Toward a theory of omnivory: Carnivory as a means to reach micronutrient requirements

Herbivores, more so than predators, struggle to meet nutritional requirements. Micronutrients like sodium are scarce in plants and away from coasts, but essential for heterotrophs. Thus, inland plant consumers often urine for sodium seeking sodium through excreta deposition or salt licks. Because animals are saltier than plants, carnivores can more easily meat nutritional requirements. Omnivores can regulate micronutrient intake via their relative consumption of animal to plant tissue. Indeed, omnivores like ants are increasingly carnivorous in sodium-limited forests. Thus, omnivore animal:plant consumption may be regulated by micronutrient, like sodium, availability and could provide a general framework for understanding omnivory.