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Related Concept Videos

Competition02:34

Competition

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When organisms require the same limited resources within an environment, they may have to compete for them. Competition is a net-negative interaction. Even if two competing individuals or populations do not interact directly, the overall fitness of both competitors is lowered as a result of not having full access to the limited resource.
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Predator-Prey Interactions02:39

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Predators consume prey for energy. Predators that acquire prey and prey that avoid predation both increase their chances of survival and reproduction (i.e., fitness). Routine predator-prey interactions elicit mutual adaptations that improve predator offenses, such as claws, teeth, and speed, as well as prey defenses, including crypsis, aposematism, and mimicry. Thus, predator-prey interactions resemble an evolutionary arms race.
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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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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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Ecological Niches02:02

Ecological Niches

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All organisms have a position within an ecosystem. The complete set of living and nonliving factors—including food resources, climate, and terrain—that define the position of a given organism are collectively referred to as the organism’s ecological niche.
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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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Bottom-up and top-down pressures mediate competition between two generalist insects.

Elizabeth E Barnes1, Shannon M Murphy1

  • 1Department of Biological Sciences, University of Denver, Denver, Colorado, USA.

Ecology
|December 15, 2022
PubMed
Summary

Competition between generalist insects can be strong, even when they feed at different times. This study shows indirect competition between western tent caterpillars and fall webworms impacts insect fitness through leaf quality and natural enemies.

Keywords:
Hyphantria cuneaLepidopteraMalacosoma californicumPrunus virginianabottom-up pressuresdietary generalistsfall webwormindirect competitiontent caterpillartop-down pressures

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Area of Science:

  • Ecology
  • Insect Ecology
  • Community Ecology

Background:

  • Dietary generalist insects are often predicted to experience weaker competition due to broad host plant use.
  • However, indirect competition can be significant and difficult to avoid, even for generalists.
  • Competition among generalist insects, especially when temporally separated, is understudied.

Purpose of the Study:

  • To investigate indirect competitive interactions between two temporally separated generalist insects: western tent caterpillar (Malacosoma californicum) and fall webworm (Hyphantria cunea).
  • To assess the impact of these interactions on insect fitness through bottom-up (leaf quality) and top-down (natural enemies) effects.
  • To determine if competition is as strong in generalists as in specialists, challenging previous assumptions.

Main Methods:

  • Laboratory-rearing trials using chokecherry host plants with varying levels of prior damage from either insect species.
  • Measurement of key fitness parameters: development time, pupal mass, and survival.
  • Field trials assessing fall webworm fitness on previously damaged host plants, with and without predator exclusion.

Main Results:

  • Western tent caterpillars exhibited reduced pupal mass when reared on plants previously damaged by fall webworms (bottom-up effect).
  • Fall webworms showed reduced pupal mass and increased development time when reared on plants damaged by western tent caterpillars (bottom-up effect).
  • In field trials, fall webworms experienced lower survival and pupal mass on plants damaged by western tent caterpillars, indicating both bottom-up and top-down effects.

Conclusions:

  • Indirect competition occurs between temporally separated generalist insects, western tent caterpillars and fall webworms.
  • Competition impacts insect fitness via changes in host plant quality (bottom-up) and predator interactions (top-down).
  • These findings highlight the significant ecological consequences of indirect competition, even among species with broad dietary niches.