Feeding, metabolism and metabolic scope in Antarctic marine ectotherms
The rise in metabolism following feeding exhibited by animals, known as the heat increment or specific dynamic action (SDA) of feeding has been well known since the 1930s when it was described in domesticated mammals (Brody, 1945). The effect is usually assessed in terms of oxygen consumed following a feeding event, and is characterised by a rapid rise in metabolism which peaks within a few hours of the consumption of a meal. In marine ectotherms, peaks are typically two to four times higher than prefeeding standard or basal metabolic rates, where basal metabolism is defined as the cost of maintaining the body tissues in the absence of factors such as activity, growth or SDA which may cause elevations. Some species are, however, capable of elevations much greater than two to four times basal metabolism, and recently Burmese pythons have been shown to have SDA peaks 45 times higher than prefeeding levels (Secor & Diamond, 1995), a metabolic scope which is as high as the greatest aerobic scopes exhibited by highly trained active species, such as racehorses (Brody, 1945; Birlenbach & Leith, 1994), under maximal workloads.
It is now generally accepted that SDA is composed of the physical costs of processing food and both the anabolic (transformation of absorbed material and growth) and catabolic (formation and excretion of wastes) processes associated with the feeding event (Pandian, 1987; Wieser, 1994