Wolf predation in a multiple-ungulate system in northern British Columbia

Caribou (Rangifer tarandus), elk (Cervus canadensis), moose (Alces alces), and Stone's sheep (Ovis dalli stonei) were either decreasing or stable in n umbers in two areas in northeastern British Columbia in 1981-1982, prior to reductions in wolf (Canis lupus) numbers. Following the reduction of wolf numbers, recruitment improved 2-5 times for all four species, and all popul ations increased, based! on either hunting statistics, census results, and (or) recruitments greater than 24 offspring at 9 months of age per 100 fema les. Recruitment of offspring at 9 months of age, when regressed against wo lf numbers, declined with decelerating slopes for all four species. This in verse functional response is hypothesized to result from the preparturient spacing of females to reduce predation risk, and in this regard moose seem the least secure and sheep the most effectively spaced. For the four specie s, mean recruitment at 9 months of age that balanced adult mortality and pr ovided a finite rate of increase of 1.00 was 24.16 +/- 0.91 offspring/100 f emales (n = 11, coefficient of variation = 12.5%). The predicted recruitmen t rate for all four species in the absence of wolves was 53-57 offspring/10 0 females. But the birth rate of moose was much higher than those of the ot her species, indicating greater loss to other factors of which bear predati on may be the greatest. Following wolf reductions of 60-86% of entire trave lling packs, the wolves quickly recolonized the removal zones, with rates o f increase ranging from 1.5 to 5.6.