Most analyses of global capacities to produce food and harness energy indicate that this figure is at or very near the absolute carrying capacity of the earth. Even allowing for increases in efficiency, it is difficult to see how the earth can support a population that is twice the size of today's. Some ecologists beleive that we may have already reached the earth's carrying capacity, and that the environmental degradation that we see in the world is the result of a human population that is not sustainable. The only realquestion is whether that control will occur through global starvation, malnutrition, and conflict, or as a consequence of planning and foresight. V. Extinction of Populations Extinction is the loss of all individuals in a population.
Local extinction refers to loss of all individuals from a given area.
The cause is environmental change or loss of habitat. The changes may be biological or physical. For example, large scale extintions occurred in South America 3 million years ago when the Panama land bridge allowed placental mammals to invade and outcompete South American marsupials.