Growth Limiting Factors
Growth limiting factors
There are a number of essential conditions which all organisms, both plants and animals, require to grow. These are known as growth factors. Plants, for example, require sunlight, water, and carbon dioxide in order to perform photosynthesis . They require nutrients such as nitrogen , phosphorus , and various trace elements in order to form tissues. The environment in which the plant is growing does not contain a unlimited supply of these growth factors. When one or more of them is present in levels or concentrations low enough to constrain the growth of the plant, it is known as a growth limiting factor. The rate or magnitude of the growth of any organism is controlled by the growth factor that is available in the lowest quantities. This concept is analogous to the saying that a chain is only as strong as its weakest link.
These factors limit population growth . If they did not exist, a population could increase exponentially, limited only by its own intrinsic lifespan. Growth limiting factors are essential to the traditional concept of carrying capacity , which rests on the assumption that the available resources limit the population that can be sustained in that area. Advances in technology have enabled people to increase the carrying capacity in certain areas by manipulating the growth limiting factors. Perhaps the best example of this is the use of fertilizers on farmland.
In the field of population ecology , identifying growth limiting factors is part of establishing the constraints and pressures on populations and predicting growth in various conditions. Algal growth in New York Harbor provides an example of the importance of identifying growth limiting factors. In New York Harbor, several billion gallons of untreated wastewater are released daily, bringing enormous quantities of nutrients and suspended solids into the water. Algae in the harbor take advantage of the nutrient loads and grow more than they would under nutrient-poor conditions. At the same time, however, the suspended solids and silts brought into harbor cause the water to become very turbid, limiting the amount of sunlight that penetrates it. Sunlight is rarely a growth limiting factor for algae; nutrients are usually what limits their growth, but in this case nutrients are in excess supply. This means that if pollution control in the harbor ever results in control of the turbidity in the water, there will probably be a sharp increase in the growth of algae.
Consideration of growth limiting factors is also very important in the field of conservation biology and habitat protection. If the goal is to protect a bird such as the heron, which may feed on fish from a lake and nest in upland trees nearby, limiting factors must be taken into account not only for the growth of the individual but also for the population. Conservation efforts must not be directed only toward ensuring there are enough fish in the lake. Enough trees must also be left uncut and undisturbed for nesting in order to address all of the growth requirements for the population. Regardless of how abundant the fish are, the number of herons will only grow to the extent allowed by the number of available nesting sites.
Environmentalists use growth limiting factors to distinguish between undisturbed ecosystems and unstable or stressed systems. In an ecosystem that has been distressed or disturbed, the nature of growth limiting factors changes, and these changes are often human-induced, as they are in New York Harbor. Though the change in circumstances may not always appear negative in impact, it still represents a shift away from the original balance, and it may have effects on other species or lead to subtle long-term changes in the system. Any cleanup or management strategy must use these new growth limiting factors to identify the nature of the imbalance that has occurred and develop a procedure to restore the system to its original condition.
Growth limiting factors are extensively used in the field of bioremediation , in which microbes are used to clean up environmental contaminants by breakdown and decomposition . Oil spills are a good example. Bacteria that can break down and degrade oils are naturally present in small quantities in soil , but under normal conditions their growth is limited by both the availability of essential nutrients and the availability of oil. In the event of an oil spill on land, the only growth limiting factor for these bacteria is nutrients. Bioremediation scientists can add nitrogen and phosphorus to the soil in these circumstances to stimulate growth, which increases degradation of the oil. Techniques such as these, which use naturally occurring bacterial populations to control contamination, are still in development; they are most useful when the contaminants are present in high concentrations and confined to a limited area.
[Usha Vedagiri and
Douglas Smith ]
Mayer, G. Ecological Stress and the New York Bight: Science and Management. Columbia, SC: Estuarine Research Federation, 1982.
Smith, R. L. Ecology and Field Biology. New York: Harper and Row Publishers, 1980.