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Explore the causes and consequences of biodiversity loss and extinction, and discover the efforts being made to protect and preserve Earth's diverse ecosystems.
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Chapter 11 Biodiversity Issues
Outline • 11.1 Biodiversity Loss and Extinction • 11.2 The Value of Biodiversity • 11.3 Threats to Biodiversity • 11.4 What Is Being Done to Preserve Biodiversity?
11.1 Biodiversity Loss and Extinction • Biodiversity is a broad term used to describe the diversity of genes, species, and ecosystems in a region. • Extinction is the elimination of all the individuals of a particular species. • Extinction is a natural and common event in the history of biological evolution. • It, and the resulting loss of biodiversity, is also a major consequence of human domination of the Earth.
11.1 Biodiversity Loss and Extinction • Over the past few hundred years, humans are estimated to have increased the extinction rate by a factor of 1,000 to 10,000 times above background rates typical over the planet’s history. • 1/8 of bird species, 1/4 of mammal species, 1/3 of amphibian species, and 1/2 of turtle species are threatened. • 10% of the world’s coral reefs have been lost. • Mangrove forests are reduced by over 1% a year. • 25% of global land is used to raise crops.
11.1 Biodiversity Loss and Extinction • Local extinctions, although relatively common, indicate the future of a species is not encouraging. • As population is reduced in size, some of the genetic diversity is likely to be lost. • Certain kinds of species are more likely to go extinct than others: • Species with small, dispersed populations • Successful breeding is difficult.
11.1 Biodiversity Loss and Extinction • Organisms in small, restricted areas, such as islands. • Environmental changes have large effect. • Specialized organisms • Relying on constancy of a few key factors. • Organisms at higher trophic levels. • Low population sizes and reproductive rates.
11.1 Biodiversity Loss and Extinction • As human populations grew, and their tools became more advanced, the impact a single human could have on surroundings increased. • Environmental modifications allowed larger, dense human populations to survive, but at the expense of previously existing ecosystems. • Nearly all the Earth’s surface has been affected in some way by human activity.
Genetic Diversity • Genetic diversity is a term used to describe the number of kinds of genes present in a population. • High genetic diversity indicates many different kinds of genes present in individuals of a population. • Low genetic diversity indicates nearly all individuals share the same genes and therefore the same characteristics.
Genetic Diversity • Several things influence a population’s genetic diversity: • Mutations introduce new genetic information into a population by modifying current genes. • Migration allows movement of genes from one population to another. • Sexual reproduction generates new genetic combinations.
Genetic Diversity • Population size is an important factor: The smaller the population, the less genetic diversity it can contain. • There are fewer variations for each characteristic. • Random events can significantly alter the genetic diversity in small populations. • Selective breeding can affect diversity because undesirable characteristics are eliminated. • Many domesticated plants and animals could not survive without human help.
Species Diversity • Species diversity is a measure of the number of different species present in an area. • Species richness refers to the number of different kinds of species in an area. • Taxonomic richness takes into account the number of different taxonomic categories of the species present.
Species Diversity • When humans exploit an area, they influence species diversity. • They convert natural ecosystems to human-managed ecosystems. • They harvest certain species for their use. • They specifically eliminate species that compete with desirable species. • They introduce nonnative species to an area.
Species Diversity • Estimates of the actual number of species range from a few million to 100 million. • About 1.4 million species have been described. • Many species are naturally rare, and others live in areas difficult to reach.
Ecosystem Diversity • Ecosystem diversity is a measure of the number of kinds of ecosystems present in an area. • Many regions of the world appear to be quite uniform in terms of the kinds of ecosystems present. • For example, many parts of the world are deserts: • While there are general similarities, each is different and has specific organisms typical to the region. • Local topographic conditions create unique patches of landscape.
11.2 The Value of Biodiversity • Biological and Ecosystem Services Values • Humans are totally dependent on the diversity of organisms on Earth. • Symbiotic nitrogen-fixing bacteria live in the roots of certain plants. • Spoil-building organisms live on the dead organic matter provided by plants and animals. • It is impossible for organisms to function optimally unless it has its supporting cast of players that are part of the ecosystem.
11.2 The Value of Biodiversity • Nutrient cycling • Carbon, nitrogen, phosphorus, and other chemical elements are cycled through ecosystems. • Cultural Uses • Enjoyment of landscapes, individual organisms, scientific study, educational activities, and the spiritual significance of places. • Water regulation and supply • Intact soil and vegetation slow water flow, allowing it to penetrate the soil and recharge aquifers. • Water is available for agriculture, industry, and domestic use.
11.2 The Value of Biodiversity • Disturbance regulation and erosion control • Land can be disturbed by fire, flood, windstorms, landslides, or human actions. • Colonization of these sites by plants and animals heals the scars and prevents continued damage. • Waste Treatment • Decomposer organisms remove excess nutrients and pollutants from air, water, and soil. • Food and Raw Materials • Many people harvest wild plants and animals as food and medicine. Plants feed livestock, provide building materials, and firewood.
11.2 The Value of Biodiversity • Atmospheric and Climate Services • Many atmospheric gases are cycled between organisms and the atmosphere. • Removal of carbon dioxide in photosynthesis helps control the warming of the planet. • Nitrogen and sulfur are modified by organisms. • Ozone provides protection from UV light. • Recreation • Natural areas provide recreational opportunities. • Biological Control Services • All organisms have complex interrelationships. Some help remove pests.
11.2 The Value of Biodiversity • Pollination Services • Many insects are pollinators. Careless use of insecticides can negatively affect agricultural production. • Habitat/Refuges • Refuges protect species, serve as nursery sites, and provide temporary stopping places for migratory species.
11.2 The Value of Biodiversity • Genetic Resources • If an organism goes extinct, we have lost the ability to use it for our own needs. • Wild ancestors of our food grains are thought to be extinct. • 50% of our common drugs come from plants and animals. • Soil Formation • Weathering of rock, aided by bacteria, fungi, tiny animals, and plants roots build soil. • Our food supply depends on the protection and management of soil.
11.2 The Value of Biodiversity • Choices between competing uses for ecosystems are often determined by economic values. • Value can be assigned to services provided by intact, functioning ecosystems. • A 1997 study estimates $33 trillion per year, but that figure may be low. • Some resources are difficult to assign specific monetary value: • Wildlife (consumed by those who harvest it) • Medicinal plants
11.2 The Value of Biodiversity • A case can be made that all species have an intrinsic value and a fundamental right to exist. • Extinction is not necessarily bad, but human-initiated extinction is. • Experiencing natural landscapes and processes is an important human right.
11.2 The Value of Biodiversity • The values held by a person are typically shaped by experience. • As the shift from rural to urban continues, there is continual erosion of natural experiences that can shape the values of people. • These values are important in determining how society will approach threats to biodiversity.
11.3 Threats to Biodiversity • Five major human activities threaten to reduce biodiversity. • Habitat loss • Overexploitation • Introduction of exotic species • Predator and pest control activities • Climate change
11.3 Threats to Biodiversity • The International Union for Conservation of Nature and Natural Resources (IUCN) estimates that 80%-90% of threatened species are under threat as a result of habitat loss or fragmentation. • Habitat loss and fragmentation are thought to be a major cause of past extinctions.
11.3 Threats to Biodiversity • About 40% of the world’s land surface has been converted to cropland and permanent pasture. • Typically, the most productive natural ecosystems (forests and grasslands) are the first to be modified by humans. • Pressures to modify the environment are greatest in areas with high population density.
11.3 Threats to Biodiversity • Originally, half of the U.S., three-fourths of Canada, and almost all of Europe, and significant portions of the rest of the world were forested. • Deforestation is the process of destroying a forest, often for the purposes of fuel, building materials, or to clear land for farming.
11.3 Threats to Biodiversity • Modern forest management practices involve a compromise that allows economic exploitation while maintaining some environmental values of the forest. • Forested areas effectively: • Reduce erosion. • Reduce runoff. • Modify the climate. • Provide recreational opportunities.
11.3 Threats to Biodiversity Changes in forest area
11.3 Threats to Biodiversity • Clear cutting is the removal of all trees in an area. It is economical but increases erosion, especially on steep slopes. • Patchwork clear cutting is clear cutting in small, unconnected patches; preserves biodiversity. • Selective harvesting is single species tree harvesting. It is not as economical, but reduces ecosystem damage.
11.3 Threats to Biodiversity Clear cutting
11.3 Threats to Biodiversity • Tropical forests have greater species diversity than any other ecosystem. • They are not as likely as temperate forests to regenerate after logging due to poor soil characteristics. • Currently, few tropical forests are being managed for long-term productivity.
11.3 Threats to Biodiversity • Several concerns are raised by tropical deforestation: • It significantly reduces species diversity in the world. • It impacts the climate via lowered transpiration. • Deforested lands are easily eroded. • Without the forests to trap CO2, there may be increased global warming. • Human population pressure is greatest in tropics, and still increasing.
11.3 Threats to Biodiversity • Many lumber companies maintain forest plantations as crops and manage them in the same way farmers manage crops. • Plant single species, even-aged forests of fast growing hybrid trees. • Competing species are controlled by fire, and insects controlled by spraying. • Trees mature to harvestable size in as low as 20 years (vs. 100). • Quality of lumber reduced. • Low species diversity and wildlife value.
11.3 Threats to Biodiversity • Rangelands are lands too dry to support crops, but receive enough precipitation to support grasses and drought-resistant shrubs. • They are often used to raise low-density populations of domesticated or semi-domesticated animals. • Wildlife are usually introduced species not native to the region.
11.3 Threats to Biodiversity Use of rangelands
11.3 Threats to Biodiversity • The conversion of rangelands to grazing by domesticated animals has major impacts on biodiversity. • Selective eating habits of livestock tend to reduce certain species of native plants and encourage others. • Important to regulate number of livestock on rangelands, especially in dry areas. • Overgrazing is a severe problem where human population pressures are great. • Desertification is the process of converting arid or semiarid land to desert because of improper human use.
11.3 Threats to Biodiversity Desertification
11.3 Threats to Biodiversity • In marine ecosystems, much of the harvest is restricted to shallow parts of the ocean where bottom-dwelling fish can be easily harvested. • Trawls are nets dragged along the bottom. • They disturb the seafloor and cause habitat damage. • About 25% of catch is undesirable, and thus discarded, but they are usually dead, and their removal further alters the ecological nature of the seafloor.
Habitat Loss in Aquatic Ecosystems • Freshwater systems are often modified for navigation, irrigation, flood control, or power production. • All of these processes may alter natural ecosystems and change numbers or kinds of aquatic organisms present.
11.3.B Threats to Biodiversity • About 4.3% of U.S. land is developed as urban centers, industrial sites, and transportation infrastructure. • Many areas are covered with impermeable surfaces that prevent plant growth and divert rainfall. • The trend is toward greater urbanization.
11.3 Threats to Biodiversity • According to the IUCN, overexploitation is responsible for over 30% of endangered animal species and 8% of endangered plant species. • Overexploitation occurs when humans harvest organisms faster than the organisms are able to reproduce, threatening some, and causing extinction in others.
11.3 Threats to Biodiversity • U.N. estimates 70% of world’s marine fisheries are overexploited or are fully exploited and in danger of being overexploited. • Amount of fish caught has remained relatively constant, while the amount produced by fish farming has increased. • The commercial fishing industry has been attempting to market species previously regarded as unacceptable.
11.3 Threats to Biodiversity • Fish farming (aquaculture) is becoming increasingly important as a source of fish production. • Currently, about 60% of all aquaculture production is from freshwater systems. • The environmental impacts are similar to those of marine systems: • Nutrient overloads • Escape into natural waters • Land conversion
11.3 Threats to Biodiversity • Meat from wild animals is often referred to as bush meat. • The Wildlife Conservation Society estimates 70% of wildlife species in Asia and Africa and about 40% of species in Latin America are being hunted unsustainably. • Hunting of wildlife is a part of all subsistence cultures. • Many kinds of wildlife are considered delicacies and are highly prized for the home and restaurant trade.
11.3 Threats to Biodiversity • Harvest of living animals for the pet and aquarium trade is a significant problem. • The method of capture is often problematic. • Destruction of bird nests. • Toxins used to stun fish. • Wildlife are also hunted because parts of the animal may have particular value. • Ivory and animal skins • Traditional medicines
11.3 Threats to Biodiversity • Some introductions of exotic species are purposeful, while others are accidental. • Globalization is responsible for spreading thousands of invasive alien species around the world. • The IUCN estimates about 30% of birds and 15% of plants are threatened because they are unable to successfully compete against invasive exotic species.
11.3 Threats to Biodiversity • Introduction of disease has had considerable impact on American forests. • Chestnut blight • Dutch elm disease • Various insects have had an effect on ecosystem structure. • Asian long horned beetle • Freshwater ecosystems have been greatly affected. • Zebra mussel
