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Abstract: Habitat selection in deserts is mainly modulated by the availability of resources. The basic hypotheses regarding coexistence of species in arid environments offer two possibilities: 1) coexisting species partition available resources (each species acting as a specialist) and 2) generalists coexist with specialists because the former use habitats which are underused or not selected by the latter. This study presents the first data on macro- and microhabitat selection by Eligmodontia moreni (Cricetidae) and Octomys mimax (Octodontidae), two rodent species which coexist in the most arid part of the Monte desert of Argentina. In order to evaluate both hypotheses, animals were trapped during two seasons (humid and dry) in six macrohabitats of the arid Monte (creosote bush scrub, mesquite woodlands, columnar cactus slopes, barrens, chical and saltbush). A multivariate analysis of variance was used to evaluate differences in PCA components of microhabitat (floristic composition and vegetation structure) among capture and control points. The resulting models suggest E. moreni to be described as a fine-grained generalist species, which would be segregated from the specialist O. mimax in shared macrohabitats by resource partitioning, basically related to substrate type and vegetation cover. Our findings accord with theories of community assembly involving generalist and specialist species. [Copyright &y& Elsevier]

Abstract: Several rodent species engage in group living, meaning that individuals share nests, resting places, and range areas. Establishing how group living varies across species is critical for comparative studies to examine the origin and the adaptive value of this behavior. Comparative approaches are more powerful when a diverse array of taxonomic groups is included. We used telemetry techniques to monitor patterns of activity, resting places, and range areas at night to examine the extent of sociality of the scarcely known viscacha rats, Octomys mimax. Seven individuals were live trapped and fitted with radio-collars. Viscacha rat activity, as measured from distance moved between consecutive telemetry scans, took place mostly during the nighttime. During day, animals used from 2 to 6 putative nest places, but one was used more frequently. The sharing of resting locations by two or more radio-collared animals was never recorded. Viscacha rats showed relatively large range areas and low-to-moderate spatial overlap with neighbors. Male rats had larger range areas than females, but spatial overlap with neighbors was similar. Results suggest that viscacha rats are solitary living animals. This study supported a solitary-to-social trend from basal to more derivate forms across Octodontidae. [Copyright &y& Elsevier]

We studied daily activity patterns of the subterranean rodent Spalacopus cyanus, in the field during summer and winter, and under laboratory conditions at two different temperatures, 15°C and 30°C. This rodent exhibited nocturnal activity in the laboratory, but diurnal above-ground activity in the field. We suggest that this discrepancy between field and laboratory results is a consequence of differential space-use inside burrows during the day, and that low external ambient temperatures appear to constrain activity of S. cyanus outside their burrows during the night in summer and winter. In contrast, we hypothesize that high summer temperatures constrain above-ground activity at midday. [Copyright &y& Elsevier]