Features of Populations
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number Usually, biologists wish to determine population size (the total
populations have a number of attributes that may be of interest.
organisms within their environment and so determine what
the of organisms in the population). It is also useful to know
particular aspects of the habitat are favored over others. One
area). The density of a population is often a reflection of the
population density (the number of organisms per unit
way to retrieve information from populations is to sample
them. Sampling involves collecting data about features of the
carrying a capacity of the environment, i.e. how many organisms
population from samples of that population (since populations
particular environment can support. Populations also have
are usually too large to examine in total). Sampling can be done
structure; particular ratios of different ages and sexes. These
directly through a number of sampling methods or indirectly (e.g.
data enable us to determine whether the population is declining
monitoring calls, looking for droppings or other signs). Some of
or increasing in size. We can also look at the distribution of
the population attributes that we can measure or calculate are
illustrated on the diagram below.
Population Distribution
and Abundance
Migration
Population Composition
Movement of individuals into and out of a
Density
population. Affects density and distribution as
Sex ratios
The number of
well as the population composition. Ultimately
The number of
organisms per unit area.
affects the dynamics of the population.
organisms of each sex.
Distribution
The location of individuals
Population fertility
within an area.
The reproductive
capacity of the females.
Total abundance
The total number of
Age structure
organisms.
The number of organisms
of different ages.
Population Dynamics
Population growth rate
Natality (birth rate)
Mortality (death rate)
The change in the total
The number of organisms
The number of organisms
population per unit time.
born per unit time.
dying per unit time.
1. Describe one example of a population attribute that would be a good indicator of each of the following:
(a) Whether the population is increasing or decreasing:
(b) The ability of the environment to support the population:
2. (a) Identify the population attributes that can be measured directly from the population:
(b) Identify the population attributes that must be calculated from the data collected:
3. Describe the value of population sampling for each of the following situations:
(a) Conservation of a population of an endangered species:
(b) Management of a fisheries resource:
