Download Habitat Fragmentation

Habitat Fragmentation
• Process of breaking contiguous unit into
smaller pieces; area & distance
components
Habitat Fragmentation
Habitat Fragmentation
• Process of breaking contiguous unit into
smaller pieces; area & distance
components (includes habitat loss?)
• Leads to:
Habitat Fragmentation
• Community & Ecosystem processes
altered
Habitat Fragmentation
• First-Order Effects: fragmentation leads
to change in a species’ abundance and/or
distribution
Habitat Fragmentation
• Higher-Order Effects: fragmentation
indirectly leads to change in a species
abundance and/or distribution via altered
species interactions
• Altered community-level interactions –
relates to 1st order effects
HABITAT FRAGMENTATION
GroundNesting Birds
- Abundance
– - Distribution
Avian Competitors
Avian Prey
Brood Parasites
Predators
- Abundance
+ - Distribution
- Foraging Behaviors
–
+
–
+
Parasites
- Abundance
- Distribution
REPRODUCTIVE SUCCESS
Formation of
Terrestrial “Islands”
#patches
Patch isolation
Patch size
Edge
Implications with Diseases
Theory predicts that small populations > P(extinction) by
random fluctuations in demography and loss of genetic
diversity through genetic drift
Isolation effects
Carnivores & Reserves
Area of Reserve (km^2)
(A) black bear
(F) lion
(I) African wild dog
(J) grizzly bear
Habitat Fragmentation
• area-sensitive species: species that
require minimum patch size for daily
life requirements
• Edge effects:
Edge Effects
250 m
250 m
31%
64%
Total Area = 1 km2
250 m
14%
Total Area = 5 km2
Total Area = 0.5 km2
Edge Effects
250 m
250 m
31%
64%
Total Area = 1 km2
250 m
14%
Total Area = 5 km2
Total Area = 0.5 km2
Edge Effects
Edge Effects
• Habitat surrounding a patch can:
- change abiotic conditions; e.g., temp.
- change biotic interactions, e.g.,
predation
Example of nest predation = edge effect of
approximately 50 m into forest patch
Carnivores & Reserves
Area of Reserve (km^2)
(A) black bear
(F) lion
(I) African wild dog
(J) grizzly bear
Habitat Fragmentation: SpeciesSpecific Sensitivity?
• Rare species = more vulnerable
• Wide ranging species = large-area
requirements
• Species with reduced mobility = more
vulnerable
• Species with low fecundity (related to
rarity?)
• Species with short life cycle (or multistage life cycle?)
Habitat Fragmentation: SpeciesSpecific Sensitivity?
• Ground-nesting birds may be more
vulnerable (30-60% reduction in last 25
yrs)
• Interior-dependent species
• Species vulnerable to human exploitation
or disturbance
• Specialist species?
Habitat Fragmentation: SpeciesSpecific Sensitivity?
Generalizations are a good start
(= hypotheses?), but a little more
complex than that……
Swihart et al. 2003.
Diversity and
Distributions 9:1-8.
Differential Sensitivities to
Habitat Alteration
• Niche breadth (diet & habitat) – inverse
relation
• Range periphery = more sensitive (W & N)
• Body size = mobility (allometric relation)
• Social and territorial behavior (limited K)
Swihart et al. 2003