Transcript Lecture 2, Human Impact

Lecture 2:
Human Impact
4 Major Activities that
Threaten Biodiversity
– 1)Habitat Destruction
– 2)Introduced Species
– 3)Overexploitation
– 4)Disruption of
Interaction Networks
1: Habitat Destruction Includes:
• 1)Habitat Alterations
• Selective Logging
• Edge Effects
• 2)Habitat Fragmentation
• 3) Clear Cutting
Effects of Habitat Destruction:
• 1) Selective logging causes gaps in the canopy thus causing
an edge effect.
• The edges slowly degrade do to wind, invasion of species, and
•
increased sunlight. Degradation of edges can lead to habitat
fragmentation.
Some species may become more susceptible to predation because of
decreased protection from the forest
• 2) Habitat fragmentation cuts species off from larger
•
populations thus causing inability to support viable
populations.
3) Clear cutting for agriculture and pastures.
• Because Tropical Rainforest soil is low in nutrient quality
•
approximately 10x more land is needed for grazing animals and the
previously cleared ag land is abandoned to clear nearby forest to
further grow crops.
Millions of hectares of Brazilian Amazon Rainforest are destroyed
every year due to human set fires for agriculture use and by ranchers.
Habitat Destruction Disrupts
Chemical Cycles of Ecosystems
• Nutrient exhaustion in the tropics due to clear-cutting effects
the Nitrogen Cycle
• This causes an increase in the decomposition rate of organic matter
• Slash and Burn practices of forests causes greater releases of
•
•
nitrogen oxides which contribute to atmospheric warming.
Excess nitrogen and runoff contaminate freshwater and
marine ecosystems.
Deforestation leads to a rise in CO2 levels
Land Behavior Affects the Oceans Too
• Runoff of sediments,
fertilizers, and pollutants
due to changes in the
nitrogen cycle,
agriculture, and tourism
increasing development
along the coasts
• Pollutants directly block the
light thus killing the corals
• Pollutants also clog polyps
on the corals so the corals
cannon perform necessary
life functions such as
gaining food and oxygen
• An increase in nutrients can
also lead to an increase
growth of algae, which
results in the death of corals
Pictured Below: Damaged Coral
Human Activities lead to Rising Atmospheric CO2
• A rise in CO2 causes the greenhouse gas effect where heat is
•
trapped, thus warming the planet.
Warming of the atmosphere causes a warming of ocean
temperatures
• Warming ocean temperatures cause coral bleaching a phenomenon that turns corals white
due to the expulsion of zooxanthella (organisms that provide up to 90% of energy to
corals) which in turn leads to coral death
• A rise in temp will melt the polar ice caps, rising the current sea
level.
What Habitat Destruction and Human
Impact Means for the Coral Reefs
Human Impact directly and indirectly effects
the coral reefs. It causes the corals inability
to recover quickly, a reduction in growth,
and reef mortality.
2: Introduced Species
• Invasive or exotic species
are species that humans
move (intentionally or
unintentionally) from the
species native habitat to
a new geographic region
• Introduced species can
disrupt the geographic
region they were
introduced to causing a
disruption of
“interaction networks”.
• Above: Zebra Mussel, an invasive
species introduced to North
America via ballast water
3: Overexploitation
• Humans overharvesting plants
and animals
• Commonly valuable wood or
trees are overexploited leading
to extinction of tree species
• Tree exploitation can cause
edge effects due to the trees
extraction. This is caused
because the extracted tree is
generally large in comparison
to surrounding trees and roads
need to be cut to remove the
tree. (similar with selective
logging)
Overexploitation of Terrestrial
Animals
• Hunting is a problem for many
•
endangered large predators due to
their trophy value
Primates are exploited for
bushmeat for subsistence/ protein
for local populations
• Species with restricted habitats or
island inhabitants are extremely
vulnerable
• Example: Lemurs on
Madagascar
Overexploitation of Marine Life:
• Blast Fishing: Indiscriminately
kills all marine life, including
coral reefs and unknowingly
endangered aquatic species
• Trawl Nets: the use of trawl
nets by fishermen damage coral
reefs and sponges due to the
weighted net being dragged
along the ocean floor. Also, sea
turtles are commonly killed as a
result of being trapped in the
net.
4: Disruption of “Interaction Networks”
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Ecosystems depend on
species interactions
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Disruptions such as habitat
destruction and
fragmentation cause
species to move into new
niches possibly displacing
previous inhabitants
Example: The decline of
Howler monkeys with the
increase of Muriquis in
Brazil’s Atlantic Forest
The extinction of one species
and especially a keystone
species will directly cause the
extinction of other species
Extinctions
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Pictured: Extinct, Caspian Tiger
Extinction is when the last
individual of a species has died.
Historical extinctions have
occurred due to meteor impacts
but current extinction rates are
faster now than previously.
Extinctions

Problems for smaller populations or a decrease in population size

Loss of Genetic Diversity
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Demographic Fluctuations
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Environmental Fluctuations
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Inbreeding depression
Genetic drift
Lack of gene flow, if isolated populations
Food Availability
These factors influence the Extinction Vortex
The Extinction Vortex
Human Impact causes
deforestation and degradation
to marine environments. This
results in global warming,
climate change, extinctions and
a decline in biodiversity.
How do we Conserve
Biodiversity?