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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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Island Biogeography Theory

Olympic National Park presentation

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