Classical theoretical models of competition assume that individuals are identical and if they differ, it is because of their different sex and age. Ignoring competitive behavior related to the differences between individuals makes the theoretical models of competition simpler and its empirical investigations much easier. This is because food intake of a single individual or of an entire population can be easily determined, but the estimation of food intakes of each individual within a competing group can be much more difficult, if not impossible. With no data on individual food intakes, one may use individual body weights as an indicator of food intakes and competitive abilities. It is justified since larger individuals are usually stronger competitors and able to acquire larger resource shares. However, individual differences are not always exhibited in body weights. They can be revealed in fat contents of the body or by the quality of individual home ranges.
From theoretical models and from the data on the distribution of body sizes several interesting patterns emerge: (1) plants and sedentary organisms are more variable in body size than the mobile ones; (2) distributions of body weights are usually skewed, close to lognormal distribution; (3) individual variation develops also between genetically identical individuals; (4) favorable environments without competition prevent the development of large variation in body weights and the variation increases with increasing competition for limited resources; and (5) in the field, the latter phenomenon may be concealed by high mortality of the smallest individuals.
Inequality, in opposition to equality, enhances the adjustment of the population size to the available resources. Individuals that do not receive enough resource to survive die, while those that receive more survive and reproduce. If resource shares are identical for all individuals, excess of resources for all of them brings about an exponential growth, but if resources fall below the minimum required for survival, the entire population may become extinct. However, inequality itself does not assure population stability and persistence. It is because resource share can be variable; but even the largest share may be insufficient for survival and reproduction. On the other hand, an increase of inequality among individuals is a common outcome during the competition for limited resources. This phenomenon can be defined as the asymmetric competition and it is partially based on multiplicative mode of body size increase; that is, animals that for random reasons were more fortunate to obtain a food item, increase their body size, energy reserves, and a chance of obtaining more food items in future. It is clearly seen in terrestrial plants competing for light, since a plant little taller than its neighbors takes a share of light that is not linearly proportional to its height but much higher. Asymmetric competition among animals is based on their behavioral interactions. For example, in a stream, strong water stri-ders may hunt for insects in the places with strong water current, where more prey can be found, while the weak ones have to stay in weak water currents, where their prey is scarce. What is more, the theory of evolutionarily stable strategy of a conflict between two unequal competitors predicts that a weaker individual should give way to a stronger one.
The extreme case of asymmetric competition is monopolization of resources by some individuals in a way that prevents others from using them. Monopolization implies that weaker individuals, newly born, immigrants, or recruits, are unable to diminish resource share of the group that monopolizes resources. An example of such a situation can be an oak forest in which light for trees cannot be diminished by oak seedlings, irrespective of how many of them are on the floor of the forest. Among animals, monopolization can be caused by territorial behavior or successful defense of a limited number of nest holes. However, ideal monopolization requires that floaters, even if in a large number, are unable to reduce size and resources of territories of their owners. This may not always be the case in territorial behavior.
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