Evolutionary Aspects of Demographic Cycles: The Relevance of Some Models of Cycles for Microtine Fluctuations

Abstract

Evolutionary aspects of some current theories for regular density oscillations are discussed. General problems in testing fitness differences are briefly discussed. It is pointed out that two different interpretations of Chitty's theory are common in literature: One states that regular density oscillations are caused by genetically based behavioural polymorphism in the absence of extrinsic changes; the other that regular cycles are the result of the interaction between genetic changes and extrinsic factors. Only the latter is concluded plausible. However, further empirical research attempting to test the hypothesized lower general fitness of the aggressive strategies is needed. Genetic changes in parasites may, on the basis of preliminary theoretical studies, be presumed likely to result in cycles. More experimental work is needed before any conclusions can be drawn. Genetic feedback interactions between predator-prey interactions are likely to be rejected as unimportant for generating limit cycles. Exceptions may be predator-prey interactions in simple habitat complexes and possibly in the optimal area of the prey's distribution range. Female biased sex ratios is discussed: It is concluded that female biased sex ratios are likely to be a result of both evolutionary and ecological forces. It is suggested that the study of skewed sex ratios may be rewarding for the study of microtine cycles.