An experimental test of the Allee effect range limitation hypothesis
Samuel A Merker1, Richard B Chandler1
1Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA, USA.
The Journal of Animal Ecology
|November 17, 2020
Summary
Socially mediated Allee effects do not limit Canada warbler populations at range edges. Climate factors and density dependence, not social cues, influence population growth, suggesting minimal role for Allee effects in species distribution.
Area of Science:
- Ecology
- Conservation Biology
- Climate Change Biology
Background:
- Species distributions are influenced by abiotic and biotic factors.
- Socially mediated Allee effects, where scarce social information limits population growth at range edges, are theoretically proposed to affect species distributions.
- Understanding these effects is crucial for predicting climate change impacts on trailing-edge populations.
Purpose of the Study:
- To determine if socially mediated Allee effects limit the geographic distribution of the Canada warbler (Cardellina canadensis) at the trailing edge of its range.
- To test predictions that local growth rates correlate with density and that adding social cues can promote colonization and increase growth rates.
- To investigate the role of abiotic factors versus social cues in limiting population growth.
Main Methods:
- Utilized 4 years of observational data from 71 sites and experimental data from 10 sites.
- Conducted experiments adding social cues to formerly unoccupied sites to test for colonization and increased growth rates.
- Analyzed the influence of local density, temperature, precipitation, and negative density dependence on population growth rates.
Main Results:
- No colonization of experimental sites occurred after the addition of social cues.
- No evidence of Allee effects limiting Canada warbler distribution was found.
- Population growth rates were significantly influenced by temperature, precipitation, and negative density dependence, not social cues.
Conclusions:
- Socially mediated Allee effects appear to play a minimal role in limiting the distribution of Canada warblers at their trailing-edge range.
- Abiotic factors (temperature, precipitation) and negative density dependence are stronger drivers of population growth rates in this species.
- Empirical findings challenge theoretical models suggesting Allee effects significantly accelerate climate-induced range shifts or local extinctions.
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