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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

Which statement best describes the relationship between the theory of evolution and the origin of life? a. The theory includes an explanation of life鈥檚 origins. b. The theory cannot explain the origin of life. c. The theory does not try to explain the origin of life. d. The theory does not contribute understanding to pre-life processes.

a. searching horizontal rock layers in any class of rock and trying to find those that contain the greatest number of fossils b. collecting fossils from rock layers deposited prior to the Permian period that contain some early vertebrate bones c. looking in sedimentary layers next to bodies of water in order to find marine fossils of bivalves and trilobites d. using relative dating techniques to determine the geological ages of the fossils found so they can calculate the rate of speciation of early organisms

Given your understanding of evolutionary theory and the relationship between evolution and the genetic makeup of populations, which statement is false? a. Homologous characteristics that have evolved more recently are shared only within smaller groups of organisms. b. The genetic code is a homologous characteristic shared by all species because they share a common ancestor in the deep past. c. DNA sequence data would likely support any evolutionary tree drawn from anatomical data sets. d. The degree of relatedness between groups of organisms is only sometimes reflected in the similarity of their DNA sequences.

Which statement about postzygotic barriers is false? a. They occur after fertilization. b. They include hybrids that are sterile. c. They include hybrid organisms that don鈥檛 survive the embryonic stage. d. They include reproductive organ incompatibility

Each of the following observations comes from a different scientific discipline. Which is the best support for Darwin鈥檚 concept of descent with modification? a. Geologists provide evidence that earthquakes reshape life by causing mass extinctions. b. Botanists provide evidence that South American temperate plants have more in common with South American tropical plants than temperate plants from Europe. c. Zoologists provide evidence that fewer animal species live on islands than on nearby mainlands. d. Ecologists provide evidence that species diversity increases closer to the equator
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