I got myself interested in what's really happening with the wildebeest population. Why has it stabilized? What is limiting the wildebeest population growth?
[NARRATOR:] To consider the factors that might regulate the wildebeest, imagine an ecosystem as a pyramid. At the base of the pyramid are primary producers like plants that get their energy from the sun. Those plants are eaten by herbivores like wildebeest, which are in turn eaten by predators like lions at the top.
[SIMON:] Wildebeest being at the middle of the pyramid, you can think of two things which could be limiting the wildebeest population growth. One would be food because herbivores have to feed on plants, which is at the bottom of the pyramid. On the other hand, it could be from above, which are predators feeding on the herbivores.
[NARRATOR:] When a population is limited by its food supply, we say that it's regulated from the bottom up. If, however, the population is limited by predators, we say that it's regulated from the top down. To figure out how the wildebeest population was regulated, Simon and Tony needed, of all things, dead animals.
They began examining hundreds of dead wildebeest to determine the most common cause of death — predators or lack of food.
