Distance-decay effect in stone tool transport by wild chimpanzees

Abstract

Stone tool transport leaves long-lasting behavioural evidence in the landscape. However, it remains unknown how large-scale patterns of stone distribution emerge through undirected, short-term transport behaviours. One of the longest studied groups of stone-tool-using primates are the chimpanzees of the Taï National Park in Ivory Coast, West Africa. Using hammerstones left behind at chimpanzee Panda nut-cracking sites, we tested for a distance-decay effect, in which the weight of material decreases with increasing distance from raw material sources. We found that this effect exists over a range of more than 2 km, despite the fact that observed, shortterm tool transport does not appear to involve deliberate movements away from raw material sources. Tools from the millennia-old Noulo site in the Taï forest fit the same pattern. The fact that chimpanzees show both complex short-term behavioural planning, and yet produce a landscape-wide pattern over the long term, raises the question of whether similar processes operate within other stone-tool-using primates, including hominins. Where hominin landscapes have discrete material sources, a distance-decay effect, and increasing use of stone materials away from sources, the Taï chimpanzees provide a relevant analogy for understanding the formation of those landscapes.

Bili-Uéré: A Chimpanzee Behavioural Realm in Northern Democratic Republic of Congo

“…Both Boesch and Boesch-Achermann [2000] and van Schaik and Knott [2001] reached conclusions about the presence or absence of certain great ape material traditions based on indirect data gathered during surveys of unhabituated populations of western chimpanzees (P. t. verus) and Sumatran orang-utans (Pongo abelii), respectively. At Taï Forest, researchers using archaeological methods documented the persistence of a chimpanzee nut-hammering tradition dating back several thousands of years [Mercader et al, 2002] and documented a distance-decay effect in the distribution of stone artefacts at Taï [Luncz et al, 2016]. Sept [1992] compared eastern DRC chimpanzee nest sites to hominin home bases, while used the artefacts left behind by an unhabituated Taï community to infer the natal nut-hammering habits of female chimpanzees who had transferred into a habituated community.…”

“…In order to improve our understanding of how culture evolved among our hominin ancestors, we must document the traditions of as many chimpanzee populations as possible and the specieswide variation therein [Boesch, 2012]. Studying the artefacts left behind by chimpanzees is especially important to understand hominin traditions in the fossil record [Sept, 1992;Carvalho et al, 2009;Toth and Schick, 2009;Luncz et al, 2016]. Not only do some chimpanzee populations use stone tools [Boesch and Boesch-Achermann, 2000;Kühl et al, 2016] comparable to hominin stone-knapping [Mercader et al, 2002;McPherron et al, 2015], but many of their artefacts are made of perishable material such as sticks and grass, which, if used by our ancestors, would not have fossilised and therefore would remain unknown [McGrew, 1992].…”

Food hardness and stone tool weight in wild primate nut-cracking

“…Tool weights from the capuchin Fazenda Boa Vista (FBV) site have been reported in terms of their use on 'high resistance' and 'low resistance' nuts (Spagnoletti et al 2011), and I have followed that procedure here, leading to identical weights for tools used to process each of the nut species that fall into these categories (see Table 1). Chimpanzee tools from the Taï Forest have been published in weight categories (Boesch and Boesch 1984;Luncz et al 2016a), and an average value was therefore calculated by assigning each category a weight in the centre of its range (e.g., the category '1-2.9 kg' was assigned a value of 2 kg) (Boesch and Boesch 1984). The macaque data include the two nut species processed with stone tools; however, I also included two gastropod species to reflect the fact that these monkeys predominantly use stones on shellfish.…”

“…Chimpanzees stone tool use is focused on cracking a variety of nuts and fruits (including Panda, Coula, Parinari and Elaeis) (McGrew 1992). All three primates select and transport stones to tool-use sites, for use as hammers Haslam et al 2016b;Luncz et al 2016a) and anvils (Sakura and Matsuzawa 1991;Haslam et al 2016a).…”

Distance-Decay Effect in Probabilistic Time Geography for Random Encounter

“…For example, Östh et al [18] used the exponential-type distance-decay function to study the commuting distance in Sweden, Nijkamp et al [19] detailed the problem of selecting the power-law and exponential-type distance-decay function, Stepniak et al [20] used linear regression to fit the distance-decay function to study the spatial agglomeration problem in spatial interactions, and Ladau et al [21] analyzed the similarity between biological community in the form of piecewise distance-decay functions. In recent years, distance attenuation effects have received constant attention in applications related to trajectory data, such as the similarity between plant community [21][22][23], spatial interaction between humans [24] or animals [25], and specific places. Some scholars have combined it with GIS in order to study the effects of environmental factors such as automobile exhaust on human diseases with distance attenuation [26,27].…”