WILLIAMS, T.M.; Univ. of California, Santa Cruz: Taking lab energetics to the field: How the physiology of large, carnivorous mammals is shaping marine and terrestrial ecosystems

Large mammalian predators by virtue of their body size, mobility, carnivorous feeding habits and endothermic costs have exceptionally high energetic demands in comparison to other animal groups. Although the potential impact on prey populations on which they feed may be marked, it is often difficult to demonstrate due to the logistics of conducting physiological studies in the field. Here we use a combination of laboratory measurements of basal and active metabolic rates from open flow respirometry, and daily activity budgets of cetaceans (Tursiops truncatus,Orcinus orca), sea otters (Enhydra lutris), and pinnipeds (Leptonychotes weddellii, Zalophus californianus) to estimate field energetic costs. The resulting allometric regression for field metabolic rate (FMR) in marine mammals differed from that of terrestrial mammals. For cetaceans, sea otters and pinnipeds, FMR (kcal/day) = 321.4M_b^0.76 (n = 19) where Mb is body mass in kg. In comparison, FMR = 177.6M_b^0.78 (n = 21) for canids and felids. FMR averaged three times the basal metabolic rate of sedentary marine mammals measured in water and terrestrial mammals measured in air. When combined with demographic data and the caloric content of prey species, the effects of a marine lifestyle for mammalian carnivores become apparent. The prey biomass required to support marine mammal populations is nearly twice that required for terrestrial species of similar body size, with the result that marine and terrestrial reserves based on energetic requirements of top carnivores will differ significantly. (Supported by NSF- Polar Programs, the Alaska SeaLife Center.)