Focus group: Competition and Diversity Flashcards
Define adaptive radiation theory
Predicts that niches are partitioned early in the clade history in the presence of ecological opportunity
What is correlated evolution?
Tries to answer if changes in one trait are correlated with changes in another
Use statistical analysis to see if the differences observed are down to chance or not
Regression or correlation analysis is the most common form of comparative analysis
What did Buckey & Jetz discover about the correlation between Anolis lizard density on islands and presence of competitors/predators? What did they control for? What potential trigger of ecological release did this provide evidence for?
Lizard density found to be higher on islands with fewer competitors and predators.
They controlled resource availability (variation in energy use and primary productivity) on these different islands and still found this
This shows density compensation as a result of ecological release.
What would happen to intraspecies interactions as population density increases?
Intraspecies interactions could become more frequent and stronger
Increased intraspecific competition would favour niche expansion, and increased phenotypic diversity of the population
What did Svanback & Bolnick do to those sticklebacks? What did they find out about ecological release?
Svanback & Bolnick, 2007
They manipulated the population density of three-spine sticklebacks.
Used a paired experimental design
Control measures were taken outside of the enclosures
They found that:
Prey density declined at high biomass
Thus increased population density reduced prey availability
Individuals added alternative prey types to their diets
Diet variation among individuals INCREASED relative to low-density control enclosures
Niche breadth increased across the whole population
EVIDENCE FOR ECOLOGICAL RELEASE
Divergence in Pseudomonas fluoresces - a study into niche availability
Three morphs:
S—– spreader
W—— spready
F—– spreader
All 3 mediums grow in a h————– medium in distinct areas, suggesting distinct niches associated with each morph
They compared h————– to h———— environments, finding the range of morphs to increase initially dramatically in the h————– environment compared to the h———–.
NO morphological divergence found for the h——— microcosms showing that niche availability WAS favouring divergence
Pseudomonas fluoresces, Rainey & Travisano, 1998’
Three morphs:
Smooth spreader
Wrinkly spready
Fuzzy spreader
All 3 mediums grow in a heterogenous medium in distinct areas, suggesting distinct niches associated with each morph
They compared heterogeneous to homogeneous environments, finding the range of morphs to increase initially dramatically in the heterogeneous environment compared to the homogeneous.
NO morphological divergence found for the homogeneous microcosms showing that niche availability WAS favouring divergence
Is it stable?
As long as heterogeneous conditions are maintained
Declines if returned to a homogeneous environment
Lab study on Pseudomonas found that niche availability c——- divergence in Pseudomonas m——— as the number of evolved m——– DECLINED as occupied niches INCREASED.
These results show that lack of ecological o——— CAN constrain d——– and that niche o——– CAN limit a—— r———
Brockhurst et al., 2007
Constraints, Microcosms, morphotypes
Opportunity, divergence, occupation, adaptive radiation
Define the Ecological Limits Hypothesis
Species richness at a biogeographic scale exists in a state of dynamic equilibrium
This equilibrium results from diversity dependence of speciation and / or extinction rates, much like population density dependent factors
That diversity dependence of evolutionary rates results from constraints of natural resource availability
In the ELH:
———-rate declines as species richness increases
———- increases as species richness increases
Speciation,
Extinction
Give the 3 assumptions of the ELH hypothesis
Species richness at a biogeographic scale exists in a state of dynamic equilibrium
This equilibrium results from diversity dependence of speciation and / or extinction rates, much like population density-dependent factors
That diversity dependence of evolutionary rates results from constraints of natural resource availability
Asymptotic diversity dependence:
There is a limit on the total of potential ——
Asymptotic described how the graph for this p——- as it gets closer and closer to the hypothetical m———— value for species diversity
- This constrains ——– diversity and ——— diversity/disparity too
niches,
plateaus,
maximum,
species, phenotypic
How does darwinian diversity dependence differ from asymptotic diversity dependence?
So, in Darwinian, Interspecific competition influences the dynamics of evolution above the species level (trait evolution, speciation and extinction)
So, unlike in asymptotic dependence, this doesn’t EXPLICITLY model an upper limit for diversity, but this can still emerge anyways
Which one is the process and which one is the pattern of diversity dependence?
1. Macroevolutionary diversity trajectory that shows evidence of diversity regulation similar to logistic growth in population ecology
2. : Effect of interspecific competition on macroevolutionary rates of speciation and / or extinction
- Is the pattern and 2 is the process
Give some assumptions of diversity-dependent diversification (3)
- Assumes each lineage has the same rates of speciation and extinction
- Assumes that there is a theoretical maximum number of species a clade can support
- Assumes that that speciation and extinction rates are linear functions of the number of extant species
SEE LECTURE 9 for equations
E——- and s——- dynamics in a model adaptive r——- of island lizards (A—-) -
What did they do?
What did this show about ecological opportunity?
Equilibrium & Speciation dynamics in a model adaptive radiation of island Lizards (Anolis) - Rabosky & Glor, 2010
- They modelled different equilibrium & speciation dynamics, and saw which model seemed to fit best.
- This was the one which assumed diversification rates were the same initial between islands, with island-specific linear changes in rate then occuring through time
- Model IMPERFECT but quite good
- Rate of decline correlated with island area, which is a proxy for ecological opportunity
What is a phenomenological model?
Describes a statistical pattern, instead of describing a mechanism for thiat pattrn. This is problematic for diversity dependence as same patterns can emerge from distinct evolutionary processes. The Brownian Model is an example of a phenomenological model
What is the adaptive landscape? What does it show us?
It shows us a theoretical environment in which species can evolve. There are multiple phenotypes leading to a fitness peak.
As time elapses, peaks are filled up.
This could model how some phylogenies appear to have an early burst of diversification before niches are filled up
Define limiting similarity and give an example
The principle that two species which are too ecologically similar to one another cannot co exist due to competitive exclusion. Examples:
- Macarthur’s American warblers, 1967 - warblers show an initial early burst of diversification and then appear to plateau - diversity dependent selection
- Georgy Gause’s yeast
- Hutchinson’s ratios, 1959 - different size amongst sympatric species often consisten across the taxa (a 1.3 ratio)
What were Jared Diamonds community assembly ‘rules’?
Relative to all the possibilites of species combinations, only a limited number co occur - Species exist in a “checkerboard” and there are “forbidden” species combinations dictated by principles around limiting similarity
Explain the difference between a hypothetical habitat filtered, and competition structured community.
In habitat filtering, similar species would be attracted to similar habitats, ie. similar size class of fish
In competition structuring, fish communities would be divided up by size due to competitive exclusion principles.
Therefore,habitat filtering may have more similar distributions of species across the tree of life, and competition structured ones may have more dispersed ones.
Define phylogenetic community structure. Why can it be helpful?
The phylogenetic community structure provides insights into how closely related species are distributed within a community and whether there are patterns of clustering or dispersion based on their evolutionary history. Relates to phylogenetic niche conservatism wherin closely related species may be expected to be more similar in traits to one another.
This can be helpful, as the ecological niche is multidimensional, and it can be difficult to measure all axes of niche variation
Phylogenetic o——–: The sum of branch lengths connecting species in a community is high (they are spread out) indicating potentially high competition
Overdispersal
Phylogenetic c———-: Sum of branch lengths connecting species in a community is low indicating perhaps habitat filtering
clustering
Compare randomisation and simulation null models used in understanding phylogenetic community structure
So randomisation would compare observed with expected patterns of species presence in a community based on chance alone. Simulation would generate emergent patterns based on plausible processes like colonization, extinction and speciation.
Both sum the resultant branch lengths of the species generated