Crowding And Reproductive Rates In Planaria
Posted 07 April 2012 - 11:22 AM
"E. N. Smith has reported on his study of the effect of crowding on asexual reproduction of the planaria Dugesia dorotocephala. (37) As Smith pointed out, there are two possible mechanisms for regulating population densities. Individuals within a population might reproduce maximally near their physiological limit, with the population density being regulated by negative outside forces (predation, disease, starvation, etc.). Those individuals which are better able to compete against these outside forces and reproduce more offspring are said to be more fit and thus to be selected. Alternately, the individuals within a population might possess some internal regulating force which in some way regulates population density and maintains a form of density homeostasis.
Evolutionists generally prefer the former view. Natural selection is said to favor the individuals that can leave the most reproducing offspring. On the other hand, if the alternate view is correct, there would be no real competition between populations and no selection. The postulated cause of the evolutionary process would fail.
The freshwater planaria, Dugesia dorotocephala, reproduce asexually by fissioning. Smith maintained the planaria in identical containers, and conditions in each experiment were the same in each container, except the population density was maintained at different levels. Smith found that crowding clearly reduced the fissioning rate of the planaria. This reduction did not appear to be due to slime, oxygen depletion or carbon dioxide build-up, but appeared to be due to some water-soluble inhibitor produced by the planaria.
The planaria thus appeared to have a built-in density-dependent reproduction regulatory mechanism. Smith postulated that these creatures (and other animals) regulate their own numbers without the necessity of outside forces such as predation, starvation, and disease. He pointed out that built-in density dependent reproduction rates were mandatory after creation and before the fall, and that it is quite conceivable that living organisms had a mechanism for regulating their numbers without intervention of external conditions such as predation, starvation and disease."
Posted 07 April 2012 - 11:44 AM
In the human situation, the choice is often made to limit the number of children in order to advance the chances of the children one does actually have. Doesn't such a choice make some kind of sense?
Posted 07 April 2012 - 01:47 PM
Posted 07 April 2012 - 02:18 PM
I don’t believe that is analogous Paul, as humans have the wherewithal to use birth controlling initiatives, but gazelles on the other hand, do not possess this capability.
You have a point there. Perhaps, in the case of Gazelles, it is the Lions themselves that God uses to keep the herds down to where they remain healthy.
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