forest fragmentation (lecture 13) Flashcards

1
Q

What is forest fragmentation?

A
  • rapid conversion of tropical forest e.g. to agriculture, often intensive plantations
  • however often fragments of forests retained
  • tiny patches to massive swathes cut off from contiguous forest
  • habitat fragmentation
  • large expanse of habitat
  • transformed to number of smaller patches
  • isolated by matrix of habitats unlike original
  • initial habitat loss
  • isolation of blocks of habitat
  • inreased isolation bc further land-use change
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2
Q

How does non-random deforestation affect fragmentation?

A
  • some habitats preferentially cleared
  • bc geography e.g. topography, soils climate
  • bc physical accessibility e.g. roads, rivers
  • fragments often a non-random subset of original habitats & microhabitat
  • some species absent or poorly represented in fragments from outset - “sample effect”
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3
Q

What extent are forests fragmented to in Brazil?

A

Brazilian Amazon

  • ~180,000 fragments
  • 1-100 hectares
  • 2% of forest w/i 1km of forest edge

Brazilian Atlantic

  • ~230,000 1-100ha fragments
  • 91% of forest w/i 1km of forest edge

(Haddard et al., 2015)

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4
Q

What are the ecological foundations to fragmentation research?

  • species-area relationships
A
  • islands & mountain tops both demonstrate relationships between habitat area and number of species surviving in that area
  • species area curve
  • characterised by Arrhenius equation

S= cA^z

S = species richness, A= area, c & z are constants, c = species richness factor, z = species accumulation factor

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5
Q

What are the ecological foundations to fragmentation research?

  • island biogeography theory
A
  • macarthur and wilson, 1967
  • islands prev. viewed as relatively static in species composition
  • colonisation/extinction rare
  • M & W instead suggested island species number = dynamic equilibrium b/w opposing extinction/colonisation
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6
Q

What are the basic tenets of Island Biogeography Theory?

A
  • local extinction rate = function of island size
  • bigger islands have bigger populations have lower extinction rates have more species
  • colonisation rate = function of island isolation from mainland
  • more isolated have lower colonisation rates have fewer species
  • species number is at the equilibrium point between the two
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7
Q

How can IBT be applied to tropical forest fragmentation?

A
  • area and isolation effects
  • number of species increases with forest patch size in borneo & neotropics
  • size also impacts composition
  • fragments away from contiguous forest more isolated
  • probabilities of occupancy/abundances decrease with isolation
  • extinction probability increases
  • depends on habitat matrix severity of effect
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8
Q

Which species are lost in fragmented forest?

A
  • rapid loss of species with large area requirements
    e. g. predators, large-bodied species, elevational migrants
  • plus forest interior specialists
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9
Q

What is extinction debt?

A
  • makes identifying impacts of fragmentation more difficult
  • immediately after fragmentation many species remain
  • but are commited to future extinction
  • future ecological cost of current habitat destruction
  • increasing fragment size reduces debt
  • but 10 x reduction is species loss needs 1000 x increase in area
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10
Q

What are edge effects?

A
  • disturbances that penetrate into fragment
  • can extend far into forest, to 400m
  • can effectively cause a reduction in fragment area for many species
  • abiotic or biotic
  • microclimate and wind
  • vegetation stucture (e.g. treefall gaps), floristic and animal composition
  • e.g. higher turnover rate in tree species composition close to edge
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11
Q

How does fragmentation impact ecosystem functioning?

A
  • loss of large predators
  • massive increases in herbivores and seed predators
  • reduction in sapling numbers
  • reduced seed dispersal mutualisms
  • reduced wood density
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12
Q

What does fragmentation tell us about protected area management?

A

maintain connectivity

  • ibt stresses importance of isolation to colonisation rates
  • key recommendation for PA management
    e. g. corridors, linear (or stepping stone) habitat remnants surrounded by modified matrix that facilitates wildlife movement between patches: the wider and higher quality the better. value decreases with distance
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