(21) Discuss the difference between a R selected species and a K selected species. Give an example of an organism in each group.

A. (See table 12.1 in lecture notes)
An example of a R selected species is salmon. An example of a K selected species is human.

B.R-strategists are short lived, have high reproductive rates, rapid development, small in size, large number of offspring, and minimal parental care. Some r-strategists have wide dispersal, are good colonizers, and respond rapidly to disturbance. K-strategists are competitive species with stable populations of long lived individuals. They have slower growth rate at low populations, but they maintain growth rate at high densities. K-strategists can cope with physical and biotic pressures. They have late reproduction and have large body size and slow development. They also have few offspring and usually care for the offspring. They are efficient users of a particular environment, but their populations are at near carrying capacity and resources are limited. They lack the means for wide dispersal making them poor colonizers.
An example of a K-selected specie is whales. Whales are long lived and have small populations. Whales have very few offspring and take care of their offspring. They grow and mature over a long period of time. They reproduce at a later age when mature. An example of an R-selected are rats because they often have large litters and are always fertile. They don’t live long, grow fast, have large populations, and have rapid growth.

C. R selected species tend to have short life spans and large clutches. Examples of these include mice and frogs. K selected species tend to have long lives and long juvenile periods as well as only one child at a time an example is tortoises.

D.http://en.wikipedia.org/wiki/R/K_selection_theory


r-selection (unstable environments)
In unstable or unpredictable environments, r-selection predominates as the ability to reproduce quickly is crucial. There is little advantage in adaptations that permit successful competition with other organisms, because the environment is likely to change again. Traits that are thought to be characteristic of r-selection include: high fecundity, small body size, early maturity onset, short generation time, and the ability to disperse offspring widely. Organisms whose life history is subject to r-selection are often referred to as r-strategists or r-selected. Organisms with r-selected traits range from bacteria and diatoms, through insects and weeds, to various semelparous cephalopods and mammals, especially small rodents.

[edit] K-selection (stable environments)
In stable or predictable environments, K-selection predominates as the ability to compete successfully for limited resources is crucial and populations of K-selected organisms typically are very constant and close to the maximum that the environment can bear (unlike r-selected populations, where population sizes can change much more rapidly). Traits that are thought to be characteristic of K-selection include: large body size, long life expectancy, and the production of fewer offspring that require extensive parental care until they mature. Organisms whose life history is subject to K-selection are often referred to as K-strategists or K-selected. Organisms with K-selected traits include large organisms such as elephants, trees, humans and whales, but also smaller, long-lived organisms such as Arctic Terns.