Biodiversity and Conservation — Part 2: Loss of biodiversity: visual lesson, CBSE Class 12 Biology

Lesson

Loss of biodiversity

Part 2 — species are disappearing far faster than in pre-human times, mainly because of human activities.

In this lesson you will

Describe the scale of recent extinctions
Explain the effects of biodiversity loss
Explain the four major causes ("evil quartet") with examples

Concept

Recent extinctions

The IUCN Red List (2004) documents 784 extinctions in the last 500 years: 338 vertebrates, 359 invertebrates and 87 plants. In the last twenty years alone, 27 species have disappeared.

Table of recent extinctions with places
Extinct species	Where
Dodo	Mauritius
Quagga	Africa
Thylacine	Australia
Steller’s sea cow	Russia
Three subspecies of tiger (Bali, Javan, Caspian)	Asia

Concept

The sixth extinction

Earth has seen five episodes of mass extinction since life originated. The sixth extinction, now in progress, differs: current species extinction rates are estimated to be 100 to 1,000 times faster than in pre-human times, and human activities are responsible.

Table of the share of species in four groups that face the threat of extinction
Group	Share facing threat of extinction (percent)
Birds	12
Mammals	23
Amphibians	32
Gymnosperms	31

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