and plant populations naturally regulate themselves in an amazing process that sustains all
life on earth. In an environment that houses many
plants and animals, an increase in the population of one species
could cause a great disruption in the food
web, and in the functioning of the ecosystem. Thus, populations
within all ecosystems have internal regulating mechanisms
like births and deaths to ensure everything stays in order.
There are four basic processes that regulate the size of populations: births and immigration (both of which cause an increase in population) and death and emigration (which result in a decrease in population).
These processes are mostly restricted to mobile creatures, like animals.
resources are plentiful, more individuals will be attracted to the area, and there will be more births. If times are not so good, however, no
new individuals will be attracted to the area and many will disperse in search of a new and better place. As a result, there will also be a decrease in the birth rate.
As a population increases in size, there is a
corresponding increase in competition for resources such as food, water, nutrients and even space. The resulting decrease in available resources slows down the population growth either through a decrease in the birth rate, an increase in the death rate, or a combination of both. Eventually, however, the birth and death rates will even out so that the population can successfully survive on the available resources.
A similar example can be seen in the search for food - a major factor that
contributes to population control. If predators find a shortage of prey, their population will be
reduced by starvation. This decrease in predators will enable the prey population to increase again as not as many of them are being killed. In turn, this increase in numbers of prey makes it easier for the predators to catch and eat once again. The predators will then
increase in population and begin to take more prey. The cycle repeats as there is a resulting shortage of prey.
As a population grows, overcrowding becomes a major problem for the
species at hand. Not only does overcrowding cause increased competition for resources as discussed above, it causes other imbalances that can be even more detrimental to the population. Disease becomes a major problem when a group of animals are in close proximity to each other. Just as the bubonic plague
spread very rapidly through the cities of Europe, diseases are passed along very easily when there is not enough room for a population to spread out. Some diseases, if fatal, can cause
population numbers to drop rapidly. Other diseases can debilitate the entire population, causing a decrease in the birth rate through different means, such as sterility.