Understanding plants to understand primates

This post was written by Sarah du Plessis, a primate research assistant from Cardiff University. Sarah is volunteering with the PPP between October 2015 and August 2016 as part of her undergraduate degree’s professional training year programme.

One of the main aims of the Primate and Predator Project (PPP) is studying predator-prey interactions, for example how primate species such as the samango monkey interact with predators, such as leopards or eagles. One related area of interest is ascertaining which factors determine primate group movements. Do the samango troops move away from areas they perceive to be high risk, with low visibility and canopy height or do they move towards areas they believe to have lots of resources, for example food, water and sleeping sites? Studying changes in primate food availability through the year (phenology) will help us to answer these questions.

In 2011 we chose 29 plant species to monitor on a monthly basis, as previous studies at Lajuma determined that these plant species were frequently eaten by baboons, samango and vervet monkeys. From each species, 20 individual trees were tagged, from which monthly phenology data is collected. These data includes the number of leaves, fruits, seed pods and flowers from all 580 tagged trees. Combined over a long time period, these data give us an understanding of when each plant species is producing leaves, flowers, seeds and fruits.

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A research assistant measures the circumference at breast height of a phenology tree for our core data (photo Sarah du Plessis)

Primate assistants also collect data from vegetation plots, in which a random GPS point within the larger habituated baboon troop home range (which also encompasses the habituated samango and vervet troops’ ranges) is used as a corner of a 5×5 m square within which all vegetation data is recorded. This includes which plant species are present, and gives us an idea of the spatial distribution of our 29 recorded plant species. Combining the temporal data from phenology and spatial data from vegetation plots allows us to understand which species are fruiting and where, enabling us to determine food availability within the home ranges of our troops.

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The primate team taking vegetation plot data (photo Sarah du Plessis)

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Determining visibility around a vegetation plot using a checkerboard (photo Sarah du Plessis)

Recently, when following the primates and collecting behavioural data, we have recorded them eating a broader range of plant species. In turn, we decided to increase the number of plant species we monitor on a monthly basis. A further 28 plant species frequently eaten by the primates have been identified, added to our ID guide and tagged in areas within the primates home ranges. This will allow our understanding of food availability within the home ranges to improve and the interactions of primates, their surroundings and predators to be better understood.

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Adult female vervet monkey, Violet, eating Prickly Pear, Opuntia ficus-indica, one of the new plant species (photo Koen Groenevelt).

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