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
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”
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)
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
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
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
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
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
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
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
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
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
