From: Rafal Smigrodzki (rafal@smigrodzki.org)
Date: Tue Aug 05 2003 - 13:42:06 MDT
BillK wrote:
>
> There are two basic strategies for populations, r-Strategists and
> K-Strategists.
>
> r-strategists
>
> The r-strategists approach to continued survival is through rapid
> reproduction, i.e., a high value of r. In fact, if we consider an
> organism a pest, it is probably an r-strategist.
>
> In general r-strategists share a number of features:
>
> 1. They are usually found in disturbed and/or transitory habitats.
> 2. They have short life spans. The house mouse, with a maximum life
> span of 3 years, is an r-strategist.
> 3. They begin breeding early in life.
> 4. They usually have short generation times; that is, they have short
> gestation periods and are soon ready to produce another crop of young.
> The housefly can produce 7 generations each year (each of about 120
> young).
> 5. They produce large numbers of offspring. The American oyster,
> releasing a million eggs in one season, is an r-strategist. Most of
> its offspring will die, but the sheer size of its output increases the
> likelihood that some offspring will disperse to new habitats.
> 6. They take little care of their offspring, and infant mortality is
> huge. Although humans are not r-strategists, the higher reproductive
> rate in countries like India may well be a response to the higher
> rates of infant mortality.
> 7. They have efficient means of dispersal to new habitats.
>
> For r-strategists, alleles that enhance any of the traits listed above
> will be favored by natural selection.
>
>
>
> K-strategists
>
> When a habitat becomes filled with a diverse collection of creatures
> competing with one another for the necessities of life, the advantage
> shifts to K-strategists. K-strategists have stable populations that
> are close to K (the maximum population an environment can support).
> There is nothing to be gained from a high r. The species will benefit
> most by a close adaptation to the conditions of its environment.
> Typically, K-strategists share these qualities:
>
> 1. They are usually found in stable habitats. Most of the species in a
> mature forest will be K-strategists.
> 2. They have long life spans. The elephant and the tortoise are
> K-strategists.
> 3. They begin breeding later in life.
> 4. They usually have long generation times. It takes 9 months to
> produce a human baby.
> 5. Most produce small numbers of offspring. Birds are K-strategists,
> most species producing fewer than a dozen young each year.
> 6. They take good care of their young. Infant mortality tends to be
> low.
> 7. K-strategists typically have evolved in such a way that they become
> increasingly efficient at exploiting an ever-narrower slice of their
> environment. Thus it is not surprising that many endangered species
> are K-strategists.
>
> For K-strategists, alleles that enhance their ability to exploit the
> resources of their habitat; that is, to increase the carrying
> capacity, K, of their environment, will be favored by natural
> selection.
>
### This is a neat story. But, there is no quantified difference between the
two strategists, all the differences are given in qualitative terms (long,
short, large, small). If you only change the scale a bit, you can no longer
decide whether a given organism is a k- or r-strategist. Say, E.coli, once
the nutrients are scarce, starts changing its metabolism, no longer produces
a lot of offspring, waits long to breed, is more efficient at using
resources...etc, compared to the log-phase cell. A human family placed in
Pleistocene America starts breeding at a crazy rate, overrunning the
continent in a few hundred years, in stark contrast to the slow growth of
human lineages with established competition.
Basically, an r-strategist is a k-strategist in optimal circumstances, with
no competition. A k-strategist is an r-strategist in lean times.
No basis for assuming any strategy as universal among space-capable civs.
Rafal
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