Seasonal sexual and ontogenetic variations in the diet of the 'declining' frogs Litoria nannotis, Litoria rheocola and Nyctimystes dayi

Abstract

Faecal analyses were used to investigate the diets of the endangered frogs Litoria nannotis, L. rheocola and Nyctimystes dayi in Tully Gorge, North Queensland. Comparisons of diet and food availability indicate that thesespecies feed indiscriminately on a range of terrestrial and aquatic invertebrates. Changes in morphology and foraging behaviour significantly influenced diet composition and created subtle shifts in the degree of selectivity displayed in prey choice. Interspecific differences in numeric and volumetric diet composition were attributed to variations in gape size and microhabitat selection. Within the diets of L. nannotis and L. rheocola, a decline in prey selectivity observed during the dry season reflected a reduction in foraging activity. Differences in the gape size and foraging behaviour of males and females of L. nannotis were responsible for sex-specific differences in diet composition. L. nannotis also diplayed an ontogenetic shift in prey size and type. As snout-vent length increased, L. nannotis consumed fewer, but larger prey and increasingly discriminated against dipterans, dipteran larvae and hemipterans. Importantly, L. nannotis, L. rheocola and N. dayi demonstrated the capacity to compensate for fluctuations in food availability by feeding on less lucrative prey.