Island Biogeography Flashcards
1
Q
island characteristics
A
- loss of dispersability
- gigantism or dwarfism
- loss of anti-predator defences
- highly specialised niches
2
Q
nested pattern of insular communities
A
- key pattern is that there is a relationship between number of species and are of island
- island species are a sub-set of those on the mainland
- smaller islands have species which are a sub-set of those of neighbouring larger island
3
Q
equilibrium theory
A
- species number remains stable
- immigration brings new species
- extinction removes species
- equilibrium between both
- species turnover
4
Q
why does extinction rate increase as species no. increases
A
- more species competing for limited resources
- smaller population size
- greater extinction rate
5
Q
why does imigration rate decline as species no. increases
A
- fewer resources and less habitat
- less niche space available
- greater competition
6
Q
smaller islands have fewer species than larger islands
A
- higher extinction rate in small islands
- fewer resources
- less habitat diversity, fewer niches
- small population size
- strong competition
- greater risk of extinction by competitive exclusion
- vulnerable to random extinction by disturbance (fire, flood, wind)
7
Q
islands near mainland have more species than those further away
A
- higher immigration rates
- jump dispersal more likely close to mainland
8
Q
high species turnover
A
high immigration and extinction rates
9
Q
low species turnover
A
low immigration and extinction rate
10
Q
problems with equilibrium theory
A
- small island effect
- rescue effect
- target area effect
- biological factors and non-equilibrium effect
- historical factors and non-equilibrium effect
11
Q
small island effect
A
- theory breaks down when islands are very small
- no relationship between island size and species richness
- population may never get large enough to reduce extinction rate
- no relationship between habitat diversity and island area
12
Q
rescue effect
A
- according to the theory, islands closest to mainland have higher rates of extinction, and hence higher rates of species turnover
- contrary to the theory, evidence that some islands close to mainland have lower extinction rates than those further away
13
Q
target area effect
A
- island size is a factor too
- larger islands provide a bigger target to dispersing organisms
- more likely to be seen by animal/birds
- larger area for intercepting airborn or waterborn seeds
- therefore, higher immigration rates for large, distant islands than predicted by the model
14
Q
Biological factors and non-equilibrium effect
A
- the theory treats all species the same in terms of immigration/extinction, but clearly not true
- species richness equilibrium achieve earlier for birds and wind/water dispersed plants than for other species
- island may be in equilibrium for some plant/animal species, but in non-equilibrium for others
- immigrants may arrive early but cant colonise until habitat is suitable or food source is available (facilitation model)
- certain species must arrive fist before others can colonise
- if extinction has removed food source required by immigrant species it cannot follow extinction like theory states
15
Q
Historical factors and non-equilibrium effect
A
- equilibrium theory of island biodiversity doesn’t work over geological timescales
- species relaxation: decline in species richness when island is separated from mainland
- may still be continuing on islands, therefore not yet in equilibrium
- Landbridge island: previously connected to mainland
