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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"
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
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)
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
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
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
Draw the simple 2 species model of host-parasite coevolution. Be able to explain why this is a case of frequency dependent selection
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
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
What two factors influence the speed with which a trait can change in frequency in a population?
Benefit and cost
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
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
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
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
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
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
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