Unit 1 - Evolution Week 2: Origins of Species

Vocabulary flashcards covering key terms, concepts, and examples from the lecture notes on species concepts, reproductive isolation, and speciation.

Biological Species Concept

Species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups.

Reproductive isolation

Barriers that prevent gene flow between species, either before or after fertilization.

Prezygotic isolating mechanisms

Barriers that prevent mating or fertilization before zygote forms.

Ecological isolation

Species occupy different habitats within the same area and rarely encounter each other.

Behavioral isolation

Differences in mating rituals or signals that prevent interbreeding.

Temporal isolation

Species reproduce in different seasons or times of the day.

Mechanical isolation

Structural differences between species prevent mating or fertilization.

Prevention of gamete fusion

Gametes from different species fail to attract or fuse effectively.

Postzygotic isolating mechanisms

Barriers that operate after fertilization, reducing hybrid viability or fertility.

Hybrid inviability or infertility

Hybrids do not develop properly or are sterile or have reduced fertility.

Allopatric speciation

Speciation caused by geographic separation, reducing gene flow and allowing divergence.

Sympatric speciation

Speciation without geographic separation, often via polyploidy or disruptive selection.

Polyploidy

Having more than two chromosome sets; a common rapid route to speciation, especially in plants.

Autopolyploidy

Chromosome sets originate from a single species; tetraploids arise and are usually infertile with diploids.

Allopolyploidy

Polyploidy from hybridization between two species; offspring have chromosome sets from both and are usually infertile unless chromosome doubling occurs.

Adaptive radiation

Rapid diversification of a lineage into multiple species to fill available ecological niches.

Key innovation

A new trait that allows a lineage to exploit previously inaccessible resources or habitats.

Character displacement

Evolution of differences between similar species in the same area to minimize competition.

Mass extinction

Event of extensive species loss; five major events documented; a sixth is ongoing due to human activity.

The Pace of Evolution

Tempo of evolutionary change; gradualism vs punctuated equilibrium, viewed as a continuum.

Gradualism

Slow, incremental accumulation of small changes over time.

Punctuated equilibrium

Long periods of little change punctuated by rapid evolutionary shifts.

Ecological species concept

Species are defined by adaptations to their environment; hybrids are eliminated; selection can limit gene flow.

Geographic variation

Differences among populations across different areas, often with intermediate forms linking distant populations.

Reinforcement

Natural selection strengthens reproductive barriers when hybrids have reduced fitness.

Genetic drift

Random changes in allele frequencies, especially in small populations, promoting isolation (founder effects, bottlenecks).

Founder effect

New population started by a small number of individuals, reducing genetic variation.

Population bottleneck

Sharp reduction in population size leading to loss of genetic diversity.

Disruptive selection

Selection that favors extreme phenotypes, potentially driving divergence and speciation in sympatry.

Sympatric speciation by disruptive selection

Speciation within a shared area driven by disruptive selection creating two distinct niches.

Lord Howe Island palm trees (example)

Example of sympatric speciation by disruptive selection where two palm species diverge on an island due to soil differences.

River barrier allopatric speciation

Geographic isolation by a river can split populations, leading to allopatric speciation when interbreeding ceases.

Adaptive radiations after mass extinctions

Rapid diversification of a lineage to fill vacant niches following mass extinctions.

Mass extinction (summary)

Periods of widespread extinction that dramatically reduce biodiversity; multiple events have occurred in history.