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Feathers either play a role, or may have played a role, in _____.

all of these

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

Adaptive radiation

Mass extinctions create conditions that promote _____.

adaptive radiation

The appearance of an evolutionary novelty promotes _____.

adaptive radiation

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

adaptive radiation

A biologist spends her summer break collecting frogs from a remote jungle in Peru. She discovers two distinct color forms that could be variants of a single species or two different species. What would be the most direct test of their species status under the biological species concept?

Observe mating in the natural environment of the two groups. If the two forms do not mate with each other, they are different species

In _____ isolation, it is physically impossible for two species to mate with each other, often because their genitalia do not fit together properly.


Eastern and western spotted skunks breed at different times of the year. Therefore, they are prevented from interbreeding by _____ isolation.


The process of speciation starts with a single species. It often involves the following steps: (1) two populations become physically separated from one another by a barrier to dispersal and stop exchanging genes; (2) the populations experience independent evolutionary changes; (3) changes in one or both populations result in development of reproductive isolating mechanisms that prevent interbreeding; further changes in geography may bring the groups back into contact. When do you officially have two separate species?

step 3

Darwin thought that significant evolution was much too slow to be witnessed in a human lifetime. Recent experiments by biologists have _____.

shown that some populations can evolve quite rapidly, with important changes occurring over several generations in the laboratory

Speciation, or the formation of new species, is

responsible for the diversity of life

Which of the following would a biologist describe as microevolution?

a change in the gene pool of a population from one generation to the next

Under the biological species concept, a species is a group of organisms that

have the potential to interbreed in nature and produce fertile offspring

The biological species concept is

sometimes difficult to put into practice even for present sexual organisms, and useless for asexual organisms and fossils

Which of the following statements regarding the definition of species is false?

The morphological species concept relies upon comparing the DNA sequences of organisms

Which provides the most general and correct description of the idea of a reproductive barrier?

a biological difference between two species that prevents them from successfully interbreeding

Two populations of organisms belong to the same biological species when they

encounter each other, mate, and produce viable, fertile offspring under natural conditions

Which of the following types of reproductive barriers separates a pair of species that could interbreed except that one mates at dusk and the other at dawn?

temporal isolation

Which of the following types of reproductive barriers separates a pair of insect species that could interbreed except that one lives on goldenrod plants and the other on autumn daisies in the same general area?

habitat isolation

Which of the following types of reproductive barriers separates a pair of moth species that could interbreed except that the females' mating pheromones are not attractive to the males of the other species?

behavioral isolation

Which of the following types of reproductive barriers separates two flowering plant species that could interbreed except that one has a deep flower tube and is pollinated by bumblebees, whereas the other has a short, narrow flower tube and is pollinated by honeybees?

mechanical isolation

Which of the following types of reproductive barriers separates two species of sea cucumbers, whose sperm and eggs often bump into each other but do not cross-fertilize because of incompatible proteins on their surfaces?

gametic isolation

Two species that occasionally mate and produce zygotes, but which have incompatible genes that prevent the resulting embryo from developing, are separated by

reduced hybrid viability

Two species that sometimes mate and produce vigorous but sterile offspring are separated by

reduced hybrid fertility

Two species interbreed occasionally and produce vigorous, fertile hybrids. When the hybrids breed with each other or with either parent species, however, the offspring are feeble or sterile. These species are separated by

hybrid breakdown

Frequently, a group of related species will each have a unique courtship ritual that must be performed correctly for both partners to be willing to mate. Such a ritual constitutes a ________, ________ reproductive barrier.

behavioral . . . prezygotic

The Monterey pine and the Bishop's pine inhabit some of the same areas of central California. The Monterey pine releases pollen in February, while the Bishop's pine does so in April. This is an example of ________ isolation.


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