Biology Chapter: Adaptation and Species

Adaptation

• Adaptation: An evolutionary process where an organism becomes better suited to its habitat.
• It can be a trait advantageous to an individual or a population.

Limits of Natural Selection

• Natural selection isn't goal-oriented.
• It only acts on existing variations within a population.
• It's constrained by inherited traits from ancestors.
• Adaptations are also limited by the genetic makeup of individuals.
• Mutations create variations.

What is a Species?

• Species: A group of organisms that can interbreed and produce fertile offspring.
• Biological species concept: A group of natural populations whose members can interbreed to create fertile offspring, but cannot interbreed with other species.
• Reproductively isolated from other populations.

Defining "Species"

• Biological species concept: Defines species as groups that can interbreed and produce viable offspring.
• Hybridization: The process where different species interbreed.
• Hybrids are not always viable, meaning they cannot survive or reproduce, which makes them not considered a species.

One Species or Two?

• Scientists use biogeographical information, DNA similarities, and morphology (form and structure) to identify and distinguish species.

Speciation

• Speciation: The branching off of new species from existing ones.
• Evidence of speciation can be found in modern-day organisms.
• Evidence includes shared characteristics (homologous traits), DNA similarities and differences, vestigial traits, and patterns of embryo development.

Speciation Stages

• Speciation occurs in three stages:
• 1. Genetic isolation: Through natural selection, genetic divergence (differences in DNA), or mutations.
• 2. Genetic divergence: Accumulation of differences in DNA.
• 3. Secondary contact: Confirming speciation.

Genetic Isolation

• Geographic isolation: When a barrier prevents populations from interbreeding.
• Examples: Mountains, rivers, valleys, canyons.

Genetic Divergence

• Genetic divergence: The accumulation of differences in DNA sequences in different populations.
• It results in populations becoming increasingly genetically different.
• It happens via natural selection, mutations, and genetic drift.

Allopatric Speciation

• Allopatric speciation: The formation of new species from geographically isolated populations.
• A population gets separated and evolves in different environments.

Sympatric Speciation

• Sympatric speciation: The formation of new species in the absence of geographic isolation.
• Members of the same species start diverging in their behavioral traits, often leading to a reproductive barrier.

Reproductive Barriers

• Reproductive barriers isolate species in the same geographic area.
• Prezygotic barriers prevent the formation of a zygote.
• Postzygotic barriers operate after the zygote forms.

Coevolution

• Coevolution: When the interaction between two species significantly influences their survival, causing reciprocal adaptation.
• An adaptation in one species leads to a complementary adaptation in another species.

Recap - Examples

• Buff-tailed sicklebill hummingbirds' specifically shaped bill to match the flower shape it feeds on is an example of coevolution.
• Horses and donkeys being different species despite being able to have offspring (infertile mules) because viable offspring are needed for the species designation is an example.
• What is a Species?: A group of similar individuals who live in one geographic area and interbreed; producing fertile offspring is an example.
• What creates Reproductive Isolation: Mating rituals, rapid and severe changes in geographic features, and gamete incompatibility are examples.