Article

Multiple Allee effects and population management

Department of Theoretical Ecology, Institute of Entomology, Biology Centre ASCR, Branisovská 31, 37005 Ceské Budejovice, Czech Republic.
Trends in Ecology & Evolution (Impact Factor: 15.35). 05/2007; 22(4):185-91. DOI: 10.1016/j.tree.2006.12.002
Source: PubMed

ABSTRACT Allee effects, strongly related to the extinction vulnerability of populations and gradually becoming acknowledged by both theoretically oriented and applied ecologists, have already been shown to have important roles in the dynamics of many populations. Although not yet widely recognized, two or more Allee effects can occur simultaneously in the same population. Here, we review the evidence for multiple Allee effects and show that their interactions can take several forms, many of which are far from inconsequential. We suggest that more research is needed to assess the prevalence and interactions of multiple Allee effects, as failing to take them into account could have adverse consequences for the management of threatened or exploited populations.

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    • "In many cases, an Allee effect might even lead to a negative population growth rate, creating an extinction threshold so that the population has to fight in order to grow [15] [17] [18]. This is also well-known as strong Allee effect [14] or critical depensation [17]. In this case, that implies the species may have a bigger tendency to be less able to overcome these additional mortality causes, to have a slower recovery, and to be prone to extinction than any other species [12]. "
    • "Other important drivers of positive interactions in subtidal communities include demographic constraints, (i.e. Allee effects), whereby population fitness displays positive density dependence (Berec et al. 2007) and resource availability, whereby benefactors can increase the nutrient availability for beneficiary species (Peterson & Heck 2001). "
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    • "Allee effects occur either when total individual fitness decreases as population abundances or densities decrease (demographic Allee effect) or when some aspect of fitness (such as probability of breeding) does so (component Allee effects; Courchamp et al. 1999, Stephens and Sutherland 1999, Stephens et al. 1999). Population processes that can cause Allee effects include difficulty finding mates at low densities, cooperative breeding or antipredator behavior, predator dilution, inbreeding depression, increased exploitation risk, and social thermoregulation, among others (Stephens et al. 1999, Berec et al. 2007). Allee effects can affect the spread of invasive species (Taylor and Hastings 2005) and, along with demographic stochasticity (see next section) and other factors, contribute to the ''extinction vortex,'' whereby positive feedback pulls small populations closer and closer to extinction (Gilpin and Soulé 1986, Morris and Doak 2002, Fagan and Holmes 2006). "
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