Species become endangered due to both natural and anthropogenic causes. Since man has no control over natural causes, we should consider anthropogenic causes only. Anthropological causes may be classified into two fundamental categories: Direct Causes and Indirect or underlying causes.
DIRECT CAUSES
The direct causes of loss of biodiversity are grouped into the following categories-
A. Over-exploitation of Biological Resourceshttps://www.nature.com/articles/s41467-019-09246-2: Human beings have been exploiting flora and fauna since the emergence of civilization. However, for a few decades, the rate of exploitation has reached an unsustainable level. Illegal trade in the parts of flora and fauna has aggravated this activity further. Here are some examples that reflect unsustainable levels of exploitation of biological resources.
The demand for animal body parts in traditional medicines has gradually increased within the last few decades in South and East Asia. This has accelerated the illegal activity of poaching and hunting of tigers in South Asia; Sea-horses, tortoises, and species of river turtles; uncontrolled harvesting of fresh water and marine fishes, for example, Sturgeon in Central Asia; and poor management practices of marine resources such as blast fishing, fishing with cyanide, muroami netting or pounding reefs with weighted bags to scare fish out of crevices and coral harvesting etc.
The loss or degeneration of species worldwide is not a sudden process. Instead, it took decades, mainly due to human population growth and exploitation by human beings. In a nutshell, some of the major causes due to which species become extinct are mentioned below.
(i). Growth of human population and activities of exploitation, overuse and misuse of resources by human beings.
(ii). Unsustainable pattern of consumption of resources of nature.
(iii). The production of wastes and pollutants is increasing, followed by different types of hazards in the air, water, and land.
(iv). Development of urban areas, deforestation, mining activities, etc.
(v). International conflict.
(vi). Continuing inequalities in the distribution of wealth and resources.
(vii). Loss of habitats, habitat destruction and habitat fragmentation.
(viii). Decline and loss of species due to various reasons, such as illegal trade, poaching of animals, smuggling of wood, natural calamities, overuse, etc.
(ix). Climate change and global warming.
(x). Nitrogen deposition in the soil is due to the increasing use of nitrogenous fertilizers in agriculture.
(xi). Oil spills on the sea surface cause various bird and fish species to die.
(xii). Introduction of invasive species.
B. Loss, degradation or Fragmentation of habitats
Human development activities, including expansion of human habitation, changes in agricultural practices, expansion of agriculture, Jhoom cultivation, clearing of forests for different purposes, mining and quarrying, Pasteur development, etc., have been damaging, altering, and fragmenting habitats for a long time.
During all these activities, plants and animal species are lost to a considerable extent, directly impacting the environment. According to different assessments, about 68 per cent of reptile species, 58 per cent of amphibian species, at least three-quarters of bird species, and an equal number of mammal species have become endangered due to the loss, degradation, alteration, and fragmentation of terrestrial habitats.
Aquatic habitats, such as fresh and marine water sources, are also under severe pressure due to urbanization, agricultural expansion, river engineering, such as dam construction, drying of wetlands and backwaters, and changing flow regimes to downstream lakes and estuaries, and coastal development, including dredging, filling, breakwater construction, mining, and drilling.
The degradation of habitats due to pollution causes direct and cumulative impacts on species’ existence in ecosystems. Marine water pollution caused by contamination with oil wastes, radioactive wastes, pesticides, and other toxic chemicals causes direct impacts. The cumulative impacts of water pollution, like eutrophication and the development of algal blooms followed by water poisoning and lowering the clarity of water and the oxygen level, can also cause severe losses. The bleaching of corals is another profound impact of marine water pollution.
