Cougar predation and population growth of sympatric mule deer and white-tailed deer

Mule deer (Odocoileus hemionus) populations throughout the west appear to be declining, whereas white-tailed deer (Odocoileus virginianus) populations are increasing. We compared abundance, number of fetuses per female (maternity rate), recruitment, and cause-specific adult (greater than or equal to1 year old) mortality rate for sympatric mule deer and white-tailed deer in south-central British Columbia to assess population growth for each species. White-tailed deer were three times more abundant (908 +/- 152) than mule deer (336 +/- 122) (mean +/- 1 SE). Fetal rates of white-tailed deer (1.83) were similar to those of mule deer (1.78). There was no statistically significant difference in recruitment of white-tailed deer (56 fawns : 100 does) and mule deer (38 fawns : 100 does). The annual survival rate for adult white-tailed deer (S-WT = 0.81) was significantly higher than that for mule deer (S-MD = 0.72). The main cause of mortality in both populations was cougar predation. The lower mule deer survival rate could be directly linked to a higher predation rate (0.17) than for white-tailed deer (0.09). The finite growth rate (lambda) was 0.88 for mule deer and 1.02 for white-tailed deer. The disparate survival and predation rates are consistent with the apparent-competition hypothesis.