Island Biogeography Flashcards
What is diversity
Diversity is a function of both the number of species and how evenly the individuals are spread.
What is allopatric separation
Allopatric - geographical separation of a previously continuous population (common)
• Separation of populations
• Physical barrier (Island with three mountains becomes three Islands - Darwin’s Finches)
• Extinction of middle range
• Jump dispersal
• Barrier prevents gene flow
Adaptive divergence and/or genetic drift
What is peripatetic speciation
Peripatric - variant of allopatric involving isolation of a peripheral population (fairly common). It is very similar to allopatric speciation but involves a much smaller portion of the population, therefore you end up with founder effects and a limited bottleneck genetic diversity. For example when a small population of invasive species has been pinched of from the normal population and adapts in isolation.
• Isolation of peripheral population
• Peripheral populations create specific features:
○ Limited genetic diversity
○ Head start to divergence
• Founder effects
what is parapatric speciation
Parapatric - speciation of adjacent populations stretched over an environmental gradient (rare). The example below shows how the flowers have been fertilised by different insects, depending on the time of day.
• Creation of genetic gradients by:
○ Variation throughout range of a species
○ Local adaptation
• Decrease in gene flow across gradient
• Development of hybrid zone and reproductive isolation
• Driving force is distance over range of populations
What is sympatric speciation
Sympatric - no separation during speciation (very rare in multicellular organisms), if the yellow snails only breed with the yellow snails even when there is nothing stopping them breeding with the green or black snails. Lake with fish that are separated due to feeding habitats.
• No spatial separation of populations
○ Establishment of separate genotypes while in contact with each other
• Disruptive selection - selection of phenotypes controlled by one gene; natural selection encourages reproductive isolation (polymorphism into speciation)
• Competitive speciation - variant of disruptive selection; competition within a species selects for phenotypes
Polyploidy - multiplication of whole sets of chromosomes (extreme mutation)
Equilibrium Theory Of Island Biogeography
- The number of species on an island will eventually become approximately constant through time
- This should be the result of a continual turnover of species, some becoming extinct and new species immigrating.
- Large islands should support more species than small islands.
Species number should decline with the increasing remoteness of an island.
WIDER READING:Equilibrium Theory Of Island Biogeography
Mcathurand Wilson 1967- founders of the equilibrium island model
‘Theory pf island biogeography’
‘Adynamic equilibrium between the rate of immigration of new species onto the islandand the rate of extinction of speciesalready resident on the island’
WIDER READING: island bio geography - recolinisation
Simberloffand Wilson 1970-links to Mcarthur and Wilson model
‘Experimental zoogeography of islands. Atwo yearrecord of colonisation’
· 1966-1967 the entire arthropod faunas of six small mangrove islands in the Florida Keys were removed by methyl bromide fumigation
· Recolonization through the first year, during which the numbers of species infive of the six faunas rose.
· Number of species changes little (sites 1-5) between years 1+2, indicating equilibrium reached
· Furthest island from shore was slowest to recolonise, due to distance from source area
· The near island E2 has the most species, the distant island El the fewest.
WIDER READING: island bio geography - recolinisation
Simberloffand Wilson 1970-links to Mcarthur and Wilson model
‘Experimental zoogeography of islands. Atwo yearrecord of colonisation’
· 1966-1967 the entire arthropod faunas of six small mangrove islands in the Florida Keys were removed by methyl bromide fumigation
· Recolonization through the first year, during which the numbers of species infive of the six faunas rose.
· Number of species changes little (sites 1-5) between years 1+2, indicating equilibrium reached
· Furthest island from shore was slowest to recolonise, due to distance from source area
· The near island E2 has the most species, the distant island El the fewest.
WIDER READING: peripatric speciation
Dawson and Hamner 2005-rapid evolution of an isolated population
‘Rapid evolutionary radiation of marine zooplankton in peripheral environments’
· Jellyfish,Mastigiassp., landlocked in tropical marine lakes
· Rapid morphological evolution, andbehavioraladaptation.
· The existence of multiple independently derived populations in marine lakes and of ancestral populations in the adjacent lagoon allows comparison
View references (57)
Populations of jellyfish, Mastigias sp., landlocked in tropical marine lakes during the Holocene, show extreme genetic isolation (0.74 ≤ φST ≤ 1-00). founder effects (genetic diversity: 0.000 ≤ π ≤ 0.001), rapid morphological evolution, and behavioral adaptation. These results demonstrate incipient speciation in what we propose may be modern analogues of Plio-Pleistocene populations isolated in ocean basins by glacially lowered sea level and counterparts to modern marine populations isolated on archipelagos and other distant shores.
WIDER READING: Meta-populations
Levins 1969-The man who first proposed the idea of metapopulations
‘Some Demographic and Genetic Consequences ofEnvironmental Heterogeneity for Biological Control’
· “Classical” form = a metapopulation consists of isolated patches (islands) within an unsuitable matrix (sea), without a mainland. Thus, all local populations can become extinct, as can the entire metapopulation (i.e., when the longest-lived population becomes extinct).
· Metapopulations persist due to the balance between extinction and colonization of local populations.
