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Threats to BiodiversityMODULE 09: THREATS TO BIODIVERSITYUNIT 1: BIODIVERSITY
Objectives
At the end of this series of lectures, you should be able to: Define terms.
Understand human population growth and resource use and how they affect conservation.
Summarize anthropogenic threats to biodiversity.
Describe habitat fragmentation and island biogeography theory as applied to understanding the effect of habitat fragmentation on biodiversity.
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Threats to Biodiversity
Two major CAUSES of threats to biodiversity: Human population growth
Increased standard of living Distribution of wealth
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Human population growth
The world’s human population is estimated to total ~ 7.4 billion. http://www.census.gov/popclock/
*Optimal total human population is ~1.5 to 2 billion
Human population growth
The human population has increased due to: High birth rates
Declining mortality rates Reliable food supplies
Improved sanitation
Medicine
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Human population growth
Humans appropriate approximately 40% of all potential terrestrial net primary productivity.
Increased Standard of Living
We would need 3.5 Earths for the population on the planet to live as we do.
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Human Disturbance
The major threats to biodiversity are the result of human activity. Habitat destruction, degradation, and fragmentation
Introduction of exotic species
Overexploitation
Increased spread of disease
Pollution
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Human Disturbance
Most threatened species face two or more of these threats Threatened species are unable to adapt
Threats develop rapidly
Threats are widespread
Overexploitation
Overexploitation of species is driven by: Growing human populations
Methods of harvesting have become more efficient.
Overexploitation is thought to threaten about one third of the vertebrates of concern.
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Overexploitation
For many species direct exploitation is less important than the indirect effects of exploitation. Bycatch (Shrimp)
Other species can decline when they depend on a species that is exploited- extinction cascades.
Introduced species
Humans transport species throughout the world. European colonization
Agriculture or horticulture
Accidental transport
Biological control
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Invasive Species
Characteristics of invading species High reproductive rate
Short generation time
Early succession species
High dispersal
Vegetative or clonal reproduction
Broad native range
Habitat generalist
Broad diet
Human commensal
Invasive species
Loss of native species Change community structure
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Disease
In most aspects, disease is difficult to separate from introduced species. The diseases themselves are frequently introduced. (Example: Hawaiian
birds and avian malaria via chickens)
Disease maybe included with another introduced species. (Example: American chestnut)
Pollution
Pollution is a form of habitat degradation. DDT and biomagnification
Eutrophication by phosphates and nitrates
Erosion can increase cloudiness and decrease photosynthesis or smother sessile organisms
Acid rain: terrestrial and aquatic effects
Toxic metals: lichens
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Habitat destruction
The primary cause of the loss of biodiversity is habitat destruction. Resulting from the expansion of human populations and resource
gathering.
Demo Presentation – Spread of Agriculture
Habitat destruction
For many wildlife species, much of their habitat has been destroyed. Javan gibbon
95% of its habitat has been destroyed
It is protected in less than 2% of the remaining 5%.
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Fragmentation
The breaking of continuous natural habitat into pieces. Reduction in the total size of available habitat.
Increase the isolation of the individual pieces of natural habitat.
Increases edge habitat (ecotone)
Matrix habitat
Fragmentation
Habitat fragments differ from the original habitat in two important ways. Fragments have a greater amount of edge for the area of habitat
enclosed.
The center of each fragment is closer to an edge.
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Fragmentation
Edge effects Fragmentation produces more edge habitat
An even greater decline in the amount of natural habitat than just the habitat destruction would suggest.
Significant changes in the environmental characteristics of the fragments, including light, temperature, wind, humidity, fire.
Fragmentation
Fragmentation may limit a species’ potential for dispersal and colonization.
Species that do not cross inappropriate habitat will tend to decline even in fragments of ideal habitat. Metapopulation dynamics
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Fragmentation
Olympic National Park demonstration
Island Biogeography Theory
Species richness on islands can be explained by two factors. Island area
Island isolation
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Island Biogeography Theory
Any given island is defined by its area and its isolation. Because extinction rate (a function of area) and immigration rate (a
function of isolation) can both be described by species richness, we can combine them into a single graph.
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