Ecology

The word ecology was coined in 1870 by the German zoologist Ernst Haeckel from the Greek words oikos (house) and logos (logic or knowledge) to describe the scientific study of the relationships among organisms and their environment. Biologists began referring to themselves as ecologists at the end of the nineteenth century and shortly thereafter the first ecological societies and journals appeared. The contextual, historical understanding of organisms as well as the systems basis of ecology set it apart from the reductionist, experimental approach prevalent in many other areas of science.
This broad ecological view is gaining significance today as modern resource-intensive lifestyles consume much of nature's supplies. Although intuitive ecology has always been a part of some cultures, current environmental crises make a systematic, scientific understanding of ecological principles especially important.
For many ecologists the basic structural units of ecological organization are species and populations. A biological species consists of all the organisms potentially able to interbreed under natural conditions and to produce fertile offspring. A population consists of all the members of a single species occupying a common geographical area at the same time. An ecological community is composed of a number of populations that live and interact in a specific region.
This population-community view of ecology is grounded in natural history—the study of where and how organisms live—and the Darwinian theory of natural selection and evolution. Proponents of this approach generally view ecological systems primarily as networks of interacting organisms. Abiotic forces such as weather, soils, and topography are often regarded as external factors that influence but are apart from the central living core of the system.
In the past three decades the emphasis on species, populations, and communities in ecology has been replaced by a more quantitative, thermodynamic analysis of the processes through which energy flows and the cycling of nutrients and toxins are carried out in ecosystems. This process-functional approach is concerned more with the ecosystem as a whole than the particular species or populations that make it up. In this perspective, both the living organisms and the abiotic physical components of the environment are equal members of the system.
The feeding relationships among different species in a community are a key to understanding ecosystem function. Who eats whom, where, how, and when determine how energy and materials move through the system. They also influence natural selection, evolution, and species adaptation to a particular set of environmental conditions. Ecosystems are open systems, insofar as energy and materials flow through them. Nutrients, however, are often recycled extremely efficiently so that the annual losses to sediments or through surface water runoff are relatively small in many mature ecosystems. In undisturbed tropical rain forests, for instance, nearly 100% of leaves and detritus are decomposed and recycled within a few days after they fall to the forest floor.
Because of thermodynamic losses every time energy is exchanged between organisms or converted from one form to another, an external energy source is an indispensable component of every ecological system. Green plants capture solar energy through photosynthesis and convert it into energy-rich organic compounds that are the basis for all other life in the community.