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Keywords:

  • alternate prey;
  • bottom–up top–down;
  • carrying capacity;
  • predation–forage interactions;
  • weather effects

Abstract

  1. Mule deer and black-tailed deer Odocoileus hemionus have exhibited marked population fluctuations throughout their range over the past century. The relative contributions of predation, forage availability and weather to observed population changes remain unclear and controversial.
  2. We reviewed 48 studies on Odocoileus hemionus survival and predation from the past 30 years and quantified age-specific vital rates, population growth rates (λ) and causes of mortality. We also evaluated the effect of environmental variables on variation in vital rates and the contribution of age-specific survival to population growth.
  3. Age-specific survival (ϕ) was the most frequently studied population parameter. Odocoileus hemionus have lower and more variable fawn survival than other ungulate species (ϕsummer = 0.44, CV = 0.42; ϕannual = 0.29, CV = 0.67). Adult female survival conversely appeared to be high and stable throughout the geographical range of the species (ϕannual = 0.84, CV = 0.06). Observed low fawn survival appears to be compensated for by high fecundity rates.
  4. Predation was the primary proximate cause of mortality for all age classes, and was an important source of summer fawn mortality and of mortality in multi-prey, multi-predator systems. However, predator removal studies suggest that predation is compensatory, particularly at high deer densities, and that nutrition and weather shape population dynamics.
  5. We propose three models to explain local population dynamics of Odocoileus hemionus: (i) populations are limited by forage availability and weather; (ii) adult females are limited by forage availability, fawns are limited by forage availability and predation, and population growth is constrained by fecundity and fawn predation; and (iii) large changes in the abundance of predators or alternative prey change predation risk and destabilize population dynamics.
  6. Future research should be focused on: the effects of age-specific survival on population growth; possible interactions between predation, forage availability and weather; and the importance of multiple predator and prey species in shaping the population dynamics of Odocoileus hemionus.