Speciation Modified from http www mrcroft com Species

Speciation Modified from: http: //www. mrcroft. com/

• Species: a group of individuals that look similar and whose members are capable of producing fertile offspring in the natural environment

Morphological Species Concept • Morphological Species Concept: organisms classified by differences in their appearance – Scientists can readily communicate about characteristics, behavior, and relationships of organisms – Limited: it does not account for the reproductive compatibility of morphologically different organisms

Biological Species Concept • Biological Species Concept: organisms classified by their ability to breed with one another • Using both the biological and morphological concepts of species, modern scientists have arrived at the current definition of the term species.

Species: a group of individuals that look similar and whose members are capable of producing fertile offspring in the natural environment

Variation of Traits in a Population • Population: all the members of a species that live in the same area and make up a breeding group • Within a population, individuals vary in many observable traits.

Caribou Population Distribution

Variation is the Raw Material of Natural Selection

Disruption of Genetic Equilibrium Evolution occurs when genetic equilibrium is disrupted.

1. Mutation • Mutations produce totally new alleles for a trait • Mutations can change the frequency of the alleles already present in the gene pool. • The occurrence of mutation in most alleles is too low to cause major changes in the allele frequencies of an entire population.

1. Mutation

2. Migration • Migration: the movement of individual organisms into or out of a population, community, or biome – Immigration: movement of new individuals into a population – Emigration: departure of individuals from a population • Gene Flow: the movement of genes into or out of a population

2. Migration

3. Genetic Drift • Genetic Drift: a shift in allele frequencies in a population due to random events or chance – In small populations, chance can significantly affect allele frequencies from one generation to the next.

Genetic Drift • When the beetles reproduced, by chance there was a different gene frequency due to meiosis and fertilization

4. Non-Random Mating • If animals chose their mates then certain traits would be selected for

5. Natural Selection • Natural selection is an ongoing process in nature, and is the single most significant factor disrupting genetic equilibrium.

Formation of Species

Speciation • Disruption of genetic equilibrium leads to changes in the gene pool of a population. • Natural selection causes the most significant genetic changes in a population, however, such changes do not necessarily lead to speciation. • Speciation: the formation of a new species

Isolated Populations • For a new species to arise, interbreeding of the population of fertile offspring must cease among members of a formerly successful breeding population. – Populations or segments of populations must somehow become isolated. • Two Forms of Isolation: – Geographic Isolation – Reproductive Isolation

Geographic Isolation • Geographic Isolation: the physical separation of populations – Examples: population becomes divided by land or water barrier, colonization of new island, river changes course, highway built across field, etc.

Reproductive Isolation • Reproductive Isolation: inability of formerly interbreeding organisms to produce offspring – Prefertilization – Post-fertilization

Rates of Speciation • Punctuated Equilibrium: speciation may occur during brief periods of rapid genetic change • Gradualism: speciation may occur through a gradual change of adaptations • These are not mutually exclusive

Extinction Happens Extinct: the state of a species that no longer exists For a species to continue to exist, some members must have traits that allow them to survive and pass their genes on to the next generation.