BIOLOGY Volume 1 - A Guide to General Biology - 2004

10. ORGANISMS AND THE ENVIRONMENT

10.2. Ecosystems

10.2.2. General Structure of Ecosystems

A generalized diagram of terrestrial and aquatic ecosystems is shown in Fig. 10.2. Remarkably, despite differences in abiotic conditions and species composition, The Structure of these ecosystems is quite similar. For convenience, the biotic component of all ecosystems can be divided into autotrophs and heterotrophs. The survival of heterotrophs relies entirely upon autotrophs. This point is crucial for understanding food chains and food webs, as well as the flow of matter and energy within ecosystems (Sections 10.3 and 10.4).

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Fig. 10.2. A simplified schematic comparison of terrestrial and aquatic ecosystems (see also Section 10.3.2). (Adapted from: E. P. Odum (1975) Ecology, 2nd ed., Holt, Rinehart, Wilson.)

The non-living, or abiotic, component comprises soil, Water, and climate. Soil and water represent a mixture of organic and inorganic substances. The physical and Chemical properties of soil depend on the underlying parent rock from which it is partly formed. Similarly, water quality and salinity depend on the underlying riverbed rock, bottom sediments, as well as the rocks and soil of the surrounding area. Climate encompasses factors such as light intensity, Temperature, humidity, wind, and precipitation in the form of rain and snow. All of these factors determine the taxonomic COMPOSITION OF THE biota and the prevalence of specific organisms.

However, the core of the ecosystem approach is The Study of functional interrelationships between organisms and their abiotic environment. These interactions are driven by the flow of energy and biogeochemical cycles (nutrient cycles).