The University of Chicago Information-Mediated Allee Effects in Breeding Habitat Selection Author(s): Kenneth A. Schmidt, Jacob Johansson, and Matthew G. Betts Source: The American Naturalist, Vol. 186, No. 6 (December 2015), pp. E162-E171 Published by: The University of Chicago Press for The American Society of Naturalists Stable URL: http://www.jstor.org/stable/10.1086/683659 . Accessed: 23/11/2015 14:39 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. The University of Chicago Press, The American Society of Naturalists, The University of Chicago are collaborating with JSTOR to digitize, preserve and extend access to The American Naturalist. http://www.jstor.org This content downloaded from 23.235.32.0 on Mon, 23 Nov 2015 14:39:02 PM All use subject to JSTOR Terms and Conditions vol. 186, no. 6 the american naturalist december 2015 E-Article Information-Mediated Allee Effects in Breeding Habitat Selection Kenneth A. Schmidt,1,*JacobJohansson,2 and Matthew G. Betts3 1. Department of Biological Sciences, Texas Tech University, Lubbock, Texas 79409; 2. Department of Biology, Lund University, 22362 Lund, Sweden; 3. Department of Forest Ecosystems and Society, Oregon State University, Corvallis, Oregon 97331 Submitted December 16, 2014; Accepted June 9, 2015; Electronically published October 28, 2015 Online enhancements: appendixes. Dryad data: http://dx.doi.org/10.5061/dryad.k4c21. abstract: Social information is used widely in breeding habitat se- Schmidt et al. 2015b). However, the degree to which feed- lection and provides an efficient means for individuals to select hab- backs occur between population growth and social informa- itat, but the population-level consequences of this process are not well tion are not well explored. For instance, at low population explored. At low population densities, efficiencies may be reduced be- density, one would expect lower potential for information cause there are insufficient information providers to cue high-quality collection at the individual level because there are fewer in- habitat. This constitutes what we call an information-mediated Allee formation providers. Consequently, per capita population fi effect. We present the rst general model for an information-mediated growth should be reduced at low density through the effects Allee effect applied to breeding habitat selection and unify personal and social information, Allee effects, and ecological traps into a com- of reduced information availability. This may, in turn, pro- mon framework. In a second model, we consider an explicit mech- duce an information-driven Allee effect. In this article, we anism of social information gathering through prospecting on con- present a general model for such an information-mediated specific breeding performance. In each model, we independently vary Allee effect. personal and social information use to demonstrate how dependency Allee effects may be caused by numerous, nonmutually on social information may result in either weak or strong Allee ef- exclusive mechanisms affecting one or more fitness com- fects that, in turn, affect population extinction risk. Abrupt transitions ponents (e.g., reproduction and survival), or what Stephens between outcomes can occur through reduced information transfer or small changes in habitat composition. Overall, information-mediated et al. (1999) refer to as a component Allee effect. In turn, Allee effects may produce positive feedbacks that amplify population these may produce a demographic Allee effect, character- declines in species that are already experiencing environmentally driven ized by the presence of positive density-dependent per cap- stressors, such as habitat loss and degradation. Alternatively, social in- ita population growth (Stephens et al. 1999; Allee 1941). formation has the capacity to rescue populations from ecological traps. Demographic Allee effects are important in conservation be- Keywords: Allee effect, Allee threshold, ecological trap, habitat selec- cause they may increase the extinction vulnerability of small tion, social information. populations (Courchamp et al. 2009). Demographic Allee effects may be categorized as strong or weak. In a weak Al- lee effect, per capita population growth is reduced at low Introduction density but remains positive. In a strong Allee effect, per capita population growth is negative at low density, which By sampling their environments (e.g., patches, mates, hab- can threaten population extinction. Thus, strong Allee ef- itats) and subsequent links to performance (prey harvest fects produce two population equilibrium points (excluding rates, offspring production), organisms often both use and population size N p 0). The larger equilibrium, N* p K produce information about their environment, which in S (or carrying capacity), is stable. The smaller, unstable equi- many cases is publicly available (Danchin et al. 2004). So- librium occurs in the region of positive density dependence cial information use is likely a pervasive and important (0 ! N* ! K). This point is called an Allee threshold (Boukal process in ecology and evolution that affects species’ pop- U and Berec 2002), because below N* , the population will de- ulation growth and persistence (e.g., Doligez et al. 2003; U cline toward extinction in the absence of external influence. Explicit recognition that social information may con- * Corresponding author; e-mail: [email protected]. tribute to Allee effects has received limited attention, al- – q though several common mechanisms often implicitly in- Am. Nat. 2015. Vol. 186, pp. E162 E171. 2015 by The University of Chicago. fi 0003-0147/2015/18606-55946$15.00. All rights reserved. voke social information, such as nding mates, food, and DOI: 10.1086/683659 safety in numbers (Courchamp et al. 2009). The many-eyes This content downloaded from 23.235.32.0 on Mon, 23 Nov 2015 14:39:02 PM All use subject to JSTOR Terms and Conditions Information-Mediated Allee Effects E163 hypothesis is partially the cogent realization that more eyes ing site quality, (3) social information saturates with the scanning for predators reduce the uncertainty in an indi- number of conspecifics, and (4) the two types of informa- vidual’s estimate of the instantaneous risk of predation. tion are additive in their effect on settlement. These assump- Dilution effects also contribute to safety in numbers, hence tions yield the following relationship for total information p 1 = 1 information- and noninformation-based mechanisms may (w): w w0 aN (1 aN), where w0 is a measure of in- operate in tandem. formation available independent of the density of conspecif- Social information can influence numerous behavioral ics and a determines the rate of increase in social informa- and life-history strategies of organisms (Dall 2005; Danchin tion with density. Note that our use of the terms “personal” et al. 2004). We focus on information use as it applies to and “social” does not refer to the source of information but breeding habitat selection in spatially heterogeneous land- specifically to whether the information depends on the scapes where variation in the quality of breeding sites is number of conspecifics (i.e., social information) or not (per- manifested as differences in breeding success (e.g., variation sonal information). When placed in the context of density- in the risk of nest mortality; Schmidt et al. 2006; Schmitt and dependent population growth, there is an important func- Holbrook 2007). By sampling prospective territories, organ- tional difference between these terms. Our use of these terms, isms can collect direct or indirect information about cur- therefore, differs from that of previous authors (e.g., Wagner rent or future quality based on current territory occupation and Danchin 2010). or past reproductive performance of conspecifics (Boulinier Personal information may include experience, such as and Danchin 1997; Doligez et al. 2002; Forsman et al. 2012). prior reproductive success, natal habitat imprinting (Davis The latter can lead to simple habitat copying or settlement at and Stamps 2004), active sampling for predators (e.g., Mor- sites where conspecifics were successful (i.e., performance- ton 2005; Schmitt and Holbrook 2007) or parasites (Fors- based cues; Reed et al. 1999). man and Martin 2009), and innate preferences for habitat features (Arlt and Pärt 2007). Likewise, several mechanisms may be used to acquire social information. One mechanism A Phenomenological Model with broad empirical support is social information acquired of an Information-Mediated Allee Effect through eavesdropping on the reproductive performance of We start with a phenomenological model that incorpo- conspecifics—for example, the number and/or quality of rates density-dependent information use into the process fledged young or litter size (Danchin et al. 1998; Doligez of breeding habitat selection. We use this model to explore et al. 2002; Betts et al. 2008). the population-level phenomenon of habitat selection that Based on the above assumptions, we conceptualize a pop- is influenced by both personal