Maintaining A Balanced Diet As An Obligate Predator

As obligate predators, carnivores are faced with a tough task when it comes to maintaining a balanced diet.

Although omnivorous animals such as cockroaches and humans can adjust the relative amounts of nutrition in their diet simply by selecting foods with different nutritional values, carnivores do not have the same luxury of choice.

Can Carnivores Keep A Balanced Diet?

Organisms such as predatory beetles (Agonum dorsale), wolf spiders (Pardosa prativaga), and web-building spiders (Stegodyphus lineatus) are capable of compensating for nutritional deficiencies.

After a 24-hour pretreatment period where they were deprived of fat or protein, the beetles and the wolf spiders demonstrated a preference for a diet that contained more of the food of which they had been deprived.

They were successfully compensating for the dietary imbalances they had suffered.

How Can Web-Building Spiders Control Their Diet?

We-building spiders were found to take the complexity of nutrient selection even further. In the wild, these organisms are restricted to eating the prey that gets caught in their webs, and so they are not at liberty to hunt actively for other sources of food.

Instead of hunting for alternative foodstuffs, web-building spiders have evolved the ability to extract specific nutrients from individual prey items.

Photo by: JoaquinPortela; CC BY-SA 3.0

The spiders were found to extract a higher percentage of nitrogen from their prey if they had been exposed to a diet deficient in protein (which contains a high concentration of nitrogen).


This post is an adapted excerpt from my book “The Nature of Human Nature

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