The influence of sex and body size on food habits of a giant tropical snake, Python reticulatus

1. In many animal species, dietary habits shift with body size, and differ between the sexes. However, the intraspecific range of body sizes is usually low, making it difficult to quantify size-associated trophic shifts, or to determine degree to which sex differences in diet are due to body-size differences. Large snakes are ideal for such a study, because they provide a vast range of body sizes within a single population. 2. More than 1000 Reticulated Phythons (Phyton reticulatus) from southern Sumatra were examined, with specimens from-1.5 to > 6 m in snout-vent length, and from 1 to 75 kg in mass. Females attained much larger body sizes than did conspecific males (maxima of 20 vs 75 kg, 5 vs 7 m), but had similar head lengths at the same body lengths. 3. Prey sizes, feeding-frequencies and numbers of stomach parasites (ascard nematodes) increased with body size in both sex, and dietary composition changed ontogenetically. Small snakes fed mostly on rats, but shifted to larger mammalian taxa (e.g. pangolins, porcupines; monkeys, wild pigs, mouse deer) at 34-m body length. 4. Adult males and female showed strong ecological divergence. For some traits, this divergence was entirely caused by the strong allometry (combined with sexual size dimorphism), but in other cases (e.g. feeding frequency, dietary composition), the sexes followed different allometric trajectories. For example, females shifted from rats to larger mammals at a smaller body size than did conspecific males, and feeding frequencies increased more rapidly with body size in females than in males. These allometric divergences enhanced the degree of sex difference in trophic ecology induced by sexual size dimorphism.