Communities and ecosystems: co-evolution and competition Flashcards
What are the main selective pressures to life on earth?
Abiotic: physical environmental change leading to evolutionary change
- Court jester: Theory predicts that abiotic pressure cause the majority of evolution
Biotic: Strong interactions between species leading to evolutionary change
- Red queen: Theory prdicts that biotic pressures cause the majority of evolution.
- Species must continously evolve in order to keep up with their competitors.
- This amplifies selection pressures because communities are co-adapted so if one population is impacted, there is a knock on effect.
Do organisms be become increasingly adapted to their environemnt?
Law of constant extinction: Taxa that are older aged do not have a lower rate of exinctions showing that with time they do not become increasingly more adapted.
This is because the biotic and abiotic environment is constantly changing the species must evolve to keep up.
Example: escalation of defence trait
- Study on Brassica species showed escalation of investment in aliphatic glucosinokates and reduction in branched chain over evo time -> greater investment but reduction in diversity of chemical compounds
- Butterflies evolved counter defence
What is co-evolution?
Co-evolution is the change in genetic composition of one species in response to a change in another species.
Co-evolution causes reciprocal adaptations
Co-evolutionary depends on the realtionship between organisms:
Antagonist: Red queen dynamics (escalation)/ cyclical dynamics
Competition: Trait divergence
Mutualuasm: selection to maximise benefits
Co-evolution depends on the level of specilisation:
Organisms that are more specialised to each other will show a greater level of co-evolution and reciprocal adapations
How does competition lead to co-evolution?
Competition can cause trait divergence/ character displacement allowing niche seperation and co-existance.
Example: Stickle backs in Canade
- When 1 species is in the lake they have intermediate raker length
- When 2 or more species are in the lake there is trait divergence and the intermediate gill raker length is less common.
Most evidence comes from fossil records so hard to prove that competition was basis of divergence and that there was a genetic basis.
Other evidence come from species in allopatry of sympathy but conditions in these two often sites vary.
Example: lizards on islands in Mexico vs mainland
Best study
Example: sympatry of two mussels (edulis and Californianus) -> one on sheltered one on wave battered shores. Allopatry edulis takes up both habitats.
He was able to carry out lab experiment to show there was a genetic basis.
- C in wave beaten places as larger and thicker shell
- E in sheltered places and grows above C
- shows genetic basis but competition not proved
How does competition and co-evolution effect a species ability to adapt to climate change?
How does the co-existance and competition between species effect their ability to respond to climate change? Does competition limit their ability to adapt?
1) Competition can inhibit evolution as there are aready species with suitable traits which fit the new conditions.
2) Competition can enhance evolution as trait changes by one species can trigger trait changes by another. And co-evolutionary dynamics can promote niche partitioning and increasing competitive ability.
Model supporting competition/ diversity inhibiting evolution-> phenotypic evolution in species occupying patchy environments
Modified levene model
A theoretical model maps the distribution of temperature and the composition of species in different patches.
The species has a single phenotypic trait which determine how well matched they it is to the environment and it is affected by climate change and must evolve.
Trait evolution following climate change in these patches is matched when:
There is competition: ecological
- There are multiple species in each patch
- As warming occurs there are already species which are optimally adapted
- The other species are not able to evolve to this new optimum
- The species stays at the old optimum and disperse to conditions which match it or change in abundance
- Diveristy is inhibiting evolution and there is an ecological response to global warming.
There is no competition: evolutionary
- There is a single species in each patch.
- The species is able to adapt to the warming environment and the new optimum in each patch. Or go extinct.
- The lack of diversity is allowing evolution and there is an evolutionary response to global warming.
Only possible with environmental heterogeneity
Assumes
- 1 trait which effects fitness -> realistically even with competition likely that there are multiple different optimum
- only considered competition and no mutualism + antagonism’s -> may lead to diversify enhancing evolution (e.g. red queen)
What allowed evolution in this model
- large environmental changes outside any optima
- marginal environment
- new optima for several traits -> niche partitioning to new optima
Study showing how competition leads to enhanced ecosystem functioning: Bacteria -> increased diversity
A study using bacteria proves that diversity does not inhibit evolution and instead co-evolution in communities due to competition can increase ecosystem functioning. The species can co-evolve to use the availiable resources more effectively.
Experiment:
- Beech tree bacteria was collected, isolated and cultured in polycultures and monocultures
- They were allowed to evolve in uniform conditions.
Results
Growth
- When isolated and grown individually, the monoculture isolates had greater growth than the polycultures isolated
- One polyculture isolate had enhanced growth as co-evolution may have increased its competitive ability.
The change in interactions between the species
- Ancestral, monoculture and polyculture isolates were grown on a plate one after another (filtered off between)
- Monocluture and ancestral isolates had reduced growth
- Polyculture isolates did not have reduced growth as due to trait divergence/resource partitioning the isolates relied on different resources and also survived on the waste of eachother.
- analyses of the chemical composition of the media proved the resource partitioining
Comparing the ecosystem function
- The polyculture had a greater rate of respiration (measured CO2 production) than the monoculture proving that they use resources more efficiently and there is enhanced ecosystem fuctioning
- This is as the isolates co-evolved and live of the waste of each other.
Similair results can be seen with plants living in isolation compared to communities
- grow plants in mono culture and poly culture
- take cutting and grow in communities
- Those that have a higher biodiversity have an elevated ecosystem functioning due to niche differentiation.
A study showing that competition can lead to increased competitive ability: Phytoplankton -> reduced diversity
Co-evolution can cause the R* value of an individual to decrease.
R theory: Species with lowest minimum resource concentration (R*) will outcompete others for same limiting resource (they have a greater competitive ability)
Example: Phtoplankton
- Study observed how a community of phtoplankton changed over time when light or Nitrogen was limiting
- One species of phytoplakton dominated the community after a long period of time as the R* value decreased through time.
Competition is limiting diversity as one species is able to optimally adapt to new conditions and outcompete the others
Competition can enhance evolution
Competition enhances evolution as it leads to co-evolution resulting in:
- Enhanced ecosystem functioning (more efficient use of reasources) through niche partitioning (Bacteria)
- Increased competitive ability (phytoplankton)
Conclusion
The nature of co-evolution is dependent on the relationship between organisms.
Competition:
- Co-evolution leads to trait divergence and niche partitioning
How does competition effect evolution?
Model 1: competition and diversity limits evolution as there are species which already have the optimal traits (global warming example)
Model 2: Competition promotes evolution due to co-evolutionary dynamics leading to niche partitioning/ more efficient use of resources (Bacteria) and an increase in competitive ability (phytoplankton).
Increase In Competitive ability of one species may reduce diversity
Environmental change and mutualism/ antagonism’s
Mutualism enhancing evo:
E.g pollinator and bee provide selection pressure on eachother to move everything earlier whrn condition are favourable -> increase temp means flowed earlier and emerge earlier
Antagonism evo:
E.g. plant and parasite
- covariance of genes involved in moving optima and antagonist interaction. Both positive and negative.
- change in one species due to environmental Change drives selection pressure for other species to change
Positive covariance it genes and traits is important
Environmental change cause change in population size of one of the interacting species in important (e.g. if wipes out one species in mutualistic relationship then other species more at threat or if wipes out antagonist other species proliferates)
