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10 February 2006
Quiz: (Gaspode not allowed to answer.) What is the minimum number of individuals of a non-hermaphroditic sexually reproducing species required to establish a geographically isolated population of that species? Explain your answer.
3. 1 male and 2 females. I'm ignoring the dangers of inbreeding, because any kinks in genetic makeup should get ironed out after a lot of generations. It may not be exactly the same species, but given that the place is geographically isolated, there's bound to be a degree of evolutionary drift. I include a second female as a backup (childbirth is a dangerous thing) and to help with the child rearing.
The actual number of individuals in a population is not necessarily a good indication of a population’s genetic viability; rather, the EPS is critical. The EPS is the size of an "ideal" population in which genetic drift takes place at the same rate as in the actual population. The inbreeding coefficient should be limited to no more than 1 percent per generation, a figure which implies that maintenance EPS, in the short term, should be no fewer than 50 individuals. Because the EPS is typically only one-third to one-fourth the actual population size (being affected by sex ratio, overlapping generations, generally nonrandom distribution of offspring, and nonrandom mating), a population of 150 to 200 individuals is needed for short-term population maintenance. For long-term viability, an EPS of 500 individuals is necessary, translating into a population size of 1,500 to 2,000 individuals.
Is that true for all (non-hermaphroditic sexually reproducing)species? Would the size of a clutch or litter, or the gestation period, or other variables I don't know of, significantly change the starting number?
Now that I'm officially over 40, I'm excused from childbearing duties on Metachat Island. I will, however, be available for auntly duties such as teaching them dirty words, encouraging them to bang coconuts together as much as possible, and letting them eat bugs.
Is that true for all (non-hermaphroditic sexually reproducing)species? Would the size of a clutch or litter, or the gestation period, or other variables I don't know of, significantly change the starting number?
There are several species that are suspected to be descended from a single pregant female. Cheetas for example have such low genetic variation that skin grafts from different animals are never rejected. Some believe that cheetas are doomed to extiction because they are so inbred.