habitat degradation and loss 鄭先祐 (ayo) 台南大學 環境與生態學院 院長...
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Contents What constitutes habitat degradation and
when is habitat “lost”? Patterns of habitat transformation on land
and in the sea Human activities that cause habitat
degradation Pollution as a form of habitat degradation Protecting what’s left: approaches to
global habitat conservation Conservation of habitats: the how
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Supplements Essay6.1 scraping bottom: the impact of fishing
on seafloor habitats Essay 6.2 forest ozone injury: how physiology and
climate play a role Essay 6.3 endocrine disrupting contaminants
conservation, and the future Essay 6.4 Deft-for-nature swaps Case study 6.1 the importance of land use history
to conservation biology Case study 6.2 promoting wildlife conservation in
agricultural landscapes
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Introduction Habitat degradation and loss is the most
serious threat to biodiversity largely because it is the most sweeping in its effects.
The majority of Earth’s land surface (83%) has bee transformed by human activities to a greater or lesser extent (Fig. 1.4)
About 60% of Earth’s ecosystems are considered degraded or unsustainably used. (Fig. 6.1)
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Habitat transformation
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Habitat transformation (Fig. 6.1, p.174)
Temperate grasslands, savannas, and shrublands have lost the greatest proportion of their area (more than 80%).
More than 20% of coral reefs have been destroyed and an additional 20% degraded.
35% of assessed mangrove ecosystems have been destroyed in the past two decades.
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What constitutes habitat degradation and when is habitat “lost”? Agriculture, mining, forestry, fisheries,
aquaculture, groundwater extraction, fires, infrastructure development, dams, urbanization, industry, pollution, and biotic changes (native and invasive species) (Table 6.1)
Habitat degradation generally refers to impacts that affect many but not all species, and that may be temporary.
Habitat loss usually refers to impacts so severe that all, or nearly all, species are adversely affected, or to cases where the time span needed for recovery is extremely long.
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Habitat transformation and habitat conversion are two additional terms often used interchangeably with degradation and loss, and we will use them when referring to processes of change.
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Fig. 6.2 Effect of increasing land use intensity on the fraction of species in vertebrate taxa and plants.
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Patterns of habitat transformation on land and in the sea Although humans have transformed their envi
ronments for thousands of years, the pace of change has accelerated sharply in the last century, and particularly since 1960, as the world population more than doubled since then.
In the US, only 42% of native vegetation remains, with less than 25% remaining in the midwest (Stein, et al., 2000). (Fig. 6.3)
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Fig. 6.3 Natural vegetation has been degraded extensively in the US.
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Forest systems and deforestation patterns Over the past three centuries, about half
of the world’s forest cover has been removed to make way for croplands, pastures, and settlements.
In 25 countries, no forest remains, and in an additional 29, more than 90% of forests have been lost. Europe has the least forest cover of any
continent, most of which was lost to agriculture before 1700.
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Forests provide many ecosystem services including regulating water supplies by mediating flow rates, controlling erosion, and affecting climate through gas exchange.
The Amazon Basin is the world’s largest expanse of tropical forest, and despite efforts to reduce deforestation, rates of forest clearing remain high.
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Loss of and damage to grassland, savanna, and shrubland habitats Grasslands, savanna, and shrublands cover 52.5 millio
n KM2 or 40.5% of Earth’s surface, and are found predominately in dry subtropical and dry-humid temperate zones.
Temperate grasslands have been the most heavily converted to agriculture and secondarily to urban environments.
Nearly 97% of tallgrass prairies, and over 60% of mixedgrass and shortgrass prairies in North America have been converted since in mid 1800s.
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Degradation of freshwater systems With agricultural and urban expansion,
freshwater systems are degraded through water diversions, dams and extensive wetland losses.
Aral Sea, Kazakhstan, once the forth largest lake in the world. It has been reduced by 60% in extent over just
two decades (Fig. 6.6)
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Human activities that cause habitat degradation Agricultural activities (crop and
livestock farming, timber plantations, and aquaculture), extraction activities (mining, fisheries, logging, and harvesting) and development (human settlements, industry and associated infrastructure) are the three main proximate causes of habitat degradation and loss.
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Fig. 6.9 Bird species that are threatened by habitat degradation and loss.
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農耕地區的分佈
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Pollution as a form of habitat degradation
Light pollution Air pollution and acid rain Solid waste and plastics Chemical pollution
Chem-storm
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Habitat degradation due to excessive nitrogen inputs Not all forms of pollution are derived from
toxic chemicals Human activities have had profound
impacts on the global biogeochemical cycles of carbon, nitrogen, and phosphorous,
Humans have approximately doubled the rate of nitrogen input into the terrestrial nitrogen cycle. There are greater than 80 million metric tones
produced annually.
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The amount of nitrogen deposited in the world’s major watersheds has increased tremendously.
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Eutrophication In the aquatic and marine realms, the
most common effects of increased nutrient loads are rapid increases in the abundance of algae and aquatic plants, and reduced water clarity. (eutrophication)
Nitrogen-based agricultural fertilizers, whose use is predicted to double or triple over the next 50 years, are the primary source of nitrogen pollution worldwide.
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Protecting what’s left: approaches to global habitat conservation Globally oriented conservation groups,
Conservation International (CI), the Nature Conservancy (TNC), the Wildlife Conservation Society (WCS), and World Wildlife Fund (WWF)
Biodiversity hotspots The “Global 200” ecoregions Crisis ecoregions Wilderness protection
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Conservation of habitats: the how A number of social and economic factors are
the underlying driving force of land use change decisions, which ultimately influence habitat degradation (Fig. 6.20)
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Essay 6.4 Debt-for-Nature Swaps Since 1987 more than US $1 billion has
been channeled into nature conservation in developing countries, through a mechanism known as “debt-for-nature swaps” (DFNS).
These swaps grew out of two issues that came to the fore in the 1980s- the developing world debt crisis, and increasing concern about the rapid loss of natural ecosystems, particularly tropical forests.
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DFNS In the 1970s, commercial banks started to see
LDCs as potential clients. However, in 1981, with developed countries in
recession following the second oil shock of 1979, interest rates increased as the West tried to combat inflation.
In 1982 Mexico became the first to announce it could not make its payments. Forty two countries followed, and the “debt crisis” ( 呆帳危機 ) had begun.
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The twin crisis Because most relied on primary industries
– agriculture, forestry and mining – for the bulk of their exports, the debt crisis increased pressure on the natural environment.
Debt was therefore seen as a cause of deforestation and the twin crises of debt and environmental destruction became liked in many people’s minds.
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The Debt-for-Nature Swaps idea In 1984 Thomas Lovejoy of the World Wildlife
Fund (WWF) suggested that the crises of debt and deforestation could both be tackled it, “ debtor nations willing to protect natural resources could be made eligible for discounts or credits against their debts.
Three years later, the first “debt-for-nature swap” was concluded by Conservation International (CI), the government of Bolivia and Citicorp bank.
A debt-for-nature swap is an agreement whereby debt in “hard” currency is forgiven (cancelled) for commitments to support conservation on the part of the borrower.
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When nature conservation is not in the best interests of poor countries, rich countries will have to pay them to do it and there is evidence to suggest that “generous” bilateral DFNS have occurred.
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Case study 6.1 the importance of land use history to conservation biology
Case study 6.2 promoting wildlife conservation in agricultural landscapes
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