Science of Water : Concepts and Applications

158 The Science of Water: Concepts and Applications
Emigration The departure of organisms from one place to take up residence in another area.
Eutrophication The natural aging of a lake or land-locked body of water, which results in
organic material being produced in abundance due to a ready supply of nutrients
accumulated over the years.
Habitat Ecologists use this term to refer to the place where an organism lives.
Heterotroph Any living organism that obtains energy by consuming organic substances produced
by other organisms.
Immigration The movement of organisms into a new area of residence.
Limiting factor A necessary material that is in short supply. Because of the lack of it, an organism
cannot reach its full potential.
Niche The role that an organism plays in its natural ecosystem, including its activities, resource
use, and interaction with other organisms.
Nonpoint pollution Sources of pollutants in the landscape (e.g., agricultural runoff).
Point source Source of pollutants that involves discharge of pollutants from an identifi able
point, such as a smokestack or sewage treatment plant.
Pollution An adverse alteration to the environment by a pollutant.
Population A group of organisms of a single species that inhabit a certain region at a particular
time.
Runoff After an organic waste has been applied to a soil, the possibility exists that some of
this waste may be transmitted by rainfall, snowmelt, or irrigation runoff into surface
waters.
Sewage The liquid wastes from a community. Domestic sewage comes from housing. Industrial
sewage is normally from mixed industrial and residential sources.
Succession A process that occurs subsequent to disturbance and involves the progressive
replacement of biotic communities with others over time.
Symbiosis A compatible association between dissimilar organisms to their mutual advantage.
Trophic level The feeding position occupied by a given organism in a food chain measured by
the number of steps removed from the producers.
LEVELS OF ORGANIZATION
Odum (1983) explains, “The best way to delimit modern ecology is to consider the concept of levels
of organization.” Levels of organization can be simplifi ed as shown in Figure 6.1. In this relationship,
organs form an organism; organisms of a particular species form a population; populations
occupying a particular area form a community. Communities, interacting with nonliving or abiotic
factors, separate in a natural unit to create a stable system known as the ecosystem (the major ecological
unit); and the part of the Earth in which ecosystem operates in is known as the biosphere.
Tomera (1989) points out that “every community is infl uenced by a particular set of abiotic factors.”
Inorganic substances such as oxygen, carbon dioxide, several other inorganic substances, and some
organic substances represent the abiotic part of the ecosystem.
The physical and biological environment in which an organism lives is referred to as its habitat.
For example, the habitat of two common aquatic insects, the “backswimmer” (Notonecta) and the
“water boatman” (Corixa), is the littoral zone of ponds and lakes (shallow, vegetation-choked areas)
(see Figure 6.2) (Odum, 1983).
Within each level of organization of a particular habitat, each organism has a special role. The
role the organism plays in the environment is referred to as its niche. A niche might be that an
Organs Organism Population Communities Ecosystem Biosphere
FIGURE 6.1 Levels of organization.