All organisms display a diversity of responses to the physical factors of their environments. Some organisms are highly sensitive to certain physical factors, and the range of conditions they can tolerate is severely limited. Other organisms have broad ranges of tolerance and are much less sensitive to environmental factors. Organisms must have a suitable amount of heat, light, water, nutrients and other factors in order to carry on growth and reproduction. This balance must be maintained too much of some factors may be just as bad as too little.
Each stage in the life cycle of an organism has a limiting factor response, some stages are much more sensitive than others. The tolerance ranges of the young is much narrower that those of adults; seeds, eggs, embryos, larvae, and seedlings are much are therefore more sensitive to environmental factors than mature plant and animals.
The Law of Limiting Factors
The law of limiting factors states that the population size of any particular species may be limited by one or more factors that are present in inadequate or over abundant amounts. The law of limiting factors was first demonstrated from one simple ecosystem such as crop. Natural ecosystems have so many interacting organisms and many interconnections among them that a simple cause and effect relationships between them is often difficult to demonstrate. Sixteen different chemical elements have been identified as essential for the survival of most species. These are carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, manganese, boron, molybdenum, copper, zinc, and chlorine. There are several other elements that are required in trace amounts by some species; these elements are sodium, vanadium, cobalt, iodine, selenium, silicon, fluorine and barium. Some elements seem to be consistently low or consistently high in many ecosystems. If soils are low in phosphorus then the growth of plants will be limited; and if an essential element is present in too high a concentration then this could be toxic to a particular organism; example too much boron in a soil will be toxic to many plants and animals.
The conditions under which an organism lives may determine its requirements for a particular element. For example plants in a sunny climate may require a substantial amount of zinc, whereas the same plant growing in the shade may need very little zinc.
The question of limiting factors, the law of tolerance is extremely complex because nothing acts alone in nature. Many plants and animals responses to a given element of environmental factors are
, in that the response to one element of factor depends on the amounts of all the others, for example if nitrogen is limiting to grasses, their resistance to drought diminishes.
These are some of the factors that must be considered when ecosystems respond to human intrusion.
(a) An organism may have a wide range of tolerance to some factors and not to others.
(b) Organisms that are most tolerant are likely to be most adaptable to a range of habitats.
(c) An organism’s tolerance to a given factor may change with the availability of other factors.
(d) Organisms in nature may not always be growing under optimum conditions.
(e) During the juvenile or reproductive stages of the life cycle, an organism is least tolerant and therefore most susceptible to limiting factors.