Showing papers by "R. J. van Aarde published in 2004"
TL;DR: In this paper, the authors used verified and predicted geographic distributions of the Natal multimammate mouse and the Mastomys natalensis (M. coucha) with reference to previously reported incidents of plague in South Africa.
Abstract: The medically and agriculturally important Natal multimammate mouse, Mastomys natalensis (A. Smith, 1834) and the multimammate mouse, M. coucha (A. Smith, 1836), are sibling species and cannot easily be distinguished morphologically. As a consequence, their respective distributional ranges across South Africa remain uncertain. Consequently, locality data of positively identified (karyotyped and/or electrophoretically determined) specimens from South Africa were collated from museum records, the literature, and recently collected material in an attempt to: 1) delimit geographic distributions using positively identified specimens; 2) predict the most likely areas of occurrence of the two sibling species using a variety of selected eco-geographic variables (EGVs) associated with verified locality data; and 3) assess both verified and predicted geographic distributions with reference to previously reported incidents of plague in South Africa. Both verified and predicted distributions are broadly similar and show a geographic separation along the eastern escarpment of South Africa that seems to be influenced by altitude and rainfall. M. natalensis occurs in the low altitude/high rainfall eastern coastal region, extending to northeastern South Africa, while M. coucha keeps to the high altitude/moderate rainfall central and northeastern South Africa. Although the two species were shown to be either sympatric or to occur in close proximity at four localities, additional research is needed to determine the zone of parapatry. Univariate and multivariate analyses showed statistically significant differences between eco-geographic characteristics of collecting localities associated with each of the two species in South Africa. The derived distributions indicate previously reported cases of plague in South Africa, to some extent, coincide with the distributional range of M. coucha rather than M. natalensis.
33 citations
TL;DR: The results, which may have been affected by generally low statistical power, suggest that factors other than mice had a larger impact on invertebrates than mice alone.
Abstract: House mice (Mus domesticus L.) have been present on sub-Antarctic Marion Island since the early 1800s. Several authors have suggested that an increase in mice density as a result of a general warming trend in the sub-Antarctic climate from the 1960s has led to a decline in invertebrate biomass and abundance. These suggestions have been supported by the observation that the invertebrates of nearby mouse-free Prince Edward Island are apparently larger and more numerous than on Marion. Our experiment was designed to determine whether mice have a direct effect on invertebrate abundance, biomass and community structure, or an effect on the vegetation community and thus potentially an indirect effect on invertebrates. We constructed five wire-mesh mouse-free exclosures in one habitat type on Marion Island and recorded both the soil macro-invertebrate community and the vegetation inside and outside each of the exclosures before the start of the experiment in 1996 and twice thereafter (1998 and 2000). Mice had no significant effect on any of the eight prey groups' abundance or biomass, or on community structure (diversity and composition). Four of the prey groups changed significantly over time in either biomass or abundance, independent of the presence of mice. Our results, which may have been affected by generally low statistical power, suggest that factors other than mice had a larger impact on invertebrates than mice alone.
26 citations
TL;DR: The analyses failed to support hypotheses predicting that mothers will skew the sex ratios of their offspring in relation to their body condition, and it was concluded that maternal body condition did not affect foetal sex ratio in buffalo.
Abstract: Many species exhibit skewed sex ratios at birth. Here we investigate the relationships between environmental and maternal variables (as surrogates for maternal condition) and foetal sex in African buffalo Syncerus caffer and elephant Loxodonta africana of the Kruger National Park, South Africa. Using logistic regression no significant effect was found of year, maternal lactational status, maternal age, rainfall or density on foetal sex ratio. Using a subset of our data, it was also concluded that maternal body condition did not affect foetal sex ratio in buffalo. Our analyses failed to support hypotheses predicting that mothers will skew the sex ratios of their offspring in relation to their body condition. In this study, buffalo and elephant produced offspring with a sex ratio close to parity. Our results are discussed in light of the implications for testing such hypotheses in analyses of population level.
23 citations