Species Extinction Processes and Episodes of the Past and Current and Global Ecological Challenges

 

                                              

Extinction is the termination of a species via the death of its last member. A taxon may become functionally extinct before the death of its last member if it loses the capacity to reproduce and recover.

Mass Extinction Events

• Mass Extinction : A widespread and rapid decrease in biodiversity on Earth, where the extinction rate far exceeds the background rate.

 • Extinction: When a species becomes extinct, all its genetic heritage is lost. The species evolve into new species in order to adapt to the environmental changes or changes in the genetic heritage.

 Over 99% of all the species that once lived on the Earth, amounting to over five billion species, are estimated to be extinct. As per the estimations on the number of current species, a range from 10 -14 million, of which more than 1.2 million have been studied and more than 86% have not yet been discovered

Based on the fossil record today’s extinction rate is hundreds, or even thousands, of times higher than the natural baseline rate. A drastic, permanent reshaping of the tree of life and ecological structure

Species extinction rate: It is the number of species that go extinct within a given time, usually measured per year or per million species. 

Extinction is a fact of life. Most species, probably all, become extinct eventually. More than 99% of species known to science are now extinct. Current rates of extinction are alarmingly high (1,000 to 10,000 times higher according to IPBES, WWF)

Five Major Mass Extinctions

 • End-Ordovician (~444 million years ago): Caused by the glaciation of Gondwana leading to rapid cooling and falling sea levels. ~86% of species

 • Late Devonian (~375 million years ago):A prolonged crisis over millions of years linked to ocean anoxia and volcanism. ~75% species loss, devastating reef systems and armored fish.

 • End-Permian, "The Great Dying" (~252 million years ago): ~96% species loss. Triggered by Siberian Traps volcanism, caused extreme warming, ocean acidification. Recovery took ~10 million years. 

• End-Triassic (~201 million years ago): Driven by massive volcanism (CAMP eruptions), leading to rapid warming and acid rain. 76% of species lost.

 • End-Cretaceous (K-Pg) (~66 million years ago): Caused by an asteroid impact, led to an "impact winter," global fires, and ~80% species loss, including non-avian dinosaurs

Overexploitation

 • Bushmeat Trade: Emptying forests of wildlife in West & Central Africa, Southeast Asia.

 • Industrial Fishing: Over 1/3 of global fish stocks overfished. Bycatch (e.g., dolphins, turtles, seabirds).

 • Wildlife Trade: Rhino horn, elephant ivory, pangolin scales, exotic pets.

 • Case: North Atlantic Cod Fishery Collapse (1992)– A classic example of overexploitation leading to commercial extinction and ecosystem shift.

  Unsustainable hunting, fishing, and logging 

 Industrial-scale exploitation far exceeds sustainable yields.

  Commercial fishing removes 85 million tones of fish annually, disrupting marine ecosystems.

  Logging of old-growth forests eliminates critical habitat and carbon sinks.

  Bushmeat hunting threatens iconic species like gorillas and chimpanzees across Africa.

  The WWF Living Planet Report (2022) found that wildlife populations declined by 69%since 1970, overexploitation is one of the top causes

Rescuing Life from the Edge

Arabian Oryx (Oryx leucoryx) – Middle East 

• Once extinct in the wild due to overhunting

 • Reintroduced through breeding programs from just 9 individuals

 • Now over 1,000 living freely

 • Status: Extinct in the wild (1970s) → Reintroduced into protected desert reserves in Oman and Saudi Arabia The Arabian Oryx was the first species ever to recover from “Extinct in the Wild” status (Vulnerable now

Indus River Dolphin (Platanista gangetica minor) – Pakistan

• Nearly extinct in the 1970s due to dams, pollution, and entanglement

 • Protected under the Sindh Wildlife Protection Act; rescue programs started 

• Population grew from ~150 in the 1970s to over 1,800 today

 • Now one of the few freshwater dolphin recovery success stories in the world