Isomorph
Encyclopedia
An isomorph is an organism that does not change in shape during growth. The implication is that its volume is proportional to its cubed length, and its surface area to its squared length. This holds for any shape it might have; the actual shape determines the proportionality constants.
The reason why the concept is important in the context of the Dynamic Energy Budget
(DEB) theory is that food (substrate) uptake is proportional to surface area, and maintenance to volume. Since volume grows faster than surface area, this controls the ultimate size of the organism. Alfred Russel Wallace
wrote this in a letter to E. B. Poulton
in 1865. The surface area that is of importance is the part that is involved in substrate uptake (e.g. the gut surface), which is typically a fixed fraction of the total surface area in an isomorph. The DEB theory explains why isomorphs grow according to the von Bertalanffy curve if food availability is constant.
Organisms can also change in shape during growth, which affects the growth curve and the ultimate size, see for instance V0-morph
s and V1-morph
s. Isomorphs can also be called V2/3-morphs.
Most animals approximate isomorphy, but plants in a vegetation typically start as V1-morph
s, then convert to isomorphs, and end up as V0-morph
s (if neighbouring plants affect their uptake).
The reason why the concept is important in the context of the Dynamic Energy Budget
Dynamic energy budget
The Dynamic Energy Budget theory aims to identify simple quantitative rules for the organization of metabolism of individual organisms that can be understood from basic first principles...
(DEB) theory is that food (substrate) uptake is proportional to surface area, and maintenance to volume. Since volume grows faster than surface area, this controls the ultimate size of the organism. Alfred Russel Wallace
Alfred Russel Wallace
Alfred Russel Wallace, OM, FRS was a British naturalist, explorer, geographer, anthropologist and biologist...
wrote this in a letter to E. B. Poulton
Edward Bagnall Poulton
Sir Edward Bagnall Poulton, FRS was a British evolutionary biologist who was a lifelong advocate of natural selection...
in 1865. The surface area that is of importance is the part that is involved in substrate uptake (e.g. the gut surface), which is typically a fixed fraction of the total surface area in an isomorph. The DEB theory explains why isomorphs grow according to the von Bertalanffy curve if food availability is constant.
Organisms can also change in shape during growth, which affects the growth curve and the ultimate size, see for instance V0-morph
V0-morph
An V0-morph is an organism that changes in shape during growth such that its surface area is proportional to its volume to the power 0, so its surface area is constant....
s and V1-morph
V1-morph
An V1-morph is an organism that changes in shape during growth such that its surface area is proportional to its volume to the power 1, so to its volume...
s. Isomorphs can also be called V2/3-morphs.
Most animals approximate isomorphy, but plants in a vegetation typically start as V1-morph
V1-morph
An V1-morph is an organism that changes in shape during growth such that its surface area is proportional to its volume to the power 1, so to its volume...
s, then convert to isomorphs, and end up as V0-morph
V0-morph
An V0-morph is an organism that changes in shape during growth such that its surface area is proportional to its volume to the power 0, so its surface area is constant....
s (if neighbouring plants affect their uptake).
See also
- Dynamic energy budgetDynamic energy budgetThe Dynamic Energy Budget theory aims to identify simple quantitative rules for the organization of metabolism of individual organisms that can be understood from basic first principles...
- V0-morphV0-morphAn V0-morph is an organism that changes in shape during growth such that its surface area is proportional to its volume to the power 0, so its surface area is constant....
- V1-morphV1-morphAn V1-morph is an organism that changes in shape during growth such that its surface area is proportional to its volume to the power 1, so to its volume...
- shape correction functionShape correction functionThe shape correction function is a ratio of the surface area of a growing organism and that of an isomorph as function of the volume. The shape of the isomorph is taken to be equal to that of the organism for a given reference volume, so for that particular volume the surface areas are also equal...