A Brief Introduction to


© Gastaldo, Savrda, & Lewis. 1996. Deciphering Earth History: A Laboratory Manual with Internet Exercises. Contemporary Publishing Company of Raleigh, Inc. ISBN 0-89892-139-2

It is easy to recognize that interrelationships exist between organisms and their environment. Environmental factors that influence any organism may be abiotic (i.e., nonliving factors) or biotic (factors involving other living entities). Abiotic influences may be chemical or physical. These include water, light (particularly for photosynthesis and the synthesis of other plant pigments), temperature, atmospheric gasses, chemicals in solution, air and water currents, gravity, pressure, and the nature of the substrate (the surface upon which a plant or animal rests or moves). Organisms are able to survive within a range of tolerances for each of these parameters. Organisms not only have minimum requirements, but also have a maximal tolerance for any one of these factors (remember the last time you were badly sunburned?). The biotic factors that influence the survival of any organism are self-evident (various relationships among organisms themselves, as well as their behavioral and functional adaptations).

The study of the interrelationships between individuals, populations, and communities and their environment is placed under the discipline of ecology. Paleoecology is the investigation of individuals, populations, and communities of ancient organisms and their interactions with and dynamic responses to changing environments. Modern ecosystems (a geographically defined physical area with its biological complement) are only a very small part of all ecosystems that have existed throughout geologic history. Paleoecological perspectives are an expanded view of ecology that considers how organisms (individuals, populations, and communities) have responded to abiotic and biotic factors over long intervals of time. Modern ecosystems are a product of the trials and tribulations of ancient ecosystems; an understanding of these past associations provides insight into the present.


The interpretation of paleoecological data requires a working knowledge of biology and involves the use of substantive uniformitarianism, analogy, and parsimony. Geologists have learned that Earth's systems have changed since the Archean. The Archean-Proterozoic transition is believed to mark the beginning of a more stable planet. The concept of substantive uniformitarianism, which is based on an understanding that the materials, conditions, and rates of processes have remained relatively constant through time, has played a part in the interpretation of paleoeocological data. This idea is applicable to strata deposited since the Late Proterozoic, when metaphytes and metazoans first evolved. Analogy (or actuopaleontology) involves the application of modern organismic features to ancient organisms. This principle may be applied to individuals (with regard to form and function), community structure (species diversity, organizational and trophic structure), and population dynamics (response to time-independent environmental factors). Parsimony involves the use of the simplest, or most parsimonious, explanation to decipher the data. That is, the explanation that uses the fewest steps, beginning with the cause, through the intermediate causes, responses, and effects to the final result, is the most desirable when interpreting the information. Parsimony is not restricted to paleoecological studies, or paleontological studies in general. Parsimony is a central tenet of all scientific inquiry.

Ecological and paleoecological studies can focus on an individual species (known as autecology) or on many species (known as synecology). Autecological investigations commonly are concerned with the organism's response to its environment. Such responses may involve the morphological adaptations that the organism has evolved in order to meet the minimum requirements for survival, the organism's behavioral traits acquired to most efficiently exploit its environment, or the impact of the environment on the individual. It's true that no man is an island; organisms do not function solely as isolated individuals. Every organism is but a part of a larger population of many interacting individuals. Studies concerned with population ecology have expanded within the past several decades, and this increase is also true of paleoecological studies. Population ecological investigations also are included within the limits of autecology. Some aspects of fossil populations are difficult to evaluate because of the nature of the fossil record (e.g., time averaging of populations in marine environments). Because of this, autecological studies have focused on the structure and evolution of fossil populations rather than on population characters that may help interpret paleoenvironments. The attributes of fossil populations provide information that reflects organismic adaptions for survival within the abiotic (physical) and biotic (biological) constraints imposed during their geologic history.

Synecological studies attempt to evaluate the bigger picture involving ecosystems (communities of organisms [the total biota] interacting with their abiotic environment) and biomes (interaction of regional climates with biotic and abiotic components resulting in a large, easily recognizable community unit). The approaches taken to investigate each of these ecological units is similar, but the scale of the investigation different. Synecological investigations center on describing, understanding, and interpreting organisms in the context of other coexisting organisms. Many fossil synecological studies are concerned with the fossil community--a fossil assemblage of coexisting organisms preserved within a given area (usually taken as a common environment). Communities are differentiated using several basic criteria. These include (1) compositional and structural characteristics that separate the assemblage from others at the scale of investigation; (2) an internal homogeneity (just like homogenized milk; there is little difference between the 2% variety in any grocery store in town); (3) readily definable geographical boundaries; and (4) persistence through time and recurrence in geographical distribution.

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