All organisms are interdependent and interrelated with one another and with their environment. This concept applies at all levels from a small pond to the world. Implicit in ecological organization is the idea that plants and animals do not occur randomly, but rather that particular kinds are especially adapted to a certain complex of environmental conditions and therefore coexist with others of similar requirements and tolerance in communities.

All individuals of a particular species constitute a population. A community, therefore, is an aggregation of populations. Maintenance of a community is dependent upon flow of energy through functional strata of populations. One stratum is com posed of producers, the plant species which, through photosynthesis, convert solar energy to chemical energy contained in plant tissues. the second stratum consists of consumers, the animals which ingest plants or other animals that have fed upon plants. the third stratum is the de-composers, mainly bacteria and fungi but also including many kinds of small animals which decompose dead organisms and organic debris to release basic chemical substances to the environment to be taken up by living plants. These strata, their activities, and energy transfer through the community constitute an ecosystem. Ultimately, the total ecological organization is recognized as the world ecosystem, or ecosphere (also called biosphere).

In the context of ecological organization and the ecosystem are embodied a number of basic ideas which give meaning to the inter relatedness of life. One of the most important of these is environment, and although the term has been used freely up to this point, it bears defining. Environment comprises the sum of all the external factors, processes, and conditions that affect a living system. These may be other living systems (the biotic environment) or nonliving factors (the abiotic environment). Thus inside an animal a single nerve cell may be embedded in a biotic environment of muscle cells and other nerve cells and subjected to abiotic states such as oxygen and salt concentration in the tissue The biotic environment of a hickory tree in a deciduous forest commonly includes other hickory trees, along with beech, maple, poplar, and birch, a rich understory of shrubs, and animals such as deer, squirrels, tree-nesting birds, numerous insects, and many others. Abiotic conditions and processes, including rainfall, ice, wind, evaporation, light, temperature, and soil type, together with biotic constituents, all affect the hickory tree.

Of greatest significance in ecological organization is the concept of dynamism in ecosystems. Organisms do not simply live side by side in the abiotic environment. Rather, there are constant, often complex, action systems in which all living systems exert some effect on one another and on the nonliving surroundings, which in turn influence the living mechanisms of the organisms present. Furthermore, there is great variation among ecosystems from tropical to polar regions, from sea level to oceanic depths and mountain tops, through geological time, and through changing climates and land-water distribution, through seasons, and night and day. Abiotic factors, such as oxygen, carbon dioxide, nitrogen, and water, are constantly being cycled in various ways throughout the world community. Water, for example, covers 70 percent of the earth’s surface, and is the primary environment in which life exists since every living cell must be moist. Distribution of this important liquid is de pendent upon a world hydro-logical cycle.

Solar energy must be transformed into chemical energy and passed to all organisms for maintenance of their life and growth. Autotrophic organisms serve as the basis or core of ecosystem food webs that are actually energy-transfer systems. Unlike chemical nutrients that are cycled, energy must be supplied constantly, for it is used and transformed to heat. Thus through photosynthesis and eating and being eaten, organisms are intensely interdependent and interrelated. They are further bound through requirements and contributions relative to breeding sites, cover, shading, predation, competition, and numerous other aspects of living.