Evolutionary Ecology

Some species depend more on reproductive quantity while others depend on reproductive quality. Those that rely on quantity are said to be r-selected, while those that depend on quality are K-selected

Factor

 r-selected K-selected
Climate: Variable and unpredictable to the organism. Coarse-grained view of the environment and time. Constant and predictable. Fine-grained view of the environment and time.
Survivorship: Type III Type I & II
Population Size:
  • Variable (Lots of outbreaks).
  • Non-equilibrium.
  • Below carrying capacity.
  • Re-colonization each year.
  • Constant.
  • At equilibrium.
  • Near carrying capacity.
  • Little colonization.
Competition: Variable, Lax Keen
Selection Favors:
  • Rapid development
  • High reproductive rate (r)
  • Early reproduction
  • Small body size
  • Single reproduction
  • Slow development
  • Greater competitive ability
  • Delayed reproduction
  • larger body size
  • Repeated reproduction
Parental Care: Little or none. Extended.
Length of Life: Less than a year More than a year
Consequence: Productivity Efficiency.

Table 1

Recognizing the differences between species with high rates of reproduction and those with low intrinsic rates of increase, ecologists often describe a species as being "r-selected" or "K-selected" (Table 1). Those species whose populations levels are controlled by their reproductive rates are defined as r-selected while those whose reproduction is controlled more by environmental resistance are termed K-selected.

Species that are r-selected tend to perceive the environment as variable and unpredictable (Table 1). Insects are an example of an r-selected species while birds and mammals are often K-selected. It's important to realize that r- vs. K- is comparative. If, for example we compare mice to humans, mice would be r-selected while we would be K-selected.

NOTE: It is very important that you understand the differences between r- and K-selected organisms. These concepts will be used for much of the remainder of the semester to show how the environment will change due to pollution, climate change and so forth. Expect to see this on the test!