Also carnivores pay attention to a balanced diet

Robberies also choose prey according to their nutrient content

Females of a colored runner (Anchomenus dorsalis); This species of beetle chooses, as probably other predatory animals, their prey also on their nutrient content. © Peter Krogh
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Predatory animals are more nutritionally aware than they are supposed to be: they look for a nutrient ratio that is optimal for their reproduction when selecting their prey. An international research team has found this out from a carnivorous beetle.

In laboratory tests before the choice between different food provided, the beetles would have eaten in each case the prey animals, which balance their protein and fat balance best. Such a targeted selection of food was previously observed only in herbivores and omnivores, but not in carnivores, the researchers report in the journal "Proceedings of the Royal Society B".

Robber pickier than imagined

So far, biologists have assumed that robbers can not afford to be choosy. Her main goal, it was believed, was to take enough prey and therefore calories. "We are now showing for the first time that predators choose their food accordingly, which gives them the right balance of nutrients, " says first author Kim Jensen of the University of Exeter in England.

According to the researchers, the behavior observed on the beetles can also be transferred to other predators. The new findings have thus also far-reaching importance for the structure of food webs and the nutrient flow in animal communities.

Optimal ratio of fats and proteins sought

Their experiments were carried out by the researchers with the bright colored runner (Anchomenus dorsalis). This small, also occurring in Germany ground beetle species eats smaller insects such as aphids, caterpillars, beetle larvae and ants. The experiments with free choice of food showed that the beetles thrived particularly well when they took fats and proteins in a ratio of 1: 2, the scientists report. This relationship would always have been the goal of the animals in various experiments. display

In one of the experiments, the researchers limited the food selection of the beetle so that it received plenty of proteins, but too little fats. In this case, the ground beetles ate much more than usual. They also took in more proteins than they needed to get enough fats.

Further studies are needed

Such behavior can also lead other predators to hunt and kill more prey than they actually need for their calorie needs. "For example, this could happen right after hibernation, when both predators and prey have depleted fat reserves, " say the researchers. Then the ruffian would have to take more food according to the new findings in order to satisfy his fat needs. Whether this is indeed the case must now be further investigated. (Proceedings of the Royal Society B, 2012; doi: 10.1098 / rspb.2011.2410)

(Proceedings of the Royal Society B / dapd, 17.01.2012 - NPO)