Download 23A Conservation Biology 2 2009

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Objectives
• Conservation approaches:
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populations/species
•
entire habitats
• Conservation biology relates to landscape
ecology
• Habitat destruction/fragmentation causes much
extinction
• Plans for preserves
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Size, number, shape, step stones, corridors
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Preserve community structure
Conservation Planning: Approach 2
• Preserve habitats/areas,
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especially ‘biodiversity hotspots’
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high species number
•
high endemism
Endemic species:
restricted to small geographic area;
especially prominent on islands
Little spatial relation between species
richness, threatened species, and endemic
species
Species richness
Threatened species
Endemic species
Habitat changes caused by human land use
limit conservation strategies.
Deterministic causes of extinctions:
the ‘evil quartet’
1 habitat destruction and fragmentation
(67% of cases)
2 introduced species
3 overkill (overexploit)
4 chains of extinction
Habitat reduction and fragmentation
lead to endangered species
Species introductions (e.g. this
predatory snail) can eliminate native
species.
Decline in marine organisms
and increase in
eutrophication due to
human cultural development
Overexploitation changes species
composition of this marine community.
Whalers shifted to new, less profitable
species as populations of heavily hunted
species
declined.
Smaller fragments support fewer animals.
Figure 1
Habitat reduction and elimination
• Some habitats are eliminated altogether.
• Fragmentation causes other problems:
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reduced total area
•
reduced habitat heterogeneity
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reduced connectivity
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greater inter-fragment distance
•
unable to migrate with changing climate
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reduced interior/edge ratio
Principles for design of nature preserves:
If create preserve from large expanse of
uniform habitat:
• larger is better than smaller
• SLOSS: single large or several small?
• one large area is better than several small
that sum to same size
• add corridors or ‘stepping stones’
• circular is better than elongate with more
edge
*** What is the pattern? What explains it?
Figure 2
Which size
of area is
needed?
Will a park be
Sufficient?
Why are larger areas better?
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support more species by reducing
likelihood of stochastic extinction
promote genetic diversity
buffer populations against
disturbance
avoid ‘edge effects’
offer freedom to migrate
***Summarize two major results.
Corridors enhance migration between patches
and maintain population cohesion.
Figure 3
***What are advantages of corridors?
• Increase immigration
•
increase species richness
•
provide a ‘rescue effect’
•
prevent inbreeding; add genetic diversity
• Increase foraging area for widespread species
• Provide cover for escape from predator when
moving
• Alternative refuges from large disturbances
• Mix of habitats for species requiring them
• Are there disadvantages?
If creating preserve out of diverse
habitat:
• Several small in different habitats better
than one large in uniform habitat
• Plan for migration --->
•
use corridors
stepping stones to link habitats
•
bridge roads and pipelines that impede
movement
Consider community structure
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Top-down control of trophic abundances
Cascade effects: indirect effects extended
through multiple levels
Can have chain of extinctions if highly
dependent
Keystone organisms must be preserved
Non-redundant species, key species
that maintain stability/diversity
***What are conservation implications of the
two contrasting models? Rivet/redundancy
• Would focus be on community
dynamics or single-species dynamics?
• In which model are keystone species
important?
How does species (and functional diversity
affect community response to disturbance?
Community Principles
• An increase in the structural diversity of
vegetation increases species diversity.
• Disturbance may be necessary to maintain
all diversity.
• When disturbed, greater diversity leads to
greater stability.
• Full restoration of native plant communities
sustains diverse animal populations.
• A high diversity of plant species assures a yearround food supply for the greatest diversity of
wildlife.
• Species survival depends on maintaining
minimum population levels (>500).
Sample exam ?
You are asked to design a national park system for a
tropical country.
1) How will the concept of ‘hot spots’ of diversity
influence your choice of areas to conserve?
• You have defined your locations. What are 4
principles that you will consider in the next
phase: their spatial design?
1) What specific attributes of parks are needed to
accommodate specific flora or fauna?
2) What general criteria related to preserve size
must be met to ensure long-term survival of
species? (assume habitat requirements are met)
Population models assume: large size
(> minimum viable population size);
no variation in average birth and death rates.
• In reality, randomness affects populations,
especially small ones:
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•
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Catastrophe
Variation in environment
Stochastic (random sampling) processes
• Chance events may cause
small populations to go extinct.
Probability of extinction increases over time;
increases with smaller initial population size.
Small populations are more likely to go extinct
due to random fluctuation in population size.
Figure 4
***Summarize the two main results. Provide a
reason for each result.
What traits enable a population to rescue a
small population from extinction? Figure 5
Rescue effect:
• Immigration from a large subpopulation
can keep a declining subpopulation from
inbreeding and going extinct.
• Can produce positive densitydependence: survival of subpopulations
increases with more subpopulations.
Mainland-island model:
Source provides emigrants to sink.
source
sinks
Figure 6
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Spatial Principles
Large areas sustain more species than small areas.
Many small patches in an area will help sustain regional
diversity.
Patch shape is as important as size.
Fragmentation of habitats, communities, and ecosystems
reduces diversity.
Isolated patches sustain fewer species than closely
associated patches.
Species diversity in patches connected by corridors >
than for disconnected patches.
A heterogeneous mosaic of community types sustains
more species, including rare species.
Ecotones support a variety of species from both
communities & species specific to the ecotone.