13.3: r and k Selected Species

k selection

selection for traits that are advantageous in high density populations

r selection

selection for traits that maximise reproductive success in uncrowded or low density population

r vs k selection

• intrinsic rate of increase: R = high, K = low

• competitive ability: R = not strongly favoured, K = strongly favoured

• development: R = rapid, K = slow

• reproduction: R = early, single and semelparous, K = late, repeated and iteroparous

• body size: R = small, K = large

• Offspring: R = many and small K = few and large

r selected species

have traits that rapidly respond to favourable environmental conditions and abundant resources.

• rapid population growth = large populations

• has booms and busts

e.g. of r selected species

African locusts. Undergo population booms in response to good environment conditions. Their life history strategy makes population booms possible. Females mature early, law 100 eggs and short lifespan. Possible for 10 fold increase in population from 1 gen to next. But if resources disappear population will plummet

k selected species

better competitors in more stable environments

• slower population growth = more stable through time

• more cyclical fluctuations

Explain what is meant by “booms” and “busts” and describe what environmental conditions might lead to each rate of population change

boom = rapid population growth caused by abundant food resources and favourable conditions, low disease

busts = sharp population decline caused by resource depletion, harsh climate, predation or disease outbreaks.