Ecology in Further Detail ❮ 225
However, another possibility shown in this figure is that when a population dips below the
carrying capacity due to some major change in the environment, when all is said and done,
it may equilibrate at a new, lower carrying capacity.
Life History Strategies
You should be familiar with two primary life history “strategies,” which represent two
extremes of the spectrum:
K-selected populations:populations of a roughly constant size whose members have low repro-
ductive rates. The offspring produced by these K-selected organisms require extensive post-
natal care until they have sufficiently matured. Humans are a fine example of a K-selected
population.
R-selected populations:populations that experience rapid growth of the J-curve variety. The
offspring produced by R-selected organisms are numerous, mature quite rapidly, and
require very little postnatal care. These populations are also known as opportunistic
populationsand tend to show up when space in the region opens up as a result of some
environmental change. The opportunistic population grows fast, reproduces quickly, and
dies quickly as well. Bacteria are a good example of an R-selected population.
Survivorship Curves
Survivorship curves(Figure 18.4) are another tool used to study the population dynam-
ics of species. These curves show the relative survival rates for population members of
different ages.
Type Iindividuals live a long life until an age is reached where the death rate in the popu-
lation increases rapidly, causing the steep downward end to the type I curve. Examples of
type I organisms include humans and other large mammals.
Type IIindividuals have a death rate that is reasonably constant across the age spectrum.
Examples of type II species include lizards, hydra, and other small mammals.
Figure 18.4 Survivorship curves.
Type I Type II Type III
# of survivors # of survivors # of survivors
Age Age Age
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