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Related Concept Videos

Types of Selection01:46

Types of Selection

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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...
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What is Natural Selection?01:32

What is Natural Selection?

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Natural selection is an evolutionary process in which individuals with survival-promoting traits reproduce at higher rates. These favorable traits become more common within a population or species. Naturally selected traits initially arise via random genetic mutations. In order for selection to occur, there must be variation within a population, the trait controlling the variation must be heritable, and there must be an evolutionary advantage for variation in the trait.
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Limits to Natural Selection01:38

Limits to Natural Selection

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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.
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Frequency-dependent Selection01:21

Frequency-dependent Selection

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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.
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Mate Choice01:20

Mate Choice

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Mate choice—the decision about whom to mate with—is a type of natural selection, since animals must reproduce to pass down their genes. Mate choice is also called intersexual selection because the behavior occurs between the sexes.
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Inclusive Fitness00:57

Inclusive Fitness

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Most altruistic behavior—in which one animal helps another at a cost to themselves—occurs between relatives. Scientists think these altruistic behaviors evolved because they increase the inclusive fitness of the animal providing help.
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Field-Based Thermal Physiology Assay: Cold Shock Recovery under Ambient Conditions
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Natural selection: Fair weather cooperators.

Andrew G Zink1, Bruce E Lyon2

  • 1Department of Biology, San Francisco State University, San Francisco, CA 94132, USA.

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|November 8, 2022
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Summary
This summary is machine-generated.

Greater Ani birds show flexible group size selection based on environmental conditions. In wet years, larger groups offer predator protection, while in dry years, smaller groups reduce nestling mortality.

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Area of Science:

  • Behavioral Ecology
  • Avian Biology
  • Population Dynamics

Background:

  • Group living is a common strategy in the animal kingdom, offering benefits like predator defense and foraging efficiency.
  • However, group living can also incur costs, such as increased competition for resources and higher disease transmission rates.
  • The Greater Ani (Crotophaga major) is a cooperative breeding bird known for its complex social structure and variable group sizes.

Purpose of the Study:

  • To investigate the long-term effects of environmental variability on the selection pressures acting on group size in Greater Ani populations.
  • To determine how fluctuating resource availability and predation risk influence the optimal group size for this species.

Main Methods:

  • Long-term observational study of Greater Ani populations over multiple years, encompassing both wet and dry climatic conditions.
  • Monitoring of group size, nesting success, nestling mortality, and predator encounters.
  • Analysis of environmental data, including rainfall patterns and food availability, in relation to reproductive outcomes.

Main Results:

  • A significant correlation was found between environmental conditions (wet vs. dry years) and selection for group size.
  • In wet years with high food abundance, larger groups exhibited reduced nestling predation, favoring larger social structures.
  • Conversely, in dry years characterized by resource scarcity, larger groups experienced higher nestling mortality, indicating a selective pressure against large group sizes.

Conclusions:

  • Group size selection in Greater Ani is not static but dynamically fluctuates in response to environmental conditions.
  • The optimal group size is a trade-off between predator defense benefits in resource-rich periods and reduced competition/mortality in resource-poor periods.
  • This study highlights the adaptive plasticity of social behavior in response to environmental variability.