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Conservation biology
Chapter 60
Extinction
 All species become extinct eventually
 More than 99% of species known to science are now extinct
 Current accelerating loss of habitat
 20% of present day species will be extinct by the middle of this century
 2000 of the world’s 8600 species of birds could go extinct
The evolutionary history of extinction
 Almost 99% of the species that one time existed have become extinct
 Mass extinctions
 Extinction is usually compensated for by the creation of new species
 Overall diversity has increased
Extinction now
 Extinction rates are currently 1,000 to 10,000 times “background” extinction
rates
 As much as 20% of current biodiversity may be lost by 2050
 Humans are primary cause of extinctions today
Anthropogenic extinctions
 In recent history, extinction is almost invariably associated with human
colonization of unoccupied areas
Human-caused extinction
 Members of Homo sapiens caused extinction even in prehistoric times
 Mammoths and mastodons, giant sloths, saber-toothed tigers
 74% - 86% of mega fauna thought to have been caused by human hunting
Why have African megafauna survived ?
 Perhaps because animals coevolved with humans there
 Animals evolved counteradaptations to human predation
Island extinction
 Majority of extinctions have occurred on islands
 85 species of mammals; 60% lived on islands
 Why are islands so vulnerable ?
 Evolved in the absence of predators
 Humans introduced competitors, diseases
 Island populations are usually small which increases their risk for extinction
Sixth mass extinction
 Current mass extinctions are notable because
 It is the only such event triggered by a single species (Homo sapiens)
 A few million years is a long time to wait for recovery
 It is not clear that biodiversity will rebound this time
 Humans are utilizing resources that new species would need to evolve
Endemism
 Endemic: a species found in a particular region and nowhere else
 Levels of endemism high for areas that have been isolated for long periods of
time, especially islands
18 regions of high endemism
Some species under imminent extinction threat
Hotspots
 World Conservation Monitoring Network assessed geographical regions
according to:
 total species richness (biodiversity)
 proportion of endemic species
 extinction risk
Hotspots
 Identified “hotspots” contain:
 44% of the world’s known species of plants
 35% of terrestrial mammals
 28% of the birds
 30% of mammals
 38% of reptiles
 54% of amphibian species
 All in an area of 1.4% of the world’s total land surface
Biodiversity hotspots

Population density exceeds world average

Growth rate exceeds world average
Why do we care about losing biodiversity?
 Direct economic value
 Indirect economic value
 Ethical and aesthetic values
Benefits of biodiversity
 Food
 As many as 80,000 edible wild plant species could be utilized by humans
Agriculture
Benefits of biodiversity
 Drugs and medicines
 40% of all prescriptions contain some natural product
 Pharmaceutical companies actively prospect tropical countries for products
 Rosy periwinkle
Use fees
 USFWS estimates Americans spend $104 billion annually on wildliferelated recreation
 Ecotourism can be an important form of sustainable economic development
Value of Biodiversity
 Indirect economic value is derived from ecosystem services
 Maintain chemical quality of natural water, buffer against storms and
droughts
 Prevent loss of minerals and nutrients
 Moderate local and regional climate
 Absorb pollution
 Promote breakdown of organic wastes and cycling of minerals
Mangroves
Tropical rainforests
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
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To build plants cost $6 billon
Operating cost $300 million/year
Spend $1 billion over 10 years to preserve the ecosystem
Benefits of biodiversity
 Aesthetic and cultural benefits
 Cultural diversity inextricably linked to biodiversity
 Existence (intrinsic) value