Limiting Factors

When living conditions in an area are good, a population will generally grow. But eventually some environmental factor will cause the population to stop growing. A limiting factor is an environmental factor that causes a population to decrease. Some limiting factors for populations are food and water, space, and weather conditions.

Organisms require food and water to survive. Since there isn’t always an endless amount of food and water, they are limiting factors. Suppose a bear must eat 10 fish a day to survive. The river nearby provides about 100 fish a day without harming the fish population. Five bears could easily live in this area because they would only need 50 fish total. But if there were 15 bears they would not all survive because there would not be enough food. No matter how much shelter and water there was, the population would not get larger than 10 bears for any extended period of time.

Space is another limiting factor for populations. Seagulls, for example, come to nest on rocky shores. But the nesting shores get very crowded. If a pair does not find room to nest, they will not be able to add any offspring to the seagull population. So nesting space on the shore is a limiting factor for seagulls. If there were more nesting space, more seagulls would be able to nest, and the population would increase.

Space is also a limiting factor for plants. The amount of space in which a plant grows determines whether the plant can get the sunlight, water, and soil nutrients it needs. For example, many small plants sprout each year in a forest. But as they grow, the roots of those that are too close together run out of space and some of the plants will die. Branches from other trees may block the sunlight the small plants need. Some of the small plants might die, limiting the size of that plant population.

Weather conditions such as temperature and the amount of rainfall can also limit population growth. A cold front that comes in late spring can kill the offspring of many species of organisms, including plants, birds and mammals. A hurricane or flood can wash away nests and burrows. Such unusual events can have long-lasting effects on population size.