This data set includes the demographic (group size, focal age, and sex) and behavioral data (fruit ingestion rates)  from the Lomas Barbudal Monkey Project data set that are used in the paper 'Environmental fluctuations alter the competitive trade-offs of group size in a social primate' by Jacobson et al. These data are used to consider the impact of group size on ranging patterns in a longitudinal perspective. As group size increases, within-group feeding competition is expected to increase as well; however, the costs of within-group feeding competition can be mitigated by the advantages of large group size in between-group competition. Home range size and quality are expected to change as a function of feeding strategies; this will be affected not only by the group's own size, but by the size of neighboring groups. This paper uses a "social relations model" approach to investigating interactions between neighboring groups and the ways in which their fruit ingestion rates and ranging patterns change over time.

These data come from a wild population of monkeys (Cebus imitator, formerly known as Cebus capucinus), residing in Lomas Barbudal Biological Reserve in Guanacaste, Costa Rica, and adjacent private lands (e.g., Hacienda Pelon de la Bajura, Brin d'Amor, and the community of San Ramon de Bagaces). This population has been intensively studied by Susan Perry, with help from her research assistants and students, since 1990. The monkeys are habituated to observer presence.  They are not tagged by researchers, but are recognizable via natural markings (e.g., scars, freckles, variation in the patterning of hair color, and shape of the face). Further data on the history of the project and its core protocols can be found here: Perry, S., Godoy, I. & Lammers, W. 2012. The Lomas Barbudal Monkey Project: Two decades of research on Cebus capucinus. In: Long-term Field Studies of Primates. (Eds. P. Kappeler & D. Watts), Springer, pp. 141-165.

Every day in which a monkey group is encountered, the researchers make note of which monkeys are present in the group. Ages are known fairly reliably for those monkeys born into the studied groups, and they are estimated on the basis of physical appearance for males immigrating into the study area. Because the vegetation is often dense and group members can be spread pretty far apart, it is easy to miss a monkey unless the group has been followed for 6 hours. Therefore censuses of under 6 hours are excluded from this group size data set used in this paper.

Feeding data: Foraging behavior was recorded on a continuous basis during focal animal follows (usually lasting 10 minutes, but follows were longer during some years of the project). During July 2006-June 2021, every time the focal monkey picked up a piece of fruit, the researchers noted every bite that was taken. Whenever the focal animal's hands or mouth was out of view, rendering accurate ingest counts impossible, we called a "time out" so that we had an accurate denominator for the # ingests per unit of time the focal was observed. For this analysis, we only used focal follows collected from focal monkeys when they were residing in a permanent group.

The above data are used in combination with a data set on group movement (i.e. the daily movement tracks and the sleep sites). These data are stored separately in Movebank, with more restricted access, for ethical reasons in order to avoid putting this threatened monkey population at risk from poachers and the pet trade. The movement data are available upon reasonable request from Susan Perry, at the following url: https://www.movebank.org/cms/webapp?gwt_fragment=page=studies,path=study6448057425