Effects of ungulate availability on wolf reproductive potential in Alaska

Abstract

We compared wolf (Canis lupus) reproductive data for March and April, when ungulate biomass per wolf was high, moderate, and low. The percentage of reproductively active adult females was significantly lower (66% compared with ≥96%, P < 0.001) when ungulate biomass per wolf was low versus moderate or high. Reproductively inactive adult females had significantly less subcutaneous fat (P < 0.01) than reproductively active females when ungulate biomass per wolf was relatively abundant. Average litter size, estimated by counting blastocysts or fetuses, declined significantly (P < 0.001), from 6.9 to 4.6, as ungulate biomass per wolf declined. We conclude that wolf productivity declines as prey availability per wolf declines. However, only when ungulate biomass per wolf declined below levels previously reported in the literature did we observe significant declines in reproductive potential. Ungulate biomass per wolf was low because of large, rapid declines in ungulates and lesser declines in wolves. We recognize that functional relationships, e.g., prey vulnerability and feeding dominance, can influence wolf productivity independently of ungulate biomass per wolf.