Human Impactson the Biosphere

Chapter 49

Impacts, IssuesA Long Reach

Humans threaten other species by competing for resources, overharvesting, introducing nonnative competitors, and degrading habitats – even at the ends of the globe

49.1 The Extinction Crisis

Extinction is a natural process, but humans are accelerating it

In mass extinctions, many organisms in different habitats become extinct in a short period

Species diversity takes millions of years to recover after a mass extinction

The Sixth Great Mass Extinction

Five great mass extinctions mark boundaries of geologic time periods• Previous mass extinctions occurred as a result of

global catastrophes

Many species are currently endangered or threatened as a result of human activity, in what is being called the sixth great mass extinction

Endangered and Threatened Species

Endangered species• A species that has population levels so low that it

faces extinction in all or part of its range

Threatened species• A species that is likely to become endangered in

the near future

Extinct as the Dodo

When humans arrived on Mauritius in 1600, dodos were plentiful – 80 years later, they were extinct

Living or Extinct?

The ivory-billed woodpecker was believed driven to extinction by lumbering in the 1940s – reports of sightings are not conclusively confirmed

49.2 Current Threats to Species

Species with highly specific resource requirements are particularly vulnerable to habitat alterations

Endemic species• A species confined to the limited area in which it

evolved, often by resource requirements

Habitat Loss, Fragmentation, and Degradation

Species decline when humans destroy or fragment natural habitat, or degrade it through pollution or withdrawal of an essential resource• Example: Development of prairies and meadows

threatens the eastern fringed prairie orchid Example: Excessive withdrawals and pollution of an aquifer endanger the Texas blind salamander

Two North American Species Under Threat

Eastern fringed prairie orchid and Texas blind salamander

Giant Panda: An Endangered Species

Giant pandas are endemic to bamboo forests• As bamboo forests were destroyed or

fragmented, pandas began to disappear

Current efforts to save giant pandas:• Protecting existing habitat, creating corridors of

suitable habitat to connect isolated preserves, and captive breeding programs

Giant Panda: An Endangered Species

Pandas feed almost exclusively on bamboo

Overharvesting and Poaching

Overharvesting has caused the collapse or extinction of many commercially valuable species• Commercial hunting (passenger pigeon)

• Commercial fishing (cod, abalone)

Poaching – the illegal harvest of species – is a particular threat in less-developed countries• Food sources, black market profits

Species Introductions

Exotic predators, such as rats and snakes, endanger many island species

Intentionally introduced exotic species, such as kudzu and European brown trout, often outcompete native ones

Exotic pathogens, such as avian malaria, are carried by introduced species

Interacting Effects

Most endangered species are affected by multiple threats

Example: When buffalo were hunted to near extinction, running buffalo clover declined, and is now near extinction due to habitat conversion, competition from introduced plants, and attacks by introduced insects and pathogens

49.1-49.2 Key Concepts The Newly Endangered Species

Human activities have accelerated the rate of extinctions

Habitat loss, degradation, and fragmentation lead to extinctions, as do species introductions and overharvesting

49.3 The Unknown Losses

Existing endangered species lists focus on vertebrates; we have only begun to evaluate the threats to invertebrates and plants

Our impact on protists and fungi is essentially unknown; prokaryotes are not even addressed

49.4 Assessing Biodiversity

Three levels of biodiversity• Genetic, species, and ecosystem diversity

Three goals of conservation biology• Survey the range of biodiversity

• Investigate evolutionary and ecological origins of biodiversity

• Maintain and use biodiversity to benefit humans

Monitoring Indicator Species

Indicator species• A species that alerts biologists to habitat

degradation and impending loss of diversity when its populations decline

Example: Lichens are indicators of habitat quality; they absorb mineral ions from the air and are harmed by air pollution

Identifying Regions at Risk

Hot spots • Habitats that are rich in endemic species and

face a high degree of threat

• Hot spots take priority in conservation efforts

Ecoregions • Larger areas characterized by physical factors

and species composition

• Ecoregions represent all of Earth’s biomes

49.3-49.4 Key Concepts Assessing Biodiversity

Our knowledge of species is biased toward large land animals

Conservation biologists assess the state of ecosystems and their biodiversity, with the goal of preserving as much of it as possible

49.5 Effects of Development and Consumption

As human populations soar, their need for energy and other resources puts pressure on native species

Developed areas displace wild species and also harm them indirectly, as by introducing competing plants or causing light pollution

Negative Impact on Biodiversity

Cities displace wild species and require huge amounts of resources

Effects of Resource Consumption

Processes that extract or capture energy can destroy or degrade habitat• Oil spills, coal runoff, hydroelectric dams

Obtaining raw materials used in consumer products frequently involves degradation of the environment, which can reduce biodiversity• Petroleum for plastics, copper for electronics

49.6 The Threat of Desertification

Human activities have potential not only to harm individual species, but to transform entire biomes

Desertification • Conversion of productive grassland or woodland

into a desertlike region in which little grows

• Result of poor agricultural practices or overgrazing

Mid 1930s: The Dust Bowl

Prairies of the southern Great Plains were plowed for crops, exposing rich topsoil to winds

Billions of tons of topsoil darkened the skies, until the entire region was labeled the Dust Bowl

Soil fell to earth as far away as New York – an ecological and economic disaster

The Dust Bowl

Drought and poor agricultural practices allowed winds to strip tons of topsoil from the ground

Desertification Around the World

Desertification now threatens vast areas• Africa: Sahara desert is expanding south into the

Sahel, due to overgrazing

• Northwest China: Gobi desert is expanding due to overgrazing and overplowing

The best way to avoid desertification: • Avoid farming in areas with high winds and

periodic drought

Modern Dust Clouds

Dust from the Sahara desert, blowing out over the Atlantic Ocean, falls as far away as the southern US and Caribbean

49.7 The Trouble With Trash

The US generates millions of tons of garbage

Plastics, which can persist for more than 100 years, often end up in the oceans where they harm marine life

You can minimize your environmental impact by avoiding disposable goods, and by recycling

Eat Plastics and Die

Its parents fed this albatross chick more than 300 pieces of plastic gathered from the ocean

49.5-49.7 Key Concepts Harmful Practices

Building homes, using energy, purchasing products, raising crops, and discarding trash all have harmful environmental effects that endanger species and ecosystems

49.8 Maintaining Biodiversity and Human Populations

Some people oppose environmental protections for economic reasons

Sustainable practices allow people to benefit economically from biological resources without destroying them

Sustainable Uses of Biological Wealth

Using genetic biodiversity• Mexico set aside a reserve for wild maize, which

might help domesticated corn resist viruses

Discovering useful chemicals• Costa Rica searches native plants for new

medical or commercial chemicals

Ecotourism• Costa Rica created the Monteverde Cloud Forest

Reserve as a profitable sanctuary

Sustainable Use of Biological Wealth

Strip logging yields sustainable economic benefits while minimizing erosion

Sustainable Use of Biological Wealth

Excluding cattle from riparian zones (narrow corridors of vegetation along river banks) has many benefits• Flood protection

• Water conservation

• Habitat for wildlife

• Preservation of biodiversity

Riparian Restoration

San Pedro River before and after restoration

49.8 Key Concepts Sustainable Solutions

All nations have biological wealth that can benefit human populations

Recognizing the value of biodiversity and putting it to use in sustainable ways is good for Earth and all of its species