Chapter 24 - The Origin of Species

vicariance event

the specific geographic event that led to the evolution of the two species due to geographic barrier

What are the different criteria, advantages, & disadvantages of the BIOLOGICAL species concept?

-Criteria: ability to create viable, fertile offspring -Advantages: objective criteria, meshes well with gene flow concept -Disadvantages: not applicable to extinct or asexual species

What are the different criteria, advantages, & disadvantages of the PHYLOGENETIC species concept?

-Criteria: common evolutionary history -Advantages: based on actual relationships, works for asexual and extinct species -Disadvantages: requires good evolutionary histories

What are the different criteria, advantages, & disadvantages of the MORPHOLOGICAL species concept?

-Criteria: similarities in body structures -Advantages: easy to apply, works for asexual and extinct species -Disadvantages: researchers may disagree on which structures are important

Conspecifics

-individuals that are members of the same species -Genes are transferred between conspecific populations through both direct and indirect gene flow.

The morphological species (morphospecies) concept groups organisms into species based on structural features. Which of the following might be used in classifying a species by the morphological species concept?

-presence or absence of leg feathers -flower shape -skeletal features -plumage pattern -vascular arrangement in plants

What is genetic drift?

A change in allele frequencies caused by random events over time

polyploidy

A chromosomal alteration in which the organism possesses more than two complete chromosome sets.

What are the limitations of the biological species concept?

According to the biological species concept, the members of a species have the capability to interbreed in nature and produce viable, fertile offspring. These criteria apply only to living, sexually reproducing organisms. They cannot be applied to extinct organisms, asexually reproducing organisms, or organisms that cannot be observed live in nature.

_____ is rapid speciation under conditions in which there is little competition.

Adaptive radiation

Why are the large finches now living on the Galápagos Islands different from the original source population from a nearby island?

All answers: -The separation of habitats reduced gene flow between the populations. -Genetic drift occurred in the two populations. -Natural selection favored individuals that were more fit in the new environment.

Prezygotic barriers

Barriers that impede mating or hinder fertilization. Such barriers typically act in one of three ways: by impeding members of different species from attempting to mate, by preventing an attempted mating from being completed successfully, or by hindering fertilization if mating is completed successfully.

postzygotic barriers

Barriers that prevent the hybrid zygote from becoming a fertile adult after it has passed prezygotic barriers; may contribute to reproductive isolation after the hybrid zygote is formed. Developmental errors may reduce survival among hybrid embryos. Or problems after birth may cause hybrids to be infertile or decrease their chance of surviving long enough to reproduce

What is the most important factor that holds a gene pool of a species together and prevents speciation?

Gene flow - refers to the transfer of alleles among populations. As long as populations are exchanging alleles, speciation is unlikely.

Two animals are considered members of different species if they _____.

If two individuals cannot interbreed and produce viable, fertile offspring, they are members of different species.

A population of birds colonizes an area in which the insects upon which they feed live inside trees. Which of the following events accounts for an observed increase in average beak size in the bird population over time?

Increased fitness of large-beaked birds, leading to natural selection

A subset of a population of birds leaves its habitat on the mainland and colonizes a nearby island. The birds, after a period of time, become reproductively isolated. The island sinks and the population of birds that lived on the island returns to itsoriginal habitat. Which of the following statements about these bird populations is true?

The populations will not be able to interbreed because they are different species

Reinforcement

a type of natural selection called disruptive selection, which favors extreme phenotypes over intermediate phenotypes

True or false? A flood that separates a population of frogs onto opposite sides of a lake is an example of a vicariance event that may result in allopatric speciation.

True. Allopatric speciation may occur when populations are separated geographically; this type of speciation can begin with a vicariance event, in which a geographic barrier such as water isolates a population, or a dispersal event, in which a subset of a population migrates to a different habitat.

biological species

a group of populations whose individuals may interbreed and produce viable, fertile offspring with each other but not with members of other species; The biological species concept emphasizes reproductive isolation through prezygotic and postzygotic barriers that separate gene pools

sympatric speciation

a new species originates while remaining in the same geographic area as the parent species. Plant species (and, more rarely, animal species) have evolved sympatrically through polyploidy. Sympatric speciation can also result from sexual selection and habitat shifts.

Mass extinctions create conditions that promote _____.

adaptive radiation

The appearance of an evolutionary novelty promotes _____.

adaptive radiation; The appearance of an evolutionary novelty may allow for the exploitation of previously unexploited niches.

The different finch species found on the Galápagos Islands probably arose as a result of _____.

adaptive radiation; The finches that initially immigrated to the Galápagos Islands experienced little competition, the result of which was the promotion of speciation.

A certain species of salamander was split into two populations by a wide, dry valley, and the populations began to diverge from each other. After a period of time, some members of the two populations began to interbreed in a hybrid zone at the southern end of the valley. Only weak reproductive barriers existed by this time, so the two populations could freely interbreed and re-establish gene flow. This outcome in a hybrid zone is known as _____

fusion

allopatric speciation

gene flow is reduced when two populations of one species become geographically separated from each other. One or both populations may undergo evolutionary change during the period of separation, resulting in the establishment of barriers to reproduction.

The last ice age produced many different species mainly because

of vicariance events; the glaciers physically separated populations from each other.

reduced hybrid viability

postzygotic reproductive barrier; hybrid offspring are produced but are feeble or unable to compete for mates ex: two species of fish successfully interbreed, but their offspring don't live to maturity

reduced hybrid fertility

postzygotic reproductive barrier; hybrid offspring are produced but are sterile ex: horses can be mated with zebras, but their offspring are sterile

habitat isolation

prezygotic reproductive barrier; differences in habitat occupied Ex: different ticks live on different host species

behavioral isolation

prezygotic reproductive barrier; differences in mating rituals or displays ex: different bird species display feathers of different colors during mating display

temporal isolation

prezygotic reproductive barrier; differences in the timing of mating ex: one plant species flowers before dawn; a related species flowers in the late afternoon

mechanical isolation

prezygotic reproductive barrier; reproductive structure incompatibility Ex: differently shaped snail shells prevent alignment of genital openings

gametic isolation

prezygotic reproductive barrier; sperm and egg are incompatible ex: different coral species release gametes into the water, but only gametes of conspecifics can fuse

according to the _____ model, evolution occurs in spurts; species evolve relatively rapidly then remain unchanged for long periods

punctuated equilibrium

Phylogeny

refers to the evolutionary history of a species or group of species. Phylogenetic trees are branching diagrams intended to show the evolutionary histories of related species. Because it is impossible to directly observe these relationships as they develop, phylogenetic trees are hypotheses and may change over time as new findings come to light. The phylogenetic species concept defines a species as the smallest group of organisms that share a common ancestor.

Fusion

refers to the weakening of reproductive barriers, allowing the two populations to fuse and remain (or become) one species.

hybrid zones

regions in which members of different species meet and mate, producing at least some hybrid offspring; Many hybrid zones are stable, in that hybrid offspring continue to be produced over time. In others, reinforcement strengthens prezygotic barriers to reproduction, thus decreasing the formation of unfit hybrids. In still other hybrid zones, barriers to reproduction may weaken over time, resulting in the fusion of the species' gene pools (reversing the speciation process).

What are three of the most prominent definitions of species?

the biological species concept, the phylogenetic species concept, and the morphological species (morphospecies) concept.

Hybrid zones provide an opportunity to investigate _____

the evolution of reproductive isolation; A hybrid zone allows researchers to see what happens when closely related species come together. Reproductive barriers may be strengthened or weakened, depending on environmental and genetic factors.

Speciation

the formation of new and distinct species in the course of evolution; can occur rapidly or slowly and can result from changes in few or many genes; New species can form rapidly once divergence begins—but it can take millions of years for that to happen. The time interval between speciation events varies considerably, from a few thousand years to tens of millions of years. Researchers have identified particular genes involved in some cases of speciation. Speciation can be driven by few or many genes.

dispersal event

when members of a species cross/migrate an already existing barrier and establish a new population