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- Appendix A
Folivorous primates have traditionally been assumed to experience little to no feeding competition as leaves are apparently an abundant and evenly dispersed food resource [Isbell, 1991]. However, recent studies indicated that at least some folivores experience food limitation [Borries et al., 2008; Harris et al., 2010; Koenig et al., 1998]. By exploiting high-quality, patchily distributed, temporally variable food resources, they may experience within-group scramble competition [Snaith & Chapman, 2005] as well as within- and between-group contest competition [Koenig, 2002]. Studies that take place when preferred foods are abundant may not find evidence for food limitation and feeding competition, whereas longitudinal studies on effects of reductions in main food resources may provide valuable insights into the selective pressures that diet places on folivorous primates [Harris et al., 2010].
Previous studies of Malagasy primates (Lemuriformes) revealed that feeding competition does not occur only in group-living species, but also among solitary foragers. For example, within-group scramble and contest competition as well as female feeding dominance were demonstrated for gummivorous Phaner pallescens [Schülke, 2003]. Similarly, resource distribution and resulting competitive regimes have been shown to determine distribution and association patterns of solitary omnivorous Microcebus berthae and M. murinus [Dammhahn & Kappeler, 2009]. Competition for food in solitarily foraging folivorous primates has not been studied in detail yet, however.
Sportive lemurs (genus Lepilemur) are strictly folivorous and nocturnal. As with other congeners, white-footed sportive lemurs (Lepilemur leucopus) have evolved adaptations to a folivorous diet despite small body size (<1 kg), including prolonged resting bouts, small night ranges, an enlarged caecum and caecotrophy [Hladik & Charles-Dominique, 1974]. Known predators of sportive lemurs are fossas (Cryptoprocta ferox), long-eared owls (Asio madagascariensis), Madagascar boas (Acrantophis sp.) and Harrier hawks [Polyboroides radiatus; Fichtel, 2007; Goodman et al., 1993; Rasoloarison et al., 1995; Schülke & Ostner, 2001; Sussman, 1999]. Sportive lemurs live in dispersed pairs, which are characterized by spatial overlap between one adult male and female but low cohesion between pair partners [Dröscher & Kappeler, 2013; Hilgartner et al., 2012; Méndez-Cárdenas & Zimmermann, 2009; Schülke & Kappeler, 2003; Zinner et al., 2003]. In L. leucopus, pair-partners show signs of active avoidance, and home range overlap among neighboring females is minimal [Dröscher & Kappeler, 2013].
If males defend resources that are important to females, instead of defending females directly, resource defense can explain the evolution of pair-living [Emlen & Oring, 1977; van Schaik & Dunbar, 1990; Wrangham, 1979]. Under this scenario, female reproductive success is limited by male resource holding potential [Parker, 1974], whereas male reproductive success is limited by female choice of mates with variable resource access [Balmford et al., 1992]. Pairs evolve under this scenario whenever males are unable to defend territories that can support more than one female [Hilgartner et al., 2012; Lukas & Clutton-Brock, 2013]. However, to evaluate this hypothesis, quantitative data on resource use and competition are required.
Competition for food may explain female-female avoidance [Lukas & Clutton-Brock, 2013] as well as avoidance of pair-partners. For example, pair partners in P. pallescens reduce feeding competition by avoiding competitors in time instead of space, as they rely on relatively rare gum trees [Schülke, 2003]. However, solitary foraging seems to characterize almost all nocturnal primates irrespective of their diet, suggesting that factors other than feeding competition may promote this type of social organization [Schülke, 2003]. More studies on ranging behavior, resource use and competitive regimes are therefore indicated to further our understanding of the factors that promote intra- and intersexual avoidance in solitary foragers.
The main aims of the present study were to investigate the types and consequences of feeding competition between and within social units of white-footed sportive lemurs. In particular, we predicted contest competition (i.e., displacement from food trees) as well as scramble competition (i.e., food patches shared by individuals) to increase in intensity during the pronounced lean season characterizing southern Madagascar. Alternatively, based on the fact that L. leucopus is folivorous and leaves can be expected to be relatively abundant, feeding stress could be more related to food quality than quantity. In this case, we predicted scramble as well as contest competition to be rare. In addition, we explored whether female-female avoidance as well as avoidance between pair partners is a consequence of feeding competition. Our second aim was to evaluate the importance of resource defense as a male mating strategy. In this case, we predicted that males of neighboring social units would engage in conflict over resources. In the absence of more precise measures of territory quality, we assume that differences in territory quality are related to territory size.