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.
GENERAL CONCEPTS
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.