Ecosystem concepts and characteristics

Ecosystems are changed by both biotic and abiotic factors. Biotic factors are all living things or their materials that directly or indirectly affect an organism in its environment. Biotic factors include organisms, their presence or parts, their interaction with the ecosystem, or their wastes. Additionally, parasitism, disease, and predation are considered biotic factors. Abiotic factors are factors of a non-living physical and chemical nature that affect the ability of organisms to survive and reproduce. These factors include light intensity, temperature, soil or rock type, pH levels, available water supplies, gasses, and pollutant levels (Bush, 2002).

Both types of factors change the equilibrium, but in different ways. For example, any change in temperature, an abiotic factor, may not only affect the ecosystem in general, but also affect the biotic factors in the ecosystem, such as aiding in the production of a given species. This species may then become overabundant, which can then change abiotic factors, such as water supplies and food supplies. The biotic elements interact with the abiotic factors to provide stability, and any change in either factor can cause drastic changes in the ecosystem (Bush, 2002).

Ecosystems go through a natural cycle of progression. In the beginning of an ecosystem, there is often very little life. This stage is generally called the primary or secondary stages. Over time, small temporary communities called pioneer species begin to develop, making this the serial stage. As those pioneer species develop, they alter the biotic and abiotic factors of the area, including soil stabilization, changes in water supply and temperature, and other factors. As the pioneer species advance and multiple, their efforts eventually develop to a climax stage. This climax stage is the point at which the ecosystem or biosphere has become stable (Botkins & Keller, 1997).

This progression from the beginnings of life to a stable and self renewing ecosystem is often called the progression. The amount of time need to get to the mature stage largely depends upon the type of ecosystem. In any ecosystem, the natural cycle of progression can be very easily disturbed through changes in biotic and abiotic factors, such as massive or even slight changes in water supplies, or changes in pollution levels. Only those ecosystems able to remain stable and in a state of equilibrium can survive (Botkins & Keller, 1997).

There are many mechanisms that can help and in some cases hinder an ecosystem's recovery after a disturbance. Environmental resistance, in which the biotic and abiotic factors of an area come together to limit population sizes, is one mechanism that can hurt an ecosystem recovery. Genetic drift, on the other hand, where certain species of plants left over after a disaster, can help an ecosystem recover. The genes that allowed the plant to survive are propagated to other new plants, thus encouraging growth in the ecosystem that is compatible with the new biotic and abiotic factors. This is often called the bottleneck phenomenon, and is crucial to ecosystem recovery. Also, the stratification of plants n any given ecosystem can assist in recovery, since some plants in certain strata respond better to atmospheric changes ("The Ecology and the Environment," 2003).