Digestive rate model
Encyclopedia
The digestive rate model (DRM) (of foraging
) is related to optimal foraging theory
in that the model describes the diet selection that animals should perform in order to maximize the energy (or nutrient
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 (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
or foraging, and food digestion. Optimal foraging theory describes the diet selection if the food ingestion rate is the limiting factor
. 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 in plant material, shells of molluscs or insect chitin
, 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 forage based on digestive bottleneck
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.
Foraging
- Definitions and significance of foraging behavior :Foraging is the act of searching for and exploiting food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce...
) is related to optimal foraging theory
Optimal foraging theory
Optimal foraging theory is an idea in ecology based on the study of foraging behaviour and states that organisms forage in such a way as to maximize their net energy intake per unit time. In other words, they behave in such a way as to find, capture and consume food containing the most calories...
in that the model describes the diet selection that animals should perform in order to maximize the energy (or nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...
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 (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
Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in the substance through the mouth into the gastrointestinal tract, such as through eating or drinking...
or foraging, and food digestion. Optimal foraging theory describes the diet selection if the food ingestion rate is the limiting factor
Limiting factor
A limiting factor or limiting resource is a factor that controls a process, such as organism growth or species population, size, or distribution. The availability of food, predation pressure, or availability of shelter are examples of factors that could be limiting for an organism...
. 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 in plant material, shells of molluscs or insect chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...
, 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 forage based on digestive bottleneck
Bottleneck
A bottleneck is a phenomenon where the performance or capacity of an entire system is limited by a single or limited number of components or resources. The term bottleneck is taken from the 'assets are water' metaphor. As water is poured out of a bottle, the rate of outflow is limited by the width...
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.