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