Stable Isotopes in Pocket Gopher Teeth as Evidence of a Late Matuyama Climate Shift in the Southern Rocky Mountains

Previous work in the San Luis Valley of south-central Colorado and northern New Mexico at the Hansen Bluff and SAM Cave localities has allowed reconstruction of the paleoclimate in the region during the interval from ∼0.6 myr to ∼2.6 myr. Surface exposures at Hansen Bluff have been correlated to deep-sea oxygen isotope core stages 18–23 and one of the glacial periods contained therein to the oldest “Nebraskan” till in southwestern Iowa. Deposits in SAM Cave correlate to Hansen Bluff on the basis of paleomagnetics, climate interpretation, and microtine rodent biochronology. In this paper, carbon and oxygen stable isotope data of herbivorous rodent teeth are used as indicators of change in the predominance of C3, C4, and CAM plants and of changes in temperature and precipitation. Taken together with other previously analyzed data from these localities, the evidence indicates a shift in the severity of glacial events that is mainly related to the hydrologic characteristics of the climate. This shift may have been caused by broad regional uplift that may have been instrumental in shifting global climate cycles from the 41,000-yr Matuyama cycles to the Brunhes 100,000-yr-dominated cycles.

Microhabitat use by the snow vole Chionomys nivalis in alpine environments reflects rock-dwelling preferences

Environmental conditions in mountainous regions have influenced the nature of some adaptations among small mammals and this may apply to strategies of habitat use in alpine biotopes. In the present paper, microhabitat use in relation to microhabitat availability of a population of snow voles Chionomys nivalis Martins, 1842, a nonhibernating microtine rodent that inhabits high-mountain environments exclusively, was studied. The results show that C. nivalis did not use microhabitats in proportion to availability, suggesting a preference for certain habitat characteristics. Chionomys nivalis strongly used scree areas at all times, whereas the use of available areas of mixed shrubs (Juniperus communis and Cytisus oromediterraneus) and Scots pine (Pinus sylvestris) was lower than expected. Factors other than food, such as favourable microclimate or refuge from predators, might determine regular use of rocky microhabitats. The results also revealed differences in the use of rocky structures related to sex and reproductive condition, suggesting different strategies of spatial use related to reproductive tasks. Juveniles and reproductive females used central zones of the scree and areas with scree junipers (J. communis) significantly more than expected, whereas reproductive males and nonreproductive adults used scree areas in proportion to availability. Based on its unique morphological, physiological, and ecological characteristics, C. nivalis can be considered a rock-dwelling specialist of alpine environments.

Cyclic dynamics of eastern Canadian ermine populations

Based on partial autocorrelation analysis, 20 ermine (Mustela erminea) populations in Manitoba, Ontario, and Quebec demonstrated cyclic dynamics characterized by a latitudinal gradient of decreasing first-order feedback and increasing negativity of second-order feedback. Most of these populations exhibited three cyclic peaks and a 10-year interval of noncyclic dynamics during the sampling period (1915-1940). Changes in ermine density probably reflected those in the density of microtine rodents, their primary prey. Analysis of the limited number of long-term lemming and vole series from boreal North America indicated a latitudinal gradient in cyclic dynamics similar to that of microtine rodent populations in northern Europe. Complex geographic and temporal variation in ermine population dynamics, including cyclic, noncyclic, and shifting patterns of density change, supports the specialist-generalist hypothesis of predator-prey interaction at temperate latitudes.

Postnatal development of thermoregulation in the semiaquatic muskrat (Ondatra zibethicus)

Developmental changes in thermoregulatory ability were followed in 1- to 34-d-old muskrats (Ondatra zibethicus) tested individually and in groups composed of 5 littermates. During their first 10-11 d of life, 20- to 60-g nestlings displayed limited thermogenic ability and could not maintain a stable body temperatures (Tb) during 2 h exposure to an air temperature (Ta) of 10 or 25°C. At 25°C, a Ta approximating nest temperatures in the field, nestlings were homeothermic at ca. 10-11 d of age, when they were fully furred, capable of limited swimming, and within 1-2 d of opening their eyes. The onset of thermoregulation occurred at a body mass (60 g) that was considerably less than predicted on the basis of adult body size. Huddling with littermates reduced the cooling of 20- to 60-g young at a Ta of 10°C, but did not advance the age (mass) at which they became effective homeotherms. Huddling by 20- to 60-g nestlings raised the mean Tb, leading to a substantive (64%) gain in the rate of oxygen consumption (Vo2). Conversely, in older nestlings that were close to or fully homeothermic, huddling with littermates consistently lowered Vo2, the greatest metabolic saving (38%) being realized by 17- to 21-d-old (100-140 g) young. We suggest that the rapid development of thermoregulation may be linked to the semiaquatic habit of muskrats, and that thermoregulatory behavior contributes importantly to the growth and morphological development of this prolific microtine rodent.

Differences in recovery between a deciduous and an evergreen ericaceous clonal dwarf shrub after simulated aboveground herbivory and belowground damage

Insect and microtine rodent herbivory (defoliation and branch clipping, respectively) were simulated in stands of the deciduous Vaccinium myrtillus L. and evergreen V. vitis-idaea L. Rhizome connections around the treated plots were either left intact or severed. Recovery in the plots was monitored for two growth seasons, from 1991 to 1992. It was hypothesized that the evergreen V. vitis-idaea would suffer more from the simulated herbivory treatment than V. myrtillus, but that severing the rhizome connections would decrease recovery of both species, because clonal integration is disrupted and wounding may have a harmful influence on growth. After two growth seasons, recovery was complete from simulated herbivory in V. myrtillus, whereas the new dry biomass was reduced slightly (22 – 37%) or significantly (49%) compared with that of the control in V. vitis-idaea. Rhizome severing reduced the growth of the branches and ramets and the aboveground dry biomass by 34% compared with that of the unsevered control in V. myrtillus. In the evergreen V. vitis-idaea, severing slightly reduced growth, the effect being significant only in the clipped treatment. The results suggest that the deciduous V. myrtillus recovers more rapidly from simulated herbivory than the evergreen V. vitis-idaea. Rhizome severing is more detrimental to the growth of V. myrtillus, but less detrimental to recovery from simulated herbivory. Sexual reproduction decreases more in V. vitis-idaea than in V. myrtillus after damage. Key words: compensation, growth form, herbivory, rhizome severing, Vaccinium