Local Diversity Flashcards
What is local (alpha) diversity
Number of species in a defined area
What is competitive exclusion
Most comprise species drive others to extinction
What are regulators of local diversity
Processes that enable coexistence
What are the two regulation of local diversity theories
Equilibrium theories
Non equilibrium theories
What are equilibrium theories
Community diversity is regulated by processes of competition and evolution I.e to attain a steady or stable state
What are non equilibrium theories
Community diversity is due to processes that prevent equilibrium being reached I.e interfere with competitive exclusion
When did the equilibrium theories come about
1970s
What are equilibrium theories based on
Stability
Niche concept
Heterogeneity
Island biogeography
What are niche concepts
Focus on one type of narrow part of resources per species. Specialisation enables more species to coexist in a given area.
No overlap as no competition for resource.
What is tight niche packing
Resource specialisation. If you can specialise you can pack more species in.
What is broad niches
Resource overlaps
What is heterogeneity
More diverse habitats have more niches and more niches means more discrete niches and species e.g vertical structure in a Forest - different vertical strata hosts different animals e.g ante and birds
What is the problems with niche-heterogeneity
Mainly zoological (plants have same basic needs I.e water, nutrients and CO2) Resources and conditions are not partitioned into discrete packages or niches (not natural) Doesn’t account for most diversity.
Who created the island biogeography theory
MacArthur and Wilson
What did Alfred Russel Wallace say in ‘Island Life’
It is not too much to say that when we have mastered the difficulties of island life we shall find it comparatively easy to deal with more complex and less clearly defined problems of continental life
What is the central paradigm of island biogeography
Discrete, quantifiable, numerous, bounded communities.
Capture species that readily disperse and colonise - bc when an island appears from the sea it has no native species.
Natural laboratories - simplify complexities of natural world.
What is the equation for species diversity
F(island area + isolation)
Function of size of island and how isolated it is from the continent.
What is species diversity a balance between forces of
Immigration (isolation) and extinction (area)
How does immigration and extinction cause an equilibrium
Immigration declines with time as more species become established as new immigrates will be species already present.
Extinction increases with the number of species present.
The part the lines cross is the equilibrium for number of species on an island
How does species-area relationship work in the island theory
It influences extinction. A later area has more species. When island is late the forces of extinction declines. Areas of island is defining characteristic.
Example of a species-area relationship
The Galápagos Islands - islands range from 0.2-2249km^2 with 325 plant species
What are the two components of the species-area relationship
Forces of extinction (death/outward migration). Decline with size:
Greater abundance resources
Greater habitat heterogeneity
What does isolation influence
Immigration
How does isolation influence immigration
Forces of immigration greater on near islands and speciation is more important on remote islands. More, less dispersive taxa on closer islands and fewer, more dispersive species on further islands
What is the model for the effect of immigration
Near islands: lots of species to begin with but rapid drop as less species arrive if they are already there.
Far: the rate of decline of immigration is slower as it takes longer for a species to get there. Rate of reaching the species pool will be slower.
What does area influence
Extinction as species go extinct more on small islands but less on large islands - doesn’t influence immigration
What is the model for extinction
Small islands: extinction rises rapidly
Large islands: extinction rises slowly
What are the two equilibriums in the island biogeography theory
The small/far island equilibrium and the large/near island equilibrium. Intermediate equilibriums for near/small and far/small.
What did power (1972) find
In the Californian islands area was the factor contributed to most of speciation in plants (0.58) and then it was latitude (0.25) and then unknown variation (0.17).
For birds, the number of play species was most important (0.67) then isolation (0.14) then unknown (0.19) - area strong determinant for plants but not animals.
What did Darwin’s finches show
Adaptive radiation.
Evolution, natural selection and speciation in the Galapagos.
Fragmentation of land means species living in a forest are basically in island.
Summarise the concepts behind the equilibrium theories
Niche concepts (specialisation)
Heterogeneity (diverse habitat)
Island biogeography theory (area/extinction and isolation/immigration)
What are the non-equilibrium theories
Diversity-productivity relationship
Disturbance
What is there little evidence of
That communities reach equilibrium - only constant in ecology is change
What does fluctuating environments lead to
Constrain competitive dominants (prevents exclusion)
Who created the diversity productivity relationship
Grime (1979)
What does the diversity productivity relationship state
When productivity is slow there’s few species but when it’s high we have species that dominate the community and drive other species to extinction.
Species richness is unimodally related to productivity.
Peak diversity at intermediate productivity (maximum resources). ‘Sweet spot’ for diversity-productivity.
What can disturbance be
Human but also natural like a tree falling producing a space and prevents opportunities for species.
Who created the intermediate disturbance hypothesis
Connell (1978)
What is the intermediate disturbance hypothesis
Low disturbance = competitive exclusion.
Intermediate disturbance = max diversity due prevention competitive exclusion.
High disturbance = low diversity as few species survive.
What are the most diverse communities in the intermediate disturbance hypothesis
Those subject to a little disturbance like mowed grassland to stop domination but not enough to stop diversity
Who created the dynamic equilibrium model
Huston (1979)
What is the dynamic equilibrium model
Highest diversity under conditions where neither disturbance or competitive exclusion dominate - controversial model. Research for exam.
Example of empirical test of the dynamic equilibrium model
Controlled experiment bc in field there’s too many variables. Can do all the possibilities that you don’t find in the real world. Low grazing plummets productivity.
Why is the disturbance model bad
Proposing enormous disturbance to natural communities.
Need to be sustainable.
Key points
Local diversity determined by balance between forces of extinction and immigration.
Forces regulated by range of factors including resource availability, proximity and disturbance.
What are the resource conditions
Competition Predation Disease Immigration Extinction
