Factorial scope of ingestion and the potential functional response of puff adders (Bitis arietans) to high prey abundance.

Historically, snakes have been considered to have a weak functional response to changing prey abundance due to their ectothermic physiology and slow digestion. I measured aspects of food consumption in a captive colony of puff adders (Bitis arietans) to evaluate their functional response. I introduce a new metric for this evaluation, the 'factorial scope of ingestion', defined as the maximum food intake divided by maintenance consumption. Rates of weight loss during fasting were also quantified to assess the potential for puff adders to persist through periods of low prey abundance. To maintain a constant body mass, puff adders must consume 63% of their body mass in rodents annually. However, when provided with unlimited food, they increased their food intake by an average factor of 12 times above maintenance levels for extended periods, which resulted in dramatic increases in body mass. Regression analysis between annualized food intake and changes in body mass, and direct measures of weight loss, independently estimated an annualized weight loss of ~ 23% body mass for fasting puff adders while metabolising fat. This suggests that a puff adder with a high initial body condition index could fast for more than 2 years. The extreme flexibility of puff adder feeding biology suggests that this species has a significant functional response to high prey abundance, and this response is likely to be much more profound than the functional response of mammalian predators. These findings highlight the importance of snakes as potential ecosystem stabilizers and for the control of agricultural rodent pests.