L14 Forest fragmentation Flashcards
What is habitat fragmentation?
where a large expanse of habitat is transformed into q number of smaller patches of smaller total area, isolated from each other by a matrix unlike the original
What are the three stages to the fragmentation process?
Initial habitat loss
Isolation of blocks of habitat
Increased isolation due to further land use change
What factors are considered when clearing habitat?
Geography
Physical accessibility
How does non ransom deforestation affect fragmentation?
Some habitats cleared preferentially
Fragments are often a non-random subset of original habitats and microhabitats
Some species are absent or poorly represented in fragments from outset
What is the extent of fragmentation seen in the Brazilian amazon?
18000 fragments of 1-100ha, 25% of the forest is now within 1km of an edge
What is the extent of fragmentation seen in the Brazilian Atlantic?
230000 fragments of 1-100ha, 91% of the forest is now 1km of an edge
What are species area relationships?
Relationship between the area of a habitat, or of part of a habitat, and the number of species found within that area
What do islands and mountain tops have in common?
Both demonstrate relationships between area of habitat and number of species that survive in that area
What equation characterises the species are relationship curve?
Arrhenius equation
What is the theory of island biogeography?
MacArthur and Wilson postulated that the number of species on an island is a dynamic equilibrium between the opposing forces of extinction and colonisation
What are the basic tenets of island biogeography theory?
Local extinction rate is a function of island size
Colonization rate is a function of island isolation from the mainland
What would you expect for the number of species on bigger islands?
Can have larger population sizes, so lower extinction rate and hence more species
What would you expect for the number of species on islands far from the mainland?
Lower rates of colonisation, hence a fewer number of species
How can IBT be applied to the biodiversity impacts of fragmentation in tropical forests?
Look at the area and isolation effects - see if there is an impact on species richness from area.
What are the species area effects sen in borneo and the neotropics?
number of species increases with forest patch size, as well as a change in composition of species
Which species are likely to be lost as a consequence of fragmentation
Rapid loss of species with large area requirements, such as predators, large bodied species and elevational migrants. Also see a loss of forest interior specialists
What makes a forest fragment more isolated
Increased distance from contiguous forest
What is the habitat Matrix?
The habitat that surrounds forest fragments and connects them to other fragments or contiguous forest, may support populations of some species found in the forest. Fragments are connected for these species
What occurs if there is a large disparity between forest and matrix?
Matrix is inhospitable for forest species, and colonisation rate declines, and the amount of useable habitat shrinks
What occurs if there is only a small disparity between matrix and forest?
Matrix is hospita ble for some forest species, so colonisation rate increases and useable habitat expands
What is extinction debt?
the future extinction of species due to events in the past, occurs because of time delays between the impacts on a species and the species ultimate disappearance from the habitat
When is extinction debt seen in fragmentation?
Immediately after fragmentation many species remain, however, many are committed to extinction over time
What does extinction debt look like for fragments in the amazon?
100 ha fragments see a loss of half of their species in <15 years
How can extinction debt be reduced?
Increasing fragment size
Why is it difficult to reduce extinction debt by fragmentation?
To reduce species loss but 10-fold requires a 1000-fold increase in fragment area
What is an edge effect?
A disturbance that penetrates into the fragment, changes in population or community structures that occur at the boundary of two or more habitats
What are the changes seen in habitats due to abiotic and biotic edge effects?
Myriad changes, such as differences in the microclimate and wind, in vegetation structure, in floristic composition and in animal composition - can cause a reduction in fragment area for many species
How do edge effects impact tree composition?
Plots close to an edge have a higher rate of species turnover that plots far from an edge
Whatare the different roles species play in an ecosystem?
Predators
Seed dispersers and pollinators
Carbon storage
Forest structure
What happens if you remove predators from an environment?
no top down regulation, so unlimited expansion of herbivores means herbivores able to overexploit vegetation,
seed predators and herbivores increase, which causes a reduced number of saplings and seeds
What does removing predators in fragments mean for forest composition?
Reduced wood density
What does fragmentation tell is about protected area management?
It is important to maintain connectivity
IBT stresses the importance of isolation to colonisation rates
What is the value of corridors?
Corridor is a linear habitat remnant, surrounded by modified matrix, that facilitates the movement of wildlife between fragments, number of surviving species increases with corridor width
