''Ecology is the scientific study of the interactions that determine the distribution and abundance of organisms'' (Krebs, 1994). The effects of pollutants can be detected at all levels of the biological hierarchy. Our concern about these impacts falls mainly into two groups of organisms: humans and everything else. We are concerned directly with all types of impacts on humans. However, in nonhuman populations our primary concern is about loss of desirable species and the proliferation of undesirable ones resulting from our activities. Therefore, ecology provides an appropriate framework for examining our impact on the natural world.
The word ecology has as its root oikos, the Greek word for "house." The word economy is based on the same root. Thus, one can be thought of as the study of where we live; the other is its management. It is interesting that these two disciplines are commonly considered to conflict with each other. However, economics is now being brought to bear on environmental problems. Some think that if the true value of unspoiled ecosystems were taken into account, much destructive human activity would actually be seen not to be economically beneficial. In this view, the apparent economic advantages of polluting or destroying ecosystems comes from the costs being borne by others than those who receive the profits (the "tragedy of the commons").
Recall the following definitions from Section 2.2:
A group of individuals of the same species living in the same environment and are actively interbreeding.
A group of interacting populations occupying the same environment. The physical and chemical surroundings in which individuals live. The combination of a community and its environment.
Environmental Biology for Engineers and Scientists, by David A. Vaccari, Peter F. Strom, and James E. Alleman Copyright © 2006 John Wiley & Sons, Inc.
TABLE 14.1 Biomes of the Biosphere
Tundra: arctic and alpine
Boreal coniferous forests
Temperate deciduous forests
Tropical grassland and savanna
Chaparral: winter rain / summer drought
Desert: herbaceous and shrub
Semievergreen tropical forest: pronounced wet and dry seasons Evergreen tropical rain forest Freshwater ecosystems
Lentic (standing water): lakes, ponds, etc. Lotic (running water): rivers and streams Wetlands: marshes and swamp forests Marine ecosystems Pelagic (open ocean) Continental shelf (inshore waters) Upwelling regions
Estuaries (coastal bays, sounds, river mouths, salt marshes, etc.) Source: Odum (1987).
These are the entities with which we are concerned directly in the study of ecology. A biome is a major type of ecosystem. Table 14.1 lists the most important biomes. The individual biomes are discussed in more detail in Chapter 15.
The range of environments in which a species lives is called its habitat. Each type of organism is thought to occupy a unique functional position, called its niche, in an ecosystem. The idea of a niche can be defined as a subset of the environmental and ecological variables that are favorable to a species. For example, two aquatic insects, the backswimmer (Noto-necta) and the water-boatman (Corixa), occupy the same habitat among aquatic plants at the edge of a pond. But they have different niches because the former is a predator and the latter feeds on dead plant matter. Niche may be characterized by many variables, such as food source or tolerated physical conditions. The niches of two species may overlap but not coincide. It is said that two organisms in a particular ecosystem cannot occupy the same niche. However, they can coexist if there are even slight differences in their behavior.
Let us now systematize and categorize the ecological roles taken by organisms. Much of this is in terms that engineers will find familiar. For example, one important way to look at ecosystems is to examine their energy and material balances. Changes in sizes of populations are modeled in a way not very different from chemical or microbial kinetics. Most unique, perhaps, are the types of interactions between species such as competition or symbiosis. However, even these are studied in part using the mathematics of population dynamics. As you learn the ways in which we describe ecological roles and phenomena, think about how pollution could affect each.
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