The Allee effect is a phenomenon in biology named after W. C. Allee, who first wrote extensively on it. It describes a positive relation between population density and the per capita growth rate. In other words, for smaller populations, the reproduction and survival of individuals decrease. This effect usually saturates or disappears as populations get larger. Biology is the branch of science dealing with the study of life. ... Warder Clyde Allee (June 5, 1885 - March 18, 1955) was an American zoologist and ecologist who taught animal ecology at the University of Chicago. ...
The effect may be due to any number of causes. In some species, reproduction—finding a mate in particular—may be increasingly difficult as the population density decreases. Other species may use strategies (such as schooling in fish) that are more effective for larger populations. School of juvenile herring - many fish have the opercula wide open for ram feeding and you can see the red gills The term swarm (schooling or swarming) is applied to fish, birds and insects and describes a behavior of an aggregation (school) of animals of similar size and body orientation... Atlantic herring, Clupea harengus: one of the most abundant species of fish in the world. ...
A distinction is made between a strong Allee effect, in which there is a population size or density called the critical size/density below which the population declines on average and above which it increases on average, and a weak Allee effect in which there is no critical density, though there is acceleration in population size at small densities.
References
What is the Allee Effect?. Stephens PA, Sutherland WJ & Freckleton RP (1999) Oikos 87, 185-190.. URL accessed on February 4, 2005.
Underpopulation (Allee) effects. Alan A. Berryman, Principles of Population Dynamics. URL accessed on February 4, 2005.
February 4 is the 35th day of the year in the Gregorian Calendar. ... 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ... February 4 is the 35th day of the year in the Gregorian Calendar. ... 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ...
Further reading
Animal Aggregations. A study in General Sociology., W. C. Allee, University of Chicago Press
In its simplest form, the demographic effects of environmental perturbations are assumed to be equally distributed across all individuals in a particular age or stage class in a population.
Interactions between an Alleeeffect and environmental variability in larger colonies were more deleterious than the sum of their independent influences; a few years with bad conditions reduced population density to a level where negative population growth eventually led to extinction (Grevstad, 1999a,b).
Because of the local effect of selection by host resistance on the diversity and complexity of the pathogen population, immigrations by new genotypes are often detected on the basis of abrupt changes in pathogenicity or mating type.
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