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Human Impacts
on the Biosphere
Chapter 49
Impacts, Issues
A 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
Five Great Mass Extinctions
Five Great Mass Extinctions
Fig. 49-2a, p. 892
Era Period Major extinction under way
With high population growth rates and cultural practices (e. g., agriculture, deforestation), humans become major agents of extinction.
QUATERNARY
1.8 mya
CE
NO
ZO
IC
65.5 Major extinction event
Slow recovery after Permian extinction, then adaptive radiations of some marine groups and plants and animals on land. Asteroid impact at K–T boundary, 85% of all species disappear from land and seas.
CRETACEOUS
TERTIARY
145.5
JURASSIC
ME
SO
ZO
IC
199.6
TRIASSIC
251
PERMIANPangea forms; land area exceeds ocean surface area for first time. Asteroid impact? Major glaciation, colossal lava outpourings, 90%–95% of all species lost.
299
CARBON-IFEROUS
Major extinction event
359 Major extinction event
DEVONIANMore than 70% of marine groups lost. Reef builders, trilobites, jawless fishes, and placoderms severely affected. Meteorite impact, sea level decline, global cooling?
416
PA
LE
OZ
OIC
SILURIAN
443 Major extinction event
ORDOVICIAN Second most devastating extinction in seas; nearly 100 families of marine invertebrates lost.
488
CAMBRIANMajor extinction event542
(Precambrian)
Massive glaciation; 79% of all species lost, including most marine microorganisms.
Fig. 49-2b, p. 892
Cenozoic
Mesozoic
Paleozoic (mammalian diversity
for ten families studied)
Protozoans Trilobites Bony
Fishes
Amphibians Reptiles Birds Mammals
CenozoicMesozoic
Paleozoic
b Gymnosperms Angiosperms Insects
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
Introduced Kudzu
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
2007 Global List of Threatened Species
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
Important Land Ecoregions
Critical or Endangered US Ecoregions
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
2006 US Energy Consumption
Fig. 49-9, p. 899
Petroleum
(supplies 39.8% of
total energy)
Percent of source Percent of sector
24 96Transportation
(consumes 28.3%
of total energy)
69
5 2
2Natural Gas
(supplies 22.4% of
total energy)
32
33 45
3729
Industry
(consumes 21.6%
of total energy)
35
Coal (supplies
22.6% of total
energy)
99
<1 2191 72 Residential and
Commercial Uses (consumes 10.3%
of total energy)
28Renewable energy
(supplies 6.8% of
total energy)
9
6
562
16
52Nuclear energy
(supplies 8.2% of
total energy)
10100 21
Electric Power Generation
(consumes 39.7% of total energy)
17
9
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
Fig. 49-11, p. 900
Africa
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
Fig. 49-13, p. 902
uncut
forest
cut 1
year ago
dirt road
cut 3–5
years ago
cut 6–10
years ago
uncut forest
stream in watershed
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
