Questions about the behavioral ecology of these savanna-woodland chimpanzees center on two (potentially related) topics: the social consequences of low population density, and the use of chimpanzee adaptation to arid, open (mosaic) habitats as a model for understanding early hominin adaptation to similar paleoenvironments.
Central to both is the observation that at Issa, chimpanzee population densities are as little as 1/50th of those seen at forested sites. At such low densities, it would be impractical for a typical community of individuals to patrol territorial boundaries; range sizes of more than 100 square kilometers are not defensible in the way described at forested sites, and conspecific intruder pressure must be dramatically reduced.
Variations in intruder pressure can have profound consequences for primate social structure and behavior (e.g. Moore 1999) and we hope to discover how chimpanzee party stability and (consequently) social relationships are affected by the low population density. Already we have confirmed that, for example, Issa chimpanzees have a minimum community size of 85 individuals and a single individual a home range of at leas 27km2. Both of these figures stem from genotyping of chimpanzee faecal samples and subsequent association indices (Issa chimpanzees are only partially habituated), yet speak to the hypotheses described above concerning how savanna chimpanzee sociality may differ from that of their forest-dwelling cousins.
There has been controversy over using chimpanzees as “referential models” of early hominins, with some claiming that such modeling cannot be useful because modern savanna-living chimpanzees are not in fact 4 million-year-old hominins. This argument both echoes (sterile) debates in early 20th century physics and is based on a misunderstanding of what a “model” is; Moore (1996) discusses these points further. Issa chimpanzees are similar in body size, cranial capacity and overall biology to early (i.e., pre-Homo) hominins, living in an environment similar to that of Ardipithecus and early Australopithecus. To be useful models, insights gained from observing them must be integrated with information from the fossil record, in a manner informed by behavioral ecological theory, before drawing provisional conclusions about our ancestors. This is one goal of our research.
To better understand how Issa chimpanzee behaviour and environment interact, we collect and sieve each fresh chimpanzee feces that we encounter in the forest. Data on diet composition are recorded, with all plant matter (fruits, leaves, skins), especially seed names and quantities, and animal (vertebrate and invertebrate) matter included. Below, Mashaka and Shedrack record data from said sample.
It is not always clear from which plants seed originate, though, and so we have recently built a seed nursery to cultivate seeds of unknown species. Our seed nursery is at camp, where researchers can try to germinate seeds from various primate faeces to build the growing database of consumed plants across the study area.
Additionally, not only knowing WHATchimpanzees eat, but also from WHERE they’re eating something can help us understand how these apes exploit a heterogeneous habitat. To help elucidate feeding tree abundance and distribution, at right, Emily Greathead (left), then a 3rd year undergraduate in Biological Anthropology at the Univ. of Cambridge, UK collected data on how chimpanzee preferred feeding species are distributed in the study area, which will help us answer questions about chimpanzee use of the landscape.
Further, to better understand the extent of Issa chimpanzee ranging across this vast landscaoe, but also to expand our conservation efforts at deterring illegal human encroachment in the study area, we conduct monthly patrols to the periphery of the study area. During these week-long safaris, teams of 3-5 UPP members (see right) camp in remote locations targeting resource rich areas that draw both humans and chimpanzees alike. We remove snares and confiscate illegal forest (timber and bushmeat) harvests, in addition to collecting chimpanzee fecal samples for DNA analyses. Genotyping chimpanzees allows us to track movements of individuals across space and time, providing critical data on ranging patterns and landscape-wide habitat use. Some of this work was recently supported via our debut at crowd-sourcing, at Experiment.com. Fiona Stewart has already begun genetic analyses on some of the samples collected on these safaris, and we are excited to learn more about the Issa chimpanzee ranging patterns later in the year!
Meet some of the Issa chimpanzee community!
In March 2015, we began to see dramatic improvement in habituation progress. That is, whilst previously chimpanzee encounters would last 1-2 hours, and typically be from 40-50 metres, in March, contact durations grew and contact distances shrank, although most individuals remain elusive and often difficult to observe. Nonetheless, we have begun to identify individuals, and introduce you to a few here (photo credits: S. Ramirez Amaya; E. Wondra):