Tight quarters: ranging and feeding competition in a Colobus angolensis ruwenzorii multilevel society occupying a fragmented habitat

Multilevel societies (MLSs) are present in several animal clades and our understanding of them is growing at a time with increasing habitat loss. The ways individuals in these complex societies respond to habitat restriction and fragmentation are unknown. We examined ranging and feeding competition in a Ruwenzori Angolan colobus MLS in a forest fragment at Nabugabo, Uganda. We analyzed GPS points collected over 2 years and scan samples collected over 10 months on 12 core units in one band to compare sex- and core unit-specific activity budgets and near-neighbor distances. The 95% home range size estimate of this band was 1.75 km(2), much smaller than the ranges of similar-sized bands of primate MLS in continuous habitats. Day range length was also shorter. The colobus rarely utilized the matrix and over the two-year period core units' home ranges overlapped by 93%. Indicators of scramble competition included more time spent feeding in larger core units, near-neighbors at greater distances when feeding relative to resting, and greater feeding for females compared to males. A quadratic relationship was found between core unit size and home range and core area size, where intermediate-sized units showed the smallest ranges. All units showed similarly tortuous paths; however, the smallest core units had the longest day range lengths and the fastest rates of travel. We conclude that while large core units suffer some food competition, small units may be displaced more in inter-unit contests because they appear to suffer the highest energetic costs searching for food within this constricted area. Significance statement Wildlife worldwide is faced with increasing habitat loss and fragmentation. How this impacts animals that live in large, complex societies (e.g., multilevel societies) is an important question to investigate for future conservation. We examined ranging behavior and food competition for a multilevel society of Rwenzori Angolan colobus monkeys (12 core units, 139 monkeys) in Uganda that occupies a relatively small forest fragment. We found scramble competition for food, especially in the largest core units. However, membership in the smallest core units seemed to be the most energetically costly. These units moved the most per day and the fastest, perhaps because they were unable to displace larger core units from food patches. Overall, this multilevel society occupied an area many times smaller than similar-sized primate multilevel societies in continuous habitat and moved far less, suggesting that fragmentation is constraining their range.