The digestive rate model (DRM) (of

foraging Foraging is searching for wild food resources. It affects an animal's Fitness (biology), fitness because it plays an important role in an animal's ability to survive and reproduce. Optimal foraging theory, Foraging theory is a branch of behaviora ...

) is related to

optimal foraging theory Optimal foraging theory (OFT) is a behavioral ecology model that helps predict how an animal behaves when searching for food. Although obtaining food provides the animal with energy, searching for and capturing the food require both energy and t ...

in that the model describes the diet selection that animals should perform in order to maximize the energy (or

nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...

s) available to them. It differs from the main body of Optimal Foraging Theory in stating that animals can select food in order to make optimal use of their

digestive tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans a ...

(maximize digestion rate) rather than the maximization of the food ingestion rate, which is the base of Optimal foraging theory. The basic tenet of the DRM is that the intake of energy by an animal passes through two consecutive processes, food

ingestion Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in a substance through the mouth into the gastrointestinal tract, such as through eating or drinking. In single-celled organisms ingest ...

or foraging, and food digestion. Optimal foraging theory describes the diet selection if the food ingestion rate is the

limiting factor A limiting factor is a variable of a system that causes a noticeable change in output or another measure of a type of system. The limiting factor is in a pyramid shape of organisms going up from the producers to consumers and so on. A factor not l ...

. The DRM describes diet selection and foraging behavior if digestion is the rate limiting process. Food can consist of varying fractions of largely indigestible parts such as

fibre Fiber or fibre (from la, fibra, links=no) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorporate ...

in plant material, shells of

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

s or insect

chitin Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...

, which can be thought of as 'rate limiting' for the digestion process or somewhat more intuitively as 'bulk' that takes up capacity that can be spent better for material with a higher digestibility. The original description of the model positioned the DRM as an alternative to the contingency model (CM) of optimal foraging and pointed out that some of the predictions of the DRM provide a better match than did the CM with observed diet choice and behavior of e.g. herbivores. The DRM went largely unnoticed, but a recent paper by Van Gils describes how red knots ''

Calidris canutus The red knot or just knot (''Calidris canutus'') is a medium-sized shorebird which breeds in tundra and the Arctic Cordillera in the far north of Canada, Europe, and Russia. It is a large member of the ''Calidris'' sandpipers, second only to the ...

'' forage based on digestive

bottleneck Bottleneck literally refers to the narrowed portion (neck) of a bottle A bottle is a narrow-necked container made of an impermeable material (such as glass, plastic or aluminium) in various shapes and sizes that stores and transports liquids ...

s and confirmed their foraging according to the DRM rather than the CM model of optimal foraging. The case is particularly interesting as a major difference in individual foraging behavior is related to a large intraspecific difference in the digestive tract of the knots.

References

{{reflist Behavioral ecology Eating behaviors

See also

References