The opposite parental-investment strategy is to invest a great deal in each offspring, and to produce only a small number of them. This general strategy is typical of birds and mammals. Typically, one or both parents feed and protect the offspring for some time after they are hatched or born.
One disadvantage of this strategy is that since so few offspring are produced, population growth tends to be slow, even under ideal circumstances. On the other hand, survivorship of offspring is generally very high, so each offspring has an excellent chance of living long-enough to reproduce.
An African Bush Elephant (Loxodonta africana
) and her calf. She has only one calf at a time, or maybe two,
but each calf has an excellent chance of surviving to adulthood.
In the field of ecology, this sort of reproductive strategy is known as an
equilibrium strategy. That is because species that employ this strategy tend to have stable populations, and they are unlikely to overpopulate. That is, they tend to remain in a state of equilibrium with their environments.
Populations with equilibrium reproductive strategies tend to show what is known as a
logistic growth curve. When the population is small and resources are relatively abundant, the population’s growth rate is relatively high. As the population size approaches the carrying capacity, the growth rate begins to slow. This is because there are fewer resources available per individual, and so fewer offspring are produced, on average.
The result is that the population stabilizes at or near the carrying capacity, and there is little fluctuation in the population’s size from then on, so long as the environment remains stable.
Populations of species with equilibrium reproductive strategies tend to
experience logistic growth. The population stabilizes at or near the
carrying capacity, and then remains in a state of equilibrium.
Invest Much, Produce Few
Linear Mode
