The Ecological Context

Ecology is the study of the relations between organisms and the totality of the physical and biological factors affecting them or influenced by them, or more simply, as the study of patterns in nature. Ecologists investigate the biology of organisms, looking for consistent patterns in their behavior, structure, and organization. Although a relatively new field in comparison to systematics, ecology has already provided considerable insights into the organization of taxa.

Ecosystem function refers to the sum total of processes operating at the ecosystem level, such as the cycling of matter, energy, and nutrients. The species in a community influence its productivity, nutrient cycling, and fluxes of carbon, water, and energy. Ultimately, species may be responsible for such factors as the maintenance of atmospheric composition, the dispersal and breakdown of waste material, the amelioration of weather patterns, the hydrological cycle, the development of fertile soils, and even the protection of many coastal areas.

Biogeochemical cycling is the movement of materials including carbon, nitrogen, phosphorus, and calcium through an ecosystem as individuals of different trophic levels are consumed by others at higher trophic levels. These nutrients are returned eventually to the abiotic "nutrient pool," where they are again available to primary producers.

Some of the important roles played by different species in biochemical cycling can be outlined briefly.

By their photosynthetic activity, plants play a fundamental role in the carbon cycle, introducing carbon into the food web. Microorganisms are also crucial. It is estimated that algae and cyanobacteria are responsible for 40% of the carbon fixed by photosynthesis on Earth. At the other end of the process, wood-decaying fungi release approximately 85 billion metric tons of carbon into the atmosphere each year as carbon dioxide. Termites also play an important role in global carbon cycling (hence, potentially, in global climate change) through their production of methane. Earth's nitrogen cycle is dependent on bacteria for nitrogen fixation and the release of nitrogen by denitrification. The microbial community thus controls the amount of nitrogen available to an ecosystem, determining ecosystem productivity in areas where nitrogen is limiting. By absorbing water from soils or other surrounding media, plants have a fundamental effect on the water cycle.

There is an ongoing debate between those who believe that all species in a given ecosystem are important and those who say that some are "functionally redundant." That is, if a species is removed from an ecosystem, can other species fulfill the same role? Two factors influence the importance of a species in ecosystem functioning: the number of ecologically similar species in the community and the extent to which a species has qualitative or quantitative effects on the ecosystem.

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