Need to - increase due to limitation of number of nest...

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Need to distinguish between individual fitness and population fitness . wbar is a description of the average fitness of all individuals in the population. Does this determine the fitness of the population? If we think of the population as the unit of "survival" a population with high fitness is one that has a high tendency to out reproduce other populations . This is largely a demographic question since drought, predators, parasites, etc. could alter a populations' probability of survival irrespective of the number of individuals it is producing each generation. A highly fit population is one that has a high reproductive output or is unlikely to go extinct. These qualities can be unrelated to the average fitness in the population (although they can be related). Consider wasps living in nest holes . Population is limited by a fixed number of nest holes. Now a mutation occurs that doubles the egg output of individuals carrying the mutation. Those individuals with mutation are more fit, but the population will not
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Unformatted text preview: increase due to limitation of number of nest holes. Consider prey switching in birds: mutation increases the fecundity of a moth. More caterpillars present, birds switch their search image and prey more heavily on the abundant caterpillars: reduces population size clearly the population is less fit. These examples have assumed that population size is some measure of average fitness May not be the case depending on the mode of selection: Soft versus hard selection . Soft selection is like grading on a curve: there are always a certain number of As (or F's). Regardless of the absolute fitness of individuals or the population the "better" ones will survive to fill those spots. Hard selection assumes some threshold level of "fitness" that could be set by the environment. If all individuals are below this level, population crashes; if all are above, population grows....
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