Interspecific interactions between sympatric apes

Abstract

Gorillas reside in sympatry with chimpanzees over the majority of their range. Compiling all known reports of overlap between apes and augmenting these with observations made over twenty years in the Ndoki Forest, we examine the potential predation-related, foraging, and social contexts of interspecific associations between gorillas and chimpanzees. We reveal a greater diversity of interactions than previously recognized, which range from play to lethal aggression. Furthermore, there are indications that interactions between ape species may serve multiple functions. Interactions between gorillas and chimpanzees were most common during foraging activities, but they also overlapped in several other contexts. From a social perspective, we provide evidence of consistent relationships between particular chimpanzee-gorilla dyads. In addition to providing new insights into extant primate community dynamics, the diversity of interactions between apes points to an entirely new field of study in early human origins as early hominins also likely had opportunities to associate.

Keywords: Animal; Behavioral neuroscience; Biological sciences; Zoology.

Graphical abstract

Figure 1

Costs and benefits of interspecific interactions between great apes The contexts of interspecific associations are predation-related, foraging, and social. The potential benefits of interspecific associations are listed, as well as the deterrents of chimpanzee and gorilla association. It should be noted that these are not mutually exclusive and that interspecific interactions occur in several contexts and may serve multiple functions.

Figure 2

Species distribution and range overlap of wild chimpanzees and gorillas Both western lowland gorillas (Gorilla gorilla) and mountain gorillas (Gorilla beringei) reside in sympatry with chimpanzees (Pan troglodytes) throughout most of their ranges. Inset shows members of the Moto chimpanzee community and Loya gorilla group cofeeding in the crown of a Treculia africana tree in the Goualougo Triangle, Republic of Congo.

Figure 3

Networks of dyadic associations between chimpanzees and gorillas across time periods Chimpanzees (rose-colored nodes) and gorillas (green-colored nodes) maintained a selective set of relationships with particular individuals. Also, gorillas associated twice as much with chimpanzee females that had dependent offspring (0.37 ± 0.14) compared to either chimpanzee males (0.18 ± 0.09) or females without dependents (0.12 ± 0.07). Female apes are represented by circles and males as squares. All nodes are shaded darker with age and scaled in size to represent eigenvector centrality. Strong relationships are represented by thicker and darker lines.

Figure 4

Multidimensional social network of interspecific relationships across contexts and time The graphs show gorillas (green-colored nodes) and chimpanzees (rose-colored nodes) encountered in parties together while cofeeding on Ficus from 2014 to 2016, cofeeding on Ficus from 2017 to 2020, in other social contexts from 2017 to 2020, and aggregated across all contexts from 2014 to 2020. Node size is scaled to layer-specific eigenvector centrality (larger nodes indicate greater network importance) and shaded darker with age. Edge widths are scaled to the strengths of gorilla-chimpanzee dyadic relationships (thicker lines indicate stronger relationships). Horizontal lines across these network layers connect nodes that represent the same individual across all contexts. Overall, the integrated structure of these networks across time and contexts highlights the consistency in relationships between chimpanzees and gorillas.