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Question

Enlist four causes that may lead to the loss of biodiversity.

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Solution

The world is facing accelerated rates of species extinctions, largely due to human activities. There are four major cause of biodiversity losses, called as ‘The Evil Quartet’.
  • Habitat loss and fragmentation: It is the most important cause driving animals and plants to extinction.
  1. When people cut down trees, fill a wetland, plough a grassland or burn a forest, the nature habitat of a species is changed or destroyed. These changes can kill or focus out many plants, animals and microorganism as well as disrupt complex interaction the species. The amazon rain forest harbouring probably millions of species is being cut and cleared for cultivating soya beans or for conversion to grasslands for raising beef cattle.
  2. Besides total loss, the degradation of man y habitats by pollution also threatens the survival of many species. Pollution may reduce and eliminate populations of sensitive species. For example, pesticide linked decline of fish-eating birds and falcons.
  3. Large habitats and broken into small fragments in habitats fragmentation. It is due to various human activities like human settlements, building of roads, digging of canals etc. Forest patched having croplands, orchards, plantations and urban settlements on their outskirts are examples of fragmented habitats. Animals requiring large territories and migrating animals are badly affected, leading to population declines.
  • Over-exploitation: Humans have always dependent on nature for food and shelter, but when need turns to greed, it leads to over-exploitation of nature resources. It means, biological systems should not be exploited beyond the degree of their renewability. Overexploitation of a particular species reduces size of its population to an extent so that it become vulnerable to extinction. Dodo, Steller’s sea cow and Passenger pigeon have become extinct in the last 500 year due to overexploitation by humans.
  • Alien species invasions: New species entering a geographical region are called exotic or alien or non-nation species. When alien species are introduced unintentionally or deliberately for whatever purpose, they may cause disappearance of nation or indigenous species through changed biotic interactions. For examples, carrot glass is a weed which came into-India as a contaminant with imported wheat. It has occupied all open areas extermination many herbs and shurbs.
  • Co-extinctions: there are many obligate associations amongst different species in ecosystems. When one of them become extinct, the plants and animals species associated with it in an obligatory way also become extinct. For example, coevolved plant-pollinator mutualism will result in extinction of one partner if the other is eliminated in nature. If the host fish become extinct, all the parasites exclusively found on it will also become extinct.

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