Volume 68, Issue 1

The coexistence of desert small mammals can be explained by differences in microhabitat use, morphology, body size, diet and foraging. The aim of this study was to quantify the structure of small mammal assemblages and the seasonal fluctuations in their abundance using mark – recapture techniques in habitats of different structural heterogeneity (mesquite forest, creosotebush community, and sand dunes) in the temperate Monte desert of Argentina. Habitat heterogeneity was characterised by 10 vegetation variables. The mesquite forest and the creosotebush community showed the highest diversity and habitat heterogeneity. The relative abundance of each species underwent remarkable variations between habitats. The sigmodontinae rodents Graomys griseoflavus and Eligmodontia typus were the dominant species in the mesquite forest and sand dunes, respectively, whereas no dominant species was observed in the creosotebush habitat. Abundance varied throughout the year, reaching maximum density in autumn and spring.

Ctenomys (tuco-tuco) is a small fossorial herbivorous rodent of the Monte desert, and is probably the most abundant and widely distributed rodent in these arid lands. The aim of this study is to describe the impact of C. mendocinus herbivory on shrubs in two plant communities (Reserve of Divisadero Largo and Villavicencio) in the upper limit of the Monte desert, and to assess the association between environmental variables and level of damage caused by tuco-tucos. Herbivory by tuco-tucos affected 39% of the total shrubs in Villavicencio, and 9.37% of the total plants sampled in Divisadero Largo. In Villavicencio, the most highly damaged species were Larrea divaricata (65%), Lycium aff. chilensis (41%), Junellia seriphioides (38%) and Menodora decemfida (33%). In Divisadero Largo, damage was lower: J. seriphioides (14%), Lycium chilensis (9%), and M. decemfida (6%). With respect to the association between level of damage caused by tuco-tucos and environmental variables, in Divisadero Largo the level of damage was negatively associated with both maximum and mean soil depth, while in Villavicencio it was negatively associated with plant cover, and positively associated with maximum and mean soil depth. There was no association between level of damage caused by tuco-tucos and mean stone diameter.

Milk stealing and fostering care is rare among mammals (Packer et al . 1992). Such behaviour can benefit neonates and possibly the nursing foster mother (Roulin 2002, 2003). However, it also likely comes at a cost to the fostering mother and her dependent young. Neonates may increase their chances of survival by sneak-suckling unrelated females, or by obtaining milk with the consent of mothers of other neonates. However, chances are greater that females protective of their limited milk resources will aggressively prevent unrelated young from suckling. Risks of being bitten, attacked or killed by adult females presumably outweigh the potential benefits that might be achieved by sneak-suckling.

Natural diets of Didelphidae species vary in the amounts of invertebrates, fruits and small vertebrates eaten. We investigated the digestive morphology of ten species of didelphid marsupials varying in food habits. The purpose was to describe and to compare the shape and relative size of the digestive tract portions among species studied and relate them to food habits. The form of the gastrointestinal tract in this family is simple, with a unilocular stomach, small intestine, large intestine and caecum. Caluromys philander was the species with highest association between digestive tract measurements and its frugivorous habits. However, although its caecum is morphologically distinct from the other species, the relative length is small when compared to the more faunivorous Metachirus nudicaudatus . Stomach length of Philander frenata is related to a more carnivorous diet, while large intestine length of Didelphis aurita is related to its omnivore diet. The digestive tract measurements of the other species appear to be related with a variable degree of morphological differentiation from a generalized form related to omnivory toward a more carnivorous diet. Great caecum relative size distinguished Metachirus nudicaudatus from the most other species and its relationship with diet is not well understood.

Coat-colour polymorphism, the relative frequencies of red, brown and black fur-morphs, was examined in nine populations of the Eurasian red squirrel ( Sciurus vulgaris L.) in northern Italy. The proportions of the three different coat-colours differed between populations. Red morphs were most common in mixed woodlands of the Upper Po-plain, but rare in populations from the Alps. The highest frequencies of black morphs were found in subalpine conifer forests in the western Alps (Gran Paradiso) and in montane mixed conifer forests in the central Alps (Valtellina). Coat-colour did not affect juvenile survival, and there were no significant differences in mean foot length or body mass among subadults and adults of different colour-morphs. However, inter-population variation in the frequency of black morphs was positively correlated with the proportion of spruce (and/or fir) in the forest and with the density of trees. We suggest that the combination of a denser and more cryptic fur in black morphs gives them a selective advantage over other coat colour morphs in wet, dense spruce-fir forests of the Italian Alps, which could explain the within- and between population variation in the relative frequencies of coat colour phenotypes observed in this study.

Carollia perspicillata feeds primarily on plants of the family Piperaceae, as reported in the literature. Although this preference occurs throughout this species’ geographic range, in some situations they may eat other items. This study analyzed variations in the feeding habits of this bat species over an 18-month period. Although C. perspicillata consumed mostly Piper plants, they also ate other fruits (e.g. Cecropia and Solanum plants), and insects as well. Food choice followed a seasonal pattern, related to the availability of Piper plants. The seasonal absence of these fruits may have necessitated bats to eat alternative items.

Three different new cytotypes of the L. flavopunctatus sensu lato species group are reported for Tanzania, suggesting chromosomal rearrangements are coupled or favour divergence within this area. These are characterised by 2n=68 and NFa=90 (the most widespread), 2n=68 and NFa=84, and 2n=70 NFa=86. The karyotypes present striking differences from the others reported for this species complex.