Biological and Ecological Concepts of Speciation and Population Variation

Distinctiveness

Different species living in the same area look and act differently.

Connection

Populations of the same species can look different in different locations but are still connected genetically.

Geographic Variation

Differences in physical traits among populations of the same species living in different locations.

Why Geographic Variation Happens

Different environments → different selective pressures.

Ring Species

A series of neighboring populations that can interbreed with close neighbors, but the populations at the ends of the ring cannot interbreed.

Importance of Ring Species

Shows how gradual change can lead to speciation.

Gene Flow

The exchange of genes between populations through mating.

Importance of Gene Flow

Maintains species unity and reduces differences between populations.

Biological Species Concept

Defines species as populations that can interbreed and produce viable, fertile offspring.

Reproductive Isolating Mechanisms

Biological barriers that prevent species from mating successfully.

Prezygotic Isolating Mechanisms

Prevent mating or fertilization from occurring.

Ecological Isolation

Species live in the same area but use different habitats or niches.

Behavioral Isolation

Differences in mating behaviors prevent mating.

Temporal Isolation

Species breed at different times (day, season, or year).

Mechanical Isolation

Physical incompatibility prevents mating.

Postzygotic Isolating Mechanisms

Problems occur after fertilization.

Hybrid Inviability

Fertilized egg fails to develop properly.

Hybrid Weakness

Hybrid survives but is weak or unhealthy.

Hybrid Sterility

Hybrid survives but cannot reproduce.

Criticisms of the Biological Species Concept

Does not explain all cases of species boundaries.

Ecological Species Concept

Species are defined by their ecological role, not just reproduction.

Stabilizing Selection

Selection favors the average phenotype.

Adaptation Leading to Speciation

Accumulated adaptations can create reproductive isolation.

Allopatric Speciation

Speciation due to geographic separation.

Sympatric Speciation

Speciation occurs without physical separation.

Disruptive Selection

Selection favors extreme phenotypes, not intermediates.

Adaptive Radiation

Rapid evolution of many species from a single ancestor.

Gradualism

Slow accumulation of small changes over time.

Punctuated Equilibrium

Long periods of little change (stasis) followed by rapid bursts of evolution.

Mass Extinctions

Large-scale extinction events.

Geographic Variation example

Beach rattlesnakes are light; forest rattlesnakes are dark.

ring species example

Salamanders around a mountain range. (Gradual geographic variation accumulates around a barrier.)

Biological Species Concept example

Horses can breed with horses but not donkeys. (Sexual reproduction and reproductive isolation define species.)

Ecological Isolation (example)

One species lives in trees; another lives on the ground. (Niches do not overlap.)

Behavioral Isolation example

Frogs with different mating calls.

Species rely on specific signals to choose mates.

temporal isolation example

One species breeds in spring, another in fall.

Timing of reproduction differs.

Mechanical Isolation

Ducks with incompatible reproductive structures.

Male and female anatomy does not fit.

Hybrid Inviability example

Embryo dies early.

Genes from different species don't work together.

Hybrid Weakness (example)

Development is incomplete or inefficient. genetic issues

Adaptation Leading to Speciation Example

Lizards with different dewlap colors

Color works in one habitat but not another

Leads to mating isolation

Ecological Species Concept

Orca populations

Some eat fish

Others eat marine mammals

Different behaviors = different species under this concept

sympatric speciation example

Moths with different color patterns

Live in same area but don't interbreed due to Different niches