chapter 60 onservation Biology Flashcards
Biodiversity Crisis
Extinction is a fact of life: 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
Members of Homo sapiens wreaked havoc, even in prehistoric times
In North America, 74%–86% of mega fauna became extinct after humans arrived
Caused by hunting and burning/clearing of forests
40,000 years ago Australia had a wide variety of large animals
All disappeared at about the same time humans arrived
Smaller islands also devastated by human arrival
Africa has not had mass extinctions
African species had been coevolving with humans
The majority of recent extinctions have occurred in the past 150 years
Increase in rate of extinction is the heart of the biodiversity crisis
Birds recognized as critically endangered increased 8% from 1996 to 2000
Half of Earth’s plant species may be threatened
2/3 of vertebrate species could perish by the end of this century
Majority of extinctions have occurred on islands
85 species of mammals have gone extinct in last 400 years
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
Current mass extinction is notable because
It is the only such event triggered by a single species (Homo sapien)
Recovery takes a few million years
It is not clear that biodiversity will rebound this time
Humans are utilizing resources that new species would need to evolve
Endemic species: species found naturally in only one geographic area and no place else
Usually occupy restricted ranges
Example: Mauna Kea silversword only lives in a single volcano crater on the island of Hawaii
Hotspots: areas where species have high endemism and are disappearing at a rapid rate; red areas are hotspots
Human population growth in hotspots
By protecting 1.4% of the world’s land surface
44% of the worlds vascular plants
35% of its terrestrial vertebrates can be preserved
In 1995, 20% of the human population were located in hotspots
Growth rate exceeds the average in 19 hotspots
Why are species going extinct in hotspots?
High rates of habitat destruction
Land cleared for agriculture, housing, economic development
More than 70% of the original area of each hotspot has already disappeared
Only 15% or less of original habitat remains in 14 hotspots
90% Madagascar forest lost
95% Brazilian Atlantic coast forest lost
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Value of Biodiversity
Direct economic value includes resources for our survival
Sources of food, medicine, clothing, biomass (for energy and other purposes), and shelter
Food crop genetic variation
May be needed in the future to improve crops
40% of prescription and nonprescription drugs have active ingredients extracted from plants
Aspirin
Cancer-fighting drugs
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
Economists have recently been able to compare the societal value, in monetary terms, of intact habitats compared with the value of destroying those habitats
In Thailand, coastal mangrove habitats are cleared for shrimp farms
Shrimp farm value is vastly outweighed by the benefits in timber, charcoal production, offshore fisheries, and storm protection provided by the mangroves
Tropical rainforests provide more economic benefits if they are left standing than if they are destroyed and the land used for other purposes
Case Study: New York City watershed
90% of 9 million people’s water comes from the Catskill Mountains and Delaware River
Dilemma: Protect functioning ecosystem or construct filtration plants
To build plants cost $6 billon
Annual operating cost $300 million/year
Spend $1 billion over 10 years to preserve the ecosystem
Problems of valuing ecosystems
Do not have a good estimate of the monetary value of services provided by ecosystems
People who gain the benefits of environmental degradation are often not the same people who pay the costs
Ethical and aesthetic values are based on our conscience
Every species has a value of its own
Humans should act as guardians or stewards for the diversity of life around us
How do we place a value on beauty?
What if it no longer existed?
Factors Responsible
Variety of causes for extinctions Overexploitation Habitat loss Introduced species Disruption of ecosystem interactions Pollution Loss of genetic variation Catastrophic disturbances
Case Study: Amphibians on the decline 1963, Jay Savage Costa Rica Many breeding toads, bright orange Bufo periglenes, Golden Toad 1989, only a single male was observed Today, no toads They have gone extinct
Frogs in trouble
Frog populations that had once been abundant – now decreasing or entirely gone
43% of amphibian species experienced decreases in population size
1/3 are threatened with extinction
Why worry about amphibian declines?
Many species have declined in pristine, well-protected habitats
Particularly sensitive to the state of the environment because of their moist skin
Chemicals pass into their body
Larval habitats are aquatic
No single cause for amphibian decline is apparent
Different species are afflicted by different problems
Global environment is deteriorating in many different ways
Habitat loss devastates species richness Natural habitats may be adversely affected by humans Destruction Pollution Disruption Habitat fragmentation
Destruction of habitat
Clear-cut harvesting of timber
Burning of tropical forests
Urban and industrial development
10-fold increase in habitat area leads to ~ doubling in the number of species
Relationship suggests that if the area is reduced by 90% then half of all species will be lost
Pollution
Species can no longer survive
Aquatic environments particularly vulnerable
Many lakes “sterilized” by acid rain
Disruption
Visitors to bat caves: four visits per month caused 86%–95% decline in population size
Habitat fragmentation: dividing the habitat up into small, unconnected areas
Disastrous consequences because of the relationship between range size and extinction rate
Edge effects: changes in microclimate along the edge of a habitat
Landowners in Manaus, Brazil, preserved patches of rain forest of different sizes to examine the effect of patch size on species extinction
Extinction rate was negatively related to patch size
Even the largest patches (100 hectares) lost half of their bird species in less than 15 years
