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Related Concept Videos

Limits to Natural Selection01:38

Limits to Natural Selection

Organisms that are well-adapted to their environment are more likely to survive and reproduce. However, natural selection does not lead to perfectly adapted organisms. Several factors constrain natural selection.For one, natural selection can only act upon existing genetic variation. Hypothetically, redtusks may enhance elephant survival by deterring ivory-seeking poachers. However, if there are no gene variants—or alleles—for redtusks, natural selection cannot increase the prevalence of...
Types of Selection01:46

Types of Selection

Natural selection influences the frequencies of particular alleles and phenotypes within populations in several different ways. Primarily, natural selection can be directional, stabilizing, or disruptive. Directional selection favors one extreme trait and shifts the population towards that phenotype while selecting against individuals displaying alternate traits. Stabilizing selection favors an intermediate trait with a narrow range of variation. Deviation from the optimal phenotype towards an...
Frequency-dependent Selection01:21

Frequency-dependent Selection

When the fitness of a trait is influenced by how common it is (i.e., its frequency) relative to different traits within a population, this is referred to as frequency-dependent selection. Frequency-dependent selection may occur between species or within a single species. This type of selection can either be positive—with more common phenotypes having higher fitness—or negative, with rarer phenotypes conferring increased fitness.Positive Frequency-Dependent SelectionIn positive...
Conservation of Small Populations02:04

Conservation of Small Populations

Small population sizes put a species at extreme risk of extinction due to a lack of variation, and a consequent decrease in adaptability. This weakens the chances of survival under pressures such as climate change, competition from other species, or new diseases. Large populations are more likely to survive pressures such as these, as such populations are more likely to harbor individuals that have genetic variants that are adaptive under new stresses. Small populations are much less likely to...
Speciation Rates01:07

Speciation Rates

Speciation can proceed at markedly different rates, and evolutionary biologists commonly describe these differences through the models of gradualism and punctuated equilibrium. Both patterns explain how new species arise, but they differ in the tempo and continuity of evolutionary change. In both cases, evolutionary change arises from heritable variation within populations, with natural selection often shaping traits that improve survival and reproduction under specific environmental conditions.
Conservation of Declining Populations02:07

Conservation of Declining Populations

Conservation of declining population focuses on ways of detecting, diagnosing, and halting a population decline. The approach uses methods to prevent populations from going extinct.

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Related Experiment Video

Updated: Jul 3, 2026

Resurrection of Dormant Daphnia magna: Protocol and Applications
07:37

Resurrection of Dormant Daphnia magna: Protocol and Applications

Published on: January 19, 2018

Reduced responses to selection after species range expansion.

Benoit Pujol1, John R Pannell

  • 1Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK.

Science (New York, N.Y.)
|July 5, 2008
PubMed
Summary

Species range expansion can decrease genetic diversity, hindering adaptation. This study shows plant populations that expanded into new areas have reduced adaptive potential compared to those in historical refugia.

Area of Science:

  • Evolutionary biology
  • Ecology
  • Genetics

Background:

  • Species range expansion is predicted to reduce genetic variation at range margins.
  • This reduction in genetic diversity may compromise the adaptive potential of marginal populations.
  • The adaptive consequences of range expansion have not been empirically tested.

Purpose of the Study:

  • To test the hypothesis that range expansion reduces adaptive potential.
  • To investigate the adaptive capacity of marginal populations of Mercurialis annua.

Main Methods:

  • Studied Mercurialis annua populations that expanded from North Africa into Spain and Portugal post-Pleistocene.
  • Compared the response to selection on a key life-history trait between marginal and refugium populations.

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Examination of Thymic Positive and Negative Selection by Flow Cytometry
14:29

Examination of Thymic Positive and Negative Selection by Flow Cytometry

Published on: October 8, 2012

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Last Updated: Jul 3, 2026

Resurrection of Dormant Daphnia magna: Protocol and Applications
07:37

Resurrection of Dormant Daphnia magna: Protocol and Applications

Published on: January 19, 2018

Demonstration of the Sequence Alignment to Predict Across Species Susceptibility Tool for Rapid Assessment of Protein Conservation
16:02

Demonstration of the Sequence Alignment to Predict Across Species Susceptibility Tool for Rapid Assessment of Protein Conservation

Published on: February 10, 2023

Examination of Thymic Positive and Negative Selection by Flow Cytometry
14:29

Examination of Thymic Positive and Negative Selection by Flow Cytometry

Published on: October 8, 2012

Main Results:

  • Populations of Mercurialis annua that expanded their range showed a reduced ability to respond to selection.
  • Marginal populations exhibited less adaptive potential compared to populations from the species' historical refugium.

Conclusions:

  • Provides direct evidence for a decline in adaptive potential following species range shifts.
  • Highlights the importance of genetic heterogeneity and spatial dynamics in predicting evolutionary responses to environmental change.