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Phenologic Influences on Cohort‐Specific Reproductive Strategies in Mice (Peromyscus Polionotus)

Dapson, Richard W.
Ecology 1979 v.60 no.6 pp. 1125-1131
Peromyscus polionotus, breeding season, females, lactation, litter size, mice, models, mortality, risk
Breeding seasons and birth cohorts were defined for two populations of mice (Peromyscus polionotus). Cohort—specific differences in reproductive effort were correlated with residual reproductive value. In one population, mice lived nearly 2 yr, reproduced at moderate rates, and showed few differences in cohort—specific reproductive strategy. Mice from the other population lived <1 yr, and spring—, summer—, and fall—born females exhibited markedly different reproductive strategies. Cohorts able to breed in a future season had moderate reproductive efforts, which did not increase risk of mortality. Extraordinary efforts (being pregnant and lactating simultaneously), which seriously increased mortality rate, were undertaken when residual reproductive value became zero. Nestling mortality increased with litter size when there were more than three young per litter, but larger litters still resulted in more weaned young than did smaller litters. These observations provide additional confirmation of the model of Pianka and Parker (1975). It is possible that populations of very short—lived mammals characteristically have seasonal cohorts operating under different reproductive strategies.