Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Population Change Populations can change and diverge when they are isolated from one another. • Speciation is a splitting event that creates two or more distinct species from a single ancestral group. Figure 23.1 Large ground finch Small ground finch Population Change Speciation is the outcome of isolation and divergence. • Isolation is created by reductions in gene flow. • Divergence is created when mutation, genetic drift, and selection act on populations separately. Defining and Identifying Species Species are distinct types of organisms because they represent evolutionarily independent groups. Lack of gene flow makes a species independent. Figure 23.2 A B C D E F G H I J Defining and Identifying Species Species are defined based on several different concepts: • The biological species concept is based on reproductive isolation. • The morphospecies concept is based on identifying evolutionarily independent lineages. • The phylogenetic species concept is based on reconstructing the evolutionary history of populations. Table 23.1 Willow and Alder Flycatcher Isolation and Divergence in Sympatry Sympatric speciation occurs in populations that occupy the same geographic area. Gene flow is occurring. • Natural selection can cause this process to occur in spite of gene flow. • Polyploidy, a type of mutation, can also cause sympatric speciation. Soapberry bugs Figure 23.5a Beak length correlates with fruit size. Balloon vine (native species) Flat-podded golden rain tree (non-native species) Short-beaked population growing on non-native plants 12 Long-beaked population growing on native plants 8 Frequency 4 0 2 3 6 7 8 9 Beak length (mm) 10 11 12 11 12 8 Non-native plant (small fruit) 4 Native plant (large fruit) 0 2 3 6 7 8 9 Fruit radius (mm) 10 Figure 23.5b This correlation appears to be a product of natural selection. 9 Beak length (mm) 8 7 6 5 1880 1900 1920 1940 Date 1960 1980 Figure 23.6 Diploid parent Tetraploid parent (Two copies of each chromosome) Meiosis (Four copies of each chromosome) Mating Haploid gametes Diploid gametes (One copy of each chromosome) (Two copies of each chromosome) Triploid zygote Meiosis (Three copies of each chromosome) When these gametes combine, most offspring have incorrect number of chromosomes. Isolation and Diversion in Allopatry Allopatric speciation occurs when populations become physically separated from each other. • A population can colonize a new habitat. • A new physical barrier can split a widespread population into two or more isolated groups.