Local Diversity Flashcards by Abbie Pilkington

What is local (alpha) diversity

Number of species in a defined area

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What is competitive exclusion

Most comprise species drive others to extinction

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What are regulators of local diversity

Processes that enable coexistence

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What are the two regulation of local diversity theories

Equilibrium theories

Non equilibrium theories

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What are equilibrium theories

Community diversity is regulated by processes of competition and evolution I.e to attain a steady or stable state

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What are non equilibrium theories

Community diversity is due to processes that prevent equilibrium being reached I.e interfere with competitive exclusion

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When did the equilibrium theories come about

1970s

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What are equilibrium theories based on

Stability
Niche concept
Heterogeneity
Island biogeography

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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.

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What is tight niche packing

Resource specialisation. If you can specialise you can pack more species in.

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What is broad niches

Resource overlaps

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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

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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.

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Who created the island biogeography theory

MacArthur and Wilson

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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

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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.

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What is the equation for species diversity

F(island area + isolation)

Function of size of island and how isolated it is from the continent.

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What is species diversity a balance between forces of

Immigration (isolation) and extinction (area)

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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 ```