The terms r-selection and K-selection have also been used by ecologists to describe the growth and reproductive strategies of various organisms. Those organisms described as r-strategists typically live in unstable, unpredictable environments. Here the ability to reproduce rapidly exponentially is important. Such organisms have high fecundity glossary and relatively little investment in any one progeny individual, they are typically weak and subject to predation and the vicissitudes of their environment.
Organisms that are r-selected have short life spans, are generally small, quick to mature and waste a lot of energy. Typical examples of r-strategists are. K-strategists , on the other hand occupy more stable environments. They are larger in size and have longer life expectancies.
They are stronger or are better protected and generally are more energy efficient. They produce, during their life spans, fewer progeny, but place a greater investment in each. Their reproductive strategy is to grow slowly, live close to the carrying capacity of their habitat and produce a few progeny each with a high probability of survival.
Typical K-selected organisms are elephants, and humans. In one family, with ten children, for example, there is no way for the parents to put as much time, energy, or resources into all of them as could be done with an only child. But, with humans, it gets complicated by the fact that others, including siblings, grandparents, blood-relatives, and the larger community all play a role in the nurturing and education of children. Even plants are capable of r- and K-selected reproductive strategies.
Wind pollinated species produce much more pollin that insect pollinated ones, for example, because the pollin has to be carried at random by the wind to a receptive female flower. Eggs too, can be r- or K-selected. The amount of nutrient energy placed in an egg gives it a lesser or greater ability to survive in adverse conditions. One can even compare the reproductive stragies of males and females within a species, when sperm and egg represent different levels of energy investment. Often sperm are resource poor, and produced in large quantities, while eggs are resource rich and produced in smaller numbers.
This can lead to differences in behavior between the sexes, often with the result that the female is the choosier sex when it comes to reproduction. This trend is further extended if the female also carries the young in the case of internal fertilization or has a greater role in parental care once the babies are born.
There are some interesting exceptions that illustrate the rule. Male seahorses are the choosier sex, and they are the ones that incubate the young.
In a small fish called the stickleback, the male is also choosier, it is believed, because the female lays her eggs in a nest he constructed and then leaves. The male guards the nest and tends the young for an extended period. It should be noted that r- and K-selection are the extremes at both ends of a continuum and that most species fall somewhere inbetween. Here the ability to reproduce rapidly exponentially is important.
Such organisms have high fecundity glossary and relatively little investment in any one progeny individual; they are typically weak and subject to predation and the vicissitudes of their environment. Organisms that are r-selected have short life spans, are generally small, quick to mature and waste a lot of energy. K-selected species , also called K-strategist , species whose populations fluctuate at or near the carrying capacity K of the environment in which they reside. K-selected species possess relatively stable populations and tend to produce relatively low numbers of offspring; however, individual offspring tend to be quite large with high probability of survival in comparison with r-selected species.
K-selected species are characterized by long gestation periods lasting several months, slow maturation and thus extended parental care , and long life spans.
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