Speciation (Macroevolution)

Speciation

The formation of new and distinct species in the course of evolution.

Macroevolution

Refers to broad patterns of evolutionary change above the species level.

Biological Species Concept

A species is one or more populations of individuals that are interbreeding under natural conditions and producing fertile offspring, and are reproductively isolated from other such populations.

Ecological Species Concept

Species that share the same ecological niche.

Phylogenetic Species Concept

Species that share a common ancestor.

Morphological Species Concept

Species that have similar body shape/form.

Limitations of the Biological Concept

Cannot be applied to fossils or asexual organisms (prokaryotes) and emphasizes no gene flow.

Gene Flow

The mixing of genes that can occur between distinct species.

Genetic Divergence

The gradual accumulation of differences in the gene pools of genetically separate populations.

Natural Selection

A process that can contribute to genetic divergence.

Genetic Drift

A process that can contribute to genetic divergence.

Mutations

Changes in DNA that can contribute to genetic divergence.

Reproductive Isolating Mechanisms

Any heritable feature of body, form, functioning, or behavior that prevents breeding between one or more genetically divergent populations.

Prezygotic Barriers

Obstacles that prevent mating or fertilization of eggs if mating occurs.

Postzygotic Isolation

Isolating mechanisms that take effect after fertilization.

Reduced Hybrid Viability

Hybrids that don't survive.

Reduced Hybrid Fertility

Hybrids that are sterile.

Hybrid Breakdown

Hybrids that are not sterile but future generations are not viable.

Geographic Isolation

Physical barriers that prevent mating.

Ecological Isolation

Different habitats in the same region.

Temporal Isolation

Populations that are fertile at different times.

Behavioral Isolation

Organisms that don't recognize/react to each other or the mating rituals.

Mechanical Isolation

Morphological (form) differences that prevent mating.

Gamete Isolation

Sperm and egg do not chemically recognize each other.

Postzygotic barriers

Barriers that occur after fertilization, affecting hybrid offspring.

Habitat isolation

Species live in different habitats and do not meet.

Gametic isolation

Sperm and egg of different species are incompatible.

Hybrid fertility

Hybrids are viable but sterile.

Hybrid viability

Hybrids fail to develop properly and die before reaching maturity.

Allopatric speciation

Speciation that occurs due to geographic separation.

Sympatric speciation

Speciation that occurs without geographic isolation.

Gradualism

The theory that evolution occurs slowly and steadily over time.

Punctuated equilibrium

The theory that evolution occurs in rapid bursts followed by long periods of stability.

Cladogenesis

A pattern of speciation where a lineage splits, resulting in genetic isolation.

Anagenesis

A pattern of evolution where changes accumulate in a single lineage.

Divergent evolution

When two related species evolve to be less similar.

Convergent evolution

When unrelated species develop similar traits due to similar environmental pressures.

Parallel evolution

When two related species evolve similarly while separated geographically.

Coevolution

The process where two or more species influence each other's evolution.

Adaptive radiation

Rapid speciation where new species fill available niches after a mass extinction.

Background extinctions

Normal, ongoing extinctions due to changing local conditions.

Mass extinction

A global event resulting in the die-off of a large number of species.

Permian-Triassic Extinction

The largest extinction event in Earth's history, with 96% of marine species and 70% of terrestrial species becoming extinct.

Cretaceous (K-T) Extinction

An extinction event approximately 65 million years ago that resulted in the extinction of 75% of plant and animal species, including dinosaurs.