vol. 185, no. 6 the american naturalist june 2015 Natural History Note The Comparative Effects of Large Carnivores on the Acquisition of Carrion by Scavengers Maximilian L. Allen,1,*L.MarkElbroch,2 Christopher C. Wilmers,3 and Heiko U. Wittmer1 1. School of Biological Sciences, Victoria University of Wellington, P.O. Box 600, Wellington 6140, New Zealand; 2. Panthera, New York, New York 10018; 3. Center for Integrated Spatial Research, Environmental Studies Department, University of California, Santa Cruz, California 95064 Submitted April 21, 2014; Accepted December 18, 2014; Electronically published March 19, 2015 Online enhancements: videos. Dryad data: http://dx.doi.org/10.5061/dryad.dh2vr. abstract: Pumas (Puma concolor) and black bears (Ursus america- of other species, including birds and herbivores (Estes and nus) are large carnivores that may influence scavenger population Palmisano 1974; Rogers and Caro 1998; Courchamp et al. dynamics. We used motion-triggered video cameras deployed at deer 1999; Prugh et al. 2009). Large carnivores also have cascad- carcasses to determine how pumas and black bears affected three ing effects solely on other carnivores; increases in gray aspects of carrion acquisition by scavengers: presence, total feeding wolves (Canis lupus) in Minnesota resulted in suppression time, and mean feeding-bout duration. We found that pumas were of coyotes (Canis latrans), which in turn allowed an in- unable to limit acquisition of carrion by large carnivores but did limit crease in smaller red foxes (Vulpes vulpes; Levi and Wil- aspects of carrion acquisition by both birds and mesocarnivores. mers 2012). Within their respective communities, large car- Through their suppression of mesocarnivores and birds, pumas ap- fl parently initiated a cascading pattern and increased carrion acquisi- nivores are thought to exert population-level in uences tion by small carnivores. In contrast, black bears monopolized car- on other species, either directly via predation or indirectly rion resources and generally had larger limiting effects on carrion as a result of behavioral changes to avoid predation that re- acquisition by all scavengers. Black bears also limited puma feeding sult in lower fitness (Sargeant et al. 1987; Ripple et al. 2001, behaviors at puma kills, which may require pumas to compensate 2014; Ripple and Beschta 2004; Atwood et al. 2007). An un- for energetic losses through increasing their kill rates of ungulates. derappreciated mechanism by which large carnivores might Our results suggest that pumas provide carrion and selectively influ- ence species acquiring carrion, while black bears limit carrion avail- affect ecological communities is through their interactions ability to all other scavengers. These results suggest that the effects with scavengers at carcasses, where they may increase access of large carnivores on scavengers depend on attributes of both carni- to carrion resources for some species and restrict access for vores and scavengers (including size) and that competition for car- others. casses may result in intraguild predation as well as mesocarnivore Scavenging is a widespread behavior whereby species release. compete for limited resources in order to gain nutritional fi fi Keywords: carrion acquisition, competition, energy distribution, me- bene ts and increase individual tness (Houston 1995; socarnivore, Puma concolor, scavenging, Ursus americanus. DeVault et al. 2003; Selva et al. 2003; Wilson and Wilko- vich 2011). For example, numerous facultative scavengers use scavenging to increase their breeding success (e.g., An- Introduction gerbjörn et al. 1991; Watson et al. 1992). In addition, recent The effects of large carnivores in structuring ecological com- studies have highlighted the importance of scavenging to munities, including initiating trophic cascades, are well es- ecosystem function and the transfer of energy between tablished (Estes and Palmisano 1974; Ripple et al. 2014). trophic levels (DeVault et al. 2003; Selva and Fortuna 2007; For example, by suppressing smaller carnivores, large carni- Wilson and Wolkovich 2011). Carcasses also appear to pro- vores have been shown to indirectly influence abundances vide frequent opportunities for interactions among carni- vores, and these interactions result in complex ecological relationships and resource partitioning (Root 1967; Hous- * Corresponding author. Present address: Center for Integrated Spatial Re- ton 1995; Selva and Fortuna 2007). search, Environmental Studies Department, 1156 High Street, University of California, Santa Cruz, California 95064; e-mail: [email protected]. Large carnivores not only provide carrion but also play Am. Nat. 2015. Vol. 185, pp. 822–833. q 2015 by The University of Chicago. an important role in how carrion is distributed among 0003-0147/2015/18506-55435$15.00. All rights reserved. scavengers (e.g., Wilmers et al. 2003a;ElbrochandWitt- DOI: 10.1086/681004 mer 2012; Moleón et al. 2014). For example, large carni- Large-Carnivore Effects on Scavengers 823 vores provide carrion throughout the year, rather than in the seasonal pulses characteristic of anthropogenic sources (Wilmers et al. 2003b). In addition to providing carrion, large carnivores are also capable of opening carcasses, al- lowing other species access to edible portions of the car- cass (Selva et al. 2003). Large carnivores, however, also di- rectly limit scavenger species at their kills and, through competition, limit the availability of carrion for other ob- ligate and facultative scavengers when they themselves are scavenging (Hunter et al. 2006; Allen et al. 2014b). Within western North American ecological communi- ties, both pumas (Puma concolor) and black bears (Ursus americanus) are large carnivores that have the potential to affect other scavengers. Pumas are solitary predators that frequently kill ungulates while only occasionally scaveng- ing themselves (Bauer et al. 2005; Knopff et al. 2010), and by regularly killing ungulates and other prey they act as an important source of carrion to scavenger communities Video 1: Still photograph from a video, available online, showing a (Elbroch and Wittmer 2012; Allen et al. 2014b). In con- male puma feeding on a black-tailed deer it killed. trast, black bears frequently kill newborn ungulates (Pelton 1982) but rarely kill adults (Svoboda et al. 2011). Therefore, ceived risk (Charnov 1976; video 2). We hypothesized black bears rarely provide carrion for scavengers and are that pumas and black bears would limit each aspect of car- instead a dominant scavenger of ungulates, including puma rion acquisition for all scavengers but that there would be kills (Murphy et al. 1998; Ruth and Murphy 2010; Allen variation in the magnitude of their limitation based on the et al. 2014b). The influence of black bears on the acquisition body size of scavenger species. of carrion by other scavengers, however, has been under- Previous research demonstrated that pumas are subordi- studied. nate to other large carnivores, including gray wolves, griz- The effects pumas and black bears have on the acquisi- zly bears (Ursus arctos), jaguars (Panthera onca), and some- tion of carrion by scavengers is likely species specific. Pre- times coyotes (Canis latrans; Ruth and Murphy 2010). We vious research has shown that some scavengers access and thus expected pumas to have a small effect on the acquisi- exploit carrion better than others, as a result of differences tion of carrion by large carnivores. However, pumas are in morphology and behaviors (Root 1967; Hertel 1994; known to regularly kill smaller carnivores, and both meso- Houston 1995; Cortés-Avizanda et al. 2012). Here, we eval- carnivores and small carnivores are present in the diet of uated the potential influences of competition on scaveng- pumas across much of their distribution (Murphy and Ruth ing behaviors instead, and we attempted to determine how 2010). Because of their dominance over mesocarnivores and pumas and black bears affect the acquisition of carrion by small carnivores, we expected pumas to limit all three as- scavenger classes and species. To address this question, we pects of carrion acquisition by these classes. Pumas are also conducted a series of in situ experiments at black-tailed deer known to exhibit behaviors to minimize carcass detection (Odocoileus hemionus columbianus) carcasses, comparing by avian species, including caching of kills and moving kills carrion acquisition at puma kills (video 1; videos 1–3avail- to areas of dense overhead cover (Bischoff-Mattson and Matt- able online) to that at matching control carcasses and at a son 2009; Ruth and Murphy 2010; Allen et al. 2015). Be- separate set of experimental carcasses where black bears cause of these behaviors, we expected pumas to limit the were either present or absent. Specifically, we analyzed three acquisition of carrion by avian scavengers, mainly by limi- aspects of carrion acquisition exhibited by each scavenger ting their presence. species: presence or absence at carcasses, total feeding time, Black bears are capable of rapidly eating large amounts and mean feeding-bout duration. We used presence as a of food (video 3), including carrion, and their large body proxy of the ability of scavengers to acquire energy from a size allows them to exclude other species from carrion (Mur- given carcass, and we used total feeding time as a proxy for phy et al. 1998; Allen et al. 2014b). On the basis of these the amount of energy a scavenger was able to gain from a observations,