For folivores, socio-ecological models predict scramble competition and egalitarian dominance relationships with female dispersal, but female Asian colobines do not all nicely fit these predictions. Alternative explanations concern an absence of competition, and the Folivore Paradox, where group size is limited by social factors such as infanticide. Relevant data are scarce, but our review shows that colobine foraging costs increase with group size, yet female fitness may increase or decrease. Dominance relationships vary from despotic to egalitarian, and are individualistic. The lack of female nepotism in despotic species (or populations) still requires explanation. Female dispersal is found in egalitarian and some despotic species, yet costs may be low if females migrate into a group with familiar females. Asian colobine social organization seems to follow one of two patterns. First, in seasonal species, food limits group size, while infanticide does not; these groups may experience contest competition. Second, in a-seasonal species groups are uni-male, the infanticide risk is high and infanticide, not food, may limit group size. This proposal requires further testing and may also apply to uni-male frugivores. This overview of the socio-ecological patterns in Asian colobines highlights that ecological and social selection pressures in interaction determine primate social organization.

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.

This is the first of five chapters on ecological modelling and presents basic homogenous (absence of spatial structure and variability among individuals) and deterministic (absence of stochasticity and randomness) population models. The first model describes unlimited exponential growth, which is followed by the introduction of intra-specific competition and density dependent growth. Two types of dynamics are considered: continuous in time and discrete in time. It is demonstrated that the time-discrete formulation can lead to chaotic population dynamics which in ecological models can be caused by scramble competiton where individuals share limited resources rather evenly so that all individuals suffer from the lack of resources. Opposed to this is contest competition where the share of the resources is uneven, so a few winners reproduce and/or survive, and the emerging population dynamics are not chaotic.