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What is the Red Queen hypothesis?
- Describes the coevolutionary arms races
- Selective pressure is from the other species, not the environment
- "constantly running, only to stay still"
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What are the 3 broad categories of co-evolutionary relationships?
- Specific coevolution: one predator responds to one prey
- Guild (diffuse) coevolution: multiple predators respond to one prey (they may vary in their effectiveness, but likely one will always be applying pressure to the prey)
- this is more realistic when viewing the environment
- Escape-and-radiate coevolution: multiple adaptations occur that result in different, specialized species, which require specialized species to compete with
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How does adding a 3rd species to a co-evolutionary relationship influence the basic 2 species pattern? What are the possibilities?
As seen in the diffuse coevolution pattern, adding a 3rd species requires a response by 2 species, not just one. As seen in the graph in the end only one predator has evolved appropriately (although the other had dominated earlier in time)
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What is parallel diversification? Provide an example and explain how reconstruction of the phylogenies provides evidence of this phenomenon.
- Clades are diversifying at similar points in time
- This suggests that speciation in one group will trigger a speciation response in another
- EX: phylogeny of endosymbiotic Buchnera bacteria perfectly correlates to aphid hosts
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Why is parallel diversification common in host-parasite interactions?
speciation in a host will carry the parasite with them and it is easy for a parasite to slowly change along WITH the speciation event
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What influences the likelihood of host switching in a parasite species?
- It is very challenging to completely switch hosts
- More likely when horizontal transfer is common
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Draw the simple 2 species model of host-parasite coevolution. Be able to explain why this is a case of frequency dependent selection
???
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If a difference in the two traits under selection results in Species 1 benefiting, then what is the expectation regarding the trait distributions in future generations? What if a similarity in the two traits under selection results in Species 1 benefiting?
- If a similarity in the two traits under selection results in spp 1 benefitting (eg body size between predator and prey) then it will benefit spp 2 to evolve away from the spp 1 mean trait value, and it will benefit spp 1 to follow.
- EX: bobcats and rabbits size cycling
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What evidence exists for co-evolution between garter snakes and toxic newts? Between cuckoos and warblers?
- When garter snakes are sympatric with toxic newts they evolve resistance to the prey's toxin
- Garter snakes allopatric with toxic newts are not resistant, but they do crawl faster
- **energy investment to the resistance
- Warblers are benefitted to create unique eggs so that they can discriminate against parasite eggs (the Cuckoo)
- It benefits the cuckoo to lay eggs that looks similar to the warbler so that they are not rejected
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What two factors influence the speed with which a trait can change in frequency in a population?
Benefit and cost
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What evidence exists that herbivory selects for the evolution of plant defense systems?
- Evidence of selection for defensive traits (toxin and sticky latex) in common milkweed
- toxin caused slowed progression of butterflie larva
- increased latex levels caused a decrease in herbivore families and thus a decrease in damage to the plant
- Insects subsequently evolve resistance
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Consider the co-evolutionary relationship between humans and syphilis. How has NS acted on bacterial virulence and human resistance traits over the last 600 years?
- More virulent syphilis reduced transmission rates, and thus it was under -NS
- A more benign form evolved, and transmission rates increased
- Increased transmission rates, however, select for more virulence
- Increased resistance in native hosts can allow for more virulence without direct effects (think native Americans)
- Pathogens are usually better adapted to host in their own locality
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What causes niche diversification?
- Two species can't occupy the same ecological niche simultaneously. One will always outcompete the other.
- Both spp benefit from reducing competition for a resource
- Results in resource partitioning (niche diversification) where each spp exploits only a portion of the resource
- NS acts on extreme phenotypes that do not compete with other spp
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What is character displacement? Provide an example and explain the process
- Limited resources cause character displacement amongst species
- EX: when G. fortis and G. filiginosa are allopatric their beak size overlaps
- when G. fortis and G. filiginosa are sympatric their beak size DOES NOT overlap, because they have become adapted for different sized seeds
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What is ecological release? Provide an example and explain the process.
- Ecological release describes the ability to exploit a larger range of resources than was previously available
- EX: woodpecker spp#1 - each sex exploits different resources, leading to sexual dimorphism
- woodpecker spp#2 - sex must compete for the same resource, creating competition
- EX: speciation rates may be higher on islands because of the initial freedom from competition upon arrival of a given spp
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How does intra-specific and inter-specific competition drive the development of community structure?
- Spp competing with one another within a range of microhabitat will diversify and fill available niches
- Character displacement in traits relevant for direct competition with closely related spp facilitates niche diversification
- Thus communities typically exhibit "big, medium, and small" predators within each major clade
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How can a parasitic co-evolutionary relationship develop into a beneficial, cooperative relationship? What is symbiosis? What is mutualism?
- Mutalistic species relationships can develop when one species exploits a single resource, and that resource will only be exploited by that species
- the relationship develops into mutualism when the “exploited” species gains an advantage because of the interaction
- If the mutualistic interaction occurs over the lifespan of the individuals involved, and if the interaction is necessary to basic survival or reproduction, it is symbiotic
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