Human Activities Can Alter Ecosystems

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Human Activities Can Alter Ecosystems

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• Over the past few centuries, many ecosystems have
  been affected by the rapidly growing human
  population's need for resources.
• The effects of human activities are sometimes
  felt in only a small area.
• Sometimes, though, the ecological impact is more
  widespread or even global.

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Impact on Chemical Cycles

• Human activities can affect chemical cycling by
  literally moving nutrients from one place to
  another.
• On an even larger scale, some human activities
  can disrupt the processes within global chemical
  cycles.

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Carbon Cycle Impacts

• Deforestation, the clearing of forests for
  agriculture, lumber, and other uses, also affects
  the carbon cycle by eliminating plants that
  absorb carbon dioxide during photosynthesis.
• Sometimes after being cut down, the trees are
  then burned, releasing more carbon dioxide.
• Burning after deforestation in the tropics
  accounts for about 20 percent of the carbon
  dioxide added to the atmosphere by human
  activities.
• Worldwide burning of fossil fuels accounts for
  most of the other 80 percent.

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• The process by which atmospheric gases trap heat
  is called the greenhouse effect.
• As the levels of carbon dioxide and other
  "greenhouse gases" rise, the greenhouse effect
  becomes stronger, trapping more heat in the
  atmosphere and raising Earth's average
  temperature.
• Such an overall rise in Earth's average
  temperature is called global warming.

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Nitrogen Cycle Impacts

• The high levels of nitrogen, often along with
  phosphates, feed the rapid growth of algae in
  these bodies of water, a condition called
  eutrophication.
• As the algae die, the bacteria decomposing them
  can use up so much of the oxygen in the water
  that there is no longer enough to support other
  organisms.
• Smokestacks and automobile exhaust pipes release
  certain nitrogen and sulfur compounds into the
  atmosphere.
• Precipitation that carries this acid back to
  Earth's surface is called acid rain.

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Water Cycle Impacts

• One human activity that can impact the water
  cycle is deforestation.
• A primary way that fresh water returns to the
  atmosphere is transpiration from dense tropical
  forests.
• As a result, tropical deforestation greatly
  reduces the amount of water vapor added to the
  atmosphere.
• This changes precipitation patterns and affects
  ecosystems.

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Biological Magnification

• As organisms take in nutrients and water from the
  environment, they may also take in pollutants.
• Though some pollutants may be excreted, others
  accumulate in an organism's tissues.
• The process by which pollutants become more
  concentrated in successive trophic levels of a
  food web is called biological magnification.

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Damage to the Ozone Shield

• Some pollution in the atmosphere affects a gas
  called ozone (O3) that has particular importance
  to living things.
• The ozone layer, a region of the atmosphere
  between 17 and 25 kilometers above Earth's
  surface, contains concentrations of ozone that
  absorb ultraviolet radiation, shielding organisms
  from its damaging effects.
• The consequences of ozone depletion for humans
  may include an increase in health problems such
  as skin cancer and cataracts, caused by more
  intense ultraviolet radiation reaching Earth's
  surface.
• The radiation may also harm crops and other
  producers.

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Why Diversity Matters

• The number of species in an ecosystem is one
  aspect of biodiversity, a term that encompasses
  the variety of life on Earth.
• The other aspects of biodiversity are the variety
  of ecosystems in the biosphere and the genetic
  variety among individuals within a species.
• One basic reason biodiversity matters is that
  many of the species in an ecosystem are
  interconnected.
• Species depend on community interactions for
  food, shelter, and other needs.
• If a key species disappears, other speciesand
  the health of the whole ecosystemmay be
  affected.

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Threats to Biodiversity

• Throughout Earth's history, species have become
  extinctthe last members of the population
  diedand the species no longer exists on the
  planet.
• But there are signs that species are disappearing
  at a dramatic rate
• About 11 percent of the 9,040 known bird species
  in the world are endangered.
• Of the approximately 20,000 known plant species
  in the United States, at least 680 species are
  endangered.
• Conservation biologists estimate that about 20
  percent of the known freshwater fishes in the
  world have either become extinct during
  historical times or are threatened.

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What is causing these threats to biodiversity?

• Habitat Destruction
• Clearing land for these uses and for obtaining
  natural resources such as lumber, coal, and
  minerals may harm or even destroy natural
  communities. If the organisms that require that
  habitat do not adapt or move to a new area, they
  will not survive.

• Introduced Species
• Introduced (non-native) species often prey on
  native species or compete with them for
  resources.
• Overexploitation
• The practice of harvesting or hunting to such a
  degree that the small number of remaining
  individuals may not be able to sustain the
  population.

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Conservation Biology Approaches

• Focusing on Hot Spots
• These hot spots are small geographic areas with
  high concentrations of species.
• Biodiversity hot spots also tend to be hot spots
  of extinction.

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Conservation Biology Approaches

• Planning for a Sustainable Future
• A zoned reserve includes areas of land that are
  relatively undisturbed by humans, surrounded by
  areas that are minimally impacted by humans
  called buffer zones.
• Although humans live in the buffer zones,
  destructive environmental practices such as
  massive logging, large-scale single-crop
  agriculture, and extensive mining are
  discouraged.
• The zoned reserves encourage long-term ecosystem
  conservation through a balance of human needs and
  habitat preservation.

• Understanding an Organism's Habitat
• Understanding the habitat requirements of a
  species can help biologists manage its existing
  habitat or create new habitat areas.
• Balancing Demands for Resources
• A tug of war exists between efforts to save
  species and the economic and social needs of
  people.