Impacts of human beings on biodiversity

Habitat loss and deforestation

 Habitat loss and deforestation (cutting down of trees) are greatest threat to important causes of species extinctions. As deforestation biodiversity on this Planet proceeds in tropical forests present in tropical zone of the world. it becomes the main cause of today. the mass extinction of species. All species have specific food and habitat needs. Tropical forests are important because they harbour at least 50 percent of the world's biodiversityDirect observations prove that these forests are declining. 
The original extent of tropical rain forests was 15 million square km. Now there remains about 7.5-8 million square km, so half is gone. 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. 

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 etc. Commercial hunting, both legal and illegal, is the principal threat. 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. 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 classification system.

Domino effects on species 

 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. 

Effect of pollution on species

 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. 

Effect of climate change on ecosystem

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. The race to produce cash through fruits, spices, sugar, tobacco, soap, rubber, paper, and cloth has stimulated many to get them by using soil and by destroying the forests. 

Effect of deforestation on ecosystem

 Deforestation means cutting down of trees for the conversion of a forest to non-forest land. It is done for using the land for various purposes such as pasture, urban use etc . The destruction of significant areas of forest has resulted in a degraded environment with reduced biodiversity.

 Causes and effects of deforestation

 Sometime there is slow forest degradation and sometime sudden and catastrophic clear-cutting for urban development. Deforestation can be the result of the deliberate removal of forests for agriculture or urban development, or it can be a consequence of Qrazing animals. 
 Deforestation affects the amount of water in the soil and the moisture in the atmosphere. When there are no trees to keep the soil in place, the soil becomes exposed for erosion. There is less protection from wind and rain and heavy rainfall washes the soil into rivers . Essential nutrients are washed out of the soil all-together. 
Rivers become choked up with mud and silt, which can cause floods. The silted water gets stored in dams and it reduces their water storage capacity and thus their lives. Deforestation also contributes to decrease  transpiration, which lessens cloud formation and less humidity. 
This ultimately reduces the sources of rains. Forests support considerable biodiversity, providing valuable habitat for wildlife. Moreover, forests look after medicinal conservation. The utilization of forest products, '"eluding timber and fuel wood, have played a key role in human societies, comparable to the roles of water and land. 
Today, developed countries continue to utilize timber for houses, and wood pulp for making paper. The forest products industry is a large Part of the economy in both developed and developing countries. Short-term economic gains made by conversion of forest to agriculture often leads to loss of long-term income. Forests are also important stores of organic carbon, and forests can extract carbon dioxide and pollutants from the air, thus contributing to biosphere stability. 
Forests are also valued for their aesthetic beauty and as a cultural resource and tourist attraction. Conservation of biodiversity biodiversity The conservation of biodiversity has become a global concern. Biologists consider biodiversity essential and agree on the significance of current extinction of species. 
Biologists urge the national policy makers to state a set of rules necessary to protect a species. They demand that the laws should define species which are threatened by extinction and must be protected. Though rich in biodiversity, world today faces severe threats for its biological resources. 
The greatest concern is the continuing loss of species and the loss of natural habitats. Main causes of this loss are largely associated with rapid growth in human population and the prevailing poverty in the rural areas of Pakistan.
 In addition low literacy rate and meagre resources are the reasons for limited success in conservation measures taken so far. The International Union for the Conservation of Nature and Natural Resources (IUCN) and the World Wildlife work in close coordination with Pakistan's Ministry of Environment and other government and non-government institutions. 
The IUCN has prepared the first national Red list of endangered or threatened species. According to this list following are the figures of the living and threatened species in Pakistan.Following are a few examples of environmental work that has been carried out in Pakistan in orderto conserve species and the associated habitats.