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:
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