macroevolution

speciation

the process by which one species splits into two or more species

macroevolution

the broad pattern of evolution above the species level; the creation of new groups of organisms through a series of speciation events

the biological species concept

a population/group of populations whose members interbreed to produce viable fertile offspring. when this occurs, genetic exchange between individuals is possible

reproductive isolation

any factor that impedes 2 species from producing viable, fertile hybrids, and blocking any genetic mixing between species

• causes the isolation of the gene pools of a particular species

• block gene flow, preventing the formation of hybrids; offspring that result from an interspecific mating

what are the two types of reproductive barriers?

1. prezygotic barriers

2. postzygotic barriers

what are the prezygotic barriers?

1. habitat isolation

2. temporal isolation

3. behavioural isolation

4. mechanical isolation

5. gametic isolation

what are the postzygotic barriers?

1. reduced hybrid viability

2. reduced hybrid fertility

3. hybrid breakdown

habitat isolation

when two species are prevented from mating because they live in different habitats of the same area

temporal isolation

species breed at different times

behavioural isolation

different mating rituals prevent mating

mechanical isolation

anatomical barriers that prevent mating

gametic isolation

incompatible sperm and egg

reduced hybrid viability

offspring of two species have a lower likelihood of surviving

reduced hybrid fertility

offspring of two species are sterile

hybrid breakdown

first generation of offspring are healthy but the other generations will not survive long

allopatric speciation

speciation takes place when members of a population are geographically isolated

sympatric speciation

speciation takes place without a geographic barrier

describe allopatric speciation

• occurs when gene flow is interrupted due to geography

• the  size of the geographic barrier needed depends on the organism

• once separated the populations diverge due to the microevolutionary pressures: genetic drift, natural selection etc. 

describe sympatric speciation

• speciation in geographically overlapping populations

• can occur if gene flow is reduced by such factors as polyploidy, habitat differentiation, and sexual selection

polyploidy

speciation due to an accident during cell division that results in extra sets of chromosomes

sexual selection

non random mating; mate choice

habitat differentiation

a subset of the population become reproductively isolated because of a switch of habitat food source or other resource not used by the parent population

punctuated equilibrium

periods of stasis punctuated by sudden change in an organism’s evolution

when can rapid evolution happen?

• species is isolated from its parent population

• small group migrates to a new environment

• dramatic changes on the earth

gradualism

slow change over time

adaptive radiation

periods of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill different ecological roles, or niches, in their communities after large mass extinctions