Extreme Individuals in Natural Populations

Extreme individuals (for example, the peripheral 5% or less of the population) may have specific adaptive values, particularly in unpredictable environments. The extremes, stemming from broad, especially asymmetrical, variation or from genetic polymorphism, may therefore be actively selected, rather than reflecting simply general variation about some mean value, or environmental and genetic accidents. Evidence from several fields of entomology supports this possibility. Consideration of extreme variants may contribute important information about the structure of populations. The potential significance of extreme variation should therefore be considered explicitly during ecological experiments of all kinds, rather than dismissed routinely when central measures such as the mean are emphasized.