This document discusses r-selection and K-selection, which are concepts in ecology that classify species based on their life history traits and habitat stability. R-selected species are adapted to unstable, unpredictable environments by having high reproductive rates, rapid development, small body size, and producing many offspring with low survival rates. They exploit temporary habitats and respond quickly to disturbances. K-selected species are adapted to stable environments and compete for resources. They have slower growth, delayed reproduction, low reproductive output, and provide parental care. Their populations are near the carrying capacity of their environment and are limited by resources. The terms r and K relate to parameters in the logistic model of population growth.

1. Rounak Choudhary
M.Sc. (Gold Medalist), UGC-NET & ICAR-ASRB NET Environmental Science, DCB Ornithology, PGD Industrial Safety, Health and Environment
r - and K -selection

2. • One way of classifying environments (or species
habitats) relates to their variability in time. We can
envision two contrasting types of habitats: (1) those
that are variable in time or short-lived, and (2) those
that are relatively stable (long-lived and constant), with
few random environmental fluctuations.
• The ecologists Robert MacArthur of Princeton
University, E. O. Wilson of Harvard University, and later
E. Pianka of the University of Texas used this
dichotomy to develop the concept of r - and K -
selection.

3. • The theory of r - and K -selection predicts that
species adapted to these two different
environments will differ in life history traits
such as size, productiveness, age at first
reproduction, number of reproductive events
during a lifetime, and total life span.

4. • Species popularly known as r -strategists are
typically short-lived.
• They have high reproductive rates, rapid
development, small body size, large number of
offspring (with low survival), and minimal
parental care.
• They make use of temporary habitats. Many
inhabit unstable or unpredictable environments
that can cause catastrophic mortality
independent of population density.
• Environmental resources are rarely limiting. They
exploit noncompetitive situations. Some r -
strategists, such as weedy species, have means of
wide dispersal, are good colonizers, and respond
rapidly to disturbance.

5. • K -strategists are competitive species with stable
populations of long-lived individuals.
• They have a slower growth rate.
• K -strategists can cope with physical and biotic pressures.
• They possess both delayed and repeated reproduction and
have a larger body size and slower development.
• They produce few seeds, eggs, or young. Among animals,
parents care for the young; among plants, seeds possess
stored food that gives the seedlings a strong start.
• Mortality relates more to density than to unpredictable
environmental conditions. They are specialists, efficient
users of a particular environment, but their populations are
at or near carrying capacity (maximum sustainable
population size) and are resource limited.
• These qualities, combined with their lack of means for wide
dispersal, make K -strategists poor colonizers of new and
empty habitats.

6. • The terms r and K used to characterize these
two contrasting strategies relate to the
parameters of the logistic model of population
growth.
• r is the per capita rate of growth, and K is the
carrying capacity (maximum sustainable
population size).

11. MCQs

14. Which is not the characteristic of ‘r’
selected species?
1. Reproduce quickly
2. Parental care
3. A low survival rate of progenies
4. Produce a large number of progenies