A demographic history of a population of howler monkeys (Alouatta palliata) living in a fragmented landscape in Mexico

Long-term field studies of primates are critical for our understanding of life history and the processes driving changes in demography. Here, we present the first long-term demographic data for the northernmost population of the mantled howler monkey (Alouatta palliata). We followed 10 groups of howler monkeys living in a highly fragmented landscape between 2000 and 2011. Forest fragmentation did not seem to play a major role in the dynamics of our population, as the population size remained relatively stable over the 10-year study period, and birth rates and inter-birth intervals were comparable to those of howler monkeys at other sites. Moreover, dispersal events were commonplace, particularly secondary dispersal (individuals emigrating from groups that they had previously immigrated into), which supports the suggestion that this may be an important component of the reproductive strategy of the mantled howler monkey. Finally, we found a marked effect of seasonality on the population dynamics of our study population. In particular, the period of lowest temperatures and resource scarcity between November and March was associated with higher mortality and reproductive inhibition, while the period of resource abundance between April and May was associated with the majority of conceptions and weaning of offspring. This, in turn, could be influencing dispersal patterns in our study area, as male howler monkeys seem to time some of their immigrations into new groups to coincide with the start of the period of higher fertility, while females preferentially joined new groups several months before the onset of this period.