Download Human Impact on Resources and Ecosystems

ENV 301: Environmental Science
A Study of Interrelationships
Discussion notes: Scott M. Graves
Text: Enger • Smith
Ninth Edition
Chapter 12
Human Impact on Resources and Ecosystems
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Human Impact on Resources and Ecosystems
Chapter 12
Chapter Outline
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Historical Basis of Pollution
Resource Utilization
– Mineral Resources
Ecosystem Modification
– Forests
– Rangelands
– Wilderness
– Aquatic
Managing Ecosystems for Wildlife
Extinction
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Changing Role of Human Impact
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As human population grew, and tools
became more advanced, the impact a single
human could have on surroundings
increased.
Environmental modifications allowed larger,
dense human populations to arise.
Nearly all earth’s surface has been affected
in some way by human activity.
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Historical Basis of Pollution
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Pollution—Anything released into the
environment that affects an organism’s
survival and reproduction.
– Two primary factors affect the amount of
damage done by pollution:
 Size of the population
 Level of technological development
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Historical Basis of Pollution
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When the human population was small, waste
products were generally biodegradable.
– Human-caused pollution is produced when
waste is generated faster than it can be
degraded, especially as people began to
congregate and establish cities.
 Throughout history, humans fought
ecosystem degradation with technology.
 Short-term solutions.
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Renewable and Nonrenewable Resources
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Natural Resources—Structures and
processes humans can use, but not create.
– Renewable—Can be formed or
regenerated by natural processes.
 Soil, Vegetation, Wildlife
– Non-Renewable—Not replaced by natural
processes, or, rate of replacement is
ineffective.
 Minerals, Fossil fuels
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Costs Associated With Resource Utilization
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Economic—Monetary costs necessary to
exploit the resource.
Energy—Energy expended exploiting the
resource.
Environmental—Environmental effect of
resource exploitation (often deferred).
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Mineral Resources
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Major form of nonrenewable resource.
– Distribution is not uniform.
– Many deposits have already been exploited.
– North America consumes >30% of world minerals.
Steps in Mineral Utilization
– Exploitation
– Mining
– Refining
– Transportation
– Manufacturing
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Recycling of Mineral Materials
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Many minerals are not actually consumed,
but only temporarily held.
In many industries, cost of purchasing
recycled raw materials is higher than the cost
of purchasing virgin materials.
– More costly to produce products from
recycled material than virgin materials.
Historically, monetary cost for energy has
been low, thus no incentive to recycle.
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Utilization and Modification of
Terrestrial Ecosystems
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Natural ecosystems have greater biodiversity
than human-managed ecosystems.
Impact of Agriculture on Natural Ecosystems
– 40% of world’s land surface converted to
cropland and permanent pasture.
– Most productive natural ecosystems are the
first to be modified by humans.
 Pressures to modify the environment are
greatest in areas with high population
density.
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Managing Forest Ecosystems
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1/2 of U.S., 3/4 of Canada, and almost all of
Europe was originally forested.
Because of increasing human population
growth, forested areas are under increasing
pressure to provide wood products and
agricultural land.
– Efficient methods of harvest and
transportation are important to reduce
economic cost of using forest resources.
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Economic and Energy Costs
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Major Economic Costs of Utilizing Forests:
– Purchasing or leasing land.
– Paying for equipment and labor.
– Building roads
Major Energy Costs of Utilizing Forests:
– Harvesting
– Transportation
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Environmental Costs
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Modern forest management practices involve
a compromise that allows economic
exploitation while maintaining some of the
environmental values of the forest.
Forested areas effectively reduce erosion.
– Loss of soil (nutrients) reduces soil fertility.
– Road building in forests increases erosion.
Forest areas modify climate, and provide
recreational opportunities as well.
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Environmental Implication of Harvesting
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Clear Cutting—Removal of all trees in an
area. Economical but increases erosion,
especially on steep slopes.
Patch-Work Clear Cutting—Clear cutting in
small, unconnected patches; preserves
biodiversity.
Selective Harvesting—Single-tree
harvesting. Not as economical, but reduces
ecosystem damage.
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Plantation Forestry
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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.
– Mature rate as low as 20 years (vs. 100).
 Quality of lumber reduced.
 Low species diversity and wildlife value.
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Special Concerns About Tropical Deforestation
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Tropical forests have greater species diversity
than any other ecosystem.
Not easy to regenerate after logging due to
poor soil characteristics.
Deforestation Concerns
– Significantly reduces species diversity.
– Impacts climate via lowered transpiration.
– CO2 trap—Increased global warming.
– Human population pressure is greatest in
tropics, and still increasing.
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Managing Rangeland Ecosystems
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Rangelands—Lands too dry to support
crops, but received enough precipitation to
support grasses and drought-resistant
shrubs.
– Wildlife are usually introduced species.
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Environmental Costs of Utilizing Rangelands
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Management techniques and selective
grazing of animals may lead to the
elimination of non-preferred species.
Important to regulate number of livestock on
rangelands, especially in dry areas.
Desertification—Process of converting arid
and semi-arid land to desert.
– Over-grazing
– Firewood cutting
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Wilderness and Remote Areas
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Many areas in the world have had minimal
human impact.
– Some are remote and may have harsh
environmental conditions.
 Wilderness Act (1964)—Wilderness:
 “An area where the earth and its
community of life are un-trampled by
man, where man himself is a visitor
who does not remain.”
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Managing Aquatic Ecosystems
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Aquatic ecosystems divided into:
– Freshwater, Brackish, Marine
Environmental costs related to utilizing
marine ecosystems fall into two categories:
– Over-fishing
– Environmental effects of harvesting
 UN estimates 70% of world’s marine
fisheries are over-exploited.
 Capacity should be reduced by 30%.
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Managing Aquatic Ecosystems
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Coastal regions are most productive regions
of the oceans.
– Sunlight penetration—shallow—warm
– Nutrient deposition from land
– Wind/wave action stirs nutrients
Fishing pressure and pollution are greatest in
these areas.
– Trawls—nets dragged along bottom.
 Large by-catch
 Disturbs seafloor
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Environmental Costs Associated with
Utilizing Freshwater Ecosystems
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Two primary human alterations:
– Water Quality —Erosion, toxic run-off
– Exotic Species—Introduced species
 Humans have great access to freshwater
ecosystems.
 Many North American freshwater fisheries
are primarily managed for sport fishery.
 Fisheries managers must balance:
 Sport fisheries
 Commercial harvesters
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Aquaculture
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Fish farming is becoming increasingly
important as a source of fish production.
– Currently, about 60% of all aquaculture
production is from freshwater systems.
 Problems
 Nutrient overloads
 Escape into natural waters
 Land conversion
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Managing Ecosystems For Wildlife
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Habitat Analysis and Management
Animals have highly specific habitat
requirements that change throughout the year.
Once habitat requirements are understood,
steps can be taken to alter habitat and
improve species success.
– Fire to eliminate poor habitats.
 Kirtland Warblers—Jack Pine stands.
– Encourage growth of certain plant species.
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Population Assessment and Management
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Wildlife managers use population censuses to
check if populations are within appropriate
levels.
With suitable habitat and protection, most wild
animals can maintain a sizeable population.
But high reproductive capacities and/or heavy
protection can cause very large populations.
 Whitetail Deer in Eastern U.S.
 Elephants in Zimbabwe
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Population Assessment and Management
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Wildlife management often involves harvesting
for sport and meat.
Hunting regulation is crucial.
– Seasons usually occur in the fall to take
advantage of surplus animals.
When populations get too small, artificial
introductions can be implemented.
– Native species for augmentation.
– Non-native species for empty niches.
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Managing a Wildlife Population
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Predator and Competitor Control
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At one time it was believed populations of
game species could be increased if
predators were controlled.
– Still used in some situations.
– But, in many cases, human modification of
habitat has a greater impact than natural
predation.
– Many species do require refuges where
they are protected from competing species
or human influence.
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Migratory Waterfowl Management
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Migratory birds can travel thousands of
kilometers.
– North in spring to reproduce.
– South in fall to escape cold temperatures.
International agreements necessary to
maintain appropriate habitat.
– Canada
– United States
– Mexico
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Extinction and Loss of Biodiversity
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Small, dispersed populations are more prone
to extinction.
– Successful breeding more difficult.
– Local weather conditions can severely
impact population size.
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Human-Accelerated Extinction
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Wherever humans have become the dominant
organisms, extinctions have occurred.
– Food
– Animals Parts
– Pest Status
– Habitat Alteration
 Most Important Cause
 Habitat Fragmentation
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Why Worry About Extinction ?
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Useful to Humans:
– Medical—Less than 1% of tropical
rainforest plant species have been tested
for pharmaceutical use.
– Food Resources
Ecological—Species play specific roles in
ecosystem function.
Ethical—Animals have a fundamental right to
exist.
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Extinction Prevention
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Endangered—Very low populations, could
become extinct in very near future.
Threatened—Still exist in large numbers in
current range, but are declining in most
areas.
– Could become extinct if a critical
environmental factor is changed.
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Extinction Prevention
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Most extinction prevention interest occurs in
developed countries. Most vulnerable
species already eliminated.
Less-developed and developing countries
have both highest population growth and the
majority of the world’s species.
– More concerned with immediate needs of
food and shelter than long-range issues
such as species extinction.
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Endangered Species Act (1973)
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Gave U.S. government jurisdiction over
threatened and endangered species.
– Directs that no activity by a government
agency should lead to the extinction of an
endangered species.
– Directs government agencies to use
whatever means necessary to preserve the
species in question.
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Chapter Summary
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Historical Basis of Pollution
Resource Utilization
– Mineral Resources
Ecosystem Modification
– Forests
– Rangelands
– Wilderness
– Aquatic
Managing Ecosystems for Wildlife
Extinction
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