Transcript Document

Habitat fragmentation #I
14 September 2009 – Pringle lecture
l. Components of fragmentation
A. Reduction in total amount of habitat type
B. Apportionment of remaining habitat into
smaller and more isolated patches
II. What constitutes a barrier?
III. Biological responses to habitat fragmentation
A. initial exclusion
B. isolation
C. island-area effects
D. edge effects
IV. The case of migratory songbirds
V. Protecting wildlife/biotic integrity in a fragmented landscape:
Challenges facing remnant natural areas
I. Components of Habitat Fragmentation
A. Natural heterogeneity vs fragmentation caused by humans
(rich internal patch structure vs simplified patches)
B.
Biota in human-altered fragmented landscapes are affected
at different levels of biological organization
a. changes in gene frequencies of local populations
b. continent wide changes in species distribution and
ecosystems (Panda Example)
Slide 6
Habitat loss and
fragmentation
Increasingly leading
to ex situ breeding and
conservation efforts
Components of habitat fragmentation: apportionment of
remaining habitat into smaller and more isolated
fragments
II. What constitutes a barrier?
• Species Specific
• Cumulative effects
-dams in rivers
-roads in parks
-canals
-power lines
-fences
-fire lands
-other ???
Dams as barriers
Roads as barriers
Road Impacts:
• Animal vehicle collisions cause 200 deaths per year in the US
and cost US 1 billion annually in property damage
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35 million reptiles and frogs per year in Australia
43,002 deer in Pennsylvania in 1990
30,306 deer in Ohio in 2002
>10,000 deer per year in Kansas
102 black bears in North Caroina in 2002
• Ecological hot spots of mortality:
Roads as avenues for invasion by humans and exotic species
Initial road
20 yrs later
What constitutes a barrier for domestic livestock is a
corridor for ‘wildlife:
The case of hedgerows in Britain
and the importance of protecting historical landscape features
in highly fragmented landscapes
The ‘wildlife’ in hedgerows:
Many small mammals
house mice, door mice,
shrews, weasels, voles
Most of Britain’s woodland
birds use hedgerows at
least some of the time
High diversity of plants
relative to surrounding
countryside
Greater number of species
in older hedges
In Britain, roughly a quarter of the hedgerows (96,000 miles)
were removed between 1945-85. An additional 56,000 miles lost
between 1984-90
III. Biological responses to habitat fragmentation
A. initial exclusion
B. isolation
C. island-area effects
D. edge effects
Initial exclusion, isolation and consequent loss of biota
Island Area Effects: Competition and overgrazing
Reindeer in southern Norway
Edge Effects
• temperature,
light, humidity,
wind, fire
• predation
• exotic species
• disease
• pollution
Edge Effects: increased vulnerability to predation
Nest predators
in fragmented
Landscapes
•Cowbirds parasitize the nests of >200 bird species
•Originally restricted to the northern part of the Great Plains
Endangered Kirtland’s warbler - highly parasitized by cowbirds
Brown headed cowbird chick in nest of yellow warbler
Smaller-bodied host birds have less chance of raising any of
their own young than do larger-bodied birds
Solutions?
Humanely disposing of cowbirds
Edge effects: Greater vulnerability to invasion by exotics
Edge Effects: Enhanced incidence of infectious disease
Where have all the birds gone?
Are migratory song bird declines in
North America primarily a result of
habitat fragmentation in temperate
regions or habitat destruction in the
tropics?
Decline of migratory songbirds:
• Reproductive failure in temperate breeding
areas due to habitat fragmentation
• Destruction of tropical habitat
Protecting migratory songbirds:
• Recognizing the importance of intact source areasi.e. large areas of intact forest which serve as
refuges producing surplus birds that can later
disperse and re- populate sink areas
• Restoring forests in areas that are currently sinks
Habitat fragmentation #I
I. Components of fragmentation
A. Reduction in total amount of habitat type
B. Apportionment of remaining habitat into
smaller and more isolated patches
II. What constitutes a barrier?
III. Biological responses to habitat fragmentation
A. initial exclusion
B. isolation
C. island-area effects
D. edge effects
IV. The case of migratory songbirds
V. Protecting wildlife/biotic integrity in a fragmented landscape:
Challenges facing remnant natural areas