R-selection refers to species that live in unstable environments and produce many cheap offspring, while K-selection refers to species that live in stable environments and produce few expensive offspring. Key differences are that r-selected species have highly variable populations with early reproduction and many offspring, while K-selected species have small populations with a higher risk of inbreeding and later reproduction after parental care. Characteristics of r-strategists include small size, low energy per offspring, short lifespan and multiple reproduction, while K-strategists have the opposite traits. The terms r and k come from the logistic growth equation.

1. R and K
Selection

2. R and K selection means:
 The two evolutionary "strategies" are termed r-
selection, for those species that produce many
"cheap" offspring and live in unstable
environments.
 K-selection for those species that produce few
"expensive" offspring and live in stable
environments.

3. Difference between R and K
selection
 The r selected species live in populations that are highly
variable.
 The fittest individuals in these environments have many
offspring and reproduce early.
 In K selected species, population size are often small, and
therefore, individuals run a high risk of inbreeding.

4. Characteristics of organisms which are extreme r or K
strategists
r
Unstable environment, density independent
k
Stable environment, density dependent interactions
small size of organism large size of organism
energy used to make each individual is low energy used to make each individual is high
many offspring are produced few offspring are produced
early maturity late maturity, often after a prolonged period of
parental care
short life expectancy long life expectancy
each individual reproduces only once individuals can reproduce more than once in their
lifetime
type III survivorship pattern
in which most of the individuals die within a short
time
but a few live much longer
type I or II survivorship pattern
in which most individuals live to near the maximum
life span

5. The terms r and k are derived from the logistic equation for growth of a
population (Andrews 1991)