K-selected

In ecology, r/K selection theory relates to the selection of traits which promote success in particular environments. The theory originates from work on island biogeography by the ecologists Robert MacArthur and E. O. Wilson[1].

Overview

In r/K selection theory, selective pressures are hypothesised to drive evolution in one of two generalized directions: r- or K-selection[2]. These terms, r and K, are derived from standard ecological algebra, as illustrated in the simple Verhulst equation of population dynamics[3]:



where r is the growth rate of the population (N), and K is the carrying capacity of its local environmental setting. Typically, r-selected species exploit empty niches, and produce many offspring, each of whom has a relatively low probability of surviving to adulthood. In contrast, K-selected species are strong competitors in crowded niches, and invest more heavily in much fewer offspring, each of whom has a relatively high probability of surviving to adulthood.

r/K selection and environmental stability

r-selection

In unstable or unpredictable environments r-selection predominates, as the ability to reproduce quickly is crucial, and 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, 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.

K-selection

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. 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, humans and whales, but smaller organisms also use this "strategy" successfully, such as Arctic Terns.

r/K as a continuous spectrum

It should be noted that, although some organisms are primarily r- or K-strategists, the majority of organisms fall between these two ecological extremes and may display traits considered characteristic of both ends of the r/K spectrum. For instance, trees have traits such as longevity and strong competitiveness that characterise them as K-strategists. In reproduction, however, trees typically produce thousands of offspring and disperse them widely, traits characteristic of r-strategists. Similarly, reptiles such as sea turtles display both r- and K-traits: although large organisms with long lifespans (should they reach adulthood), they produce large numbers of unnurtured offspring.

Ecological succession

In areas of major ecological disruption or sterilisation (such as after a major volcanic eruption, as at Krakatoa or Mount Saint Helens), r- and K-strategists play distinct roles in the ecological succession that regenerates the ecosystem. Because of their higher reproductive rates and ecological opportunism, primary colonisers typically are r-strategists and they are followed by a succession of increasingly competitive flora and fauna. The ability of an environment to maximise entropy, through photosynthetic capture of solar energy, increases with the increase in complex biodiversity as r species proliferate to reach a peak possible with K strategies[4]. Eventually a new equilibrium is approached (sometimes referred to as a climax community), with r-strategists gradually being replaced by K-strategists which are more competitive and better adapted to the emerging micro-environmental characteristics of the landscape. Typically, biodiversity is maximised at this stage, with introductions of new species resulting in the replacement and local extinction of endemic species[5].

See also

References

1. ^ MacArthur, R. and Wilson, E. O. (1967). The Theory of Island Biogeography, Princeton University Press (2001 reprint), ISBN 0-691-08836-5M.
2. ^ Pianka, E. R. (1970). On r and K selection. American Naturalist 104, 592-597.
3. ^ Verhulst, P. F. (1838). Notice sur la loi que la population pursuit dans son accroissement. Corresp. Math. Phys. 10, 113-121.
4. ^ Gunderson, Lance & Holling, C. S. (Eds) (2001), "Panarchy: Understanding Transformations in Human and Natural Systems" (Island Press)
5. ^ McNeely, J. A. (1994) Lessons of the past: Forests and Biodiversity. Biodiversity and Conservation 3, 3-20.
Ecology (also known as Oekologie, Okology, or Oekology[1],from Greek: οίκος, oikos, "household"; and λόγος, logos
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Natural selection is the process by which favorable traits that are heritable become more common in successive generations of a population of reproducing organisms, and unfavorable traits that are heritable become less
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character is an attribute of an organism that allows it to be compared with another. In genetics this refers to heritable features which can exist in more than one state.[1] A trait
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The study of island biogeography is a field within biogeography that attempts to establish and explain the factors that affect the species diversity of a particular community.
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Robert Helmer MacArthur (April 7, 1930 – November 1, 1972) was an American ecologist who made a major impact on many areas of community and population ecology.

MacArthur received a Master's degree in mathematics from Brown University (1953). A student of G.
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Edward Osborne Wilson (born June 10, 1929) is an American biologist (Myrmecology, a branch of entomology), researcher (sociobiology, biodiversity), theorist (consilience, biophilia), and naturalist (conservationism).
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A hypothesis (from Greek ὑπόθεσις) consists either of a suggested explanation for a phenomenon or of a reasoned proposal suggesting a possible correlation between multiple phenomena.
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In mathematics, an ordinary differential equation (or ODE) is a relation that contains functions of only one independent variable, and one or more of its derivatives with respect to that variable.
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Population dynamics is the study of marginal and long-term changes in the numbers, individual weights and age composition of individuals in one or several populations, and biological and environmental processes influencing those changes.
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Population growth is the change in population over time, and can be quantified as the change in the number of individuals in a population per unit time. The term population growth
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population is the collection of people or organisms of a particular species living in a given geographic area or mortality, and migration, though the field encompasses many dimensions of population change including the family (marriage and divorce), public health, work and the
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The equilibrium maximum of the population of an organism is known as the ecosystem's carrying capacity for that organism. Generally it is the supportable population of an organism, given the food, habitat, water and other necessities available within an ecosystem.
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niche (pronounced nich, neesh or nish)[] is a term describing the relational position of a species or population in its ecosystem[1]. The ecological niche describes how an organism or population responds to the distribution of resources and competitors (e. g.
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offspring are the product of reproduction, a new organism produced by one or more parents.

Collective offspring may be known as a brood or progeny in a more general way.
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In evolutionary biology, parental investment (PI) is any parental expenditure (time, energy etc.) that benefits one offspring at a cost to parents' ability to invest in other components of fitness (Clutton-Brock 1991: 9; Trivers 1972).
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Fecundity, derived from the word , generally refers to the ability to reproduce. In biology and demography, fecundity is the potential reproductive capacity of an organism or population, measured by the number of gametes (eggs), seed set or asexual propagules.
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Biological dispersal refers to those processes by which a species maintains or expands the distribution of a population. Dispersal implies movement—movement away from an existing population (population expansion) or away from the parent organism (population maintenance).
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Bacteria

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Actinobacteria
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Orders
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Diatoms (Greek: διά (dia) = "through" + τέμνειν
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Linnaeus, 1758

Orders
Subclass Apterygota
* Archaeognatha (bristletails)
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Subclass Pterygota
* Infraclass Paleoptera (Probably paraphyletic)

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Cuvier, 1797

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Bowdich, 1821

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Homo.
Upper Paleolithic 33 At age 15: 39 (to age 54)[3][4]
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