Exploitation of common resources – simple reasons to be different

Intraspecific competition in even-aged populations of plants and animals is very rarely the subject of ecological research. Even more rarely are ecologists interested in the important outcomes of this competition - the unequal partitioning of resources for which competition takes place and the resulting from it individual variability in the growth rate of individuals, their survival rate and the production of offspring. There are various reasons for this. The statistical methods used by ecologists deal with average values. Classical models of mathematical ecology describe the dynamics of the densities of populations, and are therefore interested in variables that by their nature neglect the important fact that a population is made up of individuals. It is also not without significance that it is generally very difficult to study interactions between individuals. The present study aims to discuss some very simple examples of how individual variability in the amount of resources taken up by individuals from the environment can arise because of the physical nature of these resources, without considering interactions between individuals. Three examples will be presented: individuals of a phytoplankton species that move chaotically in a column of water illuminated from above, sedentary organisms randomly distributed on a two-dimensional plane, and predators hunting for food in the form of particles. In all these examples, the measures of resources obtained by individuals indicate the existence of individual variability, and their distributions have a positive skewness (there are more individuals that obtained few resources than individuals with many resources). The influence that the costs of obtaining resources from the environment and interactions between individuals may have on such form of individual variability will be discussed also.