Ecology and behaviour of the lesser Egyptian gerbil (Gerbillus gerbillus) (Rodentia: Gerbillidae) from the Negev Highlands and Arava valley, Israel

Populations of rodents isolated on islands are often different from mainland populations in their life history and behaviour. We studied two populations of G. gerbillus - from a small isolated sand patch in the central Negev ("island" population), and one from a large sand massif in the Arava valley ("mainland" population). We asked (a) whether there are any between-population differences in body size, demography, reproduction rate and behaviour; (b) do these differences (if any) conform to "island syndrome" and (c) what features allow the "island" population to persist on a very small and isolated area. The period of deep density decrease and low reproductive activity was much shorter in the "mainland" than in the "island" population. Difference in gerbil density between areas was not related to the difference in food resources. Age structure of both populations was characterized by a very high proportion of adults. Animals on the "island" survived longer than those on the "mainland". Mean area of home range of males was significantly larger than that of females on the "mainland", but not on the "island". "Island" females had larger home ranges than "mainland" females. No sexual dimorphism in body mass was found in the "island" population. In contrast, "mainland" males were heavier than cohabitating females. Gerbils from the "mainland" were significantly heavier than their "island" conspecifics. Encounters of male G. gerbillus from the same population were characterized by a low level of cohesive behaviour and a significantly higher level of agonism. "Island" individuals manifested mainly direct aggressive behaviours, whereas the agonistic behaviour in the "mainland" individuals was mainly ritualized. We concluded, that the characteristics of the "island" population did not conform to those predicted based on the "island syndrome" concept.