Island Biogeography – Flashcards
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island communities patterns
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1. species richness 2. area effect 3. isolation
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colonization
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movement by species to newly created (or scoured) volcanic islands
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colonization rate
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number of new species arriving
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continental island
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1. an island formed near a continent out of the same land mass 2. could be more dominated by ecological processes 3. located on continent
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disharmonious biota
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non-representative types of organisms on island, including absence or rarity of typical mainland taxa
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dynamic equilibrium
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A condition in which several processes act simultaneously to maintain a system in an overall state that does not change with time.
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isolation effect
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1. fewer species on relatively isolated islands 2. distance is a barrier to dispersal
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land bridge island
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Connected to other land mass during low sea level periods (Have more species typically
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MacArthur-Wilson Dynamic Theory of Island Biogeography
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1. wanted to explain how many species are on an island and why 2. integrates species immigration and extinction processes 3. discounted evolution
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oceanic island
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1. Island that has never been connected to true mainland 2. could be more dominated by evolutionary processes
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relaxation effect
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1. land bridge islands tend to lose species after isolation from mainland because extinction rates exceed colonization rate until they reach lower equilibrium species richness appropriate to land size 2. takes thousands of years
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rescue effect
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1. addition to MacArthur-Wilson theory 2. distance affects not just immigration, but extinction rate 3. mechanism: new genes of immigrants reduce chance of extinction
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species-area relationship (area effect)
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1. Bigger island with more area have more species 2. use log plots (species-area curve) to describe patterns 3. x-axis is number of species
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target effect
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1. addition to MacArthur-Wilson theory 2. area affects not just extinction, but also colonization 3. mechanism: larger islands provide larger targets to colonists
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turnover
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Change in species composition on an island through time
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turnover rate
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1. species identity on island changes 2. new species arrive as others go extinct 3. highest when immigration and extinction are higher
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waif dispersal
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1. arrival by chance, based on wind, ocean current, flying off course, floating on debris 2. species that use this are best adapted to disperse and can survive during transport
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what characterizes species richness on islands?
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1. disharmonious biota 2. endemic species 3. closest relatives found on nearby mainland
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endemic
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belonging to a particular area, inherent
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Cocos Island, Costa Rica
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1. example of depauperate island 2. no native land mammals, amphibians, or bees 4. 3 landbirds, 2 insects, many insects and plants endemic 5. closest relative n Galapagos 6. isolated island
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depauperate
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lacking in numbers or variety of species
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colonization examples
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1. Krakatoa in Java Straight 2. Surtsey near Iceland 3. Mt. Saint Helens, Washington
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species-area curve equation
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S = c*A^z S: number of species on island A: island area c: constant, number of species in the smallest sampling area z: constant, slope of relationship 2. equation to show number of species is proportional to island area
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z-value in species-area curve equation
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1. slope, determined empirically using regression analysis 2. average in nature is 0.3 3. range in nature is 015-0.35
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z-value generalizations
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1. high dispersal leads to lower z-values 2. mainland z-values are generally lower than oceanic islands 3. if there is infinite dispersal, z-value would be 0 4. birds have lower slope than mammals
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MacArthur and Wilson assumptions
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1. immigration rate decreases with distance from source 2. extinction rate increases on smaller islands
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MacArthur and Wilson equilibrium theory
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predicts number of species at point that immigration (gain) rate equals extinction (loss) rate of species on island
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effect of island area, distance held constant
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1. small islands should reach equilibrium with a fewer number of species 2. small islands have greater rate of extinction
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effect of island distance (isolation), area held constant
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immigration is greater for closer islands
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What island has the fewest species?
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far, small island
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what island has the most species?
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near, large island
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deductions from dynamic theory of island biogeography
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1. number of species decreases farther from mainland-isolation effect 2. number of species decrease with smaller island-area effect 3. if island at equilibrium, species richness should remain constant over time
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when is turnover the greatest?
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1. on a small, near island 2. due to higher immigration and extinction rate
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when is there the least turnover?
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on a large, far island
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Simberloff and Wilson experiment
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1. tested MacArthur-Wilson prediction in Florida keys 2. killed all insect on island after taking census
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Simberloff's results
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1. tested four islands 2. there is great immigration, and then settle into constant equilibrium 3. equilibrium values similar before and after defaunation 4. there was turnover
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Simberloff and area
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reduced the area of the island and the number of species declined when the area declined
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Simberloff's conclusions
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1. equilibrium species diversity exists on the islands (return to pre-treatment species diversity 2. reducing area caused decrease in species 3. documented species turnover due to continual immigration and extinction on each island
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Additions to MacArthur-Wilson theory
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1. rescue effect 2. target effect 3. relaxation effect: island not in equilibrium
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criticisms of MacArthur-Wilson theory
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1. mixed results in tests 2. underemphasizes evolution on islands 3. there are ecological barriers to colonization-environments can be hostile to colonizers
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how is island age deduced?
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1. post-Pleistocene sea-level rise 2. sea depth between islands-greater depth means greater isolation
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relaxation effect assumptions
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all islands at time of formation had same species richness as current mainland source pool
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geographic ecology
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search for patterns of plant and animal life that can be put on a map
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continental island examples
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1. mountains 2. lakes
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why does rate of extinction rise with more species on an island?
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1. presence of more species creates larger pool of potential extinctions 2. as number of species on island increases, population size of each must diminish 3. as number of species on an island increases, potential for competitive interactions
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extinction rate
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percentage or number of species that go extinct within a certain time period
