The ecological roles of large predators are well recognised, but quantifying their functional impacts remains an active area of research. In this study, we examined the metabolic requirements and nutrient outputs of the estuarine crocodile population (Crocodylus porosus) in northern Australia over a 50-year period, during which the population increased from a few thousand to over 100,000 individuals. Bioenergetic modelling showed that during this period, the crocodile population's annual prey consumption increased from < 20 kg km-2 in 1979 to ~180 kg km-2 in 2019. Further, the prey consumption increase was accompanied by a significant dietary shift from predominantly aquatic prey (~65% in 1979) to a terrestrial-based diet (~70% in 2019). A substantial portion of these terrestrial-derived nutrients was excreted into the water, significantly increasing the input rates of nitrogen (186-fold) and phosphorus (56-fold). The study shows that despite being ectothermic, the high biomass of crocodiles within the environment generated nutrient inputs comparable to terrestrial endothermic predator populations. Apex ectotherm predators are generally considered not to affect ecosystems in the same manner as endothermic predators. Still, in northern Australia's oligotrophic freshwater environments, the high rates of prey consumption by dense crocodile populations are likely causing top-down and bottom-up effects.

Funding provided by: Australian Research CouncilROR ID: https://ror.org/05mmh0f86Award Number: DP210103369