>From a lecture on populations by Dr. Stephen T. Abedon
http://www.mansfield.ohio-state.edu/mans/microbio/biol1540.htm
"a very important equation:
A differential equation approximating the sigmoidal growth curve of an ideal
population is:
dN/dt = rN(K - N) / K
where r is the intrinsic rate of population growth, K is the carrying
capacity of the environment, N is the number of individuals present in a
population, and t is time.
For those of you haven't had calculus, dN/dt stands for instantaneous change
in N as a function of t, a slope.
Thus, using this equation one can determine the instantaneous rate of
increase of a reasonably well behaved population (change in N as a function
of time) so long as one has knowledge of the population's biotic potential,
actual size, and the carrying capacity of the environment in which the
population lives.
r strategist ---
adapted to exponential increases:
An organism which is particularly well adapted to an exponential increase in
population size is know as an r strategist (the r coming from the
differential equation described above).
r strategists are characterized by great rapidity in their developmental
programs combined with an ability to produce large numbers of offspring.
No organism is a pure r strategist. Most show at least some capacity to
survive at equilibrium, i.e., in carrying capacity situations.
pioneer species:
r strategists tend to be particularly good at finding disturbed environments
and then rapidly producing large numbers of progeny in such environments.
Often those offspring are ill-equipped for survival except under optimal
conditions because of the small amount of parental resource put into their
survival. However, the large numbers produced tend to both make up for low
survivorship as well as allow for great dispersal.
Wide dispersal allows at least some fraction of progeny to find and
therefore exploit newly disturbed habitats.
weeds:
A plant which is an r strategists more likely than not we would call a weed.
k strategist ---
adapted to limitation:
In contrast to r strategists, many organisms show extreme potential to
survive and prosper at or near carrying capacity, though often at the
expense of their ability to display rapid population increases under most
circumstance (i.e., their intrinsic rate of population growth is small).
Such organisms are called K strategists.
The variable K refers to carrying capacity (i.e., they display a bias in
their adaptations toward maximizing carrying capacity).
adaptation to climaxed ecosystems:
K strategists tend to be very good at surviving in mature (climaxed) ecosystems.
low fecundity:
K strategists also tend to put a great deal of resource into raising only a
few young.
example: gorilla:
A gorilla is a K strategist."
Regards,
Tom Walker
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