Individual Variation
Slide 20 of 47
All the models examined so far assume that each animal in the population has exactly the same chance of survival and reproducing, even though these rates are changing with time. What happens if each animal in the population has a different rate of survival and reproduction? Differences between the individuals in the population are termed individual heterogeneity, and creates €individual variation€. Many studies have demonstrated individual heterogeneity of individual survival and reproductions, e.g., Clutton-Brock (1982) demonstrated lifetime reproductive success of female red deer (€Cervus elaphus€) varied from 0 to 13 calves reared per female. Differences in the frequency of calf mortality between mothers accounted for a larger proportion of variance in success than differences in fecundity. Bartmann et al. (1992) demonstrated that overwinter survival of mule deer fawns was a function of the fawn’s weight at the start of the winter, with larger fawns showing better survival.
Individual variation is caused by €genetic variation€, i.e., differences between individuals because of their genome. However, €phenotypic variation€ is also possible. Animals that endure poor nutrition during their early development may never be as healthy and robust as animals that are on a higher nutritional plane, even though both are genetically identical. Animals with access to more and better resources have higher reproductive rates, e.g., red deer (€Cervus elaphus€) (Clutton-Brock et al. 1982). Thus, individual heterogeneity may result from both genetic and phenotypic variation. €omnicki (1988) develops models of resource partitioning that result in phenotypic variation of individuals.
