Adopt-A-Wetland

Density-Dependent versus Density-Independent Factors
Other factors can enter the population equation in natural environments or in biological communities. The
growth of an animal population strives to reach stability or carrying capacity (K). However, in natural
systems populations encounter forces (known as density-dependent or density- independent factors) which
will affect their density and growth. Density-dependent factors are internal forces that operate within the
population. For example, infections, diseases, or stress related health problems can occur within an oyster
population. In another instance, too many individuals of a species will cause lack of space, and depleted
resources creating competition and/or stress within the population. These problems (density- dependent
forces) occur only when the density of a population reaches a critical level (Hickman et. al. 1984). Densityindependent
factors occur outside of the population, examples include drastic changes that are
environmental in nature. For instance, extreme weather changes, unusually cold weather, hurricanes, or
drought conditions are examples of density independent forces acting against a population.
Comparison of r- and K-Selected Species
Biologists have categorized animals on adaptations they have developed to deal with density- independent
or density-dependent situations that arise and effect populations. K-selected species are animals or species
whose populations can survive controls that are density-dependent in nature. Conversely, r-selected species
are animal populations that have developed adaptations that are density-independent in nature (Hickman et.
al. 1984). Density-dependent or density-independent factors will affect all populations.
In the table below, notice the general characteristics of r-strategy species and K-strategy species.
41 DRAFT AUGUST 2015