Abstract
AbstractBiomechanical analyses of arboreal locomotion in great apes in their natural environment are scarce and thus attempts to correlate behavioral and habitat differences with variations in morphology are limited. The aim of this study was to investigate the gait characteristics of vertical climbing in mountain gorillas (Gorilla beringei beringei) and chimpanzees (Pan troglodytes) in a natural environment to assess differences in the climbing styles that may relate to variation in body size. We investigated temporal variables (i.e., cycle duration, duty factors, and stride frequency) and footfall sequences (i.e., diagonal vs. lateral sequence gaits) during vertical climbing (both ascent and descent) in 11 wild mountain gorillas and compared these data to those of eight semi‐free‐ranging chimpanzees, using video records ad libitum. Comparisons of temporal gait parameters revealed that large‐bodied mountain gorillas exhibited a longer cycle duration, lower stride frequency and generally a higher duty factor than small‐bodied chimpanzees. While both apes were similarly versatile in their vertical climbing performance in the natural environment, mountain gorillas most often engaged in diagonal sequence/diagonal couplet gaits and chimpanzees most often used lateral sequence/diagonal couplet gaits. This study revealed that mountain gorillas adapt their climbing strategy to accommodate their large body mass in a similar manner previously found in captive western lowland gorillas, and that chimpanzees are less variable in their climbing strategy than has been documented in captive bonobos.
Highlights
Vertical climbing is essential to the locomotor and foraging strategies of great apes (e.g., Hunt, 1992a; Remis, 1995; Pilbeam, 2002; Robbins & McNeilage, 2003)
Most studies agree that mountain gorillas (Gorilla beringei beringei) are less arboreal than chimpanzees (Pan troglodytes) (Tuttle & Watts, 1985; Remis, 1998; Hunt, 2004; Crompton et al, 2010; Hunt, 2016) and are thought to spend less than 1 % of total locomotor time engaging in vertical climbing (Tuttle & Watts, 1985)
Isler (2002) identified key differences in gorilla climbing performance associated with age and sex; vertical climbing in an adult male gorilla was characterised by higher duty factors, relatively shorter strides and more variable footfall patterns compared with adult female gorillas and bonobos
Summary
Vertical climbing is essential to the locomotor and foraging strategies of great apes (e.g., Hunt, 1992a; Remis, 1995; Pilbeam, 2002; Robbins & McNeilage, 2003). Attempts to correlate variations in African ape morphology (e.g., hand or limb proportions, body mass) with behavioral and habitat differences are limited because kinematics (e.g., movement of body segments, gait parameters) of arboreal locomotion, such as vertical climbing, are scarce especially in the wild. The aim of this study is to provide further insights into the arboreal locomotor strategies of mountain gorillas and chimpanzees by describing the temporal gait parameters and footfall sequences during vertical climbing (both ascent and descent) on differently-sized natural substrates. We predict that vertical climbing of large-bodied mountain gorillas will be characterized by longer cycle durations, higher duty factors, lower stride frequencies, a higher number of limbs used as support and less variable footfall patterns compared to smaller-bodied chimpanzees. We hypothesize that mountain gorillas will adapt their climbing strategy to accommodate their large body mass in a similar manner to that documented in captive western lowland gorillas (females 71.0-97.5 kg; males 162.5-175.2 kg across G. beringei, G. gorilla, G. graueri; Smith & Jungers, 1997) and, likewise, vertical climbing of smaller-bodied chimpanzees will be similar to that of bonobos given their generally similar body size (females 33.2-45.8 kg; males 42.7-59.7 kg across P. paniscus and P. t. troglodytes, P. t. schweinfurthii, and P. t. verus; Smith & Jungers, 1997)
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