Natural Selection Notes

Natural Selection

Darwin's Voyage

• Charles Darwin's voyage included stops at various locations including:
  • Packic Ocean
  • North Africa
  • Galapagos Islands
  • South America
  • Great Britain
  • Cape Horn
  • Tierra del Fuego
  • Cape of Good Hope
  • Australia
  • Teamania
  • New Zealand

Galapagos Tortoises: Adaptation

• Tortoise adaptations vary based on their island's vegetation:
  • Long neck, curved shell: Allows reaching sparse vegetation.
  • Intermediate shell: Between the other two forms.
  • Dome-shaped shell and shorter neck: Suited for abundant, ground-level vegetation.

Species Vary Locally: Galapagos Finches

• Finches on the Galapagos Islands demonstrate beak variation from a common ancestor, adapted to different islands.

Species Vary Locally: Galapagos Finches - Beak Variations

• Vegetarian tree finch:
  • Main food: Fruits
  • Feeding adaptation: Parrot-like beak
  • Habitat: Trees
• Insectivorous tree finch:
  • Main food: Insects
  • Feeding adaptation: Grasping beak
  • Habitat: Trees
• Woodpecker finch:
  • Main food: Insects
  • Feeding adaptation: Uses cactus spines
  • Habitat: Trees
• Cactus ground finch:
  • Main food: Cacti
  • Feeding adaptation: Pointed crushing beak
  • Habitat: Ground
• Sharp-beaked ground finch:
  • Main food: Seeds
  • Feeding adaptation: Large crushing beak
  • Habitat: Ground
• Large ground finch:
  • Main food: Seeds
  • Feeding adaptation: Large crushing beak
  • Habitat: Ground

Descent with Modification

• Descent with Modification: Darwin's term for evolution.
• Living things descended from preexisting species.
• Species change over time.

Darwin’s Travels: Revealing Diversity

• Darwin's travels revealed a far greater diversity of living species than previously known.
• Observations led to the theory of Natural Selection.

Adaptive Radiation in Galapagos Finches

• Adaptive radiation is evident in Galapagos finches, including:
  • Medium tree finch (Camarhynchus pauper) eating buds and fruits.
  • Small tree finch (Camarhynchus parvulus) eating buds and fruits.
  • Large tree finch (Camarhynchus psittacula) eating buds and fruits.
  • Mangrove finch (Camarhynchus heliobates) eating buds and fruits.
  • Vegetarian finch (Camarhynchus crassirostris) eating buds and fruits.
  • Cactus ground finch (Geospiza scandens) eating cactus parts.
  • Large cactus finch (Geospiza conirostris) eating seeds and cactus parts.
  • Sharp-beaked ground finch (Geospiza difficilis) mainly eating seeds.
  • Large ground finch (Geospiza magnirostris) mainly eating seeds.
  • Woodpecker finch (Camarhynchus pallidus) mainly eating insects.
  • Warbler finch (Certhidea olivacea) mainly eating insects.
  • Cocos Island finch (Pinaroloxias inornata) mainly eating insects.
  • Small ground finch (Geospiza fuliginosa).
  • Medium ground finch (Geospiza fortis).
  • The ancestral finch was a seed-eating finch.

Natural Selection: Traits for Survival

• Traits that help an organism survive in a particular environment are "selected" in natural selection.

The Peppered Moth Story

• Before Industrial Revolution:
  • Light-colored peppered moths were dominant.
  • Moths rested on light-colored tree bark covered in lichens.
  • Light coloring provided camouflage from predatory birds.
  • Dark-colored moths were rare and easily spotted by predators.

Industrial Revolution’s Impact

• Factories released soot and pollution.
• Tree bark darkened as pollution killed lichens.
• Light-colored moths became visible to predators.
• Dark-colored moths had better survival rates.
• The moth population shifted to predominantly dark moths.

Modern Evidence of Natural Selection

• As air quality improved, light-colored moths increased again.
• This shows natural selection is ongoing and reversible.
• Key evidence supporting Darwin's theory:
  • Environmental change leads to selective pressure.
  • Survival depends on advantageous traits.
  • Population characteristics can change over time.

Natural Selection in a Nutshell

• There is variation in a beetle population some are green, and some are brown.
• Predators prefer to eat the green beetles.
• The green beetles are selected against, and the brown beetles have flourished.

Natural Selection: Mechanism for Evolution

1. Overproduction: More offspring are produced than the environment can support.
2. Genetic variation: Individuals within a population have different phenotypes. These variations can be inherited.
3. Struggle to survive: Organisms face a struggle to survive.
   • Some variations improve an individual's chances of survival.
   • A trait that makes an individual successful in its environment is an adaptation.
4. Differential Survival and Reproduction: Individuals with the best variations survive and reproduce.
   • Populations may begin to differ as they become adapted to the environment.

Key components of Natural Selection

• Variation: There is natural variation in the characteristics of individuals that are part of a population.
• Overproduction: Ecosystems are unable to support all individuals within a population to an age of reproduction, causing competition among offspring.
• Selection: The more adapted individuals within a population are more likely to survive, while those who have less adapted characteristics are less likely to.
• Reproduction: The better-adapted individuals survive to reproduce and pass on their characteristics. Over time the population will see a shift to a higher proportion of adapted individuals.