases and associated research projects abound in both the biological and geological sciences.
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From page 72... ...
. There is probably no better example of how data compilations and syntheses can shape entire disciplines than the graphs illustrating the diversity of families and genera of marine fossils through geologic time (e.g., see Figure 2.4)
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From page 73... ...
Therefore, a rigorous strategy for evaluating ecological dynamics using geohistorical records -- and for integrating geological and biological methods and insights -- is essential. Intensified research on these issues over the last 15-20 years now enables the exploitation of uniquely valuable data lodged in geohistorical records (summarized from above)
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From page 74... ...
It is not the record that is inadequate but rather the availability of resources to extract and analyze the record. Using geohistorical records to their fullest potential will require an effort focused on the biological analysis of groups known to have reasonable fossil records, and on the development of proxy methods for groups of great biological interest but poor fossilization potential.
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