The biodiversity of a habitat refers to species richness and abundance of plant and animal species in that habitat.

The biodiversity is important because the greater it is, the greater the interaction between the different species, and the greater the stability of the diverse population as a whole.

The different species of plant and animal are linked together in food chains and food webs. This is because the primary source of food for all living things (including us!) comes from sunlight energy. Energy is the capacity to do work. In the case of living organisms, the “work” is metabolising, growing, and reproducing.

Food Chains: Green plants are able to photosynthesise: to trap the energy from the sun using their green chlorophyll, converting simple chemicals from the environment into the complex chemicals which they need to work: to grow and multiply. The simple chemicals include carbon, hydrogen, nitrogen, oxygen, phosphorus, potassium.

Animals are unable to photosynthesise, so they live by eating plants, thus gaining their food energy “second hand”. So herbivorous animals graze on plants, and grow and multiply.

Carnivorous animals live, not by eating plants, but by eating other animals, and so they gain their energy “third hand” and can grow and multiply.
Omnivorous organisms, including ourselves, eat both plant and animal foods. (Think of what you had for lunch today. What path did your food energy take from the sun?)

Simple Food ChainA simple food chain: Fig. 1

Food webs: In general, food chains are interlinked. For example, blackbirds eat a wide range of food items such as worms, insects, slugs, snails, berries.
Cabbage white butterfly larvae are also eaten by hedgehogs, thrushes and others.
Blackbirds themselves are eaten by sparrowhawks, foxes and others.

A simple food webA food web: Fig 2.

The greater the web of linkages between the food chains, the greater the stability of the ecosystem. This is because each organism has a range of food choices: For example, if there are no butterfly larvae on the cabbages, the blackbird can eat more slugs, berries or insects and not go hungry.
When an animal such as a fox dies, it still provides food for a host of other decomposer organisms: bacteria, fungi, carrion beetles, worms: each gaining its food, until the fox carcase has disintegrated and the complex chemicals of its body reduced to simple chemicals and the energy has all been used. These simple chemicals are thus returned to the environment.

Cycle of LifeThe cycle of life: Fig.3

The sun’s energy flows through the cycle of life. At each step in the food chain, as the chemical energy is used up, about 90% of the energy is lost as heat. So there is a limit to the length of the food chain when all the trapped energy has been used up. For this reason, life is dependent on the ongoing availability of sunlight energy.

On the other hand, the simple chemicals used by plants in photosynthesis are continuously recycled through the cycle of life.

Máire Mulcahy is a member of the SMA Justice Committee.

Find more resources here: Biodiversity