Habitat fragmentation

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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
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I. Components of Habitat Fragmentation

• A. Natural heterogeneity vs fragmentation caused
  by humans
• (rich internal patch structure vs
  simplified patches)
• 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)

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Slide 6
Habitat loss and fragmentation Increasingly
leading to ex situ breeding and conservation
efforts
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• Components of habitat fragmentation
  apportionment of
• remaining habitat into smaller and
  more isolated
• fragments

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II. What constitutes a barrier?

• Species Specific
• Cumulative effects
• -dams in rivers
• -roads in parks
• -canals
• -power lines
• -fences
• -fire lands
• -other ???

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Dams as barriers
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Roads as barriers
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• Road Impacts
• Animal vehicle collisions cause 200 deaths per
  year in the US and cost US 1 billion annually in
  property damage
• 35 million reptiles and frogs per year in
  Australia
• 43,002 deer in Pennsylvania in 1990
• 30,306 deer in Ohio in 2002
• gt10,000 deer per year in Kansas
• 102 black bears in North Caroina in 2002
• Ecological hot spots of mortality

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Roads as avenues for invasion by humans and
exotic species
20 yrs later
Initial road
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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
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The wildlife in hedgerows Many small mammals
house mice, door mice, shrews, weasels,
voles Most of Britains 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
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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
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III. Biological responses to habitat
fragmentation A. initial exclusion
B. isolation C. island-area
effects D. edge effects
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Initial exclusion, isolation and consequent loss
of biota
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Island Area Effects Competition and overgrazing
Reindeer in southern Norway
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Edge Effects

• temperature,
• light, humidity,
• wind, fire
• predation
• exotic species
• disease
• pollution

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Edge Effects increased vulnerability to
predation
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Nest predators in fragmented Landscapes
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• Cowbirds parasitize the nests of gt200 bird
  species
• Originally restricted to the northern part of the
  Great Plains

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Endangered Kirtlands warbler - highly
parasitized by cowbirds
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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
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Solutions?
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Humanely disposing of cowbirds
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Edge effects Greater vulnerability to invasion
by exotics
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Edge Effects Enhanced incidence of infectious
disease
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Are migratory song bird declines in North America
primarily a result of habitat fragmentation in
temperate regions or habitat destruction in the
tropics?
Where have all the birds gone?
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Decline of migratory songbirds

• Reproductive failure in temperate breeding areas
  due to habitat fragmentation
• Destruction of tropical habitat

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Protecting migratory songbirds

• Recognizing the importance of intact source
  areas- i.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

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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