Variation of life history traits and mating patterns in female langur monkeys (Semnopithecus entellus)

To determine nutritional and social influences on life history traits and m ating behavior in female langur monkeys, new long-term data for a feral pop ulation living in mufti-male groups under poor nutritional conditions are p resented and compared with published longterm data for the same species liv ing in one-male groups under excellent nutritional conditions. Under poor n utritional conditions, conceptions were confined to 5 months per year, coin ciding with the period of the highest mating activity. Age at first parturi tion, gestation periods, lactation periods, and interbirth intervals were a ll significantly increased resulting in a more than 50% reduced reproductiv e rate under poor conditions. The pattern of sexual behavior during gestati on was influenced by neither nutritional nor social conditions but the freq uency was higher in mufti-male groups. Furthermore, estrus length was signi ficantly increased in mufti-male groups where females tended to mate with a s many resident males as available. Both phenomena, together with a high pe rcentage of sexual behavior occurring outside the mid-cycle estrus, are int erpreted in the light of paternity confusion in mufti-male groups in a spec ies where infanticide by males is regularly observed. The extreme variation in life history traits and mating patterns disclosed here in one species s uggests that future cross-species comparisons should strictly select datase ts based on local ecological and social conditions.