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Related Concept Videos

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.
Habitat Fragmentation02:31

Habitat Fragmentation

Habitat fragmentation describes the division of a more extensive, continuous habitat into smaller, discontinuous areas. Human activities such as land conversion, as well as slower geological processes leading to changes in the physical environment, are the two leading causes of habitat fragmentation. The fragmentation process typically follows the same steps: perforation, dissection, fragmentation, shrinkage, and attrition.
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.
Threats to Biodiversity01:50

Threats to Biodiversity

There have been five major extinction events throughout geological history, resulting in the elimination of biodiversity, followed by a rebound of species that adapted to the new conditions. In the current geological epoch, the Holocene, there is a sixth extinction event in progress. This mass extinction has been attributed to human activities and is thus provisionally called the Anthropocene. In 2019 the human population reached 7.7 billion people and is projected to comprise 10 billion by...
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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.
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...

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JenaTron - An Experimental Approach to Study the Effects of Plant History and Soil History on Grassland Ecosystem Functioning
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Comment on "Conspecific negative density dependence and forest diversity".

Ian A Dickie1, Jennifer M Hurst, Peter J Bellingham

  • 1Landcare Research, Lincoln, 7640 New Zealand. dickiei@landcareresearch.co.nz

Science (New York, N.Y.)
|November 1, 2012
PubMed
Summary

The study challenges the claim that negative density dependence universally drives forest diversity. Researchers found that excluding joint absences created a statistical bias, invalidating previous conclusions about rare tree species.

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Area of Science:

  • Ecology
  • Forestry
  • Biodiversity Science

Background:

  • Conspecific negative density dependence is proposed as a key factor influencing forest tree diversity.
  • This mechanism is particularly highlighted as important for the survival of rare tree species.

Purpose of the Study:

  • To re-evaluate the findings of Johnson and colleagues regarding conspecific negative density dependence.
  • To identify potential biases in the statistical methods used in prior research on forest diversity.

Main Methods:

  • Statistical analysis of forest diversity data.
  • Investigating the impact of excluding joint absences on density dependence models.
  • Re-analyzing data previously interpreted by Johnson et al.

Main Results:

  • The pervasive influence of conspecific negative density dependence on forest diversity is questioned.
  • A significant statistical bias was identified in the original analysis, stemming from the exclusion of joint absences.
  • The exclusion of joint absences led to an overestimation of density dependence effects, particularly for rare species.

Conclusions:

  • The claim that conspecific negative density dependence universally drives forest diversity, especially for rare species, is not supported by this analysis.
  • Statistical methodology, specifically the handling of joint absences, is critical for accurate ecological inference in diversity studies.