Intraspecific Competition

Liebig's Law of the Minimum was developed for the nutrition of agricultural plants, but can also be applied to populations. Reproduction (birth of new organisms) and death are the fundamental processes regulating change in population size over time. Low abundance of resources, or other nonideal environmental conditions, reduces the reproduction rate or increases the death rate in a population, in addition to lowering rates of growth or activity for individual organisms. Reproductive rates are more sensitive to changes in the environment than metabolic rates or death rates since an individual can often survive under conditions under which it cannot reproduce. If a population grows, resources decline and some individuals will not obtain resources in adequate supply. This affects individual reproduction. It is also an example of natural selection, since the individuals that are more successful at obtaining and using resources will make a greater contribution to the genetic makeup of the next generation. If the organisms within a population are members of the same species, this is "intraspecific competition."

For each species there is a gradient of habitat suitability that is determined by environmental conditions and resources. Ecologists need quantitative information on the suitability of habitats to predict population dynamics in other areas, in the future, and due to changes in community structure. The theoretical basis for these relationships was formalized by Pearl and Reed (1920), who promoted the logistic growth equation that had been previously described by P. F. Verhulst in 1838. The equation is an attempt to relate the specific growth rate of a population (p) to the environment. The probability of an individual reproducing (b) minus the probability of death (d) per unit time is equal to p and is a direct manifestation of the suitability of the habitat. The differential equation for logistic growth is dN

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