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Predators pick prey that balances their diet


12 January 2012

The study looked at the eating choices of ground beetles.
The study looked at the eating choices of ground beetles.

University researchers have debunked the dogma that predators aren't picky eaters, with a new study finding predator animals that are given a choice of foods will select a diet that maximises their chances of reproducing.

The researchers, including Professor Stephen Simpson, an internationally renowned biologist from the University of Sydney, have shown for the first time that predatory animals choose their food on the basis of its nutritional value rather than just overall calorie content.

The findings, published in the Proceedings of the Royal Society B on Wednesday 11 January, are based on a study of the ground beetle, Anchomenus dorsalis, a garden insect that feasts on slugs, aphids, moths, beetle larvae and ants.

The international team of scientists from the University of Sydney, the universities of Exeter and Oxford in the UK, Aarhus University in Denmark and Massey University in New Zealand, collected female beetles from the wild and split them into two groups in the laboratory.

Half of the beetles were offered a choice of foods - some that were high in protein and some that were high in fat. The other half were not given a choice of foods: some of these beetles were only given high protein food, while the rest were just given high fat foods.

The beetles that were given a choice of foods ate the proportions of protein and fat that were optimal for producing healthy eggs. These beetles produced more eggs than the other beetles in the study that had no choice of foods.

"Contrary to standard dogma, predators do balance their diet and show nutritional wisdom," said Professor Simpson, an ARC Laureate Fellow in the School of Biological Sciences at the University of Sydney and the paper's senior author.

"Although we previously demonstrated this characteristic in spiders, predatory beetles, fish, mink and cats, this is the first study to show the adaptive reasons and benefits of diet selection," Professor Simpson said.

The finding could have implications for predator killing and eating patterns in particular environments, with important consequences for food webs and ecological communities, said Professor Simpson.

"Immediately after winter hibernation, when both predators and the prey are likely to have depleted fat stores, predators are likely to kill and eat more prey than if the prey were rich in fats. Conversely, if some prey species contain a higher concentration of fats than is optimal for the predator, then predators should switch their focus towards more protein-rich prey species."

Previous research on insects has shown that herbivores such as butterfly larvae and grasshoppers, and omnivores such as fruit flies and crickets, select food to give them a balanced diet. This is the first research to show that predators also select food on the basis of nutritional value.

Lead researcher Dr Kim Jensen of the University of Exeter said: "At a time of year when many of us are focused on healthy eating, it is interesting to see that predators are also selective about what they eat.

"Biologists have previously assumed that predators cannot afford to be fussy and are simply focused on getting the right quantity of food, rather than quality. We show for the first time that they do actually select the foods that will give them the right balance of nutrients."


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Media enquiries: Kath Kenny, 0478 303 173, 02 9351 1584, kath.kenny@sydney.edu.au