SUMMARY

CONCEPT 23.1 Conservation biology is an integrative discipline that applies the principles of ecology to the protection of biodiversity.

23.1.1 Describe the different biological levels of diversity associated with conservation biology.

Conservation biology is the scientific study of phenomena that affect the maintenance, loss, and restoration of biodiversity.

Biodiversity includes genetic diversity, species diversity, and landscape diversity.

23.1.2 Evaluate the reasons why preserving biodiversity may be important.

Biodiversity is important to human society because of our reliance on natural resources and ecosystem services that depend on the integrity of natural communities and ecosystems.

23.1.3 Assess the factors that prompted the rapid development of the field of conservation biology.

With the growing awareness of accelerating losses of global biodiversity, ecologists saw a need for a separate discipline that would apply the principles of ecology to the preservation of species and ecosystems.

Conservation biology is a scientific discipline instilled with the

value of biodiversity.

CONCEPT 23.2 Diversity is declining globally.

23.2.1 Differentiate between the current anthropogenically enhanced rate of extinction and the long-term background extinction rate.

Earth is losing species at an accelerating rate, 100 to 1,000 times higher than the background rate, largely because of humanity’s growing footprint on the planet.

23.2.2 Describe the pathway to species extinction from changes in population growth to the disappearance of the species.

Extinction is the end point of incremental biological decline as species lose individuals and populations and become increasingly vulnerable to the problems of small populations.

Earth’s biota is becoming increasingly homogenized because of a rise in generalist species and a decline in specialist species.

CONCEPT 23.3 Primary threats to diversity include habitat loss, invasive species, overexploitation, pollution, disease, and climate change.

23.3.1 Compare the most important threats to diversity over the past century with the threats that are increasing the most in importance.

Habitat degradation, fragmentation, and loss are the most important threats to diversity.

23.3.2 Describe the causes of diversity losses associated with habitat loss and degradation.

Habitat degradation and habitat loss lower the sizes of populations, increasing the probability that genetic and stochastic factors will result in local extinction of species.

23.3.3 Explain the underlying mechanisms determining how invasive species, overexploitation, and water and air pollution lead to diversity loss.

Invasive species degrade local habitats by preying on or competing with native species and by altering ecosystem properties.

Overexploitation of selected species has large effects on communities and ecosystems.

Other factors that erode the viability of populations and contribute to losses of diversity include air and water pollution, diseases, and global climate change.

CONCEPT 23.4 Conservation biologists use many tools and work at multiple scales to manage declining populations.

23.4.1 Describe how advances in molecular genetics have assisted with assessing genetic diversity in populations.

Genetic analyses have been used to understand and manage genetic diversity within rare species, as well as in forensic analyses of illegally harvested organisms.

23.4.2 Evaluate the use of demographic models in projecting the

fates of endangered species.

Population viability analysis (PVA) is an approach that uses demographic models to assess extinction risks and evaluate proposed management actions.

23.4.3 Explain why ex situ conservation may be the best approach to saving a species once it appears destined for extinction.

Ex situ conservation, which involves taking organisms from the wild into human care, is a last-resort measure to rescue species on the brink of extinction.

CONCEPT 23.5 Prioritizing species helps maximize the biodiversity that can be protected with limited resources.

23.5.1 Summarize why the rarity of a species may be both helpful and misleading as an indicator of its endangerment.

Conservation biologists identify those species of the highest priority for protection—the rarest and the most rapidly declining species—by assessing numbers of individuals and populations, total geographic area occupied, rates of decline, and the degree of threat faced.

23.5.2 Describe the potential benefits of using a surrogate species to help conserve habitat and other species found in that habitat.

Identification of surrogate species can provide protection for other species with similar habitat requirements.

REVIEW QUESTIONS

1. What are the principal threats to biodiversity? Describe some examples in which multiple threats have contributed to decline of a species.

2. Describe tools that conservation biologists use to protect biodiversity at the level of genes and populations.

3. What is the difference between a species determined to be endangered by the Natural HeritageZNatureServe program and one that is listed as endangered under the U.S. Endangered Species Act? What are the consequences for management of each?

4. Identify five imperiled species that live in your region: a plant, a mammal, a bird, a fish, and an invertebrate. Are any of these species endemic to your region? For each species you have identified, try to find out whether it was rare prior to human settlement of the region. What threats does this species face today? What is being done to protect this species? Based on the ecological knowledge you have gained, what questions do you think should be researched to aid in the recovery of the species? (Much of this information is available at www. n atu reserve.org.)

HONE YOUR PROBLEM-SOLVING SKILLS

With the realization of declining abundances of fish, greater attention has been given to demographic approaches to sustainable harvests.

1. Starting with the following distribution of individuals in age cohorts, plot or tabulate the population growth for a population of this fish species for 10 years: n₀ = 30, n₁ = 30, n₂ = 20, n₃ = 10, n₄ = 10 (initial total of 100 individuals).

2. Project the same population growth if 60% of the 2- and 3- year-old cohorts are harvested for commercial use, by adjusting the survival rates. Is this level of harvest sustainable—that is, will the population be able to maintain a relatively stable size under these conditions indefinitely?

3. Now project the population growth if 40% of the 2- and 3- year-old cohorts are harvested for commercial use, and estimate whether this rate of harvest is sustainable. Try different combinations of fecundity and survival within the different age cohorts to consider how these factors influence the sustainability of populations under pressure from commercial harvest.

LIST OF KEY TERMS

Biodiversity

Conservation biology ecosystem services extinction vortex flagship species focal species Habitat degradation habitat fragmentation Habitat loss invasive species population viability analysis (PVA) surrogate species taxonomic homogenization umbrella species