Chapter 21 Glossary, Summary, and Practice Questions

KEY TERMS

biodiversity the variety of a biological system, typically conceived as the number of species, but also applying to genes, biochemistry, and ecosystems

biodiversity hotspot a concept originated by Norman Myers to describe a geographical region with a large number of

endemic species and a large percentage of degraded habitat

bush meat a wild-caught animal used as food (typically mammals, birds, and reptiles); usually referring to hunting in the tropics of sub-Saharan Africa, Asia, and the Americas

chemical diversity the variety of metabolic compounds in an ecosystem

chytridiomycosis a disease of amphibians caused by the fungus Batrachochytrium dendrobatidis; thought to be a major cause of the global amphibian decline

ecosystem diversity the variety of ecosystems

endemic species a species native to one place

exotic species (also, invasive species) a species that has been introduced to an ecosystem in which it did not evolve extinction the disappearance of a species from Earth; local extinction is the disappearance of a species from a region extinction rate the number of species becoming extinct over time, sometimes defined as extinctions per million

species–years to make numbers manageable (E/MSY)

genetic diversity the variety of genes and alleles in a species or other taxonomic group or ecosystem; the term can refer to allelic diversity or genome-wide diversity

habitat heterogeneity the number of ecological niches

secondary plant compound a compound produced as a byproduct of plant metabolic processes that is typically toxic, but is sequestered by the plant to defend against herbivores

species-area relationship the relationship between area surveyed and number of species encountered; typically measured by incrementally increasing the area of a survey and determining the cumulative numbers of species

tragedy of the commons an economic principle that resources held in common will inevitably be over-exploited

white-nose syndrome a disease of cave-hibernating bats in the eastern United States and Canada associated with the fungus Geomyces destructans

CHAPTER SUMMARY

Importance of Biodiversity

Biodiversity exists at multiple levels of organization, and is measured in different ways depending on the goals of those taking the measurements. These include numbers of species, genetic diversity, chemical diversity, and ecosystem diversity. The number of described species is estimated to be 1.5 million with about 17,000 new species being described each year. Estimates for the total number of eukaryotic species on Earth vary but are on the order of 10 million. Biodiversity is negatively correlated with latitude for most taxa, meaning that biodiversity is higher in the tropics. The mechanism for this pattern is not known with certainty, but several plausible hypotheses have been advanced.

Humans use many compounds that were first discovered or derived from living organisms as medicines: secondary plant compounds, animal toxins, and antibiotics produced by bacteria and fungi. More medicines are expected to be discovered in nature. Loss of biodiversity will impact the number of pharmaceuticals available to humans. Biodiversity may provide important psychological benefits to humans.

Crop diversity is a requirement for food security, and it is being lost. The loss of wild relatives to crops also threatens breeders’ abilities to create new varieties. Ecosystems provide ecosystem services that support human agriculture: pollination, nutrient cycling, pest control, and soil development and maintenance. Loss of biodiversity threatens these ecosystem services and risks making food production more expensive or impossible. Wild food sources are mainly

aquatic, but few are being managed for sustainability. Fisheries’ ability to provide protein to human populations is threatened when extinction occurs.

Threats to Biodiversity

The core threats to biodiversity are human population growth and unsustainable resource use. To date, the most significant causes of extinction are habitat loss, introduction of exotic species, and overharvesting. Climate change is predicted to be a significant cause of extinction in the coming century. Habitat loss occurs through deforestation, damming of rivers, and other activities. Overharvesting is a threat particularly to aquatic species, but the taking of bush meat in the humid tropics threatens many species in Asia, Africa, and the Americas. Exotic species have been the cause of a number of extinctions and are especially damaging to islands and lakes. Exotic species’ introductions are increasing because of the increased mobility of human populations and growing global trade and transportation. Climate change is forcing range changes that may lead to extinction. It is also affecting adaptations to the timing of resource availability that negatively affects species in seasonal environments. The impacts of climate change are currently greatest in the arctic. Global warming will also raise sea levels, eliminating some islands and reducing the area of all others.

Preserving Biodiversity

Five mass extinctions with losses of more than 50 percent of extant species are observable in the fossil record. Recent extinctions are recorded in written history and are the basis for one method of estimating contemporary extinction rates. The other method uses measures of habitat loss and species-area relationships. Estimates of contemporary extinction rates vary but are as high as 500 times the background rate, as determined from the fossil record, and are predicted to rise.

There is a legislative framework for biodiversity protection. International treaties such as CITES regulate the transportation of endangered species across international borders. Legislation within individual countries protecting species and agreements on global warming have had limited success; there is at present no international agreement on targets for greenhouse gas emissions. In the United States, the Endangered Species Act protects listed species but is hampered by procedural difficulties and a focus on individual species. The Migratory Bird Act is an agreement between Canada and the United States to protect migratory birds. The non-profit sector is also very active in conservation efforts in a variety of ways.

Conservation preserves are a major tool in biodiversity protection. Presently, 11 percent of Earth’s land surface is protected in some way. The science of island biogeography has informed the optimal design of preserves; however, preserves have limitations imposed by political and economic forces. In addition, climate change will limit the effectiveness of present preserves in the future. A downside of preserves is that they may lessen the pressure on human societies to function more sustainably outside the preserves.

Habitat restoration has the potential to restore ecosystems to previous biodiversity levels before species become extinct. Examples of restoration include reintroduction of keystone species and removal of dams on rivers. Zoos have attempted to take a more active role in conservation and can have a limited role in captive breeding programs. Zoos also have a useful role in education.

ART CONNECTION QUESTIONS

• Figure 21.6 The Svalbard seed vault is located on Spitsbergen island in Norway, which has an arctic climate. Why might an arctic climate be good for seed storage?

REVIEW QUESTIONS

• The number of currently described species on the planet is about .
• 17,000
• 150,000
• 1.5 million
• 10 million
• A secondary plant compound might be used for which of the following?
• a new crop variety
• a new drug
• 
  a soil nutrient
• a crop pest
• Pollination is an example of .
• a possible source of new drugs
• chemical diversity
• an ecosystem service
• crop pest control
• Converting a prairie to a farm field is an example of

.

• overharvesting

• habitat loss
• exotic species
• climate change
• Which two extinction risks may be a direct result of the pet trade?
• climate change and exotic species introduction
• habitat loss and overharvesting
• overharvesting and exotic species introduction
• habitat loss and climate change
• What kind of ecosystem are exotic species especially threatening to?
• deserts
• marine ecosystems
• islands
• tropical forests

CRITICAL THINKING QUESTIONS

• Explain how biodiversity loss can impact crop diversity.
• Describe two types of compounds from living things that are used as medications.
• Describe the mechanisms by which human population growth and resource use causes increased extinction rates.
• 
  Certain species of parrot cannot be brought to the United States to be sold as pets. What is the name of the legislation that makes this illegal?
• Red List
• Migratory Bird Act
• CITES
• Endangered Species Act (ESA)
• What is the name of the first international agreement on climate change?
• Red List
• Montreal Protocol
• International Union for the Conservation of Nature (IUCN)
• Kyoto Protocol

• Explain what extinction threats a frog living on a mountainside in Costa Rica might face.
• Describe two considerations in conservation preserve design.
• Describe what happens to an ecosystem when a keystone species is removed.