The carrying capacity of an area is the number of individuals of a species that can
survive in that area over time. In most populations, four broad categories of factors determine the carrying capacity for a population. These factors are: (1) the availability of raw materials, (2) the availability of energy, (3) the accumulation of waste products and their means of disposal and (4) interactions among organisms. The total of all of these forces acting together to limit populations size is known as environmental resistance, and certain limiting factors have a primary role in limiting the size of a population. In some cases, these limiting factors are easy to identify and may involve lack of food, lack of oxygen, competition with other species, or disease.