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Measures of species biodiversity, such as richness (i.e., the number of species present) and evenness (i.e., their relative abundance), describe an ecological community’s structure. Many factors affect community structure, including abiotic factors (e.g., sunlight and nutrients), disturbances (e.g., fire or flood), species interactions (e.g., predation or competition), and chance events (e.g., foreign species invasion). Certain species—such as keystone species—also play a...
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An ecological disturbance is a temporary disruption in the environment resulting from abiotic, biotic, or anthropogenic factors, causing a pronounced change in an ecosystem. The impact of an ecological disturbance, which can depend on its intensity, frequency, and spatial distribution, plays a significant role in shaping the species diversity within the ecosystem.
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Omnivore density affects community structure through multiple trophic cascades.

Donald J Benkendorf1,2,3,4, Howard H Whiteman5,6,7

  • 1Watershed Studies Institute, Murray State University, Murray, KY, 42071, USA. donald.benkendorf@aggiemail.usu.edu.

Oecologia
|January 4, 2021
PubMed
Summary
This summary is machine-generated.

Omnivores like speckled dace can dampen trophic cascades by feeding at multiple levels. Their density, not size, influenced community structure and ecosystem function in this mesocosm study.

Keywords:
DensityOmnivoreSize structureTop-down controlTrophic cascade

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Area of Science:

  • Ecology
  • Aquatic Ecology
  • Food Web Dynamics

Background:

  • Omnivores play a key role in regulating ecological communities by interacting at multiple trophic levels.
  • Intraspecific variation in omnivore traits can influence their ecological impact, but this is understudied.
  • Trophic cascades, the effects of predators on lower trophic levels, can be modulated by omnivore behavior.

Purpose of the Study:

  • To investigate how intraspecific variation (size and size structure) of omnivorous speckled dace affects their top-down control on invertebrate and algal communities.
  • To determine how omnivore density influences these effects and scales with community structure.
  • To understand the distinct trophic pathways (benthic and pelagic) through which omnivores impact ecosystem function.

Main Methods:

  • A mesocosm experiment was conducted manipulating speckled dace (Rhinichthys osculus) density and size structure.
  • Changes in invertebrate biomass, algal biomass, and insect emergence were monitored.
  • Trophic pathways and density-mediated indirect effects were analyzed.

Main Results:

  • Omnivores influenced both benthic and pelagic pathways, reducing macroinvertebrate biomass and increasing algal biomass.
  • Dace reduced pelagic predatory macroinvertebrates, leading to increased insect emergence, with a non-linear response to dace density.
  • Omnivore size and size structure did not significantly affect community structure, suggesting similar functional roles across sizes.

Conclusions:

  • The degree to which omnivores dampen trophic cascades is linked to their impact across multiple trophic levels.
  • Omnivore density and dietary shifts (e.g., from primary to secondary consumption) are critical factors in mediating community structure and trophic cascades.
  • Speckled dace's omnivory can dampen trophic cascades, but this effect is modulated by their density and resource availability.