This comprehensive overview of the behavioural and ecological diversity of the colobines shows that we have greatly expanded our understanding of the taxonomy, phylogeny, morphology, natural history, behaviour and conservation status of this subfamily since Glyn Davies and John Oates (1994) published the first book on them. Nonetheless, there remain many gaps in our knowledge. In Chapter 2, Roos highlights that our current understanding of the taxonomy of colobines should be considered preliminary because classifications are still largely based on phenotypic differences between museum specimens. Changes will likely need to be implemented as data become available on ecology, behaviour, morphology and especially genetics of many species and subspecies. Roos also notes that relative to the cercopithecines, colobines are neglected in study effort and thus new findings have the potential to expand our understanding of their taxonomic diversity, especially in genera such as Piliocolobus, Colobus, Presbytis, Trachypithecus and Semnopithecus that are found over large geographic areas and are species-rich.

This chapter broadly covers what we know of the natural history of the olive colobus monkey, the only monotypic African colobine that shows a suite of unique traits. Distributed in the upper Guinea forests of West Africa, these cryptic, drab-coloured monkeys tend to form long-term and often permanent polyspecific associations with guenon groups as part of their predation avoidance strategy. They carry their infants in their mouths and show several morphological and behavioural traits (e.g., sexual swellings, canine dimorphism, extra-group copulations) that indicate that sexual selection has been important in their evolutionary history. They are selective feeders that favour young leaves and often eat lianas. No long-term studies are currently being conducted on olive colobus monkeys and there is much remaining to be discovered about their behaviour and ecology.

Colobinae, which includes more than 70 species grouped into 10 genera distributed throughout Asia and Africa, show a wide range of ecological and social traits. The colobines are generally forest-living and arboreal, which can make research on this often-elusive group difficult. Despite these challenges, our understanding of colobine behaviour, ecology and morphology has increased a great deal over the decades since the first research review on this primate subfamily was published by Davies and Oates (1994). While new research has demonstrated the incredible variation of colobine natural history, and the adaptability of this group, some colobine populations have declined and are now critically endangered. The Colobines brings together experts from around the world in an innovative volume that summarizes the current knowledge on colobine populations.

Formally, African colobines were not thought to be affected by food competition because mature leaves are relatively evenly distributed and low quality. However, greater research on colobus monkeys has shown that they have varied diets and rarely rely on mature leaves and that within-group scramble and both within- and between-group contest competition for food affects them. Within-group contest competition for resources may be seasonal but appears to be sufficient to lead to dominance hierarchies among females. These dominance hierarchies tend to be individualistic and females typically do not stay with kin to defend food. Unfortunately, there are still little data available to examine whether female dominance hierarchies lead to rank-effects on female energy intake or reproductive rates. In sum, African colobines do not seem fit current socio-ecological models and instead appear to fall somewhere between species with within-group scramble and within-group contest competition, where females disperse despite forming decided dominance relations. This appears to give rise to very specific male strategies, such as male defence of food resources, that may attract females and which alter female social strategies in interesting ways, changing social organization and structure.