Lecture 14: Fragmentation Flashcards
forest clearance is rarely wholesale and after ______ are retained in the landscape
fragments of forests
habitat fragmentation:
a large expansion of habitat is transformed into a number of smaller patches isolated from each other by a matrix of habits unlike the original
3 stages to fragmentation procesS:
1) initial habitat loss
2) isolation of blocks of habitat
3) increased isolation due to further land-use changes
deforestation is usually =
NON RANDOM
- -some habitats cleared preferentially
- –geog
- –physical accessibility
some species are poorly represented or absent in fragments from
outset = sample effect
ecological foundations to fragmentation research =
species-area relationships and island biogeography theory
what do islands & mountain tops have in common?
they both demonstrate relationships between area of habitat and number of species that survive in that area
species-area relationship curve=
S=cA^z species richness area c = species richness factor z = species accumulation factor
the theory of island biogeography:
MacArthur & wilson 1967
oceanic islands were viewed as relatively static in species composition
-no. of species was a dynamic equilibrium between extinction and colonisation
IBT: (island biogeograhoy theory)
- local extinction rate is a function of island size
- colonisation rate is a function of island isolation from the mainland
- -> if these r true, no. of species is largely determined by its size and isolation
rapid loss of species with large area reuiqrements:
- predators
- large bodied species
- elevational migrants
- -and forest-interior specialists
increasing distance from contiguous forest means than fragments are more
isolated
what is the habitat matrix?
habitat that surrounds forest fragments and ‘connect;s them to other or closest forest
- can support populations of some species found in forest
- fragments conncectd for these species
matrix not suitable for species
- colonisation rates decline
- useable habitat shrinks vice versa =if hospitable
extinction debt =
long term issues, at first many species remain.
- overtime many species go extinct
- -future ecological cost of current habitat destruction
reduce extinction debt
-increase fragment size ( but lots of area required)
edge effect =
disturbance that penetrates into a fragment
abiotic edge effects =
light
temp
wind
humidity
biotic edge effects
predation
soil
transpiration rate
species turnover
edge effects can extend how far into forests
up to 400 m v far
ecosystems function: effect of fragmentation, large predator lost=
increase in herbivores, increase in seed predators–> resulting in reduce number of saplings
- reduced seed dispersal
- reduced wood density
what does fragmentation tell us about protected area management
-maintaining connectivity (IBT stresses importance) –> corridor
value of corridors
- linear habitat remnant surrounded by the modified matrix, wildlife movement
- -wider and better quality corridors, but value degrades with distance
fragment + corridors =
biodiversity
-wider & higher quality is better
