Universal adaptive strategy theory (UAST) is an evolutionary theory developed by J. Philip Grime in collaboration with Simon Pierce describing the general limits to

ecology Ecology () is the natural science of the relationships among living organisms and their Natural environment, environment. Ecology considers organisms at the individual, population, community (ecology), community, ecosystem, and biosphere lev ...

and

evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

based on the

trade-off A trade-off (or tradeoff) is a situational decision that involves diminishing or losing on quality, quantity, or property of a set or design in return for gains in other aspects. In simple terms, a tradeoff is where one thing increases, and anoth ...

that organisms face when the resources they gain from the environment are allocated between either growth, maintenance or regeneration – known as the universal three-way trade-off.

General theory

A universal three-way

produces adaptive strategies throughout the tree of life, with extreme strategies facilitating the survival of genes via: C (competitive), the survival of the individual using traits that maximize resource acquisition and resource control in consistently productive niches; S (stress-tolerant), individual survival via maintenance of metabolic performance in variable and unproductive niches; or R (

ruderal A ruderal species is a plant species that is first to colonize disturbed lands. The disturbance may be natural for example, wildfires or avalanchesor the consequences of human activities, such as construction ( of roads, of buildings, mining, e ...

), rapid gene propagation via rapid completion of the lifecycle and regeneration in niches where events are frequently lethal to the individual. It is impossible for an organism to evolve a survival strategy in which all resources are devoted exclusively to one of these investment paths, but relatively extreme strategies exist, with a range of intermediates. The system can be represented by a triangle, with the three extreme possibilities at its vertices. The different species may be located at some particular point inside this triangle, accommodating a certain percentage of each of the three strategies. It is possible to use multivariate statistics to determine the main trends in phenotypic variability in a range of organisms, which for various major animal groups (most prominently

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

s), has been shown to have three main endpoints consistent with UAST. UAST is a key part of the twin-filter model describing how species with similar overall strategies but divergent sets of minor traits coexist in ecological communities.

C-S-R Triangle theory

C-S-R Triangle theory is the application of UAST to

plant biology Botany, also called plant science, is the branch of natural science Natural science or empirical science is one of the branches of science concerned with the description, understanding and prediction of natural phenomena, based on empiri ...

. The three strategies are competitor, stress tolerator, and ruderal. These strategies each thrive best in a unique combination of either high or low intensities of stress and disturbance.

Competitors

Competitors are plant species that thrive in areas of low intensity stress (moisture deficit) and disturbance and excel in biological competition. These species are able to outcompete other plants by most efficiently tapping into available resources. Competitors do this through a combination of favorable characteristics, including rapid growth rate, high productivity (growth in height, lateral spread, and root mass), and high capacity for

phenotypic plasticity Phenotypic plasticity refers to some of the changes in an organism's behavior, morphology and physiology in response to a unique environment. Fundamental to the way in which organisms cope with environmental variation, phenotypic plasticity encompa ...

. This last feature allows competitors to be highly flexible in morphology and adjust the allocation of resources throughout the various parts of the plant as needed over the course of the growing season.

Stress tolerators

Stress tolerators are plant species that live in areas of high intensity stress and low intensity disturbance. Species that have adapted this strategy generally have slow growth rates, long-lived leaves, high rates of nutrient retention, and low phenotypic plasticity. Stress tolerators respond to environmental stresses through physiological variability. These species are often found in stressful environments such as alpine or arid habitats, deep shade, nutrient deficient soils, and areas of extreme pH levels.

Ruderals

Ruderals are plant species that prosper in situations of high intensity disturbance and low intensity stress. These species are fast-growing and rapidly complete their life cycles, and generally produce large amounts of seeds. Plants that have adapted this strategy are often found colonizing recently disturbed land, and are often annuals.

Relation to the R* theory

Understanding the differences between the CSR theory and its major alternative the R* theory has been a major goal in

community ecology In ecology, a community is a group or association of populations of two or more different species occupying the same geographical area at the same time, also known as a biocoenosis, biotic community, biological community, ecological communit ...

for many years. Unlike the R* theory that predicts that competitive ability is determined by the ability to grow under low levels of resources, the CSR theory predicts that competitive ability is determined by relative growth rate and other size related traits. While some experiments supported the R* predictions, other supported the CSR predictions. The different predictions stem from different assumptions on the size asymmetry of the competition. The R* theory assumes that competition is size symmetric (i.e. resource exploitation is proportional to individual biomass), the CSR theory assumes that competition is size-asymmetric (i.e. large individuals exploit disproportional higher amounts of resources compared with smaller individuals).

References

* Grime JP and Pierce S. 2012. ''The Evolutionary Strategies that Shape Ecosystems.'' Wiley-Blackwell, Chichester, UK * Grime JP. (1979). ''Plant Strategies and Vegetation Processes.'' John Wiley & Sons.