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Rwenzori colobus core unit SNA data - association scans between units, simple association index per dyad, male dispersal events, rainfall and food availability

Citation

Teichroeb, Julie; Adams, Frances; Arseneau-Robar, T. Jean; Bonnell, Tyler (2021), Rwenzori colobus core unit SNA data - association scans between units, simple association index per dyad, male dispersal events, rainfall and food availability, Dryad, Dataset, https://doi.org/10.5061/dryad.866t1g1px

Abstract

1. Multi-level societies are complex, nested social systems where basic social groups (i.e., core units) associate in a hierarchical manner, allowing animals to adjust their group sizes in response to variables such as food availability, predation, or conspecific threat. These pressures fluctuate over time and examining the extent to which this variation affects the clustering of core units into different tiers may be instrumental in understanding the evolution of multi-level societies.

2. The goal of our study was to determine the degree of temporal variability in inter-unit associations in a multi-level society of Rwenzori Angolan colobus monkey (Colobus angolensis ruwenzorii), and to determine the social and ecological factors that underlie association patterns. The C. a. ruwenzorii multi-level society consists of at least three tiers, with core units clustering into clans that share a home range in a band tier.

3. We performed social network analyses on 21 months of association data from 13 core units (totaling 139 identifiable individuals) at Lake Nabugabo, Uganda. We described the patterns of variation in core-unit associations over time and investigated how changes in rainfall, food availability, and inter-unit dispersals were correlated with these associations over the short-term (month to month) and long-term (year to year).

4. Although clans were relatively stable, larger-scale changes in association patterns included the formation of an all-male unit and the transfer of one core unit between clans (within the band tier). Seasonally, core units associated significantly more when fruit, their preferred food source, was abundant (i.e., social networks were denser and more clustered) and there was no direct effect of rainfall seasonality or young leaf availability. Male dispersals also occurred more during periods of high fruit availability, suggesting that greater band cohesion allowed males to prospect and transfer between core units. Once males transferred, their previous and new units associated significantly more with one another than with other core units for 1-2 months post-dispersal. The dispersal of five males from one core unit to another in a different clan co-occurred with this core unit switching its clan affiliation.

5. By examining temporal shifts in social network structure among core units, this study shows the inter-connected roles that food availability and dispersal have in shaping the C. a. ruwenzorii multi-level social system. Our findings highlight how ecological conditions can drive association patterns, impact interunit relationships, and influence social organization.

Funding

Natural Sciences and Engineering Research Council of Canada, Award: RGPIN-2016-06321