Origins of Species and Macroevolution

Macroevolution

Occurs at or above the species level.

Speciation

The process of species formation.

Species

A group of organisms that maintains a distinctive set of attributes in nature.

Currently identified species on Earth

About 2 million species.

Estimated total species on Earth

Ranges from 5 to 50 million.

Subspecies

Groups of the same species with some differences, but not enough to be called separate species.

Ecotypes

Genetically distinct bacterial populations adapted to local environments.

Morphological Species Concept

Individuals of a species share measurable traits that distinguish them from other species.

Biological Species Concept

A species is a group of interbreeding individuals reproductively isolated from other such groups.

Prezygotic Isolating Mechanisms

Prevent breeding before zygote formation.

Postzygotic Isolating Mechanisms

Prevent the development of viable, fertile individuals after fertilization.

Allopatric Speciation

Occurs when some members of a species become geographically separated.

Sympatric Speciation

Occurs when members of a species within the same range diverge into two or more species.

Gradualism

Species evolve continuously over long time spans.

Punctuated Equilibrium

Species remain in equilibrium for long periods, with sporadic bursts of rapid changes.

Heterochrony

Evolutionary changes in the rate or timing of developmental events.

Adaptive Radiation

A single species evolves into a range of descendants that differ greatly in habitat, form, or behavior.

Hybrid Inviability

Species hybrids do not survive.

Hybrid Sterility

Species hybrids cannot produce functional gametes.

Hybrid Breakdown

Reduced fitness in the F2 generation (offspring of hybrid).

Reproductive Isolation

Prevents gene pools from mixing.

Ecological Isolation

Geographic barriers prevent contact.

Temporal Isolation

Species reproduce at different times of day or year.

Behavioral Isolation

Differences in mating signals or sexual selection.

Mechanical Isolation

Incompatible reproductive structures.

Gametic Isolation

Incompatible gametes prevent fertilization.

Sexual Selection

Mate choice influences reproductive isolation.

Panthera leo

Example of Linnaeus’ classification system (Panthera = Genus, Leo = Specific epithet).

Molecular Traits

DNA sequences used to identify similarities and differences in species.

Ecological Factors

Habitat-related factors that can distinguish species, especially in bacteria.

Evolutionary Relationships

Based on phylogenies derived from fossil records or DNA sequences.

Interspecies Hybrid

Offspring from two different species, usually with reduced fitness.

Species Cluster

A group of closely related species.