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Chapter 18: Problem 37

Which type of speciation, allopatric or sympatric, is more common? Why? a. Allopatric speciation is more common because it prevents gene flow between the species. b. Allopatric speciation is more common because it involves stronger prezygotic barriers. c. Sympatric speciation is more common because it prevents gene flow between the species. d. Sympatric speciation is more common because it involves stronger prezygotic barriers.

Short Answer

Expert verified
a. Allopatric speciation is more common because it prevents gene flow between species.

Step by step solution

01

Understanding Speciation

Speciation is the process by which populations evolve to become distinct species. It can be classified into two main types: allopatric and sympatric speciation.
02

Analyzing Allopatric Speciation

Allopatric speciation occurs when populations are geographically separated. This geographical isolation prevents gene flow between the populations, leading to the evolution of distinct species over time.
03

Analyzing Sympatric Speciation

Sympatric speciation happens within the same geographical area. In this case, species evolve through mechanisms such as genetic mutations or changes in behavior that create reproductive isolation within the same habitat.
04

Comparing Frequency of Speciation Types

Both types lead to the formation of new species, but allopatric speciation is more common. The geographical isolation in allopatric speciation provides an effective barrier to gene flow, making it easier for distinct species to evolve.
05

Selecting the Correct Answer

Choices (c) and (d) discuss sympatric speciation, which is less common. Thus, eliminate them. Allopatric speciation is noted for preventing gene flow effectively, aligning it with choice (a). Choice (b) mentions prezygotic barriers, which isn't exclusive to allopatric speciation.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

allopatric speciation
Allopatric speciation happens when populations are geographically separated. This separation can be due to physical barriers such as mountains, rivers, or distance. When populations become isolated, they can no longer interbreed. Over time, genetic differences accumulate, leading to the formation of new species. The key factor here is geographical isolation. This means that the gene flow between the separated populations stops, allowing them to evolve independently. Allopatric speciation is considered the most common form of speciation because physical barriers are effective in preventing genetic mixing.
sympatric speciation
Sympatric speciation occurs within the same geographical region. Unlike allopatric speciation, populations are not separated by physical barriers. Instead, speciation arises from other mechanisms such as genetic mutations, changes in behavior, or reproductive strategies. For example, some individuals might develop a preference for a different type of food or habitat within the same environment. These preferences can reduce interbreeding with the original population, gradually leading to reproductive isolation. Although sympatric speciation is less common than allopatric speciation, it illustrates that new species can evolve without geographical barriers.
prezygotic barriers
Prezygotic barriers are mechanisms that prevent the formation of a zygote, or fertilized egg. These barriers occur before fertilization and are crucial in maintaining reproductive isolation between species. Some common types of prezygotic barriers include:
  • Temporal isolation: Species breed at different times.
  • Behavioral isolation: Differences in mating behaviors or rituals.
  • Mechanical isolation: Physical differences prevent mating.
  • Gametic isolation: Sperm and egg are incompatible.
By preventing cross-breeding, prezygotic barriers help ensure that species remain distinct.
reproductive isolation
Reproductive isolation is the end result of mechanisms that prevent species from interbreeding. This isolation can be prezygotic or postzygotic. Prezygotic barriers prevent mating or fertilization, while postzygotic barriers come into play after fertilization and can include factors like hybrid inviability or sterility. Reproductive isolation is vital for speciation as it stops gene flow between populations, allowing them to diverge genetically. In allopatric speciation, geographical barriers serve as a primary cause of reproductive isolation. In sympatric speciation, factors like behavioral changes lead to reproductive isolation even within the same environment.

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Most popular questions from this chapter

Populations of a plant species have been found growing in the mountains at altitudes above 2,500 meters. Populations of a plant that appears similar, with slight differences, have been found in the same mountains at altitudes below 2,300 meters. Describe a plan for collecting two kinds of data that could provide a direct answer to the question: do the populations growing above 2,500 meters and the populations growing below 2,300 meters represent a single species? a. Scientists could take the genetic code of a plant from each altitude and determine whether the two sets of DNA are identical. They could also insert genes from one plant into the cells from the other and see if the cells survive b. Scientists could look in the fossil record to find the plants鈥� most recent common ancestor. They could also check the surrounding mountains to determine if the most recent common ancestor is still living. c. Scientists could breed the two groups in the same environment and observe whether, over several generations, they begin to look more similar. They could also switch the groups, growing the high-altitude plants at low altitude and the low-altitude plants at high altitude, and observe whether the former begin to look like low- altitude plants and the latter begin to look like high-altitude plants. d. Scientists could collect seeds and test whether they might be cross- pollinated to produce fertile offspring. They could also investigate the area between 2,500 meters and 2,300 meters to see if fertile hybrid populations might be found living between the two other populations of plants.

Which of these statements about a natural principle that points to the inevitability of natural selection is false? a. Most characteristics of organisms are inherited. b. Offspring vary among each other in regard to their characteristics. c. Some generations of offspring do not need to compete for resources. d. Certain traits will be better represented in the next generation

Which is an example of an adaptation? a. The better nutrition of a human helps her grow taller. b. The webbed feet of a duck help it swim. c. The urban location of a raccoon helps it find food. d. The large leaves of a desert plant require more water.

In 1795, a Scottish geologist named Charles Hutton suggested that Earth鈥檚 geologic features could be explained by gradual processes that were still operating. This was in direct contrast to other scientific thought at the time, which included well-accepted proposals that geologic layers were representative of catastrophic events caused by processes no longer operating in the present time. Hutton proposed geologic features as the result of slow and consistent change, such as valleys formed by rivers wearing through rock. Hutton鈥檚 ideas were incorporated in the work of Charles Lyell, a geologist working in Darwin鈥檚 time. Lyell advocated a principle called uniformitarianism, the consistency of mechanisms of change over time. In other words, Lyell argued that the same geologic processes operating in the present had operated in the past, and at the same rate. The ideas of Hutton and Lyell influenced the work of Charles Darwin. How do Hutton鈥檚 and Lyell鈥檚 ideas connect to and provide support for Darwin鈥檚 theory of evolutionary change? a. The idea that the same processes that operate in the present also operated in the past, and at the same rate, supported Darwin鈥檚 hypothesis of natural selection because humans could select for desirable traits and produce change very rapidly, so natural selection would also be fast enough to produce the full range of diversity in living organisms. b. The idea that the same processes that operate in the present also operated in the past, and at the same rate, connects to Darwin鈥檚 hypothesis of natural selection because he had observed it happening in the present c. The idea that geologic change is the result of slow, continuous processes rather than sudden, substantial change connects to Darwin鈥檚 support of gradualism rather than punctuated equilibrium as the process that guided evolution. d. The idea that geologic change is the result of slow, continuous processes rather than sudden, substantial change connects directly to Darwin鈥檚 hypothesis that, given enough time, slow and subtle processes could produce substantial biological change.

Consider two species of birds that diverged while separated geographically but resumed their contact before reproductive isolation was complete. Which describes the first step in what would happen over time if the two species mated extensively and their hybrid offspring survived and reproduced more poorly than offspring from intra-species matings? a. Natural selection would cause prezygotic barriers to reproduction between the parent species to strengthen over time. b. The production of unfit hybrids would increase and the speciation process would complete. c. The extensive mating between the species would continue to produce large numbers of hybrids. d. The gene pools of the parent species would fuse over time, reversing the speciation process.
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