Chapter 24 Notes

The Origin of Species

The Origin of Species

There is more to evolution than just explaining how adaptations evolve in a population.

Evolution must also explain macroevolution: the origin of a new taxonomic group

Speciation: development of a new species

The Origin of Species

The fossil record displays two patterns of speciation: anagenesis and cladogenesis

Anagenesis: the accumulation of changes associated with the transformation of one species into another

Cladogenesis: the budding of new species from a parent species that still exists.

The Origin of Species

Concept 24.1

Species: means “kind” or “appearance”- we distinguish plants and animals by differences in appearance

Concept 24.1

The biological species concept emphasizes reproductive isolation- Ernst Mayr (1942)

Biological species concept: defines a species as a population whose members have the potential to interbreed in nature and produce viable, fertile offspring.

Concept 24.1

Prezygotic and postzygotic barriers isolate the gene pools of biological species- any factor that impedes two species from producing fertile hybrids contributes to reproductive isolation- reproductive isolation prevents populations form interbreeding even if their ranges overlap

Concept 24.1

Prezygotic barriers: impede mating between species or hinder the fertilization of the ova

Habitat isolation: two species live in different habitats; low occurrence of interaction

Concept 24.1

Behavioral isolation: special signals that attract mates, along with elaborate behaviors unique to a species

Temporal isolation: two species breed at different times (day, seasons, years)

Concept 24.1

Mechanical isolation: anatomically incompatible

Gametic isolation: gametes rarely fuse to form a zygote; sperm might not be able to travel to the ova

Concept 24.1

Postzygotic barriers: prevent the hybrid zygote from developing into a viable, fertile adult

Reduced hybrid viability: hybrids are completely or largely sterile- Donkey + horse = mule

Concept 24.1

Hybrid breakdown: the first generation of hybrids are fertile, but as those mate with one another, the offspring of the next generation are sterile

Concept 24.1

Evolutionary biologists have proposed several alternative concepts of species

Ecological species concept: defines a species in terms of its ecological niche, the set of environmental resources it uses- ex. A parasite may be defined by is adaptations to its host

Concept 24.1

Pluralistic species concept: the factors that are most important of the cohesion of individuals as a species vary

Morphological species concept: characterize species in terms of structural features

Concept 24.1

Genealogical species concept: defines a species as a set of organisms with a unique genetic history

Concept 24.2

There are two modes of speciation based on how gene flow among populations is initially interrupted

Allopatric speciation: speciation takes place in populations with geographically separate ranges

Concept 24.2

Concept 24.2

Concept 24.2

Concept 24.2

Adaptive radiation: the speciation of organisms through an island chain; the islands are far apart to permit populations to evolve in isolation, but close enough together for the occasional dispersion event to occur

Concept 24.2

Concept 24.2

Sympatric speciation: speciation takes place in geographically overlapping populations - chromosomal changes and nonrandom mating reduce gene flow

Concept 24.2

Concept 24.2

The punctuated equilibrium model has stimulated research on the tempo of speciation- paleontologists rarely find gradual transitions in fossil forms- long periods of stasis (equilibrium) punctuated by episodes of speciation

Concept 24.2