Formation of New Species Quiz

PDF page 744: For speciation to occur, two new populations must be formed from one original population and they must evolve in such a way that it becomes impossible for individuals from the two new populations to interbreed. Biologists have proposed mechanisms by which this could occur that fall into two broad categories. Allopatric speciation (allo- = "other"; -patric = "homeland") involves geographic separation of populations from a parent species and subsequent evolution. Sympatric speciation (sym- = "same"; -patric = "homeland") involves speciation occurring within a parent species remaining in one location. Biologists think of speciation events as the splitting of one ancestral species into two descendant species. There is no reason why there might not be more than two species formed at one time except that it is less likely and multiple events can be conceptualized as single splits occurring close in time.

PDF page 740: Speciation explains the diversity of organisms that inhabit the Earth. Although all life shares various genetic similarities, only certain organisms combine genetic information by sexual reproduction and produce viable and fertile offspring that, in turn, can successfully reproduce. Scientists call such organisms members of a biological species. As we will study in later, changes in allele frequencies within a population over generations result in microevolution. However, macroevolution leads to the evolution of new species when populations diverge from a common ancestor and, for one reason or another, become reproductively isolated from the original population. Speciation occurs along two main pathways: geographic separation (allopatric speciation) and through mechanisms that occur within a shared habitat (sympatric speciation). In both cases, populations become reproductively isolated. When populations become geographically isolated, the free-flow of alleles is prevented. Over time—and because of different selective pressures—the populations diverge and become genetically independent species. Prezygotic barriers block reproduction prior to formation of a zygote, whereas postzygotic barriers block reproduction after fertilization occurs. Obviously, if two populations are separated by a vast ocean, they will not come in contact with each other to reproduce. However, if speciation has occurred, even when brought back together, they will retain their species identity. There are many examples of this in nature, including Darwin’s finches, northern and Mexican spotted owls, and Hawaiian honeycreeper. Adaptive radiation occurs when a single ancestral species gives rise to many new species. This may occur, for example, when new habitats become available. It can also be seen historically in the rise of mammals following the extinction of dinosaurs. Other examples of prezygotic isolating mechanisms include mating seasons and unique courtship behaviors. Sometimes mating occurs between two different species, resulting in a hybrid such as the mule, which is a cross between a horse and a donkey. However, most hybrids are inviable or sterile.

PDF page 740: Speciation explains the diversity of organisms that inhabit the Earth. Although all life shares various genetic similarities, only certain organisms combine genetic information by sexual reproduction and produce viable and fertile offspring that, in turn, can successfully reproduce. Scientists call such organisms members of a biological species. As we will study in later, changes in allele frequencies within a population over generations result in microevolution. However, macroevolution leads to the evolution of new species when populations diverge from a common ancestor and, for one reason or another, become reproductively isolated from the original population. Speciation occurs along two main pathways: geographic separation (allopatric speciation) and through mechanisms that occur within a shared habitat (sympatric speciation). In both cases, populations become reproductively isolated. When populations become geographically isolated, the free-flow of alleles is prevented. Over time—and because of different selective pressures—the populations diverge and become genetically independent species. Prezygotic barriers block reproduction prior to formation of a zygote, whereas postzygotic barriers block reproduction after fertilization occurs. Obviously, if two populations are separated by a vast ocean, they will not come in contact with each other to reproduce. However, if speciation has occurred, even when brought back together, they will retain their species identity. There are many examples of this in nature, including Darwin’s finches, northern and Mexican spotted owls, and Hawaiian honeycreeper. Adaptive radiation occurs when a single ancestral species gives rise to many new species. This may occur, for example, when new habitats become available. It can also be seen historically in the rise of mammals following the extinction of dinosaurs. Other examples of prezygotic isolating mechanisms include mating seasons and unique courtship behaviors. Sometimes mating occurs between two different species, resulting in a hybrid such as the mule, which is a cross between a horse and a donkey. However, most hybrids are inviable or sterile.

PDF page 745: Additionally, scientists have found that the farther the distance between two groups that once were the same species, the more likely it is that speciation will occur. This seems logical because as the distance increases, the various environmental factors would likely have less in common than locations in close proximity. Consider the two owls: in the north, the climate is cooler than in the south; the types of organisms in each ecosystem differ, as do their behaviors and habits; also, the hunting habits and prey choices of the southern owls vary from the northern owls. These variances can lead to evolved differences in the owls, and speciation likely will occur. Adaptive Radiation In some cases, a population of one species disperses throughout an area, and each population finds a distinct niche or isolated habitat. Over time, the varied demands of their new lifestyles lead to multiple speciation events originating from a single species. This is called adaptive radiation because many adaptations evolve from a single point of origin; thus, causing the species to radiate into several new ones. Island archipelagos like the Hawaiian Islands provide an ideal context for adaptive radiation events because water surrounds each island which leads to geographical isolation for many organisms. The Hawaiian honeycreeper illustrates one example of adaptive radiation. From a single species, called the founder species, numerous species have evolved, including the six shown in Figure 18.15.

PDF page 741: Sympatric speciation does not require a geographic barrier and explains how many different species can inhabit the same area. One form of sympatric speciation begins with a serious chromosomal error during cell division. As you recall from our exploration of meiosis, sometimes errors occur in the separation of chromosomes or chromatids, resulting in gametes with extra chromosomes (polyploidy). This type of speciation is more common in plants than in animals, though some examples in animals exist. For example, two groups of cichlid fish in Africa’s Lake Victoria, which have distinct morphologies and diets, may be in the early stage of sympatric speciation without polyploidy, as genetic differences arise between the two groups. Information presented and the examples highlighted in this section support concepts outlined in Big Idea 1 and Big Idea

PDF page 747: Can divergence occur if no physical barriers are in place to separate individuals who continue to live and reproduce in the same habitat? The answer is yes. The process of speciation within the same space is called sympatric speciation; the prefix “sym” means same, so “sympatric” means “same homeland” in contrast to “allopatric” meaning “other homeland.” A number of mechanisms for sympatric speciation have been proposed and studied. One form of sympatric speciation can begin with a serious chromosomal error during cell division. In a normal cell division event chromosomes replicate, pair up, and then separate so that each new cell has the same number of chromosomes. However, sometimes the pairs separate and the end cell product has too many or too few individual chromosomes in a condition called aneuploidy (Figure 18.16).

PDF page 741: Sympatric speciation does not require a geographic barrier and explains how many different species can inhabit the same area. One form of sympatric speciation begins with a serious chromosomal error during cell division. As you recall from our exploration of meiosis, sometimes errors occur in the separation of chromosomes or chromatids, resulting in gametes with extra chromosomes (polyploidy). This type of speciation is more common in plants than in animals, though some examples in animals exist. For example, two groups of cichlid fish in Africa’s Lake Victoria, which have distinct morphologies and diets, may be in the early stage of sympatric speciation without polyploidy, as genetic differences arise between the two groups. Information presented and the examples highlighted in this section support concepts outlined in Big Idea 1 and Big Idea

PDF page 749: The cultivated forms of wheat, cotton, and tobacco plants are all allopolyploids. Although polyploidy occurs occasionally in animals, it takes place most commonly in plants. (Animals with any of the types of chromosomal aberrations described here are unlikely to survive and produce normal offspring.) Scientists have discovered more than half of all plant species studied relate back to a species evolved through polyploidy. With such a high rate of polyploidy in plants, some scientists hypothesize that this mechanism takes place more as an adaptation than as an error.

PDF page 740: Speciation explains the diversity of organisms that inhabit the Earth. Although all life shares various genetic similarities, only certain organisms combine genetic information by sexual reproduction and produce viable and fertile offspring that, in turn, can successfully reproduce. Scientists call such organisms members of a biological species. As we will study in later, changes in allele frequencies within a population over generations result in microevolution. However, macroevolution leads to the evolution of new species when populations diverge from a common ancestor and, for one reason or another, become reproductively isolated from the original population. Speciation occurs along two main pathways: geographic separation (allopatric speciation) and through mechanisms that occur within a shared habitat (sympatric speciation). In both cases, populations become reproductively isolated. When populations become geographically isolated, the free-flow of alleles is prevented. Over time—and because of different selective pressures—the populations diverge and become genetically independent species. Prezygotic barriers block reproduction prior to formation of a zygote, whereas postzygotic barriers block reproduction after fertilization occurs. Obviously, if two populations are separated by a vast ocean, they will not come in contact with each other to reproduce. However, if speciation has occurred, even when brought back together, they will retain their species identity. There are many examples of this in nature, including Darwin’s finches, northern and Mexican spotted owls, and Hawaiian honeycreeper. Adaptive radiation occurs when a single ancestral species gives rise to many new species. This may occur, for example, when new habitats become available. It can also be seen historically in the rise of mammals following the extinction of dinosaurs. Other examples of prezygotic isolating mechanisms include mating seasons and unique courtship behaviors. Sometimes mating occurs between two different species, resulting in a hybrid such as the mule, which is a cross between a horse and a donkey. However, most hybrids are inviable or sterile.

PDF page 744: For speciation to occur, two new populations must be formed from one original population and they must evolve in such a way that it becomes impossible for individuals from the two new populations to interbreed. Biologists have proposed mechanisms by which this could occur that fall into two broad categories. Allopatric speciation (allo- = "other"; -patric = "homeland") involves geographic separation of populations from a parent species and subsequent evolution. Sympatric speciation (sym- = "same"; -patric = "homeland") involves speciation occurring within a parent species remaining in one location. Biologists think of speciation events as the splitting of one ancestral species into two descendant species. There is no reason why there might not be more than two species formed at one time except that it is less likely and multiple events can be conceptualized as single splits occurring close in time.

PDF page 743: Populations of species share a gene pool: a collection of all the variants of genes in the species. Again, the basis to any changes in a group or population of organisms must be genetic for this is the only way to share and pass on traits. When variations occur within a species, they can only be passed to the next generation along two main pathways: asexual reproduction or sexual reproduction. The change will be passed on asexually simply if the reproducing cell possesses the changed trait. For the changed trait to be passed on by sexual reproduction, a gamete, such as a sperm or egg cell, must possess the changed trait. In other words, sexually-reproducing organisms can experience several genetic changes in their body cells, but if these changes do not occur in a sperm or egg cell, the changed trait will never reach the next generation. Only heritable traits can evolve. Therefore, reproduction plays a paramount role for genetic change to take root in a population or species. In short, organisms must be able to reproduce with each other to pass new traits to offspring.

PDF page 743: Populations of species share a gene pool: a collection of all the variants of genes in the species. Again, the basis to any changes in a group or population of organisms must be genetic for this is the only way to share and pass on traits. When variations occur within a species, they can only be passed to the next generation along two main pathways: asexual reproduction or sexual reproduction. The change will be passed on asexually simply if the reproducing cell possesses the changed trait. For the changed trait to be passed on by sexual reproduction, a gamete, such as a sperm or egg cell, must possess the changed trait. In other words, sexually-reproducing organisms can experience several genetic changes in their body cells, but if these changes do not occur in a sperm or egg cell, the changed trait will never reach the next generation. Only heritable traits can evolve. Therefore, reproduction plays a paramount role for genetic change to take root in a population or species. In short, organisms must be able to reproduce with each other to pass new traits to offspring.

PDF page 745: two rodent populations became divided by the formation of a new lake, continued gene flow would be unlikely; therefore, speciation would be more likely. Biologists group allopatric processes into two categories: dispersal and vicariance. Dispersal is when a few members of a species move to a new geographical area, and vicariance is when a natural situation arises to physically divide organisms. Scientists have documented numerous cases of allopatric speciation taking place. For example, along the west coast of the United States, two separate sub-species of spotted owls exist. The northern spotted owl has genetic and phenotypic differences from its close relative: the Mexican spotted owl, which lives in the south (Figure 18.14).

PDF page 745: Additionally, scientists have found that the farther the distance between two groups that once were the same species, the more likely it is that speciation will occur. This seems logical because as the distance increases, the various environmental factors would likely have less in common than locations in close proximity. Consider the two owls: in the north, the climate is cooler than in the south; the types of organisms in each ecosystem differ, as do their behaviors and habits; also, the hunting habits and prey choices of the southern owls vary from the northern owls. These variances can lead to evolved differences in the owls, and speciation likely will occur. Adaptive Radiation In some cases, a population of one species disperses throughout an area, and each population finds a distinct niche or isolated habitat. Over time, the varied demands of their new lifestyles lead to multiple speciation events originating from a single species. This is called adaptive radiation because many adaptations evolve from a single point of origin; thus, causing the species to radiate into several new ones. Island archipelagos like the Hawaiian Islands provide an ideal context for adaptive radiation events because water surrounds each island which leads to geographical isolation for many organisms. The Hawaiian honeycreeper illustrates one example of adaptive radiation. From a single species, called the founder species, numerous species have evolved, including the six shown in Figure 18.15.

PDF page 745: Additionally, scientists have found that the farther the distance between two groups that once were the same species, the more likely it is that speciation will occur. This seems logical because as the distance increases, the various environmental factors would likely have less in common than locations in close proximity. Consider the two owls: in the north, the climate is cooler than in the south; the types of organisms in each ecosystem differ, as do their behaviors and habits; also, the hunting habits and prey choices of the southern owls vary from the northern owls. These variances can lead to evolved differences in the owls, and speciation likely will occur. Adaptive Radiation In some cases, a population of one species disperses throughout an area, and each population finds a distinct niche or isolated habitat. Over time, the varied demands of their new lifestyles lead to multiple speciation events originating from a single species. This is called adaptive radiation because many adaptations evolve from a single point of origin; thus, causing the species to radiate into several new ones. Island archipelagos like the Hawaiian Islands provide an ideal context for adaptive radiation events because water surrounds each island which leads to geographical isolation for many organisms. The Hawaiian honeycreeper illustrates one example of adaptive radiation. From a single species, called the founder species, numerous species have evolved, including the six shown in Figure 18.15.

PDF page 745: two rodent populations became divided by the formation of a new lake, continued gene flow would be unlikely; therefore, speciation would be more likely. Biologists group allopatric processes into two categories: dispersal and vicariance. Dispersal is when a few members of a species move to a new geographical area, and vicariance is when a natural situation arises to physically divide organisms. Scientists have documented numerous cases of allopatric speciation taking place. For example, along the west coast of the United States, two separate sub-species of spotted owls exist. The northern spotted owl has genetic and phenotypic differences from its close relative: the Mexican spotted owl, which lives in the south (Figure 18.14).

PDF page 745: Additionally, scientists have found that the farther the distance between two groups that once were the same species, the more likely it is that speciation will occur. This seems logical because as the distance increases, the various environmental factors would likely have less in common than locations in close proximity. Consider the two owls: in the north, the climate is cooler than in the south; the types of organisms in each ecosystem differ, as do their behaviors and habits; also, the hunting habits and prey choices of the southern owls vary from the northern owls. These variances can lead to evolved differences in the owls, and speciation likely will occur. Adaptive Radiation In some cases, a population of one species disperses throughout an area, and each population finds a distinct niche or isolated habitat. Over time, the varied demands of their new lifestyles lead to multiple speciation events originating from a single species. This is called adaptive radiation because many adaptations evolve from a single point of origin; thus, causing the species to radiate into several new ones. Island archipelagos like the Hawaiian Islands provide an ideal context for adaptive radiation events because water surrounds each island which leads to geographical isolation for many organisms. The Hawaiian honeycreeper illustrates one example of adaptive radiation. From a single species, called the founder species, numerous species have evolved, including the six shown in Figure 18.15.

PDF page 746: Figure 18.15 The honeycreeper birds illustrate adaptive radiation. From one original species of bird, multiple others