'limiting factor' concept

American ecologist G.Clarke defined limiting factor as that which "first stops the growth or spread of an organism".the origin of this concept is attributed to German chemist J.V.Liebig in his treatise-"Organic chemistry & it's Application to Agriculture & Physiology" where he noted," Crops of a field diminish or increase in exact proportion to the diminution or increase of the mineral substances conveyed to it in nature". His law of minimum applied to inorganic nutrients although it got modified with the passage of time to include physical factors, temperature & rainfall etc. as well.

 

F.F.Beckman extended the Liebig's law of minimum to encompass the limiting effects of the maximum as well which came to be known as the Law of Limiting Factor. He noted that in treating physiological phenomena, assimilation, respiration, growth & the like, which have a varying magnitude under the varying external condition of temperature, light, supply of food materials etc. it is customary to speak of the three cardinal points, the minimal condition below which the phenomenon ceases to exist altogether, the optimal condition at which it is exhibited to it's highest observed degree & the maximal condition above which it ceases again.

 

It should be appointed that in one environment a given factor may be limiting while not being so in another,this is especially true for environmental factors. example- oxygen is often on land (excepting high altitudes).

 

In high altitudes where low barometric pressure & decreased molecular density of oxygen makes them the limiting factors, Species population can undergo acclimation which are short term changes in response to changed or changing environment which are often bio-geochemically based.

 

In response to rise to high altitude will be followed by deep breathing & faster heart beat rate. Even from the fact of evolutionary relationships it is not always true that closely related species would be equally tolerant to which a given limiting factor over it's geographic distribution which may be the result of genetic change due to varying physiological responses to different environment.

 

These locally adopted populations are called Ecotypes. The widespread species is not morphologically, nor physiologically identical in all parts of their range. For example-Charles Olmstead demonstrated that different populations of a common Prairie grass called 'side-oats grama', which responded differently to a given photo period.

 

In conclusion, it can be said that it's relatively easy to see the applicability of minimal, optimal & maximal conditions in organism growth. The optimum for a given factor might not be achievable without at least a subtropical amount of another factor & these are instances of Factor Integration.

 

In other words, for various physiological processes to be optimally functional, at least sub-optimal amounts of all pertinent factors must be widely distributed & when one factor becomes less than optimum the limits of tolerance for other factors may be limiting.