The Effects of Varying Density and Space on Sociality and Health in Animals

  • K. Myers
  • C. S. Hale
  • R. Mykytowycz
  • R. L. Hughes


This paper represents data on two experiments (using 31 replicates) in which populations of wild rabbits were exposed to different conditions of density and living space within the confined areas of a natural habitat. The analysis offered at this stage relates only to treatment effects.
  1. 1.

    Living space varying — population density held constant.

Under this regime, the most detrimental effects were measured in rabbits in the smallest living space, despite the fact that this was accompanied by a decrease in numbers of animals in the group. There were changes in index organs (liver, spleen, kidney), adrenal morphology and zonation, and behaviour and reproduction. In the smallest space, rates of sexual and aggressive behaviour increased significantly, especially among females, and wounding was higher. There was a fall-off in reproductive capacity in females — lower ovulation rates and smaller numbers of corpora lutea.
  1. 2.

    Living space varying — numbers of animals in population constant.


There was great improvement of the quality of individual animals in each group as living.pace increased. Index organs and endocrines all showed the development of harmful effects in individual rabbits when living space was restricted. Sexual and aggressive behaviour decreased and reproductive capacity increased with increasing space.

The effects of changes in living space were also measurable at embryonic, nestling and young animal levels. In the smallest living areas, the younger classes in the population were severely stunted.

Adult rabbits of both sexes which had been born 12 months previously into high density populations were significantly different, qualitatively, to those born in low density situations.

Such animals were sexually and aggressively very active, but possessed large adrenals and other attributes indicative of ill-health.

Survival in adults followed the trends set by physiological indices. In the young, mortality due to social factors was greatest where group size was largest, irrespective of space.

The data are discussed in relation to other findings. We conclude that the “density syndrome” in mammals is a reality. It is a reaction to a rise in numbers; but in the individual mammal, it is not a response to group size per se but to some form of spatial restriction, either in the form of space itself or some configuration of animals behaving in space.

The response of the individual mammal to this stimulus depends upon its genotype, physiological equipment, and previous social experience. Of the three, we believe that upsets in the physiological homeostases during development could rank, over the short term, as the most important by altering the biological qualities of successive generations.


Adrenal Gland House Mouse Living Space Oryctolagus Cuniculus Female Rabbit 
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© Plenum Press, New York 1971

Authors and Affiliations

  • K. Myers
  • C. S. Hale
  • R. Mykytowycz
  • R. L. Hughes

There are no affiliations available

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