# Spotted Hyena skull size variation across geography favors the energetic equivalence rule over Bergmann’s Rule

## TL;DR

Spotted hyenas' skull sizes vary geographically, with resource availability and population density influencing size more than climate.

## Contribution

New empirical evidence shows energetic equivalence, not Bergmann’s Rule, explains skull size variation in Spotted Hyenas.

## Key findings

- Female spotted hyenas are slightly larger on average than males.
- Skull size variation correlates more with population density than climate.
- Smallest individuals occur between −5.00° and 10.00° latitude and east of 28.50° longitude.

## Abstract

Much historic work has focused on establishing geographical and ecological rules that broadly explain patterns in size variation. We examined geographic variation in Spotted Hyena skull size using geometric morphometrics and spatial statistics. We quantified size variation and sexual size dimorphism of the skull, and evaluated the influence of temperature, precipitation, land cover type, and population density on skull size. We found that female spotted hyenas are slightly larger on average than males. Our analysis of regional differences did not indicate geographic variation in sexual size dimorphism. Skull size of Spotted Hyenas varies with geography but does not adhere to Bergmann’s Rule. The smallest individuals of both sexes occur between −5.00° and 10.00° latitude and east of 28.50° longitude, with larger individuals being found elsewhere. Although Spotted Hyena skull size co-varies in some views with such variables as habitat type and climate indicators, skull size in this species most strongly co-varies with population density. The highest population densities are associated with the smallest skull size, possibly reflecting a relationship between high population density and access to resources. These results suggest that geographic variation in Spotted Hyena skull size is better explained by the energetic equivalence rule than Bergmann’s Rule.

New empirical evidence suggests that access to resources influenced by competition and population density, rather than thermoregulatory needs, drives body size in Spotted Hyenas.

Graphical Abstract