Chapter 14 Speciation and Extinction Notes

Macroevolution leads to significant biological changes, including:
- Origins of new species
- Evolutionary trends
- Adaptive radiation
- Mass extinctions
Mechanisms of speciation are a key focus in macroevolution.
Speciation can be categorized into nonbranching and branching patterns.

In nonbranching evolution, a population evolves over generations and is recognized as a distinct species.

An ancestral species leads to one or more new species while the parent species may continue to exist.
This occurs through splitting an evolutionary lineage.

Mayr's expedition in New Guinea revealed significant bird diversity.
He formulated the Biological Species Concept (BSC):
- A species is defined as a population or group of populations with potential to interbreed and produce fertile offspring.

Reproductive barriers prevent interbreeding between species, divided into:
- Prezygotic barriers (prevent mating or fertilization)
- Postzygotic barriers (affect viability or fertility of hybrids)

Temporal isolation: Mating occurs in different seasons or times.
Habitat isolation: Populations live in different habitats and do not meet.
Behavioral isolation: Little to no sexual attraction between genders (e.g., Blue-footed Boobies courtship rituals).
Mechanical isolation: Structural differences prevent copulation (e.g., flower structures adapted to specific pollinators).
Gametic isolation: Failures in union of gametes during fertilization.

Three main modes of speciation are identified:
1. Allopatric speciation: Occurs when populations are geographically isolated.
2. Parapatric speciation: Takes place where populations have a shared border area.
3. Sympatric speciation: Occurs without geographic isolation.

Geographic isolation leads to genetic uniqueness in separate populations evolved by natural selection, genetic drift, or mutation.

Sympatric speciation occurs without geographic barriers; mechanisms like polyploidy (multiples of the normal chromosome number) contribute to this.
Example: Hugo de Vries noted polyploidy in evening primroses.

Definition: The evolution of many new species from a common ancestor exposed to diverse environments.
Example: Galapagos Island Finches with varied feeding habits and habitats.

Gradualist Model: New species evolve through gradual accumulation of changes over time.
Punctuated Equilibrium Model: Species evolve in bursts of rapid change interrupted by periods of stability, explaining the rarity of transitional fossils.

Evolutionary changes may span thousands of generations, leading to fewer transitional fossils due to limited fossil formation opportunities in small, isolated populations.

Microevolution: Small changes within a species, like color variation.
Macroevolution: Larger evolutionary changes, like the emergence of a new species.
- These processes are visible over time, counterparting micro and macro scales.

Not all species fit BSC, leading to concepts based on ancestry and evolutionary relationships, like:
- Evolutionary species concept
- Morphological species concept
- Ecological species concept
- Phylogenetic species concept

Example: Hybridization in plants during domestication leading to issues like chromosome number variations (e.g., bread wheat results from sympatric speciation events).

Humans have a unique mutation in MYH16 gene affecting jaw muscles, implying selective pressure favoring brain size over brawn, timed with similar fossil records of hominids with larger skulls.