Competition for resources and its behavioral consequences among female primates

Via the current model on the evolutionary ecology of female social relationships, Sterck et al. (1997) argue that ecological conditions determine how competition over food resources affects female fitness. The relative importance of different modes of competition then affects female social relationships and dispersal patterns. I outline the model and review relevant data. There are 3 modes of feeding competition: within-group scramble (WGS), within-group contest (WGC), and between-group contest (BGC), which occur in various combinations in different populations of nonhuman primates. Ecological measures support predictions that limiting resources lead to WGS and clumped resources induce WGC. The ecological basis of BGC remains elusive, but it is probably linked to resource abundance. Tests of the proxies of feeding competition support the idea that short-term search substrates and increasing group size lead to WGS, while high-quality patches of intermediate size relative to group size lead to WGC. However, when tested across populations, independent measures of aggression rates do not always match the actual or presumed competitive regimes. This mismatch might be explained by confounding factors and the predominately indirect measures of feeding competition. Predicted relationships between feeding competition and female social relationships/dispersal are only partly supported. This might be attributed to the fact that few studies have taken ultimate approaches using mechanistic correlates of fitness (net energy gain) or lifetime reproductive success to measure consequences of feeding competition. But to resolve existing inconsistencies, additional factors need to be taken into account as well, for example, male sexual strategies may affect female feeding competition; constraints on group size may enforce female dispersal; and demography may alter rates of alliances. More explicitly, ultimate approaches are needed to test the consistency of the socioecological model.