Chapter Summary

• Biodiversity has great value to human society in the form of goods and services, but human activities have caused its rapid decline at genetic, population, species, ecosystem, and global scales. Review Figure 58.1

• Human-caused events coupled with natural events can reduce a species’ effective population size (number of individuals that can contribute offspring to the next generation), leading to population and species extinctions. Ever-smaller effective population sizes are affected by inbreeding depression, genetic drift, and demographic stochasticity. Review Focus: Key Figure 58.2

• Humans are causing biodiversity loss at unprecedented rates, rivaling that of the five previous mass extinction events, which were the result of cataclysmic natural disasters.

• We can estimate the extinction probability of species by taking into account their population sizes, genetic variation, life history traits, and ecology. Review Figure 58.3

• Habitat loss (reduction in habitat quantity) and habitat degradation (reduction in habitat quality) have been the major causes of biodiversity loss. Estimates are that humans have transformed 50%–60% of the land surface, primarily for agriculture, timber, and livestock grazing. Review Figure 58.4

• Overharvesting of species for food, clothing, ornamentation, pets, and medicines was once the most important and rapid cause of species extinction and is still a concern for some species if conservation measures are not enacted. Review Figures 58.7, 58.9

• Deliberate or inadvertent introductions of non-native species have increased exponentially over the last 200 years, with roughly 10 percent of those species becoming invasive.

• Invasive species can endanger native species through predation, competition, and disease. They can cause changes to ecosystem functions or genetic diversity through hybridization with wild populations. Review Figure 58.10, Investigating Life: Exploring the Decline of Central American Frogs

• Human-generated emissions of greenhouse gases are contributing to global climate warming, sea level rise, increased storminess, and ocean acidification, all of which are becoming increasingly important causes of biodiversity loss.

• Scientific evidence shows that some species have been, or are currently being, affected by climate change through distributional changes, timing of life history events, and decreased growth and reproduction. Review Figure 58.11, Tables 58.1, 58.2, Animation 58.1

• Ecologists use scientific theory, empirical data, and tools from a variety of disciplines to help inform socioeconomic and institutional sectors in the protection and management of biodiversity. Review Figure 58.12

• Creating protected areas and restoring degraded habitat can curtail biodiversity loss. Creating viable protected areas requires establishing core natural areas, buffer zones surrounding them, and habitat corridors connecting them. Review Figures 58.13, 58.14

• Restoration ecology involves renewing degraded ecosystems by reestablishing their original structure and function through active removal of pollutants or non-native species, revegetation to reestablish habitat and food resources, reintroduction of native species, or reestablishment of important processes such as disturbance. Review Figure 58.15

• Captive breeding programs and ending trade can help conserve and manage a few highly threatened or charismatic species. Review Figure 58.16

• The best way to reduce the damage caused by invasive species is to either prevent their introduction through trade restrictions or eradicate them in their early establishment phase.

• Biodiversity can be conserved because of the economic value of the goods and services it provides. Review Figure 58.17