Behavioural correlates of group size and group persistence in the African ice rat Otomys sloggetti robertsi

Original Article


The relationship between group size and fitness has attracted much interest, with many attempts made to detect an optimal group size. Group size is determined by the benefits and costs influencing group formation, which also influences whether groups persist or fail. We investigated whether group size is associated with success (individual survival and reproductive output) in the African ice rat Otomys sloggetti robertsi. Ice rats form mixed-sex plural-breeding colonies that trade off the benefits of huddling below-ground against within-colony resource competition above-ground. We measured behavioural correlates of individual success in summer and winter, focusing on energy saving (basking), acquisition (foraging) and use (burrow maintenance, distance travelled for foraging) behaviours. We predicted that (1) individuals in larger colonies would forage and travel more to find food because of greater within-colony competition for resources; (2) individuals in larger colonies would bask less than individuals in smaller colonies because of the greater energy savings generated from huddling in larger groups; and (3) burrow maintenance would be greater in smaller colonies because of fewer individuals engaging in this task. We showed that colonies succumbed or persisted as a group (i.e. most individuals present or all absent). In particular, in both seasons, individuals in smaller groups (≤5 individuals) were more likely to fail, while those in larger groups (≥12 individuals) were more likely to persist. The persistence of colonies was positively predicted by foraging and negatively by basking. Foraging was greater in larger colonies and burrow maintenance was greater in smaller colonies. While females of larger colonies produced more offspring in total, reproductive output (per capita offspring production) was not correlated with colony size. Individual ice rats in larger colonies accrued fitness benefits, which were predicted, proximally, by greater foraging and possibly energy savings in larger huddling groups.

Statement of significance

What proximally determines the relationship between group size, individual success and colony persistence? In ice rats, individuals in larger groups persist, which is correlated with more foraging. Larger groups possibly enjoy the benefits of huddling in larger groups, which are re-channelled into energy-intense activities. Groups failed or persisted as a unit. Investigating the behavioural correlates of the relationship between group size and persistence provides insight into the proximal underpinnings of this relationship.


Ecological constraints Group size Reproductive output Social behaviour Sociality Thermoregulation 



We are grateful to Luke Duncan and several field volunteers, whose technical assistance has been invaluable. The comments of three anonymous reviewers greatly improved the manuscript.

Compliance with ethical standards


This work was supported by the National Research Foundation (grant number 2069110) and the University of the Witwatersrand.

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

Our study was approved by the Animal Ethics Screening Committee of the University of the Witwatersrand (2000/12/2a, 2000/21/2a). All protocols complied with the current laws and regulations in South Africa, and all applicable international, national and/or institutional guidelines for the care and use of animals were followed.

Supplementary material

265_2017_2293_MOESM1_ESM.docx (15 kb)
ESM 1 (DOCX 14 kb)


  1. Armitage KB (1987) Social dynamics of mammals: reproductive success, kinship and individual fitness. Trends Ecol Evol 2:279–284CrossRefPubMedGoogle Scholar
  2. Armitage KB, Schwartz OA (2000) Social enhancement of fitness in yellow-bellied marmots. P Natl Acad Sci USA 97:12149–12152CrossRefGoogle Scholar
  3. Arnold W (1988) Social thermoregulation during hibernation in alpine marmots (Marmota marmota). J Comp Physiol B 158:151–156CrossRefPubMedGoogle Scholar
  4. Bacon PJ, Ball F, Blackwell P (1991) Analysis of a model of group territoriality based on the resource dispersion hypothesis. J Theor Biol 148:433–444CrossRefGoogle Scholar
  5. Batchelor TP, Briffa M (2011) Fight tactics in wood ants: individuals in smaller groups fight harder but die faster. Proc R Soc Lond B 278:3243–3250CrossRefGoogle Scholar
  6. Batchelor TP, Santini G, Briffa M (2012) Size distribution and battles in wood ants: group resource-holding potential is the sum of the individual parts. Anim Behav 83:111–117CrossRefGoogle Scholar
  7. Bazin RC, MacArthur RA (1992) Thermal benefits of huddling in the muskrat (Ondatra zibethicus). J Mammal 73:559–564CrossRefGoogle Scholar
  8. Benjamini Y, Hochberg Y (1995) Controlling the false discovery rate: a practical and powerful approach to multiple testing. J R Stat Soc B 57:289–300Google Scholar
  9. Boesch C (1994) Cooperative hunting in wild chimpanzees. Anim Behav 48:653–667CrossRefGoogle Scholar
  10. Brown JL (1982) Optimal group size in territorial animals. J Theor Biol 95:793–810CrossRefGoogle Scholar
  11. Canals M, Rosenmann M, Bozinovic F (1989) Energetics and geometry of huddling in small mammals. J Theor Biol 141:181–189CrossRefPubMedGoogle Scholar
  12. Carr GM, Macdonald DW (1986) The sociality of solitary foragers: a model based on resource dispersion. Anim Behav 34:1540–1549CrossRefGoogle Scholar
  13. Creel S, Creel NM (2015) Opposing effects of group size on reproduction and survival in African wild dogs. Behav Ecol 26:1414–1422CrossRefGoogle Scholar
  14. Crofoot MC, Wrangham RW (2010) Intergroup aggression in primates and humans: the case for a unified theory. In: Kappeler PM, Silk JB (eds) Mind the gap—tracing the origins of human universals. Springer, Heidelberg, pp 171–195Google Scholar
  15. Dehn MM (1990) Vigilance for predators: detection and dilution effects. Behav Ecol Sociobiol 26:337–342Google Scholar
  16. Dittus WPJ (1988) Group fission among wild toque macaques as a consequence of female resource competition and environmental stress. Anim Behav 36:1626–1645CrossRefGoogle Scholar
  17. Dugdale HL, Ellwood SA, Macdonald DW (2010) Alloparental behaviour and long-term costs of mothers tolerating other members of the group in a plurally breeding mammal. Anim Behav 80:721–735CrossRefGoogle Scholar
  18. Ebensperger LA, Bozinovic F (2000) Communal burrowing in the hystricognath rodent, Octodon degus: a benefit of sociality? Behav Ecol Sociobiol 47:365–369CrossRefGoogle Scholar
  19. Ebensperger LA, Correa LA, León C, Ramírez-Estrada J, Abades S, Villegas Á, Hayes LD (2016) The modulating role of group stability on fitness effects of group size is different in females and males of a communally rearing rodent. J Anim Ecol 85:1502–1515CrossRefPubMedGoogle Scholar
  20. Ebensperger LA, Rivera DS, Hayes LD (2012) Direct fitness of group living mammals varies with breeding strategy, climate and fitness estimates. J Anim Ecol 81:1013–1023CrossRefPubMedGoogle Scholar
  21. Edelman AJ, Koprowski JL (2007) Communal nesting in asocial Abert’s squirrels: the role of social thermoregulation and breeding strategy. Ethology 113:147–154CrossRefGoogle Scholar
  22. Emlen ST (1982) The evolution of helping. I. An ecological constraints model. Am Nat 119:29–39CrossRefGoogle Scholar
  23. Emlen ST (1994) Benefits, constraints and the evolution of the family. Trends Ecol Evol 9:282–285CrossRefPubMedGoogle Scholar
  24. Foster KR, Fortunato A, Strassmann JE, Queller DC (2002) The costs and benefits of being a chimera. Proc R Soc Lond B 269:2357–2362CrossRefGoogle Scholar
  25. Gettinger RD (1984) Energy and water metabolism of free-ranging pocket gophers, Thomomys bottae. Ecology 65:740–751CrossRefGoogle Scholar
  26. Gilbert C, McCafferty D, Le Maho Y, Martrette J-M, Giroud S, Blanc S, Ancel A (2010) One for all and all for one: the energetic benefits of huddling in endotherms. Biol Rev 85:545–569PubMedGoogle Scholar
  27. Gilbert P, Price J, Allan S (1995) Social comparison, social attractiveness and evolution: how might they be related? New Ideas Psychol 13:149–165CrossRefGoogle Scholar
  28. Gilchrist JS (2004) Pup escorting in the communal breeding banded mongoose: behaviour, benefits, and maintenance. Behav Ecol 15:952–960CrossRefGoogle Scholar
  29. Glaser H, Lustick S (1975) Energetics and nesting behaviour of the northern white-footed mouse, Peromyscus leucopus noveboracensis. Physiol Zool 48:105–113CrossRefGoogle Scholar
  30. Grab SW, Deschamps CL (2004) Geomorphological and geoecological controls and processes following gully development in alpine mires, Lesotho. Arctic Antarct Alpine Res 36:49–58CrossRefGoogle Scholar
  31. Hatchwell BJ, Komdeur J (2000) Ecological constraints, life history traits and the evolution of cooperative breeding. Anim Behav 59:1079–1086CrossRefPubMedGoogle Scholar
  32. Hayes LD (2000) To nest communally or not to nest communally: a review of rodent communal nesting and nursing. Anim Behav 59:677–688CrossRefPubMedGoogle Scholar
  33. Hinze AJ (2005) Social behaviour and activity patterns of the African ice rat Otomys sloggetti robertsi. PhD thesis, University of the Witwatersrand, Johannesburg South Africa, pp 1–139Google Scholar
  34. Hinze A, Pillay N (2006) Life in an African alpine habitat: diurnal activity patterns of the ice rat, Otomys sloggetti robertsi. Arctic Antarct Alpine Res 38:540–546CrossRefGoogle Scholar
  35. Hinze A, Pillay N, Grab S (2006) The burrow system of the African ice rat Otomys sloggetti robertsi. Mammal Biol 7:356–365CrossRefGoogle Scholar
  36. Hinze A, Rymer T, Pillay N (2013) Spatial dichotomy of sociality in the African ice rat. J Zool Lond 290:208–214CrossRefGoogle Scholar
  37. Hodge SJ (2005) Helpers benefit offspring in both the short and long-term in the cooperatively breeding banded mongoose. Proc R Soc Lond B 272:2479–2484CrossRefGoogle Scholar
  38. Janson CH (1988) Food competition in brown capuchin monkeys (Cebus apella): quantitative effects of group size and tree productivity. Behaviour 105:53–76CrossRefGoogle Scholar
  39. Judge DS, Carey JR (2000) Postreproductive life predicted by primate patterns. J Geront 55A:B201–B209CrossRefGoogle Scholar
  40. Kenward R, South A, Walls S (2002) Ranges 6. Anatrack Ltd, DorsetGoogle Scholar
  41. Killick DJB (1963) An account of the plant ecology of the Cathedral Peak area of the Natal Drakensberg. Botanical Survey of South Africa, Memoir No. 34. Republic of South Africa, Government Printer, PretoriaGoogle Scholar
  42. Kinnaird MF, O’Brien TG, Nurcahyo A, Prasetyaningrum M (2002) Inter-group interactions and the role of calling among siamangs. XIXth Congress of the International Primatological Society. Beijing, ChinaGoogle Scholar
  43. Krause J, Ruxton GD (2002) Living in groups. Oxford University Press, New YorkGoogle Scholar
  44. Lacey EA (2004) Sociality reduces individual direct fitness in a communally breeding rodent, the colonial tuco-tuco (Ctenomys sociabilis). Behav Ecol Sociobiol 56:449–457CrossRefGoogle Scholar
  45. Liker A, Bókony V (2009) Larger groups are more successful in innovative problem solving in house sparrows. P Natl Acad Sci USA 106:7893–7898CrossRefGoogle Scholar
  46. Macdonald DW, Carr GM (1989) Food security and the rewards of tolerance. In: Standen V, Foley R (eds) Comparative socioecology: the behavioural ecology of humans and animals, vol 8. Blackwell Scientific, Oxford, pp 75–99Google Scholar
  47. Markham AC, Gesquiere LR, Alberts SC, Altmann J (2015) Optimal group size in a highly social mammal. P Natl Acad Sci USA 112:14882–14887CrossRefGoogle Scholar
  48. Martin P, Bateson P (1986) Measuring behaviour. An introductory guide. Cambridge University Press, New YorkGoogle Scholar
  49. McComb K, Packer C, Pusey A (1994) Roaring and numerical assessment in contests between groups of female lions, Panthera leo. Anim Behav 47:379–387CrossRefGoogle Scholar
  50. McGuire B, Getz LL, Oli MK (2002) Fitness consequences of sociality in prairie voles, Microtus ochrogaster: influence of group size and composition. Anim Behav 64:645–654CrossRefGoogle Scholar
  51. Mokotjomela T, Schwaibold U, Pillay N (2009) Does the ice rat Otomys sloggetti robertsi contribute to habitat change in Lesotho? Acta Oecol 35:437–443CrossRefGoogle Scholar
  52. Mokotjomela T, Schwaibold U, Pillay N (2010) Population surveys of the ice rat Otomys sloggetti robertsi in the Lesotho Drakensberg. Afr Zool 45:225–232CrossRefGoogle Scholar
  53. Mosser AA, Packer C (2009) Group territoriality and the benefits of sociality in the African lion, Panthera leo. Anim Behav 78:359–370CrossRefGoogle Scholar
  54. Mumme RL, Bowman R, Pruett MS, Fitzpatrick JW (2015) Natal territory size, group size, and body mass affect lifetime fitness in the cooperatively breeding Florida Scrub-Jay. Auk 132:634–646CrossRefGoogle Scholar
  55. Oli MK, Armitage KB (2003) Sociality and individual fitness in yellow-bellied marmots: insights from a long-term study (1962-2001). Oecologia 136:543–550CrossRefPubMedGoogle Scholar
  56. Parker GA (1974) Assessment strategy and the evolution of fighting behaviour. J Theor Biol 47:223–243CrossRefPubMedGoogle Scholar
  57. Parrish JK, Edelstein-Keshet L (1999) Complexity, pattern, and evolutionary trade-offs in animal aggregation. Science 284:99–101CrossRefPubMedGoogle Scholar
  58. Pollock GB (1994) Social competition or correlated strategy? Evol Ecol 8:221–229CrossRefGoogle Scholar
  59. Putaala A, Hohtola E, Hissa R (1995) The effect of group size on metabolism in huddling grey partridge (Perdix perdix). Comp Biochem Physiol B 111:243–247CrossRefGoogle Scholar
  60. Radford AN (2003) Territorial vocal rallying in the green woodhoopoe: influence of rival group size and composition. Anim Behav 66:1035–1044CrossRefGoogle Scholar
  61. Rasa OAE (1989) The costs and effectiveness of vigilance behaviour in the dwarf mongoose: implications for fitness and optimal group size. Ethol Ecol Evol 1:265–282CrossRefGoogle Scholar
  62. Richter TA (1997) Does the southern African ice rat (Otomys sloggetti) show morphological adaptation to cold? J Zool Lond 242:384–387CrossRefGoogle Scholar
  63. Richter TA, Webb PI, Skinner JD (1997) Limits to the distribution of the southern African ice rat (Otomys sloggetti): thermal physiology or competitive exclusion? Funct Ecol 11:240–246CrossRefGoogle Scholar
  64. Roberts G (1996) Why individual vigilance declines as group size increases. Anim Behav 51:1077–1086CrossRefGoogle Scholar
  65. Rowe-Rowe DT, Meester J (1982) Habitat preferences and abundance relations of small mammals in the Natal Drakensberg. S Afr J Zool 17:202–209CrossRefGoogle Scholar
  66. Rubenstein DR (2011) Spatiotemporal environmental variation, risk aversion, and the evolution of cooperative breeding as a bet-hedging strategy. P Natl Acad Sci USA 108:10816–10822CrossRefGoogle Scholar
  67. Rymer TL, Kinahan AA, Pillay N (2007) Fur characteristics of the African ice rat Otomys sloggetti robertsi: modifications for an alpine existence. J Therm Biol 32:428–432CrossRefGoogle Scholar
  68. Saltzman W, Ahmed S, Fahimi A, Wittwer DJ, Wegner FH (2006) Social suppression of female reproductive maturation and infanticidal behaviour in cooperatively breeding Mongolian gerbils. Horm Behav 49:527–537CrossRefPubMedGoogle Scholar
  69. Scantlebury M, Bennett NC, Speakman JR, Pillay N, Schradin C (2006) Huddling in groups leads to daily energy savings in free-living African four-striped grass mice, Rhabdomys pumilio. Funct Ecol 20:166–173CrossRefGoogle Scholar
  70. Schradin C, Schneider C, Yuen CH (2009) Age at puberty in male African striped mice: the impact of food, population density and the presence of the father. Funct Ecol 23:1004–1013CrossRefGoogle Scholar
  71. Schradin C, Schubert M, Pillay N (2006) Winter huddling groups in the striped mouse. Can J Zool 84:693–698CrossRefGoogle Scholar
  72. Schwaibold UH (2005) Foraging biology and habitat use of the southern African ice rat, Otomys sloggetti robertsi. PhD thesis, University of the Witwatersrand, Johannesburg, South Africa, pp 1–138Google Scholar
  73. Schwaibold U, Pillay N (2003) The gut morphology of the African ice rat, Otomys sloggetti robertsi, adaptations to cold environments and sex-specific seasonal variation. J Comp Physiol B 173:653–659CrossRefPubMedGoogle Scholar
  74. Schwaibold U, Pillay N (2006) Behavioural strategies of the African ice rat Otomys sloggetti robertsi in the cold. Physiol Behav 88:567–574CrossRefPubMedGoogle Scholar
  75. Schwaibold U, Pillay N (2010) Habitat use in the ice rat Otomys sloggetti robertsi. S Afr J Wildl Res 40:64–72CrossRefGoogle Scholar
  76. Silk JB (2007) The adaptive value of sociality in mammalian groups. Philos T Roy Soc B 362:539–559CrossRefGoogle Scholar
  77. Sitch S, Huntingford C, Gedney N et al (2008) Evaluation of the terrestrial carbon cycle, future plant geography and climate-carbon cycle feedbacks using five dynamic global vegetation models (DGVMs). Glob Change Biol 14:2015–2039CrossRefGoogle Scholar
  78. Solomon NG, Hayes LD (2009) The biological basis of alloparental behaviour in mammals. In: Bentley G, Mace R (eds) Substitute parents: biological and social perspectives on alloparenting in human societies. Berghahn Books, Herndon, pp 13–49Google Scholar
  79. Snaith TV, Chapman CA (2007) Primate group size and interpreting socioecological models: do folivores really play by different rules? Evol Anthropol 16:94–106CrossRefGoogle Scholar
  80. Stahler DR, MacNulty DR, Wayne RK, von Holdt B, Smith DW (2013) The adaptive value of morphological, behavioural and life-history traits in reproductive female wolves. J Anim Ecol 82:222–234CrossRefPubMedGoogle Scholar
  81. Stapp P, Pekins PJ, Mautz WM (1991) Winter energy expenditure and the distribution of southern flying squirrels. Can J Zool 69:2548–2555CrossRefGoogle Scholar
  82. Tschinkel WR, Adams ES, Macom T (1995) Territory area and colony size in the fire ant Solenopsis invicta. J Anim Ecol 64:473–480CrossRefGoogle Scholar
  83. Vickery WL, Millar JS (1984) The energetics of huddling by endotherms. Oikos 43:88–93CrossRefGoogle Scholar
  84. Watts DP (1985) Relations between group size and composition and feeding competition in mountain gorilla groups. Anim Behav 33:72–85CrossRefGoogle Scholar
  85. Willan K (1990) Reproductive biology of the southern African ice rat. Acta Theriol 35:39–51CrossRefGoogle Scholar
  86. Young AJ, Jarvis JUM, Barnaville J, Bennett NC (2015) Workforce effects and the evolution of complex sociality in wild Damaraland mole rats. Am Nat 186:302–311CrossRefPubMedGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2017

Authors and Affiliations

  1. 1.School of Animal, Plant and Environmental ScienceUniversity of the WitwatersrandJohannesburgSouth Africa
  2. 2.College of Science and EngineeringJames Cook UniversityCairnsAustralia
  3. 3.Centre for Tropical Environmental and Sustainability SciencesJames Cook UniversityCairnsAustralia

Personalised recommendations