57 Introduction The problem of human-caused extinction of species led to the development of the discipline of conservation biology: the scientific study

57 Introduction

• The problem of human-caused extinction of species led to the development of the discipline of conservation biology: the scientific study of how to preserve the diversity of life.

• Conservation biology draws on population genetics, evolution, biogeography, wildlife management, economics, and sociology.

57 Why Care about Species Extinctions?

• The value of biodiversity to humans:

Humans depend on other species for food, fiber, and medicine.

Humans derive aesthetic pleasure from interacting with other organisms.

Causing the extinction of other species raises serious ethical issues.

Extinctions make the study of ecological relationships and species interactions difficult.

Species are necessary for the function of the ecosystems of which they are a part.

57 Why Care about Species Extinctions?

• The benefits provided to humans by functioning ecosystems are enormous.

• These include, among others, prevention of soil erosion, regulation of hydrologic cycles, and detoxification and recycling of waste products.

57 Estimating Current Rates of Extinction

• The number of species on an island increases with the size of the island.

• Conservation biologists have applied this species–area relationship to habitat patches on the mainland as well.

• Findings suggest that a 90% loss of habitat will result in the loss of half of the species living there.

• If the current rate continues, about 1 million species living in the tropical evergreen forests will become extinct in this century.


• To assess extinction risk for a population, biologists analyze many factors including genetic variation, morphology, physiology, behavior, and environment.

• Species in imminent danger over a significant portion of their range are labeled endangered species.

• Species that are likely to become endangered in the near future are labeled threatened species.


• Rarity is not always a reason for concern.

• However, species in which a few individuals are confined to a small range are more likely to be eliminated by local disturbances such as fire and disease.

57 Preserving Biodiversity

• The human activities that threaten species include habitat destruction, introduction of invasive species, overexploitation, disease, alteration of disturbance patterns (urban sprawl), and climate change.

• Conservation biologists determine how these activities are affecting species and devise strategies to preserve endangered or threatened species.


• Habitat loss is the most important cause of endangerment of species in the U.S., especially species that live in fresh waters.

• As habitats are destroyed, the remaining patches become fragmented (smaller and more isolated).

• Small patches cannot maintain populations that require larger areas and can support only small numbers of species that can survive in them.


• People have moved organisms between continents deliberately and accidentally.

• A species that has evolved in a community and become accustomed to the natural predators or competitors may be driven to extinction by newly introduced predators or competitors.

• A major human-caused environmental change is the introduction of non-native species that then become invasive in the their new environments.


• Hundreds of species of plants have been introduced as ornamentals. An example is purple loosestrife.

• Almost half of the medium-sized marsupials in Australia have become extinct due to the introduction of predators (cats and foxes) and competitors (rabbits) to the continent.

• Proliferation of introduced pathogens, such as the fungus that causes Dutch elm disease, has caused much destruction to North American forests.


• The best way to reduce the damage caused by invasive species is to prevent their establishment in the first place.

• The shipping industry spreads invasive species in ballast water, which is pumped into ships at one port and discharged at another. Deoxygenating ballast water before it is pumped out would control the problem of invasive aquatic species.


• Until recently, humans caused most extinctions primarily by overhunting.

• The passenger pigeon, one of the most abundant species of bird in North America in the 1800s, became extinct by 1914 due to hunting.

• Elephants and rhinoceroses are threatened with extinction because poachers kill them for their tusks and horns.

• The houseplant and pet trades currently threaten many species of orchids, parrots, and reptiles.


• Programs have been developed to help us use species in a way that does not threaten their survival.

• Certification programs: Organizations such as the Forest Stewardship Council (FSC) and the Marine Stewardship Council determine whether commercial operations harvest and market their products in ways that meet their criteria.


• The Convention on International Trade in Endangered Species (CITES), an international organization, determines and prohibits trade in endangered species or their products (e.g., whale meat, rhinoceros horn, many parrots and orchids).


• Many species depend on particular patterns of disturbance to persist.

• Humans often try to control such disturbances, but conservation biologists try to determine where disturbances should be reestablished.

• For example, annual growth rings on ponderosa pines show that low-intensity fires were once common in New Mexico.

• Because of sheep grazing and fire suppression, buildup of dead branches and needles has resulted in intense, tree-consuming fires.

• Today ground fires are deliberately started to imitate historic patterns.


• If Earth warms as predicted, climatic zones won’t just shift. New climates will develop and some existing climates will disappear.

• New climates are likely to develop at low elevations in the tropics. A warming of even 2°C would result in climates that are warmer than any that exist today.

57 Habitat Restoration and Species Recovery

• The field of restoration ecology has developed to study methods of restoring natural habitats.

• Some damaged habits will not recover without assistance, and biologists try to maintain some endangered species in captivity until suitable habitat is available.

• Conservation biologists have only a limited ability to restore natural ecosystems and many attempts have been only partially successful.


• Wetland restoration is a high priority in southern California, where 90 percent of the coastal wetlands have been destroyed..


• Threatened species can sometimes be maintained in captivity while external threats to their existence are reduced or removed.

• Captive propagation is a temporary measure, however, because zoos, aquariums, and botanical gardens have only a limited capacity.

• Some species have benefited from captive breeding programs.


• Captive breeding is helping to save the California condor..

• Captive breeding was initiated in 1983 and by 1993 the captive breeding population was 60 birds.

• As of 2003 there were 81 wild condors in California and Arizona.

57 Healing Biotas: Conservation Medicine

• On land and sea, diseases among wild organisms are threatening biodiversity.

• In parts of the Hawaiian Islands, nearly all endemic bird species have been eliminated by avian malaria introduced into the island by exotic birds.

• The West Nile bird virus has exploded across the U.S. and has spread to humans.

57 Healing Biotas: Conservation Medicine

• A new field of conservation medicine is developing to help identify the causes of increases in wildlife diseases and to devise ways to prevent transmission and limit the effects.

• Molecular techniques are used to identify species, strains, and life cycles of pathogens.

57 Setting Limits: The Legacy of Samuel Plimsoll

• In the nineteenth century, Samuel Plimsoll, an English MP, persuaded Parliament to require a “load line” on the hull of every merchant ship to prevent overloading and thus to reduce the rate of shipwreck.

• The increasing loss of Earth’s species suggests that we need such a “Plimsoll line” to limit the load of human activities on the planet.

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57 Introduction The problem of human-caused extinction of species led to the development of the discipline of conservation biology: the scientific study