BIOLOGY Volume 1 - A Guide to General Biology - 2004

10. ORGANISMS AND THE ENVIRONMENT

Ecology is the scientific Study of the interactions between living organisms and with their non-living, or physical, environment. Ecological research provides the scientific foundation for agriculture, forestry, and fisheries; it enables us to predict, prevent, and mitigate the consequences of environmental pollution; it helps evaluate the potential outcomes of large-scale landscape modifications, such as the construction of dams or canals; and finally, it provides the means for the rational management and conservation of natural resources.

The relationship between ecology and other biological disciplines is summarized in Fig. 10.1, which illustrates that living organisms can be studied at various Levels of Organization. The right-hand side of this diagram corresponds to ecology, encompassing individual organisms, populations, and communities. Ecologists refer to these entities as the biotic component of ecosystems, or simply the biota. An ecosystem also includes the non-living, or abiotic component, consisting of matter and energy. The terms "population", "community", and "ecosystem" have precise ecological Structure/97.html">Definitions, as given in Fig. 10.1. The totality of the planet's ecosystems constitutes its biosphere, or ecosphere, which unites all organisms with the physical environment they interact with. Thus, the oceans, the land surface, and the lower atmosphere are all PARTS OF THE biosphere.

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Fig. 10.1. Levels of biological organization From Genes to ecosystems. The entire planet Earth Functions as a single ecosystem. Oceans, forests, grasslands, and so on represent smaller ecosystems interconnected by Energy Flow and the exchange of matter into the global biosphere. A population is a group of organisms of the same species inhabiting a defined area and usually isolated to some degree from similar groups. A community is any group of organisms belonging to different species that coexist in a particular habitat or locality, with all these organisms linked by trophic and spatial interactions. An ecosystem is a community and its surrounding physical environment interacting as an integrated whole.

10.1. Approaches in Ecology

A defining feature of ecology is its holistic approach, which places greater emphasis on the whole rather than its individual parts. Ideally, an ecologist should account for all interacting factors in a given Location simultaneously. Naturally, this is impossible, and in practice, most researchers focus their studies on one of the "imperfect" approaches listed below.

1. The ecosystem approach. This approach focuses the ecologist's attention on the flow of energy and cycling of matter between the biotic and abiotic Components of the ecosystem. Emphasis is placed on the functional relationships among organisms (e.g., food chains) and with their physical environment. The species COMPOSITION OF THE biota and The Fate of its individual taxa are relegated to the Background.

2. The synecological approach, or The Study of communities, places the biotic component of the ecosystem at the forefront. Key subjects in such research include succession and climax communities (Section 10.6).

3. The population (autecological) approach currently relies primarily on mathematical Methods to study the patterns of growth, maintenance, or decline in the numbers of single-species populations. It provides the scientific basis for understanding population "outbreaks" of agricultural pests or pathogens, and helps determine the critical population size required for the survival of a rare species. Traditional autecology investigates the relationship between a specific species and its environment. It attempts to link features of its Morphology, behavior, dietary preferences, and the like with habitat types, distribution, and evolutionary history.

4. The ecotopical approach. An ecotope, or habitat, is a spatially bounded entity. It refers to that part of the biosphere with which an Organism, population, community, or ecosystem interacts closely (Section 10.5). Any habitat is heterogeneous and can be subdivided into microhabitats with conditions distinct from the average (e.g., beneath tree bark or on its leaves). This approach is useful for studying specific environmental factors closely associated with plants and animals, such as soil composition, humidity, and light intensity.

5. The evolutionary (historical) approach. By studying changes in ecosystems, communities, populations, and habitats over time, we can understand the causes of these changes, providing a basis for reasonably reliable predictions about the future. Evolutionary ecology deals with changes occurring on a geological timescale. It is concerned, for instance, with how events such as mountain building have shaped the formation and distribution of species and taxa. It can answer questions such as why kangaroos are found only in Australia or why tropical rainforests exhibit such high species diversity. It helps identify the factors that led to the speciation or extinction of particular species, and at a more detailed level, explains THE ORIGIN OF specific morphological features or reproductive strategies. Paleoecology applies knowledge gained from modern ecosystems to fossil organisms. It attempts to reconstruct past ecosystems and, in particular, to understand how ecosystems and communities functioned prior to human Interference. Historical ecology examines anthropogenic changes in ecosystems—that is, The impact of developing human technologies and cultures on natural systems. Recognizing that humans are a primary destructive force acting upon the environment is vital for its conservation. In this context, particularly when providing economic justifications for various conservation strategies, it is crucial to distinguish between genuinely anthropogenic processes and natural processes within the biosphere. For instance, is the acidification of waters and soils a purely natural phenomenon, or is it entirely driven by industrial atmospheric pollution and therefore remediable through technological intervention?

These ecological approaches are interrelated and lack rigid boundaries. Nevertheless, distinguishing them from a methodological standpoint is highly useful. It is impossible to give equal attention to all approaches in this chapter; therefore, we will focus primarily on the first three: ecosystems, communities, and populations.