MINIMUM GROUP-SIZE AND OTHER CONSERVATION LESSONS EXEMPLIFIED BY A DECLINING PRIMATE POPULATION

Examining the dynamics of naturally declining populations can be usefu l in understanding some of the problems encountered by endangered popu lations. A study of a declining population of vervet monkeys Cercopith ecus aethiops provides a unique opportunity to examine factors associa ted with minimum social group size, a potentially key variable in popu lation viability analysis. The minimum group size in vervets ranged fr om three to six individuals, but always with a minimum of two adults. Groups appeared to be stable as long as there were at least two adults , but ceased to exist as independent groups within days of losing thei r penultimate adult. For species with discrete group structure, popula tion extinction could occur if all individual groups fall below a mini mum social group size, even if the overall population is above a 'mini mum' size. However, group fusions may minimum population losses. Group fusion in vervets is rare, and appears to occur only as a behavioural response to minimum group size. We also review evidence of the costs vervets incur through movement into unfamiliar places or groups (analo gous to translocation and reintroduction), and the benefits they can r eceive from living in proximity to humans.