Have you ever seen a diagram that shows a pyramid of living things in an ecosystem? There has to be a whole lot of grass to feed a grasshopper, a whole lot of grasshoppers to feed a rat, a whole lot of rats to feed a snake, and a whole lot of snakes to feed a hawk.
It reminds me of a children's story! (“This is the cat that ate the rat that ate the malt that lay in the house that Jack built...”)
This food chain of grass → grasshopper → rat → snake → hawk is oversimplified, since each of the consumers eats other things as well. However, the point is that the numbers of organisms at each higher level of the food chain tend to get smaller. That's why we can represent such food chains as pyramids.
The ecological “pyramid of numbers” was first presented by today's birthday boy, English scientist Charles Elton. He was born on this date in 1900, and he did several studies on Arctic ecosystems.
Aside from the pyramid of numbers, Elton described ecological niches and studied what happens to an ecosystem when an invasive species is introduced. Here are some websites to help you explore Elton's ideas:
- Here is a nice website on food chains. Notice the diagram of an ecological pyramid.
- BBC's Bitesize offers more pyramid diagrams.
- Happenin' Habitats features a habitat web activity.
- An ecological niche is kind of like a job or role that a plant or animal does within a particular habitat. For example, in the coastal waters of Washington state, I got to see a pod of dolphins that fit in the niche of feeding on smaller porpoises and seals, and later I saw another pod of dolphins that fit in the niche of feeding on salmon. Because the two different pods eat different things, they behave in different ways; their hunting patterns are different, and the mammal-eaters are always on the move, while the fish-eaters pretty much stay in one place. It's like comparing two groups of humans, deer-hunters and wheat-growers. Other creatures who live in the same coastal waters include Dungeness crabs, which eat clams and small fish but which freelance as scavengers, eating bits of “trash” and debris—dead bodies and body parts that would mess up the habitat if there were no scavengers. Gulls also eat small fish and act as scavengers, but they feed in deeper water than do crabs.
- National Geographic Kids tells us about plant invaders.
Also on this date: