Predators too prefer food with nutritional value

Predators can also be quite finicky about food, preferring that which offers high nutritional value rather than calorie content.

A new study has found that such insect predators, given a choice of food, will select a diet that maximises their chances of reproducing.

"Contrary to standard dogma, predators do balance their diet and show nutritional wisdom," said Stephen Simpson, professor of biology at the University of Sydney and study co-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," Simpson added.

The findings 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 journal Proceedings of the Royal Society B reports.

Researchers from the Universities of Sydney, Exeter and Oxford, Britain, Aarhus University, Denmark and Massey University in New Zealand collected female beetles from the wild and split them into two groups in the lab, according to a Sydney statement.

Half 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.

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

Study co-author 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."