Which of the following is not a cause of biodiversity loss?

The correct answer is Option (3) → Co-evolution

Option (1) Fragmentation — A cause of biodiversity loss. When large habitats are broken up into small pieces, animals that need large territories, such as mammals and birds, are badly hit and their numbers fall.

Option (2) Over-exploitation — A cause of biodiversity loss. Too much harvesting of a species by humans drove Steller’s sea cow and the passenger pigeon to extinction.

Option (3) Co-evolution — Not a cause of biodiversity loss. Co-evolution is the evolution of two species together, each changing in step with the other, as a plant and its pollinator do (the fig and its wasp). It is a process that builds diversity. The cause in the list is co-extinction, a different word.

Option (4) Alien species invasion — A cause of biodiversity loss. Introduced species can turn invasive. The Nile perch put into Lake Victoria wiped out more than 200 species of cichlid fish.

NCERT Extract:
Loss of Biodiversity – “In general, loss of biodiversity in a region may lead to (a) decline in plant production, (b) lowered resistance to environmental perturbations such as drought and (c) increased variability in certain ecosystem processes such as plant productivity, water use, and pest and disease cycles. Causes of biodiversity losses: The accelerated rates of species extinctions that the world is facing now are largely due to human activities. There are four major causes (‘ The Evil Quartet ’ is the sobriquet used to describe them).
(i) Habitat loss and fragmentation: This is the most important cause driving animals and plants to extinction. … When large habitats are broken up into small fragments due to various human activities, mammals and birds requiring large territories and certain animals with migratory habits are badly affected, leading to population declines.
(ii) Over-exploitation: Humans have always depended on nature for food and shelter, but when ‘need’ turns to ‘greed’, it leads to over-exploitation of natural resources. Many species extinctions in the last 500 years (Steller’s sea cow, passenger pigeon) were due to overexploitation by humans.
(iii) Alien species invasions: When alien species are introduced unintentionally or deliberately for whatever purpose, some of them turn invasive, and cause decline or extinction of indigenous species. The Nile perch introduced into Lake Victoria in east Africa led eventually to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish in the lake.
(iv) Co-extinctions: When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct. When a host fish species becomes extinct, its unique assemblage of parasites also meets the same fate. Another example is the case of a coevolved plant-pollinator mutualism where extinction of one invariably leads to the extinction of the other.”