SUSTAINING BIODIVERSITY
Chapter 9
Sustaining Biodiversity: The Species Approach
Key Concepts
9-1 Species are becoming extinct 100 to 1,000 times faster than they were before modern humans arrived
on earth, and by the end of this century, the extinction rate is projected to be 10,000 times higher than that
background rate.
9-2 We should avoid speeding up the extinction of wild species because of the ecosystem and economic
services they provide, because it can take millions of years for nature to recover from large-scale
extinctions, and because many people believe that species have a right to exist regardless of their
usefulness to us.
9-3 The greatest threats to species and ecosystem services are (in order) loss or degradation of habitat,
harmful invasive species, human population growth, pollution, climate change, and overexploitation.
9-4 We can reduce species extinction and sustain ecosystem services by establishing and enforcing
national environmental laws and international treaties, creating protected wildlife sanctuaries, and taking
precautionary measures to prevent such harm.
Chapter Outline
CORE CASE STUDY: Where have all the honeybees gone?
Honeybees play a key role in pollination. Bee experts have reported a 30% drop in populations in the
European honeybee populations in the United States. The bees do not return in the spring - a phenomenon
termed Colony Collapse Disorder (CCD). Scientists project that during this century, human activities,
especially those that contribute to habitat loss and climate change, are likely to play a key role in the
extinction of one-fourth to one-half of the world’s identified plant and animal species.
9-1 What role do humans play in the extinction of species?
A. Biological extinction: a species has disappeared from the earth.
B. Background extinction is an historic, continuous, low level of extinction.
C. Extinction rate is the percentage or number of species that go extinct each year.
D. Mass extinction is the loss of many species in a short period of time.
E. Extinction is natural, but there is evidence to suggest that it has accelerated as humans have
populated the earth.
1. Humans have disturbed 50-80% of the earth.
F. Human activities increase the pace of extinction.
1. Possibly one-fourth to one-half of all species could be extinct by the end of the century.
3. Extinction estimates are likely conservative.
a. Rates will likely increase with the growing human population.
b. Rates tend to be much higher in biodiversity hotspots.
c. Habitat fragmentation limits the potential for speciation to occur.
SCIENCE FOCUS: Estimating extinction rates.
Estimating rates of extinction is problematic because extinction takes a long time, we are uncertain of
how many species there are on earth, and we know little about the species that have been identified.
There are several methods for estimating extinction rates, such as studying fossil records and rates of
mutation, applying a species-area relationship to habitat destruction, and building mathematical
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models. Scientists acknowledge the shortcomings of estimates of extinction rates, but are certain that
humans have caused an increase in the rate of extinction.
G. Species heading toward biological extinction are either endangered or threatened.
1. Endangered species are so few in number that the species could soon become extinct.
2. Threatened/vulnerable: still abundant but likely to become endangered in the near future.
a. The World Conservation Union has kept Red Lists that are the world standard for listing all
threatened species throughout the world.
9-2 Why should we care about the rising rate of species extinction?
A. Biologists site four reasons we should prevent our activities from causing extinctions.
1. Species are a vital part of the earth’s life support system.
2. Species support our economy (materials, medicines, ecotourism).
3. It will take millions of years for natural speciation to rebuild biodiversity.
4. Species have a right to exist, regardless of their usefulness.
9-3 How do humans accelerate species extinction?
A. There are several causes of depletion and premature extinction of wild plants and animals. The
acronym HIPPCO describes these causes.
B. The loss, degradation, and fragmentation of habitat are the greatest threat to a species.
C. After habitat loss, introduced species are the biggest cause of extinction.
1. The alien species can be introduced accidentally or deliberately.
2. Some of these species threaten and endanger native species.
CASE STUDY: The Kudzu vine and Kudzu bugs. The Kudzu Vine was deliberately introduced in
the 1930s to control erosion, but got out of hand. It is prolific and difficult to control, engulfing
hillsides, gardens, and trees, among other things. Kudzu may eventually be used to make paper.
D. Population growth, overconsumption, pollution, and climate change.
1. Overpopulation and excessive consumption of resources eliminate habitat.
2. Pollution from chemicals like pesticides can have unintended effects on species.
3. Human activities induce rapid climate changes, increasing extinction rates.
CASE STUDY: Burmese pythons are eating their way through the Florida Everglades.
Burmese pythons have been accidentally introduced into the Everglades in Florida. The Burmese
python can live 20-25 years and grow to 5 meters in length. They are hard to find and kill and
reproduce rapidly. They have huge appetites and can kill alligators. Researchers say the population
cannot be controlled. This is an excellent example of an invasive top predator appearing in an
ecosystem where it has no natural enemies.
SCIENCE FOCUS: Honeybee losses: a search for causes. Over the past 50 years the European
honeybee population in the U.S. has been cut in half. Potential causes include parasitic insects,
harmful interactions between viruses and fungi, pesticides, and stress and poor nutrition.
D. Poaching—illegal killing of protected species.
1. Some protected species are killed for their valuable parts or are sold live to collectors.
E. Global legal and illegal trade in wild species for pets is a very profitable business.
F. Bushmeat supplies indigenous people with food and has been harvested sustainably, but as
demand has gone up illegal hunting has skyrocketed.
1. These hunting practices have resulted in negative ecological impacts and have driven at least
one species to extinction.
3. Butchering and eating bushmeat has helped spread Ebola and AIDS from animals to humans.
CASE STUDY: Polar bears and climate change. Polar bears are threatened because of climate
change. The total polar bear population is expected to decline by 30-35% by 2050.
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CASE STUDY: A Disturbing Message from the Birds. About 70% of the world’s bird species are
declining in number, and about 12 % is threatened with extinction. The primary cause of decline is
habitat loss and fragmentation. Birds are seen as indicator species, signaling environmental change
in their habitats. Birds play a number of important economic and ecological roles. Their loss could
trigger a cascade of extinctions.
9-4 How can we protect wild species from extinction?
A. Treaties help protect endangered and threatened species, but enforcement is difficult and
punishment inadequate.
B. The 1975 Convention on International Trade in Endangered Species (CITES) protects 900 species
from being commercially traded and restricts international trade for 29,000 species that may
become threatened.
1. Enforcement is difficult and varies from country to country.
2. Many countries are not signatories and still trade in animals.
3. The Convention on Biological Diversity (CBD) binds governments to reverse the global
decline in biological biodiversity. The United States has not ratified this treaty. There are no
severe penalties or other enforcement mechanisms in place.
CASE STUDY: The U.S. Endangered Species Act.
The Endangered Species Act of 1973 (ESA) identifies and legally protects endangered species in
the U.S. and abroad. Identification of endangered, threatened ocean species is made by the
National Marine Fisheries Service, and the U.S. Fish and Wildlife Service is responsible for
identifying and listing all other endangered and threatened species. Biological facts form the
basis of inclusion on the endangered list. Habitats of endangered species must be protected.
Efforts have been made to repeal/weaken the Endangered Species Act.
Conservation biologists believe that the ESA should be strengthened and modified to correct
deficiencies.
C. The sanctuary approach is being used to protect wild species.
1. 548 federal refuges protect wildlife but the habitats are deteriorating due to invasive species,
pollutants, and little operational or maintenance funding.
D. Gene banks, botanical gardens, and farms can be used to raise threatened species and help protect
species from extinction, but funding is inadequate.
1. The world’s 1600 Botanical Gardens and Arboreta contain almost one-third of the world’s
known plant species, but only 3% of the world’s rare and threatened species.
2. Raising some threatened or endangered species on farms can take some of the pressure off
them and perhaps offer some for commercial sale.
E. Zoos and aquariums can help protect some endangered animal species as well.
1. Egg pulling collects wild eggs laid by endangered bird species and hatches them in
zoos/research centers.
2. Captive breeding takes wild individuals into captivity for breeding with the commitment to
reintroduce the offspring back into the wild.
3. Artificial insemination, use of surrogate mothers, use of incubators, and cross-fostering by a
similar species are other ways to increase populations of rare species.
4. The ultimate goal is to reintroduce these species into the wild.
5. Reintroductions of endangered species to the wild fail because:
a. There is not suitable habitat.
b. Individuals bred in captivity are not able to survive in the wild.
c. There is renewed overhunting/capture of the returned species.
CASE STUDY: Protecting Honeybees and other pollinators. Failure to protect honeybees can
lead to the loss of the ecosystem service they provide - pollination. Steps are being taken to protect
pollinators.
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H. Precautionary Principle: When substantial preliminary evidence indicates that an activity can
harm human health or the environment, we should take precautionary measures to reduce or
prevent such harm.
Key Terms
background extinction rate
biological extinction
endangered species
HIPPCO
extinction rate
habitat fragmentation
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precautionary principle
threatened (vulnerable) species
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