`star` Mass Extictions
`star` Cause of Biodiversity losses
`star` Habitat loss and fragmentation
`star` Over-exploitation
`star` Alien species invasion
`star` Co-extinctions


● From a `color{violet}("study of the history of life")` on earth through `color{violet}("fossil records,")` we learn that `color{violet}("large-scale loss")` of species like the one we are currently witnessing have also happened earlier, even before humans appeared on the scene.

● During the `color{violet}("long period (> 3 billion years)")` since the `color{violet}("origin")` and `color{violet}("diversification")` of life on earth there were five episodes of `color{brown}("mass extinction of species.")`

● How is the `color{brown}("‘Sixth Extinction’")` presently in progress different from the previous episodes

● The difference is in the `color{violet}("rates")`; the current species `color{violet}("extinction rates ")` are estimated to be `color{violet}("100 to 1,000")` times faster than in the pre-human times and our activities are responsible for the faster rates.

● `color{violet}("Ecologists")` warn that if the present trends continue, nearly half of all the species on earth might be wiped out within the next 100 years.

● In general, `color{violet}("loss of biodiversity")` in a region may lead to

(a) Decline in `color{violet}("plant production")`

(b) Lowered resistance to `color{violet}("environmental perturbations such as drought")`.

(c) Increased variability in certain `color{violet}("ecosystem")` processes such as `color{violet}("plant productivity, water")` use, and `color{violet}("pest")` and `color{violet}("disease cycles.")`


● The `color{violet}("accelerated rates")` of species extinctions that the world is facing now are largely due to human activities.

● There are four major causes (`color{brown}("‘The Evil Quartet’")` is the sobriquet used to describe them).

(i) `color{violet}("Habitat loss and fragmentation")`
(ii) `color{violet}("Over-exploitation")`
(iii) `color{violet}("Alien species invasions")`
(iv) `color{violet}("Co-extinctions")`


● This is the most `color{violet}("important cause")` driving `color{violet}("animals")` and `color{violet}("plants")` to extinction.

● The `color{violet}("most dramatic")` examples of `color{brown}("habitat loss")` come from `color{violet}("tropical rain forests")`.

● Once covering more than `color{violet}(14%)` of the `color{violet}("earth’s land surface")`, these rain forests now cover no more than `color{violet}("6 %)`

● They are being `color{violet}("destroyed fast.")`

● By the time one finishes reading this chapter, `color{violet}("1000 more hectares")` of `color{violet}("rain forest")` would have been lost.

● Besides `color{violet}("total loss")`, the `color{brown}("degradation")` of many `color{violet}("habitats")` by `color{violet}("pollution")` also threatens the survival of many species.

● When large `color{violet}("habitats")` are broken up into small `color{violet}("fragments")` due to various human activities, mammals and birds requiring large `color{violet}("territories")` and certain animals with `color{violet}("migratory habits")` are badly affected, leading to population declines.


● Humans have always depended on `color{violet}("nature for food")` and `color{violet}("shelter,")` but when `color{violet}("‘need’")` turns to `color{violet}("‘greed’")`, it leads to over-exploitation of ●

● Many species extinctions in the last `color{violet}("500 years (Steller’s sea cow, passenger pigeon)")` were due
to `color{violet}("overexploitation")` by humans.

● Presently many marine `color{violet}("fish populations")` around the world are `color{violet}("over harvested")`, endangering the continued existence of some commercially important species.


● When `color{brown}("alien species")` are introduced `color{violet}("unintentionally")` or `color{violet}("deliberately")` for whatever purpose, some of them turn invasive, and cause `color{brown}("decline")` or `color{brown}("extinction of indigenous species.")`

● The `color{violet}("Nile perch")` introduced into `color{violet}("Lake Victoria")` in east Africa led eventually to the extinction of an ecologically unique assemblage of more than `color{violet}("200 species of cichlid fish")` in the lake.

● One must be familiar with the `color{violet}("environmental damage")` caused and threat posed to our native species by invasive weed species like carrot grass `color{violet}("(𝘗𝘢𝘳𝘵𝘩𝘦𝘯𝘪𝘶𝘮)")`, Lantana and water hyacinth `color{violet}("(𝘌𝘪𝘤𝘤𝘩𝘰𝘳𝘯𝘪𝘢)")`.

● The recent illegal introduction of the African catfish `color{violet}("𝘊𝘭𝘢𝘳𝘪𝘢𝘴 𝘨𝘢𝘳𝘪𝘦𝘱𝘪𝘯𝘶𝘴")` for aquaculture purposes is posing a threat to the indigenous catfishes in our rivers.


● When a species becomes extinct, the `color{violet}("plant")` and `color{violet}("animal")` species associated with it in an obligatory way also become extinct.

● When a `color{violet}("host fish species")` becomes extinct, its `color{violet}("unique assemblage")` of parasites also meets the `color{violet}("same fate.")`

● Another example is the case of a `color{violet}("coevolved plant-pollinator mutualism")` where extinction of one invariably leads to the extinction of the other.