Transcript Human Activities Can Alter Ecosystems

Human Activities Can Alter
Ecosystems
36.4 & 36.5
 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.
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.
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.
 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.
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.
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.
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.
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.
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 species—and
the health of the whole ecosystem—may be
affected.
Threats to Biodiversity
 Throughout Earth's history, species have
become extinct—the last members of the
population died—and 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.
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.
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.
Conservation Biology
Approaches
 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.
 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.