Ecology and life history of the Vlei Rat, Otomys Irroratus (Brants, 1827), on the Van Riebeeck Nature Reserve, Pretoria

[摘要] The ecology and life history of the vlei rat, Otomys irroratus(Brants, 1827), were studied in a population on the Van RiebeeckNature Reserve near Pretoria. Two main procedures were used to collectthe basic information and material for the project. First, a permanentlive-trapping grid was established where 333 animals were captured,marked, released, and recaptured over a period of 26 months, Second,snap-trapping and live-trapping were conducted elsewhere in the studyarea for supplementary material. Because Otomys angoniensis Wroughton,1906, a sibling species of 0. irroratus, also occurred in the study area and grid, it was necessary to define the differences in morphology and ecological distribution between the two species.The ecology and life history of 0. irroratus are described and discussed in regard to the following major topics: taxonomy and morphology, distribution, population dynamics, reproduction, postnatal growth and development, activity, behavior, and economic importance.In addition to the presently used means of distinguishing 0. irroratus and 0. angoniensis, it was found that the hind foot length of the two species differed, being 29-34 mm in 0. irroratus and 25-28 mm in O. angoniensis. The baculum of the two species was also found to be distinct in both shape and size.In Southern Africa 0. irroratus occurs primarily in the grasslandsubregion of the Southern Savanna biotic zone, whileO. angoniensisoccurs primarily in the woodland subregion of the same biotic zone.The preferred habitats of the two species on the study grid weredetermined. There was little overlap of niches and each species hada high degree of association with a different veld type, O. irroratusbeing associated with the more mesic habitat.The population size ofO. irroratus reached a peak in May and alow in September. The population also fluctuated considerably fromone year to the next, with rainfall possibly being the main contributing cause.The ratio of juveniles, subadults, and adults fluctuated primarily in respect to the season when the young were born. The sex ratio did not depart significantly from 1:1. Males comprised 49,5 per cent of the total and females 50,5 per cent.The rate of disappearance after one month from first capture was41 per cent, indicating that a large number of transients and individualsdispersing from their birth site were involved. The overall rateof disappearance, excluding the high first month rate of disappearance,was 3,1 per cent per month.The mortality rate appeared to be at its highest between Augustand September when the food and cover were of very poor quality andquantity. This was also the period when males demonstrated a significantloss in body weight. The major factors causing mortality appeared to be flooding ofthe habitat and owl predation. Floods not only reduced the populationbut significantly interrupted breeding. Otomys irroratus was one ofthe most prominent prey species of both barn and grass owls. The major factors causing mortality appeared to be flooding ofthe habitat and owl predation. Floods not only reduced the populationbut significantly interrupted breeding. Otomys irroratus was one ofthe most prominent prey species of both barn and grass owls.Recapture data revealed that the mean home range size was 1 443m2, while that of males (1 730 m2) was highly significantly different(P

[发布机构] University of Pretoria