The Main Treats to Biodiversity

Source: Food and Agriculture Organization of the United Nations, 2013, Kieran Noonan-Mooney, CBD and Christine Gibb, CBD and FAO, "The Youth Guide to Biodiversity" 1st Edition (Chapter 2) Youth and United Nations Global Alliance. Reproduced with permission.

Chapter 2. Verbatim

1. Habitat loss occurs when natural environments are transformed or modified to serve human needs. It is the most significant cause of biodiversity loss globally. Common types of habitat loss include cutting down forests for timber and opening up land for agriculture, draining wetlands to make way for new development projects, or damming rivers to make more water available for agriculture and cities.
Habitat loss can also cause fragmentation, which occurs when parts of a habitat (the local environment in which an organism is usually found) become separated from one another because of changes in a landscape, such as the construction of roads. Fragmentation makes it difficult for species to move within a habitat, and poses a major challenge for species requiring large tracts of land such as the African forest elephants living in the Congo basin. Though some habitat loss is necessary to meet human needs, when natural habitats are changed or modified with little concern for biodiversity the results can be very negative. 

2. Climate change, which is caused by a build-up of greenhouse gases such as carbon dioxide in the Earth’s atmosphere, is a growing threat to biodiversity. Climate change alters the climate patterns and ecosystems in which species have evolved and on which they depend. By changing the temperature and rain patterns species have become accustomed to, climate change is changing the traditional ranges of species. This forces species to either move in order to find favourable conditions in which to live, or to adapt to their new climate. While some species may be able to keep up with the changes created by climate change, others will be unable to do so. Biodiversity in the polar regions (see box: “Arctic Sea Ice and Biodiversity”) and mountain ranges is especially vulnerable to climate change. 

3. Overexploitation, or unsustainable use, happens when biodiversity is removed faster than it can be replenished and, over the long term, can result in the extinction of species. For example: 

•• the once-plentiful cod fishery off the coast of Newfoundland, Canada has all but disappeared
because of overfishing; 

•• freshwater snakes in Cambodia are declining from hunting pressure; 

•• Encephalartos brevifoliolatus, a cycad, is now extinct in the wild after being overharvested for use in horticulture; 

•• Overexploitation, especially when combined with destructive harvesting practices, is a major cause of biodiversity loss in certain ecosystems.

4. Invasive alien species (IAS), or species that have spread outside of their natural habitat and threaten biodiversity in their new area, are a major cause of biodiversity loss. These species are harmful to native biodiversity in a number of ways, for example as predators, parasites, vectors (or carriers) of disease or direct competitors for habitat and food. 

In many cases invasive alien species do not have any predators in their new environment, so their population size is often not controlled (see box: “The Troublesome Toad”). Some IAS thrive in degraded systems and can thus work in conjunction with or augment other environmental stressors. IAS may also cause economic or environmental damage, or adversely affect human health. 

The introduction of invasive alien species can be either intentional, as with the introduction of new crop or livestock species, or accidental such as when species are introduced through ballast water or by stowing away in cargo containers. Some of the main vectors (carriers) for IAS are trade, transport, travel or tourism, which have all increased hugely in recent years.

5. The final driver of biodiversity loss is pollution. Pollution, in particular from nutrients, such as nitrogen and phosphorus, is a growing threat on both land and in aquatic ecosystems. While the large-scale use of fertilisers has allowed for the increased production of food, it has also caused severe environmental damage, such as eutrophication (see box below).