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Caravel Undergraduate Research Journal

Abstract

Many animals live in social groups for a variety of reasons, whether it is for hunting strategies, predator avoidance, or enhanced resource acquisition. These groups often develop a social network and/or dominance hierarchy within the population, with certain individuals gaining advantages or disadvantages based upon one’s rank within a group. Dominance hierarchies can be assessed on the grounds of structure, and, more recently, steepness.  Structure can be assessed by determining and comparing the rank of each individual (quantified by David’s scores). These scores can then be plotted and analyzed to determine the steepness of the dominance hierarchy. A dominance hierarchy with a high degree of steepness has a greater separation between adjacent ranks than a hierarchy with a low degree of steepness.

This study examines a group of eight Western Lowland Gorillas (Gorilla gorilla gorilla) at the Cincinnati Zoo and Botanical Garden (CZBG) by observing resolved agonistic behaviors in order to quantify dominance and rank individuals using David’s scores, which are then used to quantify the steepness of the dominance hierarchy.

The group in this study exhibits a structure that resembles a pyramidal organization, with a small group of individuals exhibiting a significantly greater David’s score than a larger group of lower ranked individuals. The steepness was calculated to be 0.307, which is a fairly shallow slope. This may be a result of the captive setting, where the competition for resources and external pressures are limited.

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