Ecological and dietary differences between Ugandan chimpanzee communities with possible implications on tool use

Abstract

20To advance our knowledge of the role of ecological factors in the emergence of tool use in 21 chimpanzees, a nuanced understanding of the ecological conditions different chimpanzee 22 communities experience is needed. We studied four Ugandan chimpanzee communities in 23 two forests. One of these communities, Sonso, in the Budongo Forest, is well-known for its 24 restricted range of tool types, including a total absence of stick use. Food diversity and 25 2 abundance were highest, and stick tool use opportunities (abundance of sticks and insect 26 nests) were lowest for the core-habitat of the Sonso chimpanzees in contrast to the other 27 communities. We argue that ecological factors play a role in their unusual pattern of tool use, 28and make predictions about the expected types of tool use in the other communities based 29 on their ecology. Thus, our study provides information that may help advance our 30 understanding of how tool use arises under varied socioecological circumstances. 31 32 AUTHOR CONTRIBUTIONS 33 TG and IB formulated the idea. DM and IB conducted the transects. IB did the feeding 34 observations and faecal analyses. MB and IB analysed the data. IB, TG, CH and MB wrote 35 the manuscript. 36 37 ABSTRACT 38 Some East African chimpanzee (Pan troglodytes schweinfurthii) communities, such as the 39 Sonso chimpanzees, display an unusually limited range of tool-use, but it remains unclear 40 whether this is due to ecological and/or cultural factors. Information on ecological conditions 41 and the diet of the Sonso chimpanzees in relation to neighbouring communities is needed. 42Here, we studied three adjacent communities in Budongo Forest (Sonso, Waibira, and 43 Kamira), and the presumed core area of an undescribed community (Mwera), in the 44 neighbouring Bugoma Forest. Through line-transects, we investigated (i) whether there were 45 differences in food diversity and abundance between the communities' home ranges; (ii) 46 whether the home ranges differed in abundance of sticks and insect nests; and (iii) whether 47 availability may partially explain the Sonso chimpanzees' lack of stick-tool-use, and low 54 levels of insectivory. The tool repertoire of the other communities is currently unknown; 55 however, we make predictions based on our ecological data. More detailed knowledge of 56 small-scale variation in ecology within and between forest habitats may be important to 57 advancing our understanding of the drivers of tool-use. 58 KEYWORDS 59 Tool use; chimpanzee; food availability; diversity; ecological influence on behaviour 60 61