Impact of human beings on biodiversity:

To improve the living conditions for 600 million humans, we are imposing serious threats to the survival of much biodiversity.

1. Habitat loss and deforestation:

Habitat loss and deforestation (cutting down of trees) are important causes of species extinctions. As deforestation proceeds in tropical forests, it becomes the main cause of the mass extinction of species. All species have specific food and habitat needs.

Importance of Tropical forests:

Tropical forests are important because they harbor at least 50 percent of the world's biodiversity. Direct observations prove that these forests are declining. The original extent of tropical rain forests was 75 million square km. Now there remains about 7.5-8 million square km, so half is gone.

The closed canopy forest in the North West Frontier Province NWFP (KPK) of Pakistan is reported to be shrinking at approximately 1 % per year. More significant is the persistent spread of farmers into the forests: the killing of trees through lopping, burning, and tapping the development of small agricultural plots among the trees, and excessive grazing by domestic animals.

1. Over-hunting:

Over-hunting has been a significant cause of the extinction of hundreds of species and the endangerment of many more, such as whales, ibex, urial, Markhor (the national animal of Pakistan) etc. Commercial hunting, both legal and illegal, is the principal threat.

1. Introduction of new species:

Introduction of non-native species is an important and often overlooked cause of extinction. When new species are introduced to ecosystems the established species in that ecosystem may not survive. The new organisms may be predators, parasites, or simply aggressive species that deprive the established species of nutrients, water and light. For example, Eucalyptus plants were imported from Australia and introduced in Pakistan. These plants consume more water and have disturbed the water table (level of underground water). It harms other small plants that grow near Eucalyptus trees.

1. Domino effects:

Domino effects occur when the removal of one species (an extinction event) or the addition of one species (an invasion event) affects the entire biological system.

Domino effects are especially likely when two or more species are highly interdependent. For example, a starfish, facilitates the coexistence of many other invertebrates by eating mussels, which otherwise would harm other organisms. If starfish are eliminated from an ecosystem, mussels grow in number and prey on other animals.

1. Pollution:

Pollution from chemical contaminants certainly poses a further threat to species and ecosystems. While not commonly a cause of extinction, it harms those species whose range is extremely small.

1. Climate change:

A changing global climate (due to pollution and global warming) threatens species and ecosystems. The distribution of species (biogeography) is largely determined by climate. When changes in climate disturb the distributions of species, many species find it difficult to adjust themselves in new climates.