Transcript Document

Chapter 57: Conservation Biology
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Overview of the Biodiversity Crisis
Losing Biodiversity
Vulnerable Species
Species Endemism and Hotspots
Costs of Extinction, Ecosystem Services
Factors Responsible for Extinction
Introduced Species
Ecosystem Disruption
Perils of Small Population Size
Preserving Endangered Species
Conservation Whole Ecosystems
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Overview of the Biodiversity Crisis
As much as 20% of the world’s biodiversity may
be lost during the next 30 years (and 50-66%
by the end of the century):
- 50000 out of 250000 plant species
- 4000 out of 20000 butterfly species
- 2000 out of 9000 bird species
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SLIDE SHOW on biodiversity crisis at
http://io.uwinnipeg.ca/~simmons/CHAP5598/sld001.htm
BUT we may lose even more unknown species,
because no more than 15% of the world’s
eukaryotic organisms have been described yet.
Question: how much of Stellenbosch’s
University books or buildings would you burn?
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The new science of conservation biology
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we are in the midst of one of the
great extinction events in earth’s
history
concerned biologists have come
together to use their knowledge to
save species from extinction
this emerging discipline has been
called
CONSERVATION BIOLOGY
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Prehistoric and historic extinctions
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Extinction due to prehistoric humans
Shortly after humans arrived, 74-86% of large
animal species became extinct.
 caused by hunting and habitat alteration (e.g.
fires to replace forest with grasslands)
Extinctions in historical time since 1600
Historical extinction rates are best known for
birds (~ 113 species) and mammals (~ 85
species)
=> this rate of extinction is increasing due to
human activities = BIODIVERSITY CRISIS
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Prehistoric North American animals, extinct after arrival of humans
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Historic extinctions
Tasmanian Tiger (1936)
Dodo (1681)
Carolina Parakeet
(1918)
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Island species are particularly vulnerable
The majority of historic extinctions have
occurred on islands because
- island species have small populations
- island species often do not have any
behavioural defenses against introduced
predators or immunological defenses
against introduced diseases
- island species were outcompeted for
resources by introduced species
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The snake that ate all the birds
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If you visit the island of Guam, you won't see
the Mariana Fruit Dove, Guam Flycatcher,
Rufous Fantail, Cardinal Honeyeater, or
Guam Rail. They have become extinct since
the late 1940s, when the Brown Tree Snake
is believed to have first colonized the island.
Guam Rail,
extinct in the
wild because of
snake predation
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Species Endemism and Hot Spots
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A species found naturally in only one geographic
area is termed endemic
Isolated geographical areas, such as islands, lakes
or mountain ranges, often have many endemic
species
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Notable hotspots of endemism are Madagascar,
SE Asia, the Caribbean, and SOUTH AFRICA!
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Unfortunately, many experiencing high rates
of habitat destruction
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Endemism hotspots contain
many species and many humans
By protecting just 1.4% of the world’s land surface containing
all the endemism hotspots, 44% of the world’s vascular plants
and 35% of its terrestrial vertebrates could be preserved.
BUT, these hotspots also contain 20% of the world’s population,
most of them rapidly increasing, and are therefore areas of
intense commercial exploitation and habitat destruction.
=> Therefore, successful conservation cannot focus on
wilderness areas alone!
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1. Losing Biodiversity incurs huge costs
Direct economic value
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production of foods, fibres, fuels, medicines
maintainance of biodiversity (gene
prospecting)
Rosy periwinkle
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2. Losing Biodiversity incurs huge costs
Indirect economic value
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purification of air and water
mitigation of droughts and floods
generation and preservation of soils and renewal of
their fertility
detoxification and decomposition of wastes
pollination of crops and natural vegetation
dispersal of seeds
cycling and movement of nutrients
control of the vast majority of potential agricultural
pests
protection of coastal shores from erosion by waves
partial stabilization of local, regional and global climate
moderation of weather extremes and their impacts
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Mangrove, Thailand
80,000
60,000
40,000
20,000
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Intact
Shrimp
farming
3,000
Economic value
(US$ per hectare)
Economic value
(US$ per hectare)
Economic value of intact habitats
Tropical forest, Cameroon
2,000
1,000
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-1,000
Reduced- Smallimpact
scale
logging farming Plantation
-2,000
The total economic value of intact natural habitats (accounting
for all the economic benefits they produce) is often much higher
than that of converted habitats
=> special business interests of small groups of stakeholders,
such as large international timber corporations, put their interests
above those of the common good
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6000000000 dollars per year …
… earned by bees and other pollinators in
the United States alone
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3. Losing Biodiversity incurs huge costs
Ethical and aesthetic value
· provision of aesthetic beauty and
intellectual stimulation that lift the human
spirit
· future generations have the right to enjoy
the same benefits from biodiversity and
ecosystem services as we do
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Where would you like
to go on vacation?
Here or …
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… here?
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4. Losing Biodiversity incurs huge costs
Consequences of biodiversity loss
· loss of genetic diversity and the opportunity to
use it for crops, medicines, etc.
· droughts and floods
· soil erosion, and land slides
· desertification, mineralization and water logging
of productive lands
· polluted water, loss of water
· crop loss due to decrease of pollinators, seed
dispersers and biological control
· coastal erosion (storm and tsunami damage)
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· some rather angry and disappointed children
12000000000 dollars
lost in the Mississippi floods in 1993
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Extinction Crisis
Factors responsible for extinction:
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Habitat loss
Habitat fragmentation
Overexploitation (hunting, fishing ..)
Introduced species
Disruption of ecological interactions
Pollution
Loss of genetic variability due to
small populations
Catastrophic disturbances (storms, floods, etc.)
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Habitat Loss
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Natural habitats adversely affected by
human influences in four ways:
– destruction
 clear-cut tree harvesting
– pollution
 habitat degradation,
 e.g. acid rain
– disruption
 park visitors
- habitat fragmentation
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Fig. 57.12(TE Art)
Extinction rate (per year)
0.5
0.4
0.3
0.2
0.1
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10-2
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Area (km2)
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The smaller the islands, the larger the risk of extinction for bird species.24
Habitat Loss
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Habitat fragmentation
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fragmenting of population
into unconnected patches
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Edge effects can significantly alter the
microclimate near the edge and may
reduce appropriate habitat for many
species.
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Expanding edges opens up
opportunities for parasites and predators
to invade new areas.
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Long edges decrease the
value of habitat fragments
because conditions in edges
are different
The effects of
fragmentation can
be alleviated if the
habitats between
the fragments are
allowing animals at
least to move
through them
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Fragmentation of a Woodland Habitat
in Wisconsin, USA
Less total area, less area per patch, more edges,
longer distance between patches
=> All making it harder for forest specialists to survive
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Case Study 3:
North American songbirds
American Redstart
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In many areas of the eastern USA, more than 75% of
migrant bird species have experienced a significant
decline. Species experiencing the greatest declines
are those which are both long-distance migrants and
deep forest dwellers. The reasons are two-fold:
Forest fragmentation and loss both on
 wooded summer nesting grounds
 winter habitats in Central and South America
Increased brood parasitism by cowbirds along forest
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edges
Case Study 4: Overexploitation of whales
Commercial whaling began in sixteenth century
and reached its height in early 20th century.
 As whalers reduced the numbers of one
species, they simply switched species.
 In 1974, the International Whaling
Commission (IWC) banned hunting on
all blue, gray, and humpback whales
and instituted partial bans on others.
 1986 - worldwide moratorium
 as a result, some species have
recovered, but others have not
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As whalers
reduced
the
numbers
of one
species,
they
simply
switched
species.
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Ecosystem Disruption
Species often become vulnerable to extinction
when their web of ecological interactions
becomes disrupted.
 e.g. commercial whaling initiated a
series of changes causing disastrous
effects on kelp forests
Whales down -> zooplankton up -> pollock fish
up -> herring and perch down -> sea lions
and seals down -> orcas switch to sea otters
-> sea urchins up -> kelp forest and fish
living there down
=> complex interaction of top-down and
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bottom-up effects
Introduced Species
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Detrimental effects
 Natural or man-made colonization may
bring together species with no previous
history of interaction which may lead to
extinction
– Damage to human economy and health
 Effects of introductions on humans has
been enormous.
 Non-native species cost US economy
alone $140 billion annually.
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Case study 5:
Avian extinctions on Hawaii
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Goats and
more than ten
other
introduced
mammals
have
drastically
altered the
flora and fauna
of Hawaii
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In addition, avian malaria was introduced to which
native Hawaiian bird species have no resistance
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As a consequence, the Akiapolaau and many other
Hawaiian bird species are endangered or already extinct
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Efforts to combat introduced species
– 1. Eradication
 difficult, expensive, time-consuming, and
potentially impossible, but possible on
small islands
– 2. Prevention
 needs strong policies and enforcement,
e.g. inspection of shipments, tourists
 e.g. http://academic.sun.ac.za/cib/
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Preserving Keystone Species
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Keystone species are usually characterized
by the strength of their impact on their
community, ensuring the structure and
functioning of an ecosystem
Community importance = change in some
quantity of the ecosystem (e.g. species
richness) per unit change
in keystone numbers
 e.g. flying foxes
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Cascading extinctions
• Flying foxes are driven to extinction by forest
loss and human persecutation
• The function of flying foxes in their
ecosystem, i.e. pollination and seed
dispersal, is lost
• Consequently, all the plants depending on
them for pollination and seed dispersal are
losing out
• With the plants, all the animals, e.g. insect
herbivores, are disappearing, too
=> Ecosystem disruption leads to a much
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simpler, species-poor ecosystem
The Perils of Small Population Size
- or the Downward Spiral towards Extinction
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1. Demographic factors
– By nature of their small size, small
populations are ill equipped to withstand a
catastrophic event (density-independent
effects), e.g. fires, storms, etc.
– Remaining individuals may all be old males
2. Lack of genetic variability
– Small populations are prone to the loss of
genetic variation as a result of genetic drift,
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making them susceptible to disease
The Perils of Small Population Size
- or the Extinction Vortex
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3. Spatial effects
– Individuals may simply not find each other
anymore to mate, e.g. tigers with large
home ranges (the Allee effect)
4. Metapopulation breakdown
– Small and fragmented populations are not
connected anymore, so suitable habitat is
not re-colonized by immigrants from other
habitat patches anymore
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Preserving Endangered Species
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Preservation approaches:
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habitat restoration
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pristine restoration
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removal of introduced species
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cleanup and rehabilitation
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captive breeding
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Conserving Whole Ecosystems
Isolated patches of habitat lose species much
more rapidly than large areas:
- habitat loss and fragmentation
- species-area effect and island biogeography
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Mega-reserves are large areas of land that
contain a core of one or more undisturbed
habitats.
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focus on preserving intact ecosystems
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This lecture will NOT be part of the exam!
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EXAM includes
All 9 ecology lectures except today’s
Corresponds with chapters 53 - 56 plus the
lectures on South African biomes
45 marks = 25 marks are multiple choice
questions and 20 marks are essay questions
(4 questions for 4 - 6 marks)
Marks are almost evenly distributed among
chapters
Thank you and good luck!
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