L12. Diversification: Adaptive Radiation Flashcards
Adaptive Radiation
- evolutionary changes shape traits allowing organisms to adapt to their environment, and convey fitness advantages
- evidence: a significant association between environments and the morphological and physiological traits used to exploit those environments
- leads to the development of many species in a relatively short time
- seems to correlate with a sudden abundance of open niches
Ecological niche
- specific place a species holds in its biotic and abiotic environment
- the physical space where it feeds/reproduces, the role it plays in the food chain of its community, and its interactions with other organisms
- no two species can hold the same niche in the same environment because one will always outcompete the other
Creation of new open niches
- could occur through dispersal to a new environment
- innovation traits can create new previously unexploited niches
- modification of habitat is called ecosystem engineering
- could happen through mass extinction
- change in physical landscape (creation of new land by volcanic processes) (actually what happened in Darwin’s finches)
New habitat volcanic island example
- single colonizing finch species gave rise to many species that evolved to fill diverse open niches
- common ancestor arrived 2 million years ago
- now 18 species
- differ in body size, beak shape, song and feeding behaviour
- Galapagos island
New habitat rift lake example
- one of the largest adaptive radiations: East African cichlid fishes
- so many evolved in a short time (less than 10 million years)
- different sizes, variation in appendages and jaws
- eat different things
Emptying niches: End-cretaceous extinction
- mass extinction (meteor impact and possibly other factors)
- loss of dinosaurs caused an abundance of empty niches
- led to incredible adaptive radiation in mammal species
- resulted in the domination of mammal species today
Why did mammals recover and dinosaurs did not?
- up to 90% of mammals species may have been lost during extinction event but they were able to come back
- small size gave them a fast reproduction rate
- generalist habit means they could survive on a diverse range of foods
Cambrian Explosion
- massive radiation
- rapid emergence of new traits
- maybe new environmental niches
Key innovations in flowering plants
- coevolved with insect pollinators
- creation of niches through ecosystem engineering
- adaptive radiation: became attractive to pollinators, this is because pollinators greatly improved pollen transmission since an insect can travel much farther than wind dispersed pollen
- major diversification of angiosperm pollinators along with angiosperms (new pollination niches)
- first angiosperms arose in forests dominated by conifers
- over 35 Ma dominant plant group changed form conifers to angiosperm, one they were dominant they changed the abiotic and biotic landscape to favour their own growth
- explains why we see the majority of conifers in colder areas where angiosperms cannot thrive due to short growing seasons
What about when species become more similar?
- convergent evolution: independent evolution of analogous traits in two or more lineages (trait in question is not present in the last common ancestor of both groups)
Examples of convergent evolution
- bats and birds
- venom injection arose separately in cobras and vipers
- platypus and ducks
- scorpions and bees
- crabs
- seeds in plants
Carcinization
“the urge to become a crab”
- a crab-like body plan has arisen independently 5+ times
How to prove convergent evolution
map a trait into a phylogeny, look for the presence of trait in fossil ancestors
What is the mechanism of convergent evolution
- similar environments shape similar traits
- certain traits are more easily modified (fewer gene mutations required, co-option of existing structures)
Mimicry
- example of convergent evolution
- ex. non-toxic species evolving to resemble an unrelated/dangerous one to deter predation
Parallel evolution
similar development of a trait in distinct species that are not closely related, but share a similar original trait, in response to similar evolutionary pressure
- this is different from convergent in that ancestors shared the trait
- ex. placental mammals and marsupials (each lineage developed similar forms on different continents after they diverged to fill similar niches
Founder effect
- new population colonizing an island
- smaller than source population
- contains only a sub-set of the genetics of the original population
- may also have harmful recessive founder mutations
- leads to faster evolution because of genetic drift and the bottleneck effect (new mutation in a small gene pool makes a large overall contribution to genetic diversity compared to a large population)
Founder mutation
rate mutation in one of the founding members of population
- makes super rare trait everywhere else super common in community
Modern Genetic diversity
- like discussed before: highest diversity in Africa, lower in Europe, lowest in South America
- more rare alleles in Africa, this is because rare alleles are more likely to become lost in founder population unless they become dominant
