PCE - 10 Flashcards
what are the 2 major problems with islands?
1) forefront of the biodiversity crisis
2) different conservation challenges
which 2 scientists developed a model predicting species richness on islands?
Macarthur and Wilson
what is species richness a balance of?
immigration and extinction
describe when immigration rates are high and low for an island depending on species number already on the island?
immigration = high when the island doesn't have species or many immigration = low when the island has many species
describe when extinction rates are high and low for an island?
extinction = low when the island doesn’t have species or many
extinction =higher when the island has many species
what are the 2 key predictions of species richness on islands?
1) Number of species on an island reaches
equilibrium: numbers of species present are
roughly constant through time once equilibrium is reached
2) Species composition is dynamic: new species arrive via immigration and replace or drive to extinction resident species
what catastrophe provided a natural experiment to test the equilibrium theory?
Krakatoa - volcanic eruption
when does equilibrium species richnesss decline?
with isolation as immigration rates are reduced
what is the rescue effect?
when the a nearby island can easily re-stock populations from mainlands reducing extinction rates - equilibrium species richness increases
describe the effect area has on equilibrium species richness?
equilibrium species richness increases with area
- immigration rates are increased on a larger island\
- large islands buffer against extinction
summarise the immigration and extinction rates for both isolation and area
Immigration rates increase with area
• Immigration rates decline with isolation
• Extinction rates decrease with area
• Extinction rates increase with isolation
what are the 4 key predictions of the equilibrium theory?
1) Number of species on an island reaches
equilibrium
2) Species composition is dynamic
3) Large islands support more species than small
islands
4) Alpha diversity (species richness) declines with
isolation of island
how can birds of the California channel islands be used to test SAR and SIR and what were the results?
- have varying distances from mainland therefore varying island isolation
- all have varying island areas
- showed a strong SAR and weak SIR - weak SIR is possibly due to small variation in distances - not big enough to show a link
describe simberloff and wilsons defauntation experiment in the florida keys
- they fumigated small mangrove islands
- collected all terrestrial arthropods
- repeated surveys of recolonising fauna following the perturbation
what were the results from the defaunation experiment?
- equilibrial species richness prediction supported
- but rate of turn- over of species is very slow - didnt have extinction effects
- similar set of species return
what are 6 limitations of equilibrium theory island biogeography?
1) islands may not be in equilibrium
2) extinction and immigration rates vary among species
3) assumes no speciation on islands
4) extinction and immigration not independent from each other (high immigration rates save species from extinction)
5) slopes of extinction and immigration curves not known and can vary from island to island
6) multiple mainlands and island to island immigration = multiple immigration routes and rate
describe the florida keys colonisation curve?
show immigration affects the number of species and how that will vary depending on the location of the island:
- the number of species on the nearby island soon equaled pre defaunation levels, while the number of species on the far island was still below the original level
what is an evolutionary species relationship?
its not just ecological processes that affect species richness on islands e.g. immigration emigration etc - they can also independently evolve their own species
Evolutionary processes are interlinked with ecological processes
