Populations Bill Nye, the Science Guy : Season 3 Episode 19

Populations need a couple of basic things to survive – food and a place to live. When two or more populations of living things are crowded into a small area, there is competition for food and space. A population of birds and a population of squirrels compete for seed and bread crumbs in a park. Competition is a natural part of life, but problems can arise if populations get out of balance.