The definition of extinction is very simple and occurs when "the last existing member of a given species dies".

Extinction can occur on a global scale where the last member of that species on the planet becomes extinct, or it can happen on a local scale where the last member of the species in an area dies.

But no matter how small or large the area is, a loss in species means a loss in overall biodiversity as well as the roles they play in our ecosystems, such as pollinators, predators, biological control agents, just to name a few. But why do species go extinct? What are the reasons?

If we know this maybe we can stop this destruction of our biodiversity.

One of the most influential causes of extinction is habitat loss and degradation, which affects about 86% of birds, 86% of mammals and 88% of amphibians whose existence on this planet is considered threatened. A suitable habitat must provide its occupants with protection from the elements, food, water and mates. But our increasing global human population means that more and more land is cleared to build businesses, industries, health and education facilities as well as to cultivate crops.

Deforestation and pollution can destroy or remove these habitats completely. A change in habitat can also cause extinction, for instance, when an area of land is cleared, for farming, mining or quarrying.

The first occupants that regrow in the area are grasses, so that the original occupants of the area that called the forests home become locally extinct, as the species composition changes.

Destruction of the habitat in some cases may not mean extinction to some species that live there.

Fragments or patches of habitat left behind may not be able to support native species in the area, for a variety of reasons, for example, they may not contain prey in adequate amounts. Mobile species like birds, butterflies, bats and small mammals are able to move between patches, therefore getting steady access to resources and are more likely to avoid becoming extinct.

However, smaller or less mobile animals would be trapped in these fragments. The existence of the species would persist for some time after the fragments have been formed but with time in-breeding would take place resulting in offspring with genetic diseases or defects or lower resistance to disease in general.

However, these weak offspring would themselves produce weaker offspring if they are lucky to survive to reproduce.

Some species are what can be regarded as specialists so that changes in the environment brought about by various types of pollution and climate change, may place the conditions out of the tolerance range for those animals. So if an animal can tolerate a certain temperature, even a slight change can make it go locally extinct in that area.

Predation is another cause of extinction, simply because predators can eat all the prey in one area.

Predators can multiply in an area if the resources and conditions are favourable.

So in order to supply their increasing population, the predators must consume more prey, therefore making their prey species locally extinct.

The introduction of invasive alien species that is, species that are not native to the area is another cause of extinction. Species of this nature can introduce diseases to the native species. They can also out-compete the native species for habitat space, food and other resources.

However, in closing I would like to emphasise that not every bad thing that happens in the environment can be blamed on human activities. Some cases of extinction are actually caused by nature. Natural disasters like floods, droughts and volcanoes can also destroy or alter the landscape and the habitats they contain. In general, natural factors cause extinction to occur at a slower rate compared to that caused by human activities. Unfortunately human activities are responsible for present day extinction rates.

The rate of extinction caused by human activities is estimated by some experts to be between 100 to 1,000 times and by others to be 1,000 to 11,000 higher. But if we know the cause of an environmental problem it is up to us to make a difference and stem the rate of extinction.

Our survival depends on it.