leo), African wild dogs, East Africa black-backed jackal ( Canis mesomelas schmidti), and spotted hyenas. Possible predators of red-tailed monkeys at Issa include five large carnivores: leopards, lions ( P. To our knowledge, this is the only long-term study of red-tailed monkeys in a savanna-mosaic habitat. A single adult male was present in each group. At the time of this study, K1 group numbered approximately 30 individuals and K2 group numbered 10 individuals. In 2018, two study groups (K1 and K2) were followed by two-person research teams for 5–10 days per alternate month. Red-tailed monkeys at Issa have been habituated since 2012. Canopy cover is mostly closed in gallery forest, and mostly open in woodland. Remaining vegetation is made up of a small proportion (4% cover) of evergreen and semi-deciduous gallery forest found in thin strips, as well as swamps and open grasslands. with a savanna grass understory (Piel et al. Vegetation is a savanna-mosaic, consisting primarily of miombo woodland dominated by Brachystegia and Julbernardia spp. Climate is characterized by two distinct seasons: a wet season during November–April and an extended dry season (< 100 mm total monthly rainfall) during May–October (Hernandez-Aguilar 2009). Human presence in the study area occurs, primarily due to illegal poaching, logging, and cattle herding in the peripheries of the site (Piel et al. The nearest settlement to the site (Mishamo) is 20 km away. The site has no formal protection status. Research at Issa focuses on an approximately 60 km 2 area of steep valleys and flat plateaus at an elevation of 1150–1712 m. The Issa Valley study site is located approximately 90 km inland of Lake Tanganyika and equidistant between Gombe and Mahale Mountains National Parks. Specifically, we observed a leopard ( Panthera pardus) that preyed upon on a single monkey at the Issa Valley, a savanna-woodland mosaic landscape in western Tanzania. We describe an incident of predation on a red-tailed monkey ( Cercopithecus ascanius schmidti), a species that typically inhabits primary and secondary forests, as well as open habitats (Sarmiento et al. African wild dogs, Lycaon pictus spotted hyenas, Crocuta crocuta-Baldwin et al. The diversity of potential primate predators also varies between open and closed environments, with open habitats hosting species that are no longer found or have never been historically present in tropical forests (e.g. tropical forests Crook and Gartlan 1966 Anderson 1986 Dunbar 1988 Cords 1990 Isbell 1994). savanna-woodland mosaics) predation pressures may differ compared to closed canopy, densely vegetated habitats (e.g. As such, for primates in open habitats (e.g. The diversity and densities of predators should also affect encounter and predation rates (Anderson 1986). For example, harpy eagles ( Harpia harpyja) may preferentially hunt primates in clearings or open canopy forest (Eason 1989), and chacma baboons ( Papio ursinus) avoid vegetation types that are associated with higher predation risk (Cowlishaw 1997). Habitat structure should determine optimal opportunities for predators as well as prey vulnerability (Isbell 1994). Multiple factors likely influence primate vulnerability to predation. While the evolutionary significance of predation is therefore of interest, testing the extent of predation as a selective pressure is difficult due to the rarity of direct observations of predation events. Despite this, larger groups are more conspicuous and more likely to be detected by predators (Boinski et al. mobbing), and greater dilution of risk among group members (Morse 1977 Boinski et al. Group-living primates benefit from increased collective vigilance, better defence against predators (e.g. For example, predator avoidance is a primary explanation for the evolution of group living-an otherwise disadvantageous strategy given increased rates of intra-group feeding and mate competition (Isbell 1991 Majolo et al. Predation is predicted to be a critical selection pressure in primate evolution (Anderson 1986 Treves 1999 Zuberbühler and Jenny 2002).
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