Crocodilians inhabit many estuarine and freshwater systems in Northern Australia. They exist at the interface of the aquatic and terrestrial environment and may well represent the most abundant top-level predator. They are undoubtedly influential on the eco-systems they inhabit, and the consequential effects of the growing population are increasingly questioned. Nevertheless, the ecological impact of crocodiles in terms of predatory pressure and ecosystem energy flow has received little study.

Bioenergetics can be an important tool in assessing the ecological impact of a population. This works by quantifying daily energy requirements and thus the minimum daily food intake for survival. Energy acquired from food will be consumed by metabolic processes, and these can be subdivided into the metabolic cost of daily maintenance (standard metabolism), metabolic cost of feeding (specific dynamic action), and the metabolic costs of locomotion activity. Once the costs of metabolism are satisfied surplus energy can be utilised for somatic and reproductive growth.

In ectothermic organisms metabolic processes will be largely dependant on body temperature, and crocodiles undertake behavioural and physiological strategies to maintain their body temperature within their preferred thermal range. In farmed animals where food is abundant crocodiles that maintain a higher body temperature have greater somatic and reproductive growth than those that do not. However, in the wild food supply for a crocodile will vary both spatially and temporally, and the animal must be faced with decisions in regards to energy optimisation. On going studies suggest that crocodilians reduce energy costs during dry winter months when food availability is low by reducing both activity and body temperature.

Researchers
 
Dr Hamish Campbell

Ornella Sissa Zubiate