Social Organization and Effective Population Size in Carnivores

Abstract

Abstract Real populations rarely match the assumptions of population genetic theory. The concept of effective population size (N e) was developed to describe how a population can lose genetic variability (through genetic drift) more quickly than would be predicted by population size alone (Wright, 1931, 1938, 1943). Effective population size is defined as the size of an ideal population that would lose genetic variation at the same rate as a given real population (Wright, 1969; Lande and Barrowclough, 1987). In this definition, an ideal population meets five assumptions: (1) population size is constant through time, (2) the number of breeding males and females are equal, (3) individuals’ reproductive success is Poisson distributed, (4) individuals mate at random, and (5) generations do not overlap. Because few real populations meet these assumptions, Ne is usually lower than the censused population size (Nunney and Elam, 1994). Quantitative methods exist to measure the reduction in Ne when each assumption is not met (Wright, 1943,1969; Crow and Kimura, 1970; Lande and Barrowclough, 1987) and these methods are well developed in theory (Wright, 1943,1969; Crow and Kimura, 1970; Lande and Barrowclough, 1987), but they are not often applied to data from the wild. A recent review by Nunney and Elam (1994) includes estimates of Ne for 14 species, with only one carnivore (the grizzly bear Ursus horribilis’. Harris and Allendorf, 1989) and one endangered species (the spotted owl Strix occidentalis).