Adult sex ratios and partial dominance of females over males in the rock hyrax

Charlotte K. Hemelrijk, Lauren Seex, Matteo Pederboni, Amiyaal Ilany, Eli Geffen, Lee Koren

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4 Scopus citations

Abstract

Competition in group-living animals often results in a dominance hierarchy. The sex that is larger (usually the males) generally dominates the one that is smaller (the females). In certain species, however, despite being smaller, the females dominate several males. Female dominance over males may here arise from the self-reinforcing effects of winning and losing fights, the so-called winner-loser effect, as demonstrated in the model DomWorld. In the model, females may become dominant over more males when the percentage of males in the group is higher due to the higher intensity of aggression of males than females combined with the higher frequency of male–male fights. This association between female dominance and the percentage of adult males in the group has been confirmed in several primate species. Since in the model DomWorld this association requires few assumptions, it should be tested beyond primates. In the present study, we investigated it in the group-living rock hyrax (Procavia capensis), because it fulfilled most requirements. We used data on adults from six groups, collected over 20 years in natural colonies in Israel. We confirmed that body weight and intensity of aggression was greater in males than females. Three measurements indicated that females dominated ca. 70% of the males. Unexpectedly, only in the data where groups comprised several males, female dominance over males was shown to increase with male percentage, but not when including (the many) years in which groups comprised a single male. We attribute this non significance to the limited male–male interactions. One of the requirements of DomWorld is that individuals live in permanent groups, but in rock hyrax there were also bachelor males, that were not permanently associated with a group. Thus, we expected and confirmed that there was no association between the percentage of males and female dominance over males when including them. In conclusion, our results support the hypothesis that the winner-loser effect contributes to the dominance of females over males, and the association between the percentage of males in a group and female dominance over males requires an extra criterion: that most groups contain multiple males.

Original languageEnglish
Article number1004919
JournalFrontiers in Ecology and Evolution
Volume10
DOIs
StatePublished - 29 Nov 2022

Bibliographical note

Publisher Copyright:
Copyright © 2022 Hemelrijk, Seex, Pederboni, Ilany, Geffen and Koren.

Funding

The empirical study was supported by grants from and the U.S.-Israel Binational Science Foundation (2015088, 2019156) and the Israel Science Foundation (577/99, 488/05, 461/09, 550/14, 767/16, 244/19, 245/19). LS was supported by the Leverhulme Trust, SAS-2020-026/2. This cooperation came out of the Workshop of the Lorentz Center in Netherlands awarded to CH, “Dynamics of dominance of females relative to males in a group.” The authors are grateful for the logistic support provided by the staff of the Ein Gedi Nature Reserve and the Ein Gedi Field School, and to the Nature and Park Authority for permission to work at the site. The authors thank all the former students, field assistants, and guests for their valuable help in the field, and Naomi Paz for the linguistic editing. We are grateful to the statistician Gerrit Gort for his statistical advice.

FundersFunder number
Ein Gedi Field School
Ein Gedi Nature Reserve
Leverhulme TrustSAS-2020-026/2
United States-Israel Binational Science Foundation2019156, 2015088
Israel Science Foundation550/14, 767/16, 244/19, 461/09, 245/19, 488/05, 577/99

    Keywords

    • Procavia capensis
    • computational model
    • female dominance
    • intersexual dominance
    • self-organisation
    • sex ratio
    • winner-loser effect

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