Biodiversity is threatened by anthropogenic activities in many ways like habitat loss, poaching of wildlife, and man-wildlife conflicts.
Habitat loss:Habitat is the sum total of the environmental factors, food, cover, and water that a given species needs to survive and reproduce in a given area. Eg: forest habitat and forest birds, alpine habitat and associated species. Niche represents the totality of organisms, adaptations, use of resources and the species it interacts with. Limiting factor is a factor that limits the numbers of a species. For plants, the limiting factors are nutrients, water, sunlight, temperature, competitors, herbivores or parasites; and for animals, the limiting factors are food, special habitat required (like nest sites, water temperature, soil type), competitors, predators and parasites.
Habitat can be destroyed or degraded in two basic ways i.e. quantitative and qualitative losses. Quantitative losses can be measured by looking at a previously mapped area and determining how much of the habitat area is no longer present. Eg: If the area of productive forests and grasslands is reduced and turned into deserts and wastelands, it’s a quantitative loss. Wetlands have been drained to increase agricultural land.
Qualitative changes involve a change or degradation in the structure, function or composition of the habitat. Eg: If a paper company is discharging chemicals into a waterway and poisoning the water, there has been a qualitative loss. The main causes of habitat loss are
- Agriculture activities, extraction including mining, fishing, logging and harvesting, rapid population growth and development (human settlements, industry and associated infrastructure).
- Natural forests are being deforested for timber and replanted using teak, sal or either single species for their timber value which has altered the local biodiversity.
- Repeated fire started by local grazers to increase the growth of grass ultimately reduces regeneration and lowers the diversity of plant species.
- The greatest risk to biodiversity is habitat loss and habitat fragmentation. Habitat loss is in many cases irreversible.
- Mangroves have been cleared for fuel wood and prawn farming, which has led to a decrease in habitat essential for the breeding of marine fish.
- Habitat loss and fragmentation leads to the formation of isolated, small, scattered populations. These small populations are vulnerable to inbreeding depression, high infant mortality and susceptible to environmental degradation and possible extinction.
- Exploitation such as hunting, collecting, fisheries and trade are a major threat to birds (37%), mammals (34%), plants (8% ), reptiles and marine fishes.
- Habitat loss also results from man’s introduction of species from one area into another, disturbing the balance in existing communities. Eg: introduction of water hyacinth, congress grass or Parthenium have led to the extinction of many local species as well as adversely affected human health.
- A variety of traditional farming techniques like slash-and-burn cultivation in the Himalayas, and ‘rab’, lopping off tree branches to act as a wood-ash fertilizer in the Western Ghats are now unsustainable and are leading to a loss of forest biodiversity.
- The over-harvesting of fish, especially by means of large trawling boats, is leading the serious depletion of fish stocks.
- Poaching of wild life
- Man-wildlife conflicts