5.12 Speciation

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What is a species?

• A species is a group of organisms that can interbreed and produce fertile offspring under natural conditions.

• Members of the same species share similar physical characteristics, genetic traits, and behaviors.

• Species definition can be complex, considering reproductive isolation, genetic differences, and ecological roles.

Types of Selection

• In evolutionary biology, directional, stabilizing, and disruptive selection are key mechanisms that influence how populations evolve.

• These types of natural selection favor different traits within a population, which can lead to significant genetic changes over time.

• When these changes become pronounced enough, and when combined with factors like geographic isolation or environmental shifts, they can result in speciation—the formation of new and distinct species.

Stabilizing Selection

• Stabilizing selection favors individuals with average traits and selects against extremes, reducing genetic diversity.

• It occurs when stable environmental conditions make average traits more advantageous for survival and reproduction.

Directional Selection

• Directional selection favors one extreme of a trait, shifting its frequency in the population.

• This occurs when an environmental change or new selective pressure makes one extreme more advantageous, leading to a change in the population's traits over time.

Disruptive Selection

• Disruptive selection favors individuals at both extremes of a trait, rather than those with intermediate traits.

• It promotes two distinct phenotypes, increasing diversity, especially when an environment offers different resources.

• Over time, it can lead to new species if the extremes become reproductively isolated.

Match

Match the following

• Giraffes with a medium-length neck perish, and those with short and long necks survive.

• Giraffes with long necks survive, while all others perish.

• Giraffes with medium-length necks survive, while the rest perish.

disruptive selection

directional selection

stabilizing selection

• disruptive selection

• directional selection

• stabilizing selection

Speciation

• Speciation is the process by which new species arise from a common ancestor, often due to factors like geographic isolation, environmental changes, or behavioral differences.

• Over time, populations accumulate genetic differences, leading to reproductive isolation and the formation of distinct species.

• Speciation occurs through allopatric or sympatric mechanisms.

Types of Speciation

Sympatric speciation occurs when a new species develops without physical barriers, due to factors like behavioral differences, ecological niches, or genetic mutations that cause reproductive isolation within the population.

Allopatric speciation occurs when a species separates into two separate groups that are geographically isolated from each other. A physical barrier, such as a mountain, river, or glacier, can isolate two groups of the same species.

Multiple Select

Allopatric speciation occurs when a species separates into two separate groups that are geographically isolated from each other.

Which of the following are examples of allopatric speciation? SELECT TWO

• squirrel species getting separated by the Grand Canyon

• birds on nearby islands having different beaks due to different food sources on the islands

• goldendoodle dogs being bred from poodles and golden retrievers

• humans planting specific crop varieties that have higher yields

Adaptive Radiation

Adaptive radiation is the rapid evolution of an ancestral species into various forms, each suited to different ecological niches.

Example: Darwin's finches, where one species evolved into multiple with different beak shapes, each adapted to specific food sources.

Multiple Choice

Adaptive radiation is the rapid evolution of an ancestral species into various forms, each suited to different ecological niches.

How does adaptive radiation influence ecological niches?

• Adaptive radiation determines an organism‘s niche.

• Adaptive radiation leads to coevolution, thereby influencing the organism‘s niche.

• Adaptive radiation leads to a wide variety of ecological niches.

• Adaptive radiation causes ecological niches among organisms to be similar.

Divergent Evolution

Divergent evolution occurs when related species become more different over time due to environmental pressures, leading to distinct traits despite a common ancestor.

Example: The African and Asian elephants, which share a common ancestor but have diverged due to environmental differences.

Convergent Evolution

Convergent evolution occurs when unrelated species develop similar traits due to similar environmental pressures.

Example: Dolphins and sharks both have streamlined bodies, despite being mammals and fish, respectively.

Multiple Choice

A population of squirrels is split by a large river, with one group living in a forested area on one side and the other living in a mountainous region on the opposite side. Over time, the forest squirrels develop smaller, more agile bodies suited for climbing trees, while the mountain squirrels develop larger bodies and thicker fur to survive the colder, harsher conditions.

Which of the following is explains the differences that developed in the two squirrel populations?

• Adaptive Radiation

• Convergent Evolution

• Divergent Evolution

Multiple Choice

A group of finches from a single species colonizes several islands with different types of environments—some with large seeds, some with small seeds, and others with a variety of insect populations.

Over time, the finches on each island develop different beak shapes and sizes suited to their specific food sources. Some finches develop large, strong beaks for cracking large seeds, while others develop smaller, sharper beaks for eating insects.

Which of the following is responsible for these changes?

• Adaptive Radiation

• Convergent Evolution

• Divergent Evolution

Multiple Choice

The sugar glider (a marsupial from Australia) and the flying squirrel (a placental mammal from North America) both have developed gliding membranes that allow them to glide from tree to tree in their respective forest environments. Despite being from different continents and belonging to different mammalian groups, both animals have evolved similar adaptations to navigate through the trees.

Which of the following best explains these similarities in the two different species?

• Adaptive Radiation

• Convergent Evolution

• Divergent Evolution

Poll

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