Richness, Abundance, and Habitat Relations of Rodents in the Lang Bian Mountains of Southern Viet NamUltrastructure of echimyid and murid rodent spines

We sampled rodents in the Lang Bian Mountains of southern Viet Nam in June 1997 (rainy season) and January 1998 (dry season) by live-trapping. Eight transects in pine (Pinus) savanna and primary forest were sampled for 10 consecutive nights. We captured 11 species of rodents, including 10 murids and one sciurid. Niviventer fulvescens was the most frequently-captured species and apparently was a habitat generalist. That species was captured in both pine savanna and primary forest, but a distinct shift in habitat use occurred between the two seasons. During the rainy season, individuals were captured frequently in both habitats, but during the dry season, N. fulvescens was restricted mostly to forest. Fluctuation in resource abundance was the most likely explanation for that habitat shift; enormous quantities of acorns were present in the dry season, but few resources were available in the rainy season. Other species of rodents were captured less frequently, and several species appeared to be more restricted in their habitat distributions than N. fulvescens.Aristiform spines of the rodents Niviventer fulvescens, Maxomys surifer, Hoplomys gymnurus and 17 species of Proechimys (representing both recognized subgenera and all nine species groups) were studied qualitatively using scanning electron microscopy (SEM) and quantitatively by measuring seven linear dimensions. SEM was used to examine spine tips, bases, longitudinal furrows and cross sections. Spines of the murid rodents N. fulvescens and M. surifer differed from those of the echimyid rodents H. gymnurus and Proechimys spp. in possessing a smaller base with a longer, narrower neck, scaled rather than ridged longitudinal furrows, and a solid internal core and large lacunae at the spine margins. Spines of H. gymnurus differed from those of Proechimys spp. in being considerably more robust with a stout neck at the base, an abruptly-tapering tip and a dense inner layer with a series of smaller lacunae at the spine margins. A factor analysis of spine measurements revealed major differences among N. fulvescens, M. surifer, H. gymnurus, the Proechimys subgenus Trinomys and the nine Proechimys species groups within the subgenus Proechimys. However, all Proechimys species groups clustered closely together. A discriminant function analysis of the nine Proechimys species groups provided generally limited discriminatory power. Although spines are distinct at the generic and subgeneric levels, spines may possess limited diagnostic structure at the level of species within the subgenus Proechimys.