Single-species models of the Allee effect: extinction boundaries, sex ratios and mate encounters.
We critically review and classify models of single-species population dynamics subject to the demographic Allee effect with emphasis on non-spatial, deterministic approach. Inclusion of spatial movement and stochastic phenomena does not substantially change the behaviour; stochasticity only "blurs" step-like character of the Allee effect into a sigmoidal form. The outcome of all non-spatial, deterministic models is either unconditional extinction, extinction-survival scenario (ES), or unconditional survival. Three major model classes are recognized: (1) one-dimensional heuristic models, (2) one-dimensional models with mating probability and fixed sex ratio, and (3) two-sex models with variable adult sex ratio. Each class is characterized by the shape of extinction boundary which separates extinction from survival in the ES scenario. The latter two classes may give better predictions of extinction thresholds than heuristic models but require specific information and are data intensive. In one-dimensional models with fixed sex ratio, population cannot survive if density/number of males decreases below some threshold while there is no such restriction on females. Individual-based models seem to be most capable of explaining mechanisms leading to the Allee effect.
Boukal
David S
DS
Department of Theoretical Biology, Institute of Entomology, Academy of Sciences of the Czech Republic, BraniSovská 31, 370 05 Ceské Budejovice, Czech Republic. boukal@entu.cas.cz
Berec
Ludek
L
D000818:Animals; D003247:Conservation of Natural Resources; D017753:Ecosystem; D005260:Female; D008297:Male; D008954:Models, Biological; D011156:Population Density; D011157:Population Dynamics; D012098:Reproduction; D012744:Sex Ratio; D013269:Stochastic Processes