Ecological pyramids

What a lovely day to go birdwatching in the forest, right, Seamus? There are so many trees and bushes here, butterflies are everywhere, even spiders - but are there any birds here? Oh, here comes one! If we look around, we can notice that there are more plants than animals. But why is that?

Plants produce their own food using sunlight, water, and carbon dioxide. They are PRODUCERS. Butterflies eat plants - they are PRIMARY CONSUMERS. Some species eat other animals, for example, spiders eat butterflies. These are SECONDARY CONSUMERS.

Spiders are also eaten by other animals, for example birds - TERTIARY CONSUMERS. This sequence of who eats whom is called a FOOD CHAIN. Different levels of the food chain are called TROPHIC LEVELS. We can count all the individuals from different trophic levels and create a diagram to show how many there are. We do this with the plants, butterflies, spiders, and the blue tit we can see here.

Does the shape remind you of something? We created the first of the three ecological pyramids - the PYRAMID OF NUMBERS. But sometimes, the pyramid of numbers can be tricky. Imagine if all these butterflies were living on just one tree. How is it possible that so many butterflies can eat from only one plant?

The answer is simple - the tree is much bigger! Instead of counting individual organisms, we can measure how much they weigh altogether. This is their BIOMASS. If we draw it again as a diagram, we create the second ecological pyramid - the PYRAMID OF BIOMASS. But this still doesn’t answer why there are more plants than birds!

Animals eat other organisms because they need energy. Different levels of the food chain have different amounts of energy passing through them. Producers, such as plants and algae have the most energy, because they absorb energy from the sun. Consumers receive energy from the levels below, but most of the energy is lost between the levels. We can represent this with a diagram showing how much energy passes through each level.

In this way we can create the third pyramid - the PYRAMID OF ENERGY. To get all the energy it needs, the bird has to eat many spiders. And all those spiders must eat even more butterflies! Look at all the pyramids. Can you see some similarities?

They all have a big base of producers, and a very small top for the final consumer. Each trophic level relies on the levels below. This is how nature keeps in balance. What do you think happens if something goes wrong at one of the levels? It will affect the levels above.

If there is no food for the consumers, they will die or move somewhere else. Plants play a very important role: they provide energy for the whole food chain and support all the organisms above. That’s why there are more of them than birds. If there are enough plants, there should also be birds close by! And all you need to do, Seamus, is just look a little bit closer!