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A population is a group of organisms of the same species living in a definite area. The most likely example one would imagine of a population, would be one where the organisms cluster together in herds and move around together. However, this is only one of the many scenarios, and clustering is not the only characteristic of a population. Populations can be of different distributions, densities, age structures, or sizes. These qualities make up what is called population dynamics. They determine how a population changes over time, and more crucial, how that affects other populations (community). Population size determines the pace of change and the survivability rate of a population. Small populations are very vulnerable to environmental changes. Genetic diversity is limited and the chances of spread of mutations are quite high within such a population. Large populations can lead to overpopulation, stressful competition, and spread of disease. From previous discussions about the pace of evolution (Diversity of Life), it can be concluded that small populations are more prone to change and genetic disasters than larger populations. Population density is measured by the number of individuals in a defined area. Population density can be affected by migration, predation, seasonal changes and other factors that affect population size. Population density is a quantitative description, whereas population distribution is a qualitative description. Population distribution are patterns within the dispersal of a population. A population can be described as having a clustering, uniform or random distribution. Clusters of organisms enhance defense and social capability. Such a distribution is often, not always, associated with K-strategist species. Uniform distributions are suited for optimal use of resources that are evenly or abundantly found. Such distributions of resources is not usually found in nature. Random distribution occurs among populations with less social needs. Age structure of a population can determine its growth patterns and growth potential. A population whose members are mostly found in the early reproductive years is more inclined towards high population growth. It is easy to forget that plants live as populations as well, and that such characteristics are applicable to them as well. Within certain populations, plants enhance their capability to defend themselves against potential predators. Within others, wide dispersal of seeds is necessary for survival and will thus, dictate a widely dispersed population. Population growth is largely dependent upon interactions between species and their non-living environment (ecosystems, communities). Therefore, most populations are known by their population growth patterns and cycles. This particular type of population is known by three main characteristics: low number of offspring, high parental care, large body mass. They have low reproduction rates and tend to focus on less offspring, thereby increasing their chances of survival. They spend very little of their time on reproductive activities, and generally have long generation times. As a result, they are more prone to extinction. Such populations are known for producing large numbers of offspring, with low parental care. Often, a significant portion of these die early. This accounts for the population growth curve charted to the left. They may experience irruptive growth cycles as shown at the bottom. Such growth rates are associated with short generation times.
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