Departures from Classic Theory

The power oflife-history theory to predict observed patterns has been immense. Life-history models have been able to predict patterns of variation in traits such as age at maturity, number of offspring produced, life span, and the relative production of sons versus daughters. However, empirical support for predicted life-history patterns is sometimes equivocal. Phylogenetic history of a taxonomic group will often constrain the response to selection. For example, we would not expect to see an oak produce a single large acorn or a whale produce many tiny offspring. Furthermore, the detection oftradeoffs can be elusive, particularly in organisms with complex life-history traits (such as indeterminate growth, metamorphosis, or alternative reproductive tactics). In many cases, tradeoffs occur among a suite of life-history traits, which may become empirically intractable.

Environmental and genetic variation can also mask expected tradeoffs. In 1986, van Noordwijk and de Jong showed that variation in acquisition of resources will lead to undetected tradeoffs if that variation is greater than the variation in allocation. A common metaphor for this argument is the observation that people with big houses often drive expensive cars. We do not detect a tradeoff between size of house and size of car because variation in income in the population is so great. This idea has been largely successful in explaining deviations from expected life-history tradeoffs.

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