Male chimpanzees, Pan troglodytes, cooperate to defend a community range within which resident females range in smaller core areas. There has been debate over exactly what males are defending, whether mates, territory or both. One hypothesis holds that males are defending mates, and that an increase in community range size will lead directly to the acquisition of more females. However, males frequently attack females as well as males at the edge of the community range. We examined 18 years of observational data on the Gombe chimpanzees to determine the behaviour of males during extragroup encounters, and the consequences of changes in community range size on the number of adult females and indirect measures of food availability. Males were always aggressive to males from other communities, and often attacked adult females, especially those that were not sexually receptive, were older, and/or had more than one offspring. The number of females did not increase with range size, but several measures suggested an increase in food availability with range size. These measures include more time spent in large foraging parties, higher encounter rates with resident females, more encounters with sexually receptive females and higher female reproductive rates. These findings suggest that males defend a feeding territory for their resident females and protect them from sexual harassment. Although a large range may eventually attract more females, this is not an immediate consequence of range expansion. Male number was not correlated with community range size.
|Original language||English (US)|
|Number of pages||10|
|State||Published - Sep 2004|
Bibliographical noteFunding Information:
We thank Jane Goodall and the research staff at the Gombe Stream Research Centre for data collection, especially H. Matama, I. Yahaya, H. Mkono and E. Mpongo. We are indebted to Tanzania National Parks, the Tanzania Wildlife Research Institute and the Tanzania Council for Science and Technology for approval of this work over the decades. Thanks to B. Farm for writing data-entry software, J. Waterman for overseeing data entry early on, J. Schumacher-Stankey and all of the data enterers, and D. Scheel, T. Susman, T. Sperry and C. Ryan for programming on demand. Thanks also to D. Hawkins for statistical advice. David Watts, Mike Wilson, Dawn Kitchen and three anonymous referees made useful comments on an earlier version of the manuscript. This work was funded in part by National Science Foundation grants DBS-9021946 and SBR-9319909, the Graduate School and the College of Biological Sciences of the University of Minnesota, the American Philosophical Society, the Carnegie Corporation, the Jane Goodall Institute, Milton Harris, the L.S.B. Leakey Foundation, the Minnesota Base Camp and the Windibrow Foundation.