Bài giảng habitat loss and degradation

Significant and largely irreversible changes to biodiversity in the world– The distribution of species on Earth is becoming more homogenous – The population size or range or both of t

Threats to Biodiversity

Habitat Loss and Degradation

Significant and largely irreversible changes to biodiversity in the world

– The distribution of species on Earth

is becoming more homogenous

– The population size or range (or

both) of the majority of species

across a range of taxonomic groups

is declining

– Humans have increased the species

extinction rate by as much as 1,000

times over background rates typical

over the planet’s history (medium

certainty)

– 10–30% of mammal, bird, and

amphibian species are currently

threatened with extinction (medium

to high certainty)

Unprecedented change:

Ecosystems

– 5-10% of the area of five

biomes was converted

between 1950 and 1990

– More than two thirds of the

area of two biomes and

more than half of the area

of four others had been

converted by 1990

Millenium Ecosystem Assessment

Assessment Synthesis Report

http://www.maweb.org/

Unprecedented change:

Biogeochemical Cycles

• Since 1960:

– Flows of biologically available

nitrogen in terrestrial ecosystems

doubled

– Flows of phosphorus tripled

• > 50% of all the synthetic nitrogen

fertilizer ever used has been used since

1985

• 60% of the increase in the atmospheric

concentration of CO2 since 1750 has

taken place since 1959

Human-produced Reactive Nitrogen

Humans produce as much biologically available N as all natural pathways and this

may grow a further 65% by 2050

Human Population Growth

World Population Clock

Source: Data from U.S Census Bureau

Human Footprint

Source: Sanderson et al., 2002

• Biodiversity is in decline due to a

diversity of threats (direct threats:

overexploitation, habitat loss,

pollution, etc and indirect threats:

poverty, population growth etc.)

• Lack of enforcement

Road Construction

Source: NASA

- Roads damage habitat

- Roads cause habitat

fragmentation

- Roads increase disturbance

- Roads limit movement of

wildlife

- And more…

Effects of road on exotic/native plant species

Source: Gelbard and Belnap, 2003

Dam Construction

- Blocking migratory species

- Changing turbidity

- Filtering out of woody debris

which provides habitat and

sustain a food change

-Trapping silt in reservoirs and

Survival rate before and after dam construction

Source: Raymond, 1979

■ Forests cover less than 6% of

the earth’s total surface area

■ Forests are habitat for a

majority of the earth’s known

species

■ Forests are being lost faster

than they are growing

Effects and Types of Fragmentation

Area: 16 sq kmEdge: 16 km

Source: Gibbs

Dispersal and fragmentation

Habitat quality: Interior vs Edge

Edge zone:

- Windier

- Drier

- Warmer

- Higher competition between:

Native and exotic species

- More disturbance

Nature of Fragmentation

Human Caused

Distinct Edge Simplified

Patch

Natural

Complex patch

Less distinct edge

SOURCE: DEPARTMENT OF THE INTERIOR, A ADAMS SOURCE: FREY©CBC-AMNH

Loss and Degradation of

Natural Habitat

- It is estimated that forests (including mangroves) cover about 17.4 to 27.5 percent of the country, but only a small subset of this area can be considered in healthy

condition.

- Primary forest continues to decrease drastically and presently covers less than 10% of the

country’s land (MOSTE, 1998;

Poffenberger and Nguyen, 1998)

Kevin Frey/CBC-AMNH

Loss and Degradation of

Natural Habitat

Source: World Bank, 2005

• Fresh and Marine

Changes in mangrove forest area

Source: World Bank, 2005

- Fire wood collection

- Ultimately, pressures from

high population growth

Craig LiebCauses of Deforestation

Forest Islands