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Difference between r and K Selection

Difference between r selection and k selection as a reproductive strategy
Difference between r selection and k selection as a reproductive strategy
The r and K classification was originally proposed by the biologists Robert McArthur and E. O. Wilson (1967).

The r selected species live in populations that are highly variable. The fittest individuals in these environments have many offspring and reproduce early.
Examples: Oysters, Insects- Mosquitos, Daphnia, Goldenrod

K selected species live in populations that are at or near equilibrium conditions for long periods of time. Competitive for limited resources is very important in these environments.
Example: Lemurs, Bats, Elephants, Giraffes
Difference Between r selection vs K selection
r- Selection
Bacteria, insects
Primates, including humans
Reproduction rate
Reproductive age
Body size
Reproductive type
Single reproduction
Repeated reproduction
Length of life
Competitive ability

Life Histories and Risk of Extinction: Life history theory may be useful in helping us to determine which types species are more at risk of extinction.  K selected species sets it at risk of extinction because of the following reasons:
  • K selected species tend to be bigger, so they need more habitat to live in.
  • K selected species tend to have fewer offspring, so their populations cannot recover as fast from a disturbance such as over hunting or fire.
  • K selected species breed at a later age, so their generation time to grow from a small population to larger population is long.
  • In K selected species, population size are often small, and therefore, individuals run a high risk of inbreeding.
The reproductive characteristics of an r-selected mammal and K-selected mammal
r-selected mammal(the Norway rat) vs K-selected mammal (African elephant)
Reproduction in r-selected and K-selected species
Thus K-selected species are more prone to extinction than r-selected species because they mature later in life and have fewer offspring with longer gestation times. Large K selected tree such as the giant sequoia, red wood tree, large terrestrial mammals like elephants, rhinoceros and grizzlies, and large marine mammals such as blue whales and sperm whales are all competitively dominant species that run a substantial risk of extinction.

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