Limiting factor

A limiting factor of a system, is an input or variable such that a small change in it from the present value would cause a non-negligible change in an output or other measure of the system. A factor which is not limiting over a certain domain of starting conditions may yet be limiting over another domain of starting conditions, including that of the factor The identification of a factor as limiting is of use only in distinction to one or more other factors which is/are non-limiting. Disciplines differ in their use of the term as to whether they allow the simultaneous existence of more than one limiting factor (which may then be called "co-limiting"), but they all require the existence of at least one non-limiting factor when the terms are used. There are several different possible scenarios of limitation when more than one factor is present. The first scenario called single limitation occurs when only one factor, the one with maximum demand, limits the system. Serial co-limitation is when one factor does not have any direct limiting effects on the system but needs to be present in order to increase the limitation of a second factor. A third scenario, independent limitation, occurs when two factors both have limiting effects on the system but they are working through different mechanisms. Another scenario, independent limitation, occurs when both factors contribute to the same mechanism of limitation but do so in different ways.

In ecology, common limiting factor resources are environmental conditions that limit the growth, abundance, or distribution of an organism or a population of organisms in an ecosystem. The concept of limiting factors is based on Liebig's Law of the Minimum, which states that growth is controlled not by the total amount of resources available, but by the scarcest resource. In other words, a factor is limiting if a change in the factor produces increased growth, abundance or distribution of an organism, when other factors necessary to the organisms life do not. Limiting factors may be physical or biological.

Limiting factors are not all limited to the condition of the species. Some factors may be increased or reduced based on circumstances. An example of a limiting factor is sunlight in the rain forest, where growth is limited to all plants on the forest floor unless more light becomes available. This decreases a number of potential factors that could influence a biological process, but only one is in effect at any one place and time. This recognition that there is always a single limiting factor is vital in ecology; and the concept has parallels in numerous other processes. The limiting factor also causes competition between individuals of a species population. For example, space is a limiting factor. Many predators and prey need a certain amount of space for survival: food, water, and other biological needs. If the population of a species is too high, they start competing for those needs. Thus the limiting factors hold down population in an area by causing some individuals to seek better prospects elsewhere and others to stay and starve. Some other limiting factors in biology include temperature and other weather related factors. Species can also be limited by the availability of macro- and micronutrients. There has even been evidence of co-limitation in prairie ecosystems. A study published in 2017 showed that sodium (a micronutrient) had no effect on its own, but when in combination with nitrogen and phosphorous (macronutrients), it did show positive effects, which is evidence of serial co-limitation.

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