adaptive radiation

what is adaptive radiation?

rapid speciation of one of more species from the ancestral species, to fill various ecological niches

is a source of biodiversity

in which organisms does adaptive radiation occur?

in organisms of the same species that hv different characteristics & undergo selective pressures

how does adaptive radiation increase biodiversity?

the species will become adapted to their respective environment & can coexist without competing for resources. this increases biodiversity in ecosystems where there are vacant niches

whats an ecological niche

position of a species within an ecosystem or community & its interrelationships with biotic & abiotic factors

whats an example of adaptive radiation

Darwin’s finches

• ancestral finch species that arrived on the Galapagos Islands, were seed-eating birds & had a thick, short beak

• the islands were uninhabited, meaning there were abundant resources (insects, fruits, seeds, rotting wood, etc)

• variations in beaks = these food resources could be exploited

• over time, selection of favourable beaks led to a rapid diversification of the finches into diverse ecological niches 

whats hybridization

occurs when an animal or plant breeds with an individual of another species or variety

does hybridization lead to speciation

very rarely

often, the offspring is infertile, so it cant reproduce

the offspring arent reproductively isolated from parent species - ask about why this is important 

in nature, what’re 2 mechanisms that prevent hybridization? 

prezygotic mechanisms & postzygotic mechanisms 

how do prezygotic mechanisms prevent hybridization?

variation in courtship behaviour often prevents hybridization between species 

• is basically what was mentioned in behavioural isolation - im pretty sure

how do postzygotic mechanisms prevent hybridization?

can reduce the viability of zygote, reduce viability of the young one & adult, & decrease the fertility of the hybrid & its offspring (if there even is offspring from the hybrid)

this barrier results in selection against hybrids - so hybrid incompatibility prevents the mixing of alleles of parent species & subsequent transmission to future generations

whats an example of a sterile hybrid (a hybrid that cannot reproduce)

a mule :(

• donkey has 62 chromosomes & horse has 64 - mule has 63 chromosomes 

  • doesnt hv required pairs of homologous chromosomes & thus is infertile