Darwinian fitness

Abstract

The term Darwinian fitness refers to the capacity of a variant type to invade and displace the resident population in competition for available resources. Classical models of this dynamical process claim that competitive outcome is a deterministic event which is regulated by the population growth rate, called the Malthusian parameter. Recent analytic studies of the dynamics of competition in terms of diffusion processes show that growth rate predicts invasion success only in populations of infinite size. In populations of finite size, competitive outcome is a stochastic process--contingent on resource constraints--which is determined by the rate at which a population returns to its steady state condition after a random perturbation in the individual birth and death rates. This return rate, a measure of robustness or population stability, is analytically characterized by the demographic parameter, evolutionary entropy, a measure of the uncertainty in the age of the mother of a randomly chosen newborn. This article appeals to computational and numerical methods to contrast the predictive power of the Malthusian and the entropic principles. The computational analysis rejects the Malthusian model and is consistent with of the entropic principle. These studies thus provide support for the general claim that entropy is the appropriate measure of Darwinian fitness and constitutes an evolutionary parameter with broad predictive and explanatory powers.

Genomic sweep and potential genetic rescue during limiting environmental conditions in an isolated wolf population

“…These challenges for assessing genetic rescue-the relational nature of fitness and the time required for powerful tests of vital rates-might be overcome by reconsidering the definition of and standards for assessing genetic rescue. Consider, for example, that fitness 'refers to the capacity of a variant type to invade and displace the resident population in competition for available resources' [44] and that genetic rescue be quantified by this capacity. By these principles, the strength of genetic rescue's influence is quantified by the dramatic increase in the ancestry of the immigrant(s) ( figure 2).…”

Toward a general theory of evolution: Extending Darwinian theory to inanimate matter

“…In fact the difficulty in quantifying DKS is clearly reflected in attempts over many years to quantify the biological equivalent of DKS -'fitness', one that began with Fisher's use of the Malthusian parameter [44]. Since that early proposal, different fitness kinds have been suggested -relative fitness, inclusive fitness, individual fitness, population fitness, and different empirical measures of that parameter have been offered, reflecting the intrinsic difficulty in quantifying the fitness concept [45,46]. All these different quantification proposals may in a sense be viewed as attempts to square the circle.…”

Selection Against Demographic Stochasticity in Age-Structured Populations

“…Demetrius and colleagues (Demetrius and Gundlach 1999;Demetrius and Ziehe 2007) derived diffusion equations for selection on genotypes in age-structured populations where contributions of the second and higher moments in growth rate appear in the diffusion and drift coefficients. The equations they derived, in terms of first and second moments, had the same form as in Equations 1 and 2.…”