Speciation

Macroevolution

SpeciationSpecies: groups that can reproduce with each

other and produce viable offspringSpeciation: origin of a new species leads to greater diversityMacroevolution: origin and extinction of different

species, evolution of new features eg. wings

Reproductive Isolation the inability of a sp. to breed with another results from barriers, either physical (ex mtns) or

behavioural (ex. mating dance). sp. do not breed with each other in nature (even

if they are capable of it) various types:

1. Geographic Isolation Landforms, water, distance to move (or spread repro.

cells) limits reproduction Genetic drift and natural selection work together to

form unique species. For every species that forms, many more perish ex.Harris’s antelope squirrel and white-tailed antelope

squirrel divided by the Grand Canyon

2. Habitat Isolation some species have adapted to a specific

location within an ecosystem. even though contact is possible, preferences

for their habitat prevents it ex. 2 sp of garter snakes live in same area

• 1 sp lives mainly in water, other on land so don’t interact

Other Reproductive BarriersA. Temporal isolation - different breeding seasonsB. Behavioural isolation - different mating

behavioursC. Mechanical isolation - different reproductive

structuresD. Gamete isolation - different sex cellsE. Hybrid inviability - hybrids are not healthy

enough to survive or reproduceF. Hybrid infertility - hybrids born healthy, but are

unable to reproduce

Adaptive Radiation Divergent Evolution organisms arrive in different environment new habitats encourage speciation

Founder effect + natural selection + reproductive isolation = speciation

evolution from a common ancestor results in diverse species adapted to different environments

Convergent Evolution distantly related species living in similar

environments develop similar adaptations face similar selection pressures

North American antelope (left) and African impala antelope (right) appear to be very closely related, but have actually evolved convergently to resemble each other.

Rate of SpeciationGradualism: evolution of a species by gradual accumulation of small

genetic changes over a long period of time Darwin knew geologic changes occurred very slowly,

believed speciation must evolve in same way

Punctuated Equilibrium: changes to a species can occur suddenly, and can be

extensive enough to create a new species in a short period of time

fossil record shows many new species appearing abruptly

both can occur as a result of Natural Selection

Human Activity usually results in a decrease of

biodiversity island ecosystems at risk ex dodo ecosystems affected by human

activity and introduction of invasive species

modern agriculture and fishing