Cricetid Species Research Articles

Rodent abundance and distribution in habitats of Agrocenosis in Argentina∗

Physiographical and environmental factors have important effects on the distribution and abundance of small mammals. The purpose of this paper is to examine the spatial and seasonal distribution of cricetid populations on a selected part of the agrocenosis in Laguna Larga, Cordoba, Argentina. Four habitats were selected: wood, cultivated field, wood border, and cultivated field border. Trapping in all habitats consisted of trap line transects during fall and spring each year from 1979 to 1981. Five cricetid species were trapped in a total of 1285 captures in all four habitats. Calomys musculinus was the most abundant species. No differences in population number were obtained with respect to habitat, season or year. On the other hand, Calomys laucha showed differences in capture frequency between habitats and between years. Populations of Akodon dolores and Calomys venustus were not significantly different with respect to habitat, but A. dolores revealed seasonal differences. Graomys griseoflavus was captu...

Direct Observations of Owls and Heteromyid Rodents: Can Predation Risk Explain Microhabitat Use?

Coexisting heteromyid rodent species of North American deserts differ in habitat use and in locomotory morphology. Quadrupedal species forage primarily in structurally complex microhabitats, such as under bush canopies, while bipedal species forage in open spaces. A common explanation for this morphology—microhabitat association is that species differing in morphology also differ in vulnerability to predators, that microhabitat structure affects predation risk, and that animals preferentially forage in the safest microhabitats. We tested this for two bipedal and two quadrupedal heteromyid species (matched by body size), and one cricetid species, by quantifying effects of habitat and illumination on activity and on risk of predation by Great Horned Owls. Capture frequencies were lower for all heteromyid species than for the cricetid species, Peromyscus maniculatus. Heteromyid activity was lower in open habitat and under bright illumination. Illumination had no significant effect on risk, perhaps because rodents changed activity patterns under full moon to compensate for a potential increment in risk. Habitat, however, did affect risk: all species were attacked and captured more frequently in the open. Bipedal species were attacked relatively more in the open than were quadrupeds. If these results apply to all predators, they indicate that predation alone cannot account for the divergent microhabitat associations of bipedal and quadrupedal species. Bipedal heteromyids, however, escaped owl attacks more frequently than did quadrupeds of equivalent size. It is therefore conceivable that they experience lower overall risk in nature, where owls may preferentially attack more easily captured prey species when given a choice. Under these circumstances, owl predation could reinforce divergent microhabitat specializations based on some other factor, such as foraging economics, by restricting quadrupeds more strongly than bipeds to the safety of bushes.

Scanning electron microscopy of molar enamel structure of cricetodontine Neogene rodents

Ultrastructural characters of enamel were studied as a phylogenetic indicator in a family of rodent fossils: the Cricetidae. The extinct group Cricetodon-Ruscinomys is a known lineage which span 17 million of years (from t2̄0 My to −3 My). The three-dimensional organization of enamel of the left M 1 was studied in 8 cricetid species at three different levels: (1) the chewing surface; (2) the middle of the crown; (3) the cervical part, close to the root. The arrangement and other details of enamel prisms varied according to five factors: (1) tooth morphology (there were differences between the four faces of the same molar); (2) enamel thickness; (3) level of crown; (4) degree of hypsodonty; (5) chronological age of the extinct species.

Comparative water economy of sympatric rodents in a Chilean semi-arid habitat

1. 1. Water requirements, water balance components and dependence on exogenous water were estimated in four species of sympatric rodents inhabiting a Chilean semi-arid region. 2. 2. A significant increase in free water drinking was observed in all rodents when the diet composition was changed from 14 to 20% protein. 3. 3. Under water balance conditions the cricetid species ( Phyllotis darwini, Oryzomys longicaudatus and Akodon olivaceus) showed 1.66 to 1.88 times the weight-specific daily water gain of Octodon degus. 4. 4. In the three cricetid rodents, evaporation was the largest water loss component ( 2 3 to 3 4 of total loss), while in O. degus evaporative water loss amounted to only 38% of the total. 5. 5. Survival time during water deprivation ranged from 13.4 days in O. degus to only 4 days in O. longicaudatus. 6. 6. All water variables combined indicate that water dependence of O. longicaudatus > P. darwini > A. olivaceus > O. degus.

Identification of crystalline allantoin in the urine of African Cricetidae (Rodentia) and its role in their water economy.

All eleven cricetid species, examined in this investigation, produced an off-white crystalline precipitate in their urine when deprived of water, whereas not one murid examined did so. This crystalline compound was identified as allantoin, a common end product of purine catabolism. The quantity found in the solid precipitate alone accounted for 47% of the total nitrogen excreted and was approximately 14 times greater than the predicted quantity of allantoin from purine degradation. It appears that there is a shift in nitrogen excretion from urea to allantoin in the Cricetidae. Water-deprived cricetids had higher urine osmolalities, urea concentrations and lower daily percentage body water turnovers than the murids. This can be explained by the substantial water savings associated with excreting solid allantoin. The discrepancy in the mode of nitrogen excretion between the two families inhabiting the Namib Desert can be attributed to their different evolutionary histories, the Cricetidae being pre-adapted for survival in deserts.

Population Dynamics of Small Mammals in Farmstead Shelterbelts

Various aspects of the population dynamics of Sorex cinereus, Blarina brevicauda, Clethrionomys gapperi, Microtus pennsylvanicus , and Peromyscus leucopus were studied for 27 months in Minnesota farmstead shelterbelts. Total numbers of individuals of all species combined were greatest in summer and autumn; species-specific peaks in seasonal abundance were partially attributed to juvenile recruitment. Percentages of breeding adult females were similar in the three species of cricetids, but relatively fewer adult males of M. pennsylvanicus were in reproductive condition than in other cricetids. Young cricetids tended to be transient compared to adults; in P. leucopus , young females were more likely to be residents than young males. Adult transients weighed less than adult residents in both M. pennsylvanicus and P. leucopus . Distances moved within shelterbelts did not vary among species; movements between shelterbelts occurred most often in B. brevicauda but never in P. leucopus . Probabilities of recapture over months were comparable among species. Aspects of the population dynamics of the five species in these man-made habitats generally were similar to those reported by studies in less modified environments. Because of the importance of shelterbelts to populations of C. gapperi and P. leucopus and to other species of wildlife, efforts should be made to preserve these wooded islands in intensely-farmed regions of the Upper Midwest.

Resource Patitioning in a Chilean Semi-Arid Small Mammal Community

SUMMARY (1) Patterns of habitat and food utilization among small mammals were studied for 17 months in a Chilean semi-arid thorn scrub community. This community is dominated by spiny drought-deciduous and evergreen shrubs and low but variable winter rainfall. The four major small mammal species included three cricetid and one octodontid rodent, and three additional species (two rodents and one marsupial) which were low to sporadic in occurrence. (2) The four major small mammal species demonstrated significant patterns of habitat association including affinity for sites with high shrub cover and/or low to moderate grass and forb cover (three cricetid species), and affinity for sites with low grass and forb cover and high bare ground cover (the octodontid species). (3) Habitat overlap between these species as determined by similarity in utilization of trap and tracking stations over 3-month periods was high especially in comparison to values of overlap revealed in studies of California small mammal communities. (4) Trophic specializations among the seven small mammal species indicated three foraging guilds with two species each (herbivore, insectivore and granivore) and one omnivorous species were present in the community. Dietary overlap between the four major species was similar to that observed in more diverse California small mammal communities. (5) Niche overlap was relatively high for this community due primarily to high habitat overlap. Contrary to patterns revealed in California small mammal communities, but similar to other Chilean small mammal communities in the mediterranean zone, habitat overlap was usually greater than dietary overlap. (6) Levels of certain food resources including herbaceous plants, insects and seeds are at least equal and possibly greater in Chile than in California. This pattern in conjunction with the presence of similar dietary overlaps in both areas may indicate lower levels of competition among Chilean small mammals for those resources. (7) The patterns of resource utilization demonstrated by this community seem to be due more to ecological factors than to the evolutionary and biogeographical characteristics of the Chilean small mammal fauna.

Studies on the pelvis in British Muridae and Cricetidae (Rodentia)

The morphology and its variation of the bony pelvis in British species of Muridae and Cricetidae have been studied. The investigation began with the application of a mensural method for demonstrating sexual dimorphism and it is shown that for all species except those of Rattus the male os coxa can be distinguished from the female over a wide range of ages. During the study it became obvious that there are ranges of morphological variation in os coxae both inter‐ and intraspecific. There are constant interpecific differences which allow identification of os coxae of these rodents at least to genus and in many cases to species. Detailed descriptions of the morphology of the os coxa of each species are given together with an identification key. Intraspecific variation is mainly sex‐dependent and comprises sexual dimorphism, male pubertal changes and female parturition changes. The changes in the male are from epicene, through pubertal, to post‐pubertal phase, with the first of these resembling the agonadal, female, form and the last with a posterior border thickened and tuberculate in relation to the hypertrophied penis and its associated glands and musculature. These phases are not equally obvious in all species, but the pelvis in all except Rattus and Mus shows some evidence of the sexual development of the animal. In females the form of the pelvis may be modified during successive pregnancies to allow a wider pelvic outlet for parturition. Resorption and remoulding of the female pelvis allows the recognition of non‐parous, uniparous and multiparous animals in all Cricetid species, in Micromys and, more doubtfully, in Mus, but not in Apodemus and Rattus. Non‐sex‐dependent intraspecific variation, comprising differences in rugosity related to muscularity is also described.The observations are discussed in relation to earlier experimental work, to the need for basic research on small mammal reproduction and population structure, and to the use of the pelvis in the analysis of osteological assemblages, such as occur in owl pellets.