Factors influencing the distributional abundance of two trophic guilds of Peruvian cricetid rodents

The distributional abundance of 13 species of southern Peruvian rodents is significantly correlated with altitude and patterns of vegetation but vegetation is a better predictor than altitude. Coincidental reversals in the altitudinal trends of both vegetation and rodents demonstrate that rodents are responding to vegetation patterns. Abundance and diversity of rodents are greatest around 4000 m elevation which coincides with the region of greatest vegetational abundance and seasonally heavy rainfall.
The rodent communities consist of two separate feeding guilds, omnivores and insectivores and these guilds show distinctly different distributional patterns. Insectivorous species are strongly associated with the zone of seasonally heavy rainfall (4000 m) whereas omnivorous rodents are relatively abundant over a broader spectrum of elevations and habitats. In a previous study of these same communities, we showed a correspondence between rodent morphology and their diets. This study reveals a correspondence between distributional abundance of the various species and their diets. We conclude that the distributional abundance of southern Peruvian rodents is related to the physiological constraints imposed by altitude (climate) and the distributional abundance of food resources.     

Nuclear DNA Metabolism in the Tip of the Cortical Strands of Viscum album L

The tips of the cortical strands of Viscum album were investigatedby autoradiographic and cytophotometric methods. It is shown that DNA synthesis and mitotic activity of the sub-apicalmeristematic cells are constant during the whole year. Theirnuclear DNA content varies from 2C to 4C values. The elongated cells which cover the meristematic zone are characterizedby no DNA synthesis, no mitotic activity and a 2C nuclear DNAcontent. They are ‘blocked’ in the presyntheticphasc G₁ of their cellular cycle, without polyploidy. The relationship between polyploidy and secretion is discussed. Viscum album, mistletoe, nucleus, DNA, polyploidy     

Dietary and morphometric variation in some Peruvian rodent communities: the effect of feeding strategy on evolution

This study examines the relationship between feeding strategy and the evolutionary radiation of three genera of broadly sympatric cricetid rodents (Phyllotis, Akodon, Calomys) found in the Andes of southern Peru. Stomach contents from 13 species reveal that although food habits are variable, both intra- and interspecifically, there are two general feeding strategies: diurnal insectivory and nocturnal herbivory-omnivory. Intraspecific variation in diet was sometimes correlated with altitude. Patterns which might suggest competitive exclusion or ecological release were generally not observed. Interspecific dietary variation is related to morphological variation in both size and shape as revealed by regression and discriminant function analyses. There is a significant negative relationship between the degree of insectivory and body size (wt). The existence of correlated patterns of dietary variation with environment and morphology supports the hypothesis that feeding strategy is adaptive and has been a factor in the evolutionary radiation of these groups. We propose that both phyllotines and akodonts arose from small, insectivorous ancestors. In conjunction with shifts toward herbivory, most phyllotines have evolved larger size plus tooth and jaw modifications. Calomys sorellus is atypical of other phyllotines; it is small, and insectivorous. Most Peruvian Akodon are also small and insectivorous; A. jelskii is an exceptional akodont being large and principally herbivorous.