Controls on local diversity

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  • Created by: maya
  • Created on: 28-04-17 09:39

Intro

Local (alpha) diversity DEFINITION:

number of species in a defined area. 

Competitive exclusion DEFINITION:

Most competitive species which drive others to extinction

Predict more successful species dominate- often real world - doesn't happen species co-exist- food web- co-evolve millions of yrs together 

How do species co-exist without excluding one another? 
What processed/ mechanisms influence that? 

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Equilibrium

Regulation of local diversity  DEFINITION - processes that enable coexistence

EQUILIBRIUM THEORIES 
Community diversity is regulated by processes of competition and evolution i.e. to attain a steady or stable (natural) state.

a lot of these theories apply to bird- difficult to apply to microbes - cosmopolitan - ecology diverse

expectations through equilibrium concept that community dversity reach natural state steadily 

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Non-equilibrium

NON-EQUILIBRIUM THEORIES

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

response to disturbance- changes environment- alters local diversity 

are natural communities stable? 

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Equilibrium theories (stability)

Heterogeneity 

Island Biogeography

Niche Concept

Acronym: H I N 

a) Niche Concept - specialisation enables more species to coexist in a given area. 

specialisation- when environment is appropiate and resources are there- competition between species becomes more specialist as they evolve- tropics- tight packing of species around resource plant h20, water, nutrients, soil light. 

Less species colder systems productivity lower- productivity feeds into systems - greater number of species. 

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Heterogeneity

Heterogeneity- more diverse habitats have more niches. 

more phyiscal habitats, different microclimates, more diverse environment, more diverse community. 

Biodiversity increases - an example of this is 
e.g. tree height increases as biodiversity increases

niches and hetero go together 

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Problems niche-heterogeneity

(a)Mainly zoological (plants have same basic needs, i.e. water, nutrients, and CO2 so compete with each other in same space-).
Comes from zoological ecology- birds

(b)Resources and conditions are not partitioned into discrete packages or niches.

(c)Doesn’t account for most diversity.

Overall, gradient resources.

Probably doesn't account for most diversity esp funghi, bacteria, archaea 

microbial ecology - constraints on their diversity v diff- uncertainity 

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Island Biogeography theory

Macarthur and Wilson 1963

Travelled across globe- particulary SE Asia, recording diversity he saw- made him wonder why diff natural abundance in diff places- why patterns?

Central paradigm of island biogeography:

* Discrete, quanitfiable, numberous bounded communities.

* Capture species that readily disperse and colonise

* Natural laboratories- simplify complexities of natural world.

Assumption islands bounded communities to some extent- not completely isolated

Islands potential to capture species

natural laboratory- controlled natural barrier- sea 

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Theory

Theory:

Species diversity = ƒ (island area + isolation)

A balance between forces of : (look up on panopto later)

IMMIGRATION- New species arriving/colonising

EXTINCTION- Loss of species.

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Balance between immigration and extinction

Island gradient resource- potential niches- area lots of diversity far away- potential recruitment - rate of change in species due to immigration can decrease over time because these species have already moved on the island. 

Expect extnction rates to go up as immigration of species increases- community exclusion- dominate others lose out. 

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Regulators

Regulators: 
Area (extinction)
Isolation (immigration) 
1) species-areas relationship influences extinction

Galapagos Island

Relationship between number of species extinction rate influenced by immigration

Bigger the island less powerful extinctions

more species, more resources, less competition

e.g. Galapagos Islands – island range from 0.2 – 2249 km2 with 325 plant species.

Forces of extinction (death/outward migration) decline with size -
* Greater abundance resources

* Greater habitat heterogeneity 

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beep boop

a) Amphibians/reptiles West Indies 

West indies larger island more species of trees

North America- larger area= more species of breeding birds North America 

(2) ISOLATION influences immigration

immigration- how far away island is from the source of species

Further away, few species- yet species that are left able to disperse
plants- windblown seeds, coconut floats through muds 

Forces of immigration greater on near islands 

( speciation more important on remote islands) 

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limitations

Not always so clear!

Californian Islands 

area strog determinant for plants, but not birds and mammals 

but some places have poor species despite being bigger species show what proportion plant species can be predicted.

Area not good at predicting bird species despite being good at predicting plant species
process of succession too- plant species arrive, change gradient 
also.. process of competition and adaptation to resources available changes- genes of species- ALSO Evolution, natural selection and speciation
Galpagos Islands Charles Darwin Darwin's Finches

Diff finches some coexisted- reasons for differences- rely on diff food sources- heterogeneity creates a niche 

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Equilibrium theories

Processes that enable species coexistence and diversity.

Equilibrium Theories:

(Stability)

• Niche concept (specialisation) can be through natural selection, niche packing, high productivity- pack in more spcies

• Heterogeneity (diverse habitat) hyperdiverse ecosystems high gradient 

• Island Biogeography theory

(area/extinction and isolation/immigration)- process of competitive exclusion but also food web, some species wouldnt be able to exist without each other

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Non-equilibrium theories

Non-Equilibrium Theories:

(Prevent equilibrium being reached, so interfere with competitive exclusion)

•Diversity-productivity relationship (Grime 1979 

•Disturbance

Non-equilibrium - probably explain what is happening real world- disturbances, climate, resources & conditions in environment influx. These changes influence local species conditions.

- There is little evidence that communities reach equilibrium - only constant in ecology is change! 

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Diversity productivity relationship Grime (!979)

this is a non-equlibrum model of diversity:

Higher productivity system  probability greater diversity entire community

Feed tropic food web- more powerful diversity

Species richness is unimodally related to productivity: 

•peak diversity at intermediate productivity (maximum resources).

•declining diversity due to competitive exclusion
Through processes competitive exclusion - over time may start to lose species (productivity may go up - lots of trees- but in same habitats exclusion (right) 

This theory - every ecosystem has a sweet spot facilitates diversity - diversity-productivity 

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Immediate disturbance hypothesis (Connell 1978)

Immediate disturbance hypothesis: acronym HIL 

•High disturbance - low diversity as few species survive
•Intermediate disturbance – max diversity due prevention competitive exclusion
•Low disturbance – competitive exclusion

i.e. most diverse communities those subjected to disturbance – mowed and burnt grassland, wave action etc

How much disturbance needed for x level of diversity? 

systems are disturbed - people, fire, hurrcane affects env, agriculture (equilibrium concept niche light) 
Through disturbance gaps created- areas for recruitment - opportunity early sueccession of species

Crucial part for what really happens- ecosystems regulator 

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Dynamic equilibrium model (Huston 1979)

Dont have much disturbance strong process competitive exclusion

Lots of disturbance lower diversity- species highly adapted env 

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Immediate disturbance hypothesis (Connell 1978)

Intermediate disturbance hypothesis:
•High disturbance - low diversity as few species survive
•Intermediate disturbance – max diversity due prevention competitive exclusion
•Low disturbance – competitive exclusion

Intermediate disturbance hypothesis (Connell 1978)

i.e. most diverse communities those subjected to disturbance – mowed and burnt grassland, wave action etc

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SEARRP

forest important Malaysian logging-- conflict biodiversity

one of most hyperdiverse Islands on the planet good space look @ theories around ecology - oil palm plantations 

Ecology matters for sustainability too- often conflict economic obj and science obj

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Key point

1.Local diversity determined by balance between forces of extinction and immigration.

2.These forces regulated by range of interacting factors, including resource availability, proximity and disturbance.

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