Lecture 8- Coevolution Flashcards
what is coevolution?
coevultion is an evolutionary process that occurs when one species exerts a selection pressure on on another species and viceversa. This impacts eachothers evolution through natural selection.
what are the three main types of coevolution?
- Inter-specific competition
- exploitation (sometimes called predation and parasitism)
- Mutualism
which type of colevolution results in character displacement?
inter-specific competition
what is character displacement?
this is when similar species, which overlap geogrpahically, have their differences accentuated as a result of sharing the same environment.
when the species distribution doesn’t overlap, these differences are-minimised or lost
what can interspecific competition result in?
Partition of resources, which causes character displacement
explain partition of resources in the context of inter-specific evolution
this is the division of LIMITED resources by species in order to avoid competition within the ecological niche
Explain how coevolution has occurred with Hydrobia Ulvae and H.Ventrosa
these are both estuarian mollusks, found within mud and soil. they eat algae from the soil.
Character displacement has occurred as a result of competion between the two. when these two species occur in SYMPATRY, H.ventrosa eats food with larger particle sizes than H..Ulvae. This is character displacement, as both species evolve to eat particle sizes of food to avoid competition for the medium(average) sized food particles, which are what is eaten when they live in allopatry.
this makes them more favoured for survival
When inter-specific evolution occurs for the snails H.Ventrosa annd H. Ulvae, which one is larger?
h.Ulvae, at 4-4.5mm long. H.ventrosa reaches 2.5-3mm.
H.ventrosa eats larger particles
What are the two ways of interaction between predators and parasites in coevolution?
Arms race
Mimicry
what is a brood parasite?give an example
A bird that lays its eggs in another birds nest, and these other birds then raise the offspring. Cukoo
what are the three main host species for cuckoo birds? why these?
1.reed warblers- in reed beds
2.dunnocks-in farmlands
3.medow pippits- in Moorland
they have open nests and high insect diets, which the baby Cuckoos need to grow
Explain how cuckoos exploit reed warblers
reed warbler nest are open, which allows for quick access from the cuckoo
the cuckoo lands in the nest, swallows an egg and replaces it with one of their own, this is a very quick process.
once the cuckoo chick has hatched, it removes the competition by removing the reed warbler eggs from the nest. this means it doesn’t have to fight for resources from the host parent
what is the impact of cuckoo exploitation on adult reed warblers?
it removes the reproductive success of this host series
what 3 adaptations does the cuckoo bird have for effective exploitation?
- Quick laying eggs,in order the avoid the host seeing and deserting their nest.
- Lays small eggs to mimic the reed warbler
- they destroy nests that are incubating, as this causes the host bird to remake a nest where a cuckoo egg can be laid.
what arm race evolves between cuckoos and hosts?
there is strong selection on the host to reject the cuckoos, and strong selection on the cuckoo to fool the host.
how have cuckoos responded to rejection by host species?
host species sometimes reject cuckoo eggs. this has resulted in cuckoos laying eggs with consistent colours and patterns, that tend to mimic the host eggs
why do brood parasites replicate host species eggs?
this mimicry has evolved due to selection pressures of host discrimination, as host species evolve to spot “intruders” better
What percentage of Cuckoos are brood parasites?
40%
How have host species adapted to limit the impacts of brood parasites?
- they evolve egg rejection
- there’s less variation between the eggs within a singular clutch, and greater variation between clutches of different females. This makes it harder for cuckoo, as hosts are more able to spot eggs that are not exactly identical, and its harder for cuckoos to mimic
explain the eggs arm race sequence
- prior to being parasitism, birds show little, if no, rejection to foreign eggs.
- in response to parasitism, host evolve the ability to reject eggs and create eggs with more distinct signatures
- in response to host rejection, cuckoos develop egg mimicry
- if the cuckoos mimicry is sufficient, then it may be best for hosts to accept cuckoo eggs to avoid the cost of mistakenly rejecting one of their own eggs
what is the name of the experiment that looked at host discrimination
Davies and Brookes
outline the davies and brookes experiment
this was an experiment looking into egg discrimination. It found that Icelandic medow pippits do not reject cuckoo eggs, unlike the uk counterparts. this is because cuckoos do not migrate as far as iceland, so these birds never had to evolve discriminatory traits, due to the lack of selection pressures. It also found that Dunnocks do not reject cuckoo eggs (despite their eggs being bright blue), and as a response cuckoos didn’t evolve to mimmick.
Why don’t Dunnocks reject Cuckoo eggs?
this is to do with an evolutioary time lags. Dunnocks are relatively new hosts, so they have no yet adapted in the arms race to reject cuckoo eggs
What is aposematism?
when an organism displays a clear sign that they will be unprofitable prey. the signal is often a bright colour, and the cost is often a sting,foul smell,spines or other impediments to gastronomy.
What are examples of aposematism?
- yellow and black stripes on wasps
- stripes on a skunk
- poison frogs in south america
outline the Gittleman and Harvey experiment
- they presented domestic chicks with breadcrumbs
- when the breadcrumbs were not distasteful, the chicks took more of the conspicuous prey (eg. blue breadcrumbs on a green background)
- when the colourful crumbs were distasteful, the cryptic prey underwent the greatest predation
what were the results of the Gittleman and Harvey experiement?
that is pays to be distasteful
what does Mullerian mimicry rely on?
the existence of aposematism
what is mullerian mimicry?
where two species with shared predators evolve to look similar, because there’s advantages of predator education and avoidance.
How does Mullerian mimicry differ from mimicry?
mimicry occurs when once species evolves to look like one another, in order to disway predators. for example, a hoverfly is a non poisonous mimic that has evolved to avoid predation. Mullerian mimicry is when two poisionous species evolve towards similar appearance.
What is Batesian mimicry
when a harmless, edible species evolves to look like a aposematic species, as predators avoid them based o this appearance.
for example: hoverflys
what is mutualism?
where two or more species have evolved to “work together”, each benefiting from the relationship. eg. flowers and their pollinators
describe the red queen effect
evolutionary change is constant as coevolution occurs, as selection process are constantly acting on species and causing them to change.
