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

Pillay, Neville, and Rymer, Tasmin Lee (2017) Behavioural correlates of group size and group persistence in the African ice rat Otomys sloggetti robertsi. Behavioral Ecology and Sociobiology, 71. 62. pp. 1-13.

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Abstract

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 greater in smaller colonies because fewer individuals engage 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.

Item ID: 50205
Item Type: Article (Research - C1)
ISSN: 1432-0762
Keywords: ecological constraints; group size; reproductive output; social behaviour; sociality; thermoregulation
Funders: National Research Foundation, South Africa (NRFSA), University of the Witwatersrand
Projects and Grants: NRFSA grant number 2069110
Date Deposited: 13 Sep 2017 23:44
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060201 Behavioural Ecology @ 50%
06 BIOLOGICAL SCIENCES > 0608 Zoology > 060801 Animal Behaviour @ 20%
06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060304 Ethology and Sociobiology @ 30%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 60%
96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960810 Mountain and High Country Flora, Fauna and Biodiversity @ 40%
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