LIFE-HISTORY PATTERNS IN FEMALE MOOSE (ALCES-ALCES) - THE RELATIONSHIP BETWEEN AGE, BODY-SIZE, FECUNDITY AND ENVIRONMENTAL-CONDITIONS

I examined the relationship between age, body size and fecundity in 83 3 female moose (Alces alces) from 14 populations in Sweden sampled dur ing 1989-1992. Data on population density food availability and climat ic conditions were also collected for each population. Age and body ma ss were both significantly positively related to fecundity, measured a s ovulation rate, among female moose. The relationship between the pro bability of ovulation and body mass was dependent on age with (1) a hi gher body mass needed in younger females for attaining a given fecundi ty, and (2) body mass having a stronger effect on fecundity in yearlin g (1.5 year) than in older (greater than or equal to 2.5 year) females . Thus, a 40 kg increase in yearling body mass resulted in a 42% incre ase in the probability of ovulation as compared to a 6% increase in ol der females. The lower reproductive ef fort per unit body mass, and th e relatively stronger association between fecundity and body mass in y oung female moose compared to older ones, is likely to primarily repre sent a mechanism that trades off early maturation against further grow th, indicating a higher cost of reproduction in young animals. In addi tion to age and body mass, population identity explained a significant amount of the individual variation in fecundity, showing that the rel ationship between body mass and fecundity was variable among populatio ns. This variation was in turn related to the environment, in terms of climatic conditions forcing female moose living in relatively harsh/m ore seasonal climatic conditions to attain a 22% higher body mass to a chive the same probability of multiple ovulation (twinning) as females living in climatically milder/less seasonal environments. The results suggests that the lower fecundity per unit body mass in female moose living in climatically harsh/more seasonal environments may be an adap tive response to lower rates of juvenile survival, compared to females experiencing relatively milder/less seasonal climatic conditions.