Related Experiment Video

Updated: Aug 7, 2026

Methodology for Developing Life Tables for Sessile Insects in the Field Using the Whitefly, Bemisia tabaci, in Cotton As a Model System
09:23

Methodology for Developing Life Tables for Sessile Insects in the Field Using the Whitefly, Bemisia tabaci, in Cotton As a Model System

Published on: November 1, 2017

Inverse density dependence and the Allee effect

Courchamp, Clutton-Brock, Grenfell

    Trends in Ecology & Evolution
    |September 11, 1999
    PubMed

    More Related Videos

    Development of New Methods for Quantifying Fish Density Using Underwater Stereo-video Tools09:32

    Development of New Methods for Quantifying Fish Density Using Underwater Stereo-video Tools

    Published on: November 20, 2017

    Modeling the Size Spectrum for Macroinvertebrates and Fishes in Stream Ecosystems07:41

    Modeling the Size Spectrum for Macroinvertebrates and Fishes in Stream Ecosystems

    Published on: July 30, 2019

    Related Concept Videos

    Distribution and Dispersion00:54

    Distribution and Dispersion

    Ecology is the study of how organisms interact with their environment and with one another. An important aspect of ecology is understanding where species are found and how individuals are distributed within those areas. The geographic range of a species refers to the total area where its members are located, while dispersion describes the pattern of spacing of individuals within that range.Geographic Range and Dispersion PatternsWithin a species’ geographic range, individuals may be distributed...
    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...
    Hardy-Weinberg Principle01:49

    Hardy-Weinberg Principle

    Diploid organisms have two alleles of each gene, one from each parent, in their somatic cells. Therefore, each individual contributes two alleles to the gene pool of the population. The gene pool of a population is the sum of every allele of all genes within that population and has some degree of variation. Genetic variation is typically expressed as a relative frequency, which is the percentage of the total population that has a given allele, genotype or phenotype.In the early 20th century,...
    Mutation, Gene Flow, and Genetic Drift01:09

    Mutation, Gene Flow, and Genetic Drift

    In a population that is not at Hardy-Weinberg equilibrium, the frequency of alleles changes over time. Therefore, any deviations from the five conditions of Hardy-Weinberg equilibrium can alter the genetic variation of a given population. Conditions that change the genetic variability of a population include mutations, natural selection, non-random mating, gene flow, and genetic drift (small population size).Mechanisms of Genetic VariationThe original sources of genetic variation are mutations,...
    Genetic Drift03:33

    Genetic Drift

    Natural selection—probably the most well-known evolutionary mechanism—increases the prevalence of traits that enhance survival and reproduction. However, evolution does not merely propagate favorable traits, nor does it always benefit populations.Life is not fair. A deer grazing contentedly in a field can have her meal cut tragically short by a bolt of lightning. If the doomed doe is one of only three in the population, 1/3 of the population’s gene pool is lost. Random events like this can...
    Density00:56

    Density

    Density is an important characteristic of substances, crucial in determining whether an object sinks or floats in a fluid. Its SI unit is kg/m3, and its cgs unit is g/cm3. The density of an object helps in identifying its composition, and also reveals information about the phase of the matter and its substructure. The densities of liquids and solids are roughly comparable, consistent with the fact that their atoms are in close contact. However, gases have much lower densities than liquids and...