Environmental Engineering Reference
In-Depth Information
Chapter 3: Population
An ecosystem is made up of many components and their interactions. When examining at the species in a giv-
en location, assessing the populations of that species gives important information about the structure, growth,
and potential decline of that species. Many of these characteristics and structures can apply to the human popu-
lation as well, but humans are unique and, therefore, also have distinctive population dynamics. In this chapter,
the basic concepts of population dynamics are reviewed, followed by a more detailed look at the human popu-
lation.
Population Biology Concepts
A
population
is a group of individuals of the same species living in a particular area at the same time. The size
of a population is dependent upon four factors:
• Birth rates in a population (also called
natality
)
• Death rates in a population (also called
mortality
)
• Immigration of organisms into one population from another population
• Emigration of organisms leaving a population
Population Ecology
Population ecology
is the study of how individuals within a population interact with one another. Populations
of organisms are described based on characteristics that help to better understand that population and to predict
what might happen in the future. Characteristics include:
•
Population size:
The number of individuals in a population at a given time. Over time, the size of a pop-
ulation of organisms can change, remain the same, or go through cycles of increasing and decreasing
numbers.
•
Population distribution:
The spatial arrangement of organisms in an area. This can be explained as:
•
Random distribution:
With random distribution, organisms are spaced arbitrarily, with no organiza-
tion or intention, as with free-floating larvae in the ocean. This is the least common arrangement in
nature.
•
Uniform distribution:
Uniform distribution occurs when organisms are spaced evenly from one an-
other. This occurs due to necessity, such as limited resources making distance necessary for survival
of organisms that are territorial. Wolves are one example of a species with uniform distribution be-
cause they are territorial animals.
•
Clumped distribution:
The most common in nature, clumped distribution occurs because organisms
often gather around a necessary resource. Animals that live in herds demonstrate clumped distribu-
tion, such as buffalo.
•
Population density:
The number of individuals in a population per unit area. Usually more resources and
a larger area are necessary for species that are larger in size, whereas smaller organisms don't need as
much space or as many resources. With any organism, high population density could lead to increased
competition for resources and an increased chance of the transfer of disease, but it also betters the
