Age‐specific reproduction in relation to body size and condition in female Eurasian beavers

Abstract

AbstractBasic information on patterns and correlates of growth and reproduction are essential for understanding a species’ life history strategy. For the Eurasian beaver (Castor fiber), knowledge of life history is fragmentary and correlates of growth and reproduction unstudied. We related measures of somatic fitness including growth rate, body size (length), body condition (fat) and body mass to measures of reproductive investment including fecundity (number of corpora lutea (CL) and fetuses), age‐specific reproduction, age of primiparity and parturition date in 59 female beavers culled from mid‐March to mid‐May in south‐east Norway. Increase in body length ceased after age three. Primiparity at ages two and three was related to body length and mass, but not fat. Postponed primiparity beyond age two was common. Fecundity was significantly higher in fatter individuals and showed a trend to increase with age. For females ≥age three, those pregnant were significantly fatter than barren individuals. Intermittent years of non‐breeding were common among sexually mature females. The mean number of CL and fetuses alive at the females time of death among 32 pregnant individuals was 3.0 ± 0.9 (range 1–6) and 2.3 ± 0.9 (range 1–4) respectively. Females conceiving at the normal peak time in late January were significantly heavier than individuals that conceived 1–3 months later. Late breeders, however, had significantly more CL, possibly because the improved nutrient levels provided by early spring growth led to higher ovulation rates. Fat accumulated during summer and autumn prior to winter breeding appears to be an important determinant of reproduction in female beavers.