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Geographic intra-specific variation in social organization is driven by population density

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Abstract

Social flexibility enables individuals to switch between group and solitary living and is suggested to be an adaptation to varying environments. Several previous studies on different species compared two populations and hypothesized that observed differences in the social organization were due to differences in population density but lacked the necessary sample size to test this prediction. In a previous 8-year long-term study, we showed that one population of African striped mice (Rhabdomys pumilio) displayed temporal social flexibility, living solitarily in years when population density was low but in groups in years when population density was high. Building on this temporal variation, we now tested whether geographic variation reveals the same pattern. We studied 6 populations in discrete geographical locations simultaneously, predicting more solitary living in populations with lower population density. Population density correlated significantly with the percentage of striped mice living in groups whereas other (environmental) factors were not significant. Moreover, some individuals dispersed over unoccupied habitats between these populations, switching from group to solitary living. Geographic variation in population density could make social flexibility adaptive because it allows individuals to respond quickly to the prevailing conditions they experience post dispersal. Our results suggest that geographic variation drives the evolution of social flexibility in our metapopulation of striped mice, causing intra-specific variation in its social organization, which might also be important in other species, especially in species with a fast life history.

Significance statement

Populations of the same species can differ in their social organization. It has often been assumed that this is due to differences in population density. We studied 6 populations of the African striped mice, showing that more mice were solitary living when population density was low. Thus, we demonstrated that population differences in social organization were due to differences in population density.

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Data availability

All data generated or analyzed during this study are included in the supplementary information files of this published article.

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Acknowledgments

We thank P. Vuarin., C. Rochais, and L. Kotze and several field assistants for help in collecting the data. The comments of A. Ophir and of three anonymous referees significantly improved the manuscript. We are grateful to Goegap Nature Reserve. This study was made possible by the administrative and technical support of the Succulent Karoo Research Station (registered South African NPO 122-134).

Funding

This work was supported by the National Research Foundation (South Africa), the University of Witwatersrand (South Africa), and the CNRS (France) under the framework of the International Research Project DROUGHT (Response to Drought, Climate Change and Climate Unpredictability: Social Flexibility, Adaptation, and Species Range Shifts)–Laboratoire International Associé (IRP/LIA).

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Authors and Affiliations

  1. CNRS, UMR7178, 67087, Strasbourg, France

    Carsten Schradin, Gildas Lemonnier & Charlotte Anaïs Olivier

  2. School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa

    Carsten Schradin, Florian Drouard, Gildas Lemonnier, Richard Askew & Neville Pillay

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  1. Carsten Schradin
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  2. Florian Drouard
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  3. Gildas Lemonnier
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  5. Charlotte Anaïs Olivier
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Correspondence to Carsten Schradin.

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The authors declare that they have no conflict of interest.

Ethical approval

All animal experimentation met the ABS/ASAB guidelines for the ethical treatment of animals. Animal ethics clearance was provided by the University of the Witwatersrand (AESC 2007/40/01), following the guidelines for the use and care of animals in teaching and research of the University of the Witwatersrand which complies with the University’s ethical and legal practices and with the National Code.

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Communicated by A. G Ophir

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Schradin, C., Drouard, F., Lemonnier, G. et al. Geographic intra-specific variation in social organization is driven by population density. Behav Ecol Sociobiol 74, 113 (2020). https://doi.org/10.1007/s00265-020-02896-z

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  • DOI: https://doi.org/10.1007/s00265-020-02896-z

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