R and k selection is very important aspect of knowing ecology a better way. This is based on natural selection of species (that is stable condition leads to k selection & unstable one leads to r selection).

1. R &K –SELECTION IN
ECOSYSTEM
Presentation by –Bhenkatesh Padhan
M.F.Sc 1st year

2. Introduction
■ According to Darwin’s principle ,Natural selection is the force for
change ,not the individual’s conscious decision.
■ The premise behind the r/k selection model is that natural selection
pressures change according to population density.
■ r/k selection theory, one of the first predictive models in population
ecology used to explain life history evolution.
■ The first variable is r (the intrinsic rate of natural increase in
population size, density independent) and the second variable is k
(the carrying capacity of a population, density dependent)
■ The terminologies r/k selection was coined by the ecologist Robert
MacArthur & E.O.Wilson in 1970.

3. Plenty of resources
Less competition
Exponential growth
Resource limited
Competition
density dependent growth
PIONEER
COMMUNITY
CLIMAX
COMMUNITY
STORY OF AN ISLAND

4. Concept of r & k selection in ecology.
■ By theory of natural selection, in an ecosystem organisms that live in
stable environments tend to make few, "expensive" offspring.
Organisms that live in unstable environments tend to make many,
"cheap" offspring.
■ The two evolutionary "strategies" are termed
A. R-selection: for those species that produce many "cheap"
offspring and live in unstable environments
B. K-selection: for those species that produce few "expensive"
offspring and live in stable environments.

5. r-selected species
■ r–selected species also called as r- strategist are those
individual which resides in an unstable environment and
shows exponential growth pattern.
■ Example- small fishes, many shell fishes, algae, bacteria
and many small organisms.

6. r-selected species

7. Characteristic feature of r- selected species
■ High biotic potential potential.(capacity to reproduce many
organism)
■ Live in an unstable /unpredictable environment.
■ High mortality among young.
■ Short life span.
■ Goes for quantity not quality.
■ Exhibits J- shaped growth curve.
■ Density independent interaction.

8. ■ Little or no parental care.
■ Low competition.(unlimited resources)
■ Small body size.
■ Energy used to make each individual is very low.
■ Early maturity.
■ Waste a lot of energy.
■ Shows Semelparity
■ Most individual die within a short time but a few live much
longer.

9. k-Selected species
■ k- selected species also called as k-strategists, are those
individual who lives in stable environment and their
population fluctuate near to carrying capacity of the
ecosystem .
■ Example- aquatic mammals,shark,human, elephant and
large animals

10. k-selected species

11. Characteristic feature of k- selected species
■ Large size organisms
■ Energy used to make each individual is high.
■ Few offspring are produced.
■ Late maturity, after a prolonged period of parental care.
■ Long life expectancy.
■ Iteroparous life.

12. ■ Most of the individual live to near maximum life span.
■ Live in a stable environment.
■ Density dependant interaction.
■ Shows logistic growth curve .

13. r/k interaction in population growth
curve & survivorship curve
■ Population growth curve:
Population growth curve graph

14. ■ Population growth curve is plotted by taking population size
(N) on Y-axis and time (t) on X-axis.
■ If an organism is in an unstable environment, its unlikely to
ever has population growth to the point where density
dependent factors come into play. The population is still at
low values relative to the carrying capacity of the
environment and thus is growing exponentially with intrinsic
reproductive rate r , hence the name r-strategist.
■ An extreme K-strategist lives in a stable environment which
is not seriously affected by sudden, unpredictable effects.
Thus the population of a K-strategist is near the carrying
capacity K.

15. Survivorship curve
survivorship curve graph

16. ■ Survivorship curve is graphical representation of the
individual in a population that can be expected to survive to
any specific age.
■ Type -1:
 There is high probability of surviving through early &
middle life but have a rapid decline in number of
individual surviving into late life.
 There is convex curve on a graph.
 For example- extreme k-strategists ( aquatic mammals,
human and large organisms)

17. ■ Type-2:
 Very rare case.
 Roughly constant mortality rate for the species through its
entire life.
 Type-2 Curve is a diagonal line going downward on the
graph.
 Example- song bird, lizards
■ Type-3:
 Few individuals will live to adulthood & die as they got older
because the greatest mortality for these individual is
experienced early in life.
 Drawn as a concave curve on a graph.
 Example- r-strategists (,bacteria, small fishes, lower
organisms)

18. Difference between r&k-selected species
r-selected species
■ Unstable environment.
■ Small size organism.
■ Energy used to make individual
is low.
■ Many offspring are produced
and show early maturity.
■ Short life expectancy.
■ Semelparous life.
■ Density independent interaction.
■ Follow type-3 survivorship curve.
k-selected species
■ Stable environment.
■ Large size of organisms.
■ Energy used to make individual
is high.
■ Less offspring are produced and
show late maturity.
■ Long life expectancy.
■ Iteroparous life.
■ Density dependant interaction.
■ Follow type-1&2 survivorship
curve.

19. conclusion
 The essence of the concept of r- and K-selection is that
organisms strive to maximize their fitness for survival in either
unstable (r-selection) or stable (K-selection) environments.
 Since both r and K can vary within a species and are subject to
modification, the division of natural selection into r- and K-
selection is of considerable basic interest in evolutionary
ecology.
 But in reality no organism can be said completely r/k-selected
,rather all must reach some compromise between the two
extremes. Because in an ecosystem nothing is stable completely.