Teacher's Notes on Biodiversity
What does biodiversity mean?
Biodiversity or biological diversity is the variety of all forms of life – the different plants, animals and micro-organisms, the genes they contain and the ecosystems of which they form a part.
There are roughly two million species living on this planet that have been described. While this might seem like a large number, the truth is that it only represents a fraction of the sum total. Nobody is sure how big this number might be, yet in some ways it is fairly insignificant. What truly matters is how each of these species differs from one another.
Ecosystems are self-organising and self-supporting collections of species living together. They are formed by a combination of biotic (living) and a-biotic (non-living) factors. Many of these factors are influenced by one another; for instance, temperature and humidity might vary with the density of the trees, which depends on the rain and soil conditions. The animals living within the forest might rely on one another for food. Some relationships may result in protection, or the production of homes for smaller animals, or any number of tasks that make it possible for another living thing to flourish.
How can we describe biodiversity?
More than simply being a measure of the variety of species in an ecosystem, biodiversity indicates the complexity of the relationships between all of the factors making up an ecosystem.
Although the definition of ‘biodiversity’ encompasses genetic diversity through to landscape-level ecosystem diversity, it is species diversity that is most commonly targeted. Taxonomists study species variation using a classification system that resembles a family tree.
Another analogy would be a house. In each house there are five floors, called ‘kingdoms’. On each floor, there are a number of rooms, called ‘phyla’. Every room has cupboards called ‘classes’. The cupboards have shelves called ‘orders’. On every shelf sits a basket called a ‘family’. Inside these baskets are boxes labelled ‘genus’. Finally, in each box is a tiny jar called ‘species’.
Every single living thing will be contained within one of these jars inside the house. We tend to describe them according to the box (or genus) and their jar (or species).
There is one problem with this arrangement – as useful as this system is, it forces us to see every organism as if it is distinctly contained in its own category. The truth is, life is more like a rainbow. It is a hazy spectrum, where the line between ‘red’ and ‘orange’ isn’t sharply defined.
We can label two similar organisms as different species if they don’t breed under natural conditions to form reproducing offspring. However this is not always going to give clear answers. Many organisms, such as bacteria, regularly share genes regardless of their classification.
Counting the number of species in an area, and how many individuals of each species, however, remains an effective way of hinting at the extent of biodiversity.
Why is biodiversity important?
Occasionally, a sudden change in the environment leaves a species unable to cope. As the population reduces in size, other species that relied on its presence also struggle to survive. This ‘knock-on’ effect can dramatically change the nature of an ecosystem in a rather short period of time. A new ecosystem will eventually take its place; forests can become grasslands, grasslands can become deserts, deserts might even become wetlands and wetlands turn to forests. In other words, small changes can have large consequences.
Biodiversity provides a greater chance that an ecosystem will cope with such changes. Across the world, we all rely on different ecosystems to provide us with resources. Changing one ecosystem into another could create a number of problems, such as depriving us of food and water or increasing the risks of disease. We also have an ethical obligation to consider our impact on those species that share our resources.
Maintaining natural levels of biodiversity in our ecosystems also contributes to the maintenance of ‘healthy’ ecosystems – that is, ecosystems that are maximally productive (carbon fixation), that provide both a store and a supply of clean water, that provide adequate vegetation cover thus preventing erosion and other soil problems like salinity, and that provide habitat for animals.
Refer to websites for support material.
The Global Biodiversity Information Facility
World Wildlife Fund