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At 11:54 AM 18/02/02 -0800, Grant wrote:
>That seems like a very abstract way of putting it. What do the letters
>"k" and "r" stand for?
One set of life history theories considers species to fall into one of two
categories: r-selected or K-selected (the overall model is called r-K
selection.) The terms r and K come from logistic growth: r refers to the
per capita rate of population increase and K refers to the carrying
capacity. Here's how they apply to life history evolution:
Some species will occur in environments that have some kind of
unpredictable disturbance, from a factor such as weather, causing
unpredictable adult mortalities. Such species will rarely have populations
grow to carrying capacity, because disturbance will decrease population
size regularly. Such species are predicted by r-K selection to evolve
traits that result in rapid reproduction, and give a high value of the
maximum instantaneous per capita population growth rate rm. Such species
are termed r-selected.
Other species will occur in constant environments, and will grow to the
carrying capacity (K.) At carrying capacity, there is a high level of
intraspecific competition for resources. Species in such conditions are
predicted to evolve traits that result in high competitive ability of
adults and offspring, and are termed K-selected.
The following table shows how r and K selection are predicted to affect
life history traits:
r-K selection has been applied in two ways:
large groups of species have been categorized as r-selected vs. K-selected.
For example, insects have been called r-selected, mammals K-selected. A
problem with this is that there are other reasons for differences between
species besides variability versus constancy of the environment. Insects
are all small because have exoskeleton; mammals can not be that small
because they are endothermic. These size differences affect other aspects
of life history (age at maturity, etc.)
closely related species, or populations of a species, have been categorized
as relatively more r or K selected. Since close relatives are likely to be
similar in many ways, this can allow better testing of whether the
differences in life history really reflect differences in environmental
variability, as predicted by r-K selection.
>Social standing is just as important in my view as resources, although
>people with high social standing usually have access to more resources.
You could almost view high social standing as a resource itself. Keith Henson
>I remember the marxist societies of China and Eastern Europe where
>salaries were pretty much fixed and not too far apart that social standing
>got one limosines to travel around in and a lot of privileges as far as
>things such as dachas in russia and superior housing in China. You don't
>have to own something if you have unlimited use of it.
>Just the privilege of going to the head of the line was worth a lot in the
>I'll have to get my hands on the book to see how the formula applies to
>situations like that. Maybe William Calvin covers it in one of his books
>on cultural evolution. Thanks for the tip.
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