7.10 - Speciation

What is a Species?

• Biological Species Concept: A species is a population whose members can interbreed and produce viable, fertile offspring.

• Reproductive Isolation: The formation of a new species depends on barriers that prevent interbreeding.

Types of Reproductive Isolation

1. Prezygotic Barriers: Occur before fertilization.

   • Examples: Different mating seasons, mating calls, or behaviors (e.g., bird songs).

2. Postzygotic Barriers: Occur after fertilization.

   • Examples: Hybrid offspring (e.g., mules) are sterile and cannot produce viable offspring.

How Speciation Occurs

1. Allopatric Speciation ("other country"):

   • Definition: A population is isolated from other populations due to physical or geographical barriers.

   • Process:

     • Original Population -> Geographic Barrier -> Reproductive Isolation -> Speciation

   • Example: A mountain range or river separates a population, leading to the development of distinct species.

2. Sympatric Speciation ("same country"):

   • Definition: Populations remain in the same physical area but become reproductively isolated due to other mechanisms.

   • Process:

     • Original Population -> Reproductive Isolation -> Speciation

   • Example: Differences in mating preferences or ecological niches within the same area. 

Speciation Rates

1. Gradualism:

   • Definition: Gradual divergence over long periods. Big changes occur as the accumulation of many small ones.

2. Punctuated Equilibrium:

   • Definition: Rapid bursts of change followed by long periods of little or no change.

Ongoing Evolution

• Pesticide Resistance: Similar to antibiotic resistance, species continue to evolve in response to environmental pressures.

Types of Evolution

1. Divergent Evolution:

   • Definition: Groups with the same common ancestor evolve and accumulate differences, resulting in the formation of new species.

   • Example: Darwin’s finches, which evolved different beak shapes based on their food sources.

2. Convergent Evolution:

   • Definition: Different species develop similar traits despite having different ancestors.

   • Example: The wings of bats and birds, which serve the same function but have different structural origins.

   • Analogous Structures: Traits that have similar functions but different evolutionary origins.