Lecture 13 - forest fragmentation

Question 1

when does forest fragmentation occur?

Answer 1

• rapid conversion of tropical forest to agriculture is rarely wholesale and often fragments of forest are retained in the landscape from tiny patches to massive swathes that are now cut off from contiguous forest

Question 2

definition of habitat fragmentation

Answer 2

a large expanse of habitat is transformed into a number of smaller patches of smaller total area, isolated from each other by a matrix of habitats unlike the original

Question 3

what are the 3 stages of the fragmentation process

Answer 3

1) initial habitat loss
2) isolation of blocks of habitat
3) increased isolation due to further land use change

Question 4

is deforestation a random or non random process?

Answer 4

usually non random - some habitats cleared preferentially e.g. geography (soils etc) or physical accessibility (roads
- fragments are often a non random subset of original habitats and microhabitats

Question 5

what is the ‘sample effect’?

Answer 5

some species are absent or poorly represented in fragments from outset

Question 6

how vast is the problem of fragments?

Answer 6

huge - Amazon = 180,000 fragments

Atlantic=230,000 fragments

Question 7

what are the ecological foundations to fragmentation research

Answer 7

1) species area relationships

2) island biogeography theory

Question 8

describe species area relationships

Answer 8

relationships between area of habitat and number of species that survive in that area e.g. islands and mountain tops
- pattern is such a strong relationship it can graphed across many taxa

Question 9

SARS equation

Answer 9

S=cA^z - curve is characterised by the Arrhenius equation
s = species richness
A= Area
c and z are constants (c = species richness factor and z= species accumulation factor)
- species area curve appears with almost law-like consistency in empirical data sets

Question 10

who came up with the theory of Island Biogeography?

Answer 10

MacArthur and Wilson - 1967

Question 11

describe the theory of IBT

Answer 11

• oceanic islands were viewed as relatively static (i.e. slow change) in species composition - colonisation and extinction events were considered rare
• M&W postulated that the number of species on islands is a dynamic equilibrium between the opposing forces of extinction and colonisation

Question 12

what are the basic principles of IBT

Answer 12

• local extinction rate is a function of island size
  i. e. bigger islands = larger populations = lower extinction rates = more species
• colonisation rate is a function of island isolation from the mainland
  i. e. more isolated = lower colonisation rates= fewer species

Question 13

what does IBT predict

Answer 13

the number of species on an island is determined by its size and isolation

• predicts that every island has characteristic colonisation and extinction curves determined by its area of isolation
• where the extinction and colonisation curves cross is hte number of species

Question 14

what can species area effects be applied to?

Answer 14

applied to forest fragmentation and also has an impact on composition
- rapid loss of species with large area requirements (e.g. predators, large bodies species) , elevational migrants and forest-interior specialists

Question 15

what are isolation effects in forest fragmentation?

Answer 15

increasing distance from contiguous forest means increased isolation of fragments

• local extinction is much lower for connected patches than isolated ones
• habitat matrix impacts on connectivity

Question 16

what is a habitat matrix?

Answer 16

the habitat that surrounds forest fragments and ‘connects’ them to other fragments or contiguous forest - depending on the matrix it often supports populations of some species found in forest (fragments are connected for these species)

Question 17

what happens when there is large disparity between forest and matrix?

Answer 17

inhospitable matrix for forest species = colonisation rates decline = useable habitat shrinks
(small disparity = opposite)

Question 18

what is the effect of a hospitable matrix?

Answer 18

reduces the effect of fragment size on some species - allows for dispersal movements and recolonisation of fragments where species have gone extinct

Question 19

what is extinction debt over time and why is it a problem?

Answer 19

• immediately after fragmentation many species remain but are committed to extinction over time
• big issue in identifying impacts of fragmentation
• future ecological cost of current habitat destruction

Question 20

what is the though effect of fragments in the Amazon?

Answer 20

100ha fragments thought to lose half of their species in less than 15 years

Question 21

what happens if you increase fragment size?

Answer 21

it decreases debt but to decrease species loss 10 fold requires 1000 fold increase in fragment area

Question 22

what are edge effects?

Answer 22

a disturbance that penetrates into the fragment (abiotic and biotic) e.g. microclimate, vegetation structure, flora and fauna composition

Question 23

impact of edge effects

Answer 23

• can extend very fair into forest (to 400m)
• processes can effectively cause a reduction in fragment area for many species
• plots close to the edge have a higher rate of species turnover per year than plots far from edge

Question 24

what effect can large predator loss have on the functioning of an ecosystem?

Answer 24

large predator loss = increase herbivore and seed predators = decreased number of saplings and decreased seed dispersal = decreased wood density in fragments

Question 25

describe the effect of maintaining connectivity?

Answer 25

IBT stressed the importance of isolation due to colonisation rates - key recommendation for protected areas management is connectivity

Question 26

what are corridors?

Answer 26

linear habitat remnant surrounded by the modified matrix that facilitates wildlife movement between patches
e.g. brazil requires land owners to retain riparian (riverine) corridors of minimum width depending on size of river

Question 27

how does width of corridor effect

Answer 27

increased corridor width = increased corridor quality

fragments and corridors = biodiversity