The role of agonistic behaviour in the population regulation of two syntopic African grassland rodents, the striped mouse<i>Rhabdomys pumilio</i>(Sparrman 1784) and the multimammate mouse<i>Mastomys natalensis</i>(A. Smith 1834) (Mammalia Rodentia)

Abstract

The population dynamics and agonistic behaviour of syntopic striped mice Rhabdomys pumilio (Sparrman 1784) and multimammate mice Mastomys natalensis (A. smith 1834) were investigated monthly throughout a year in the midlands of KwaZulu-Natal, South Africa, to test the null hypothesis that levels of agonistic behaviour do not change with increasing population density. The second null hypothesis was that agonistic behaviour of adults does not cause mortality or dispersal of subadult mice. Levels of aggression in paired encounters of same sex, intraspecific individuals increased in each species from winter to summer, and declined in autumn; corresponding with the breeding season but not with population density. Adults of each species were significantly more aggressive towards adult conspecifics than towards subadult conspecifics. The social organizations and life histories of R. pumilio and M. natalensis are different and affect their population biology. The control of density in R. pumilio populations occurs through territorial behaviour, whereas that of M. natalensis is through a dominance hierarchy. The results obtained suggest that aggressive behaviour was generated by interference and exploitation competition among adults for resources including food, space (mainly by females) and mates (mainly by males); the survival and dispersal of young mice was not affected by the aggressive behaviour of adults.