Population Density Of Microtine Rodents Research Articles

Temporal Variability and Geographical Patterns in the Population Density of Microtine Rodents: A Reply to Xia and Boonstra

Temporal Variability and Geographical Patterns in the Population Density of Microtine Rodents: A Reply to Xia and Boonstra

Densities of microtime rodents along a pollution gradient from a copper-nickel smelter.

Population densities of microtine rodents were studied along an air pollution gradient in the Kola Peninsula, Russia, by long-term and short-term trapping. The study area is affected by high sulphur dioxide and heavy metal emissions from the Severonikel copper-nickel smelter in Monchegorsk. The density of Clethrionomys rufocanus, the most abundant vole species in the area, was lowest close to the smelter and increased with distance up to the farthest, less polluted trapping sites. Clethrionomys glareolus, C. rutilus and Lemmus lemmus were absent from the most severely damaged area and were also scarce at the moderately polluted area 28 km south of the smelter. Although the population of C. glareolus has previously been cyclic at the moderately polluted area, we were unable to demonstrate any regular cycle. The most likely explanation for the low number of microtine rodents in the damaged and moderately polluted areas in a decrease in the quantity of important food plants: epiphytic lichens for C. glareolus and possibly C. rutilus, mosses for L. lemmus and seed plants, especially Vaccinium myrtillus, for C. rufocanus. Close to the smelter, direct toxic effects of heavy metals may also reduce population densities. The results show that pollutants may change the relative proportions of microtine species.

6-Methoxy-2-benzoxazolinone and photoperiod: prenatal and postnatal influences on reproductive development in prairie voles (Microtus ochrogaster ochrogaster)

The effects of photoperiod and 6-methoxy-2-benzoxazolinone (6-MBOA) on the gonadal development of prairie voles was studied when this plant compound was available to pups in utero, during nursing, or postweaning. In part 1, pregnant voles exposed to long or short day lengths were fed food in which 6-MBOA was present (50 μg of 6-MBOA/g food) or absent prior to the birth of their young; all of these dams received a diet that lacked 6-MBOA after the pups were born. Other females were fed food without 6-MBOA throughout pregnancy, but received one of the diets during lactation. Short days inhibited reproductive development in male offspring, affected pup survival, and enhanced pelage development. Postnatal exposure to 6-MBOA did not affect the reproductive function of males. In contrast, prenatal exposure to 6-MBOA accelerated reproductive development among short-day males. Prenatal exposure to 6-MBOA did not affect survival of short-day males, but reduced survival of long-day pups. Prenatal 6-MBOA treatment affected the sex ratio of pups that survived until weaning (13:21; male:female) and of pups that died prior to weaning (26:5). In contrast, photoperiod did not affect reproductive function in female voles. Although reproductive function appears to be uncoupled from photoperiodic regulation, female prairie voles processed photoperiodic information; pelage development was enhanced among short-day females. In part II, breeding pairs were exposed to long or short days and fed food devoid of 6-MBOA prior to the birth of the young. On the day of birth, and for the following 3 weeks, either 6-MBOA-free or 6-MBOA-enriehed food was provided. After weaning, pups received their parents type of food until autopsy 3 or 7 weeks later. Again, photoperiod affected male, but not female, reproductive function. No consistent pattern of results from postnatal exposure to 6-MBOA was discerned for either males or females. Acceleration of reproductive function among short-day males because of prenatal influences may, be involved in the rapid rate of sexual maturation observed prior to peak population densities of microtine rodents. Because males of this species induce females into estrus, male prairie voles may depend on environmental cues to regulate reproductive function, while females may respond only to males. The physiological and ecological implications of these data are discussed.

Maternal diet influences reproductive development in male prairie vole offspring

The plant compound, 6-methoxy-2-benzoxazolinone (6-MBOA), is found in the meristematic tissue of young, vegetatively growing grasses, and its ingestion stimulates the reproductive system of rodents in both short and long photoperiods. The present study demonstrates the existence of a novel mechanism whereby the presence of 6-MBOA in the diet of pregnant prairie voles ( Microtus ochrogaster) enhances gonadal development in their male offspring. Female voles were fed specially milled food in which 6-MBOA was present (50 μg of 6-MBOA/g food) or absent (0 μg of 6-MBOA/g food) prior to the birth of their young; all of these dams received a diet that lacked 6-MBOA after the pups were born. Other females were fed food without 6-MBOA throughout pregnancy, but received one of the two diets during lactation. The pups from all experimental groups were weaned at 3 weeks of age and fed thereafter one of the two diets for 3 additional weeks. Prenatal exposure to 6-MBOA enhanced male reproductive development. Maternal ingestion of 6-MBOA during lactation or postweaning intake of 6-MBOA by the young did not influence reproductive development of males. This mechanism may be involved in the rapid rate of sexual maturation observed prior to peak population densities of microtine rodents.

Effects of Food Availability and Predation on Prairie Vole Demography: A Field Experiment

Nutrition, spacing behavior, and predation have been proposed as major factors limiting the population density of microtine rodents (lemmings and voles). However, there is no general agreement as to the relative importance of these factors, nor have their interactions been carefully examined. This paper reports on a factorial experiment designed to test the general hypothesis that predation and the availability of high—quality food act simultaneously and additively to limit densities of microtine rodent populations. Our results showed that supplemental high—quality food significantly increased body growth rates, proportion of adults in the population, adult male body size, reproductive activity, recruitment, and density of prairie vole populations. Food availability had no effect on survival nor on sex ratio in any of the 3 yr of this study. Protection from predation significantly increased adult survival (somewhat sporadically), recruitment, and density, but it did not directly affect growth, population structure, or reproduction. Improved survival of young animals could not be detected, but increased recruitment suggested that it may have occurred, perhaps before the young reached trappable size. Food supplementation and protection from predation generally had additive and equal effects on density. The only significant food—predator interactions were for body growth rates and adult body size. The presence of predators appeared to inhibit the growth response to supplemental food, possibly because of more restricted movement and, therefore, less access to food.

Environmental Factors, Reproductive Success and Population Dynamics in the Montane Vole, Microtus montanus

Multiannual fluctuations in population density ("cycles") have been known since antiquity (Elton 1942). Numerous hypotheses have been proposed to explain this phenomenon (for reviews see Krebs and Myers 1974, Finerty 1980, Taitt and Kreh; 1985). However, none of these hypotheses, alone or in combination, can either explain the causality of cycles or predict their dynamics. The ultimate objectives of this long-term study are to answer two questions: (1) What causes multiannual fluctuations in the population density of microtine rodents?; and (2) How can cycles be predicted? The proximate objectives are to determine to what extent environmental variables - acting through reproductive responses of Microtus montanus- contribute to the population density cycles of these rodents.

Effects of Environmental Variables on some Physiological Responses of Microtus montanus under Natural Conditions

Cyclic fluctuations in the population density of microtine rodents have been known since antiquity. However, factors responsible for this phenomenon are not known. The objectives of this long term study are essentially three-fold. First, to characterize those environmental variables that might affect Microtus montanus in different seasons of the year. Second, to record the growth, maturation and reproductive activity of the voles under natural conditions. Third, to determine the maturational as well as the seasonal pelage changes of these rodents. The data resulting from the execution of the above objectives would be correlated in an attempt to determine the causes underlying the multiannual fluctuations in the population density of these microtine rodents in Grand Teton National Park.

Effects of Environmental Variables on Some Physiological Responses of Microtus montanus under Natural Conditions

Cyclic fluctuations in the population density of microtine rodents have been known since antiquity. However, factors responsible for this phenomenon are not known. The objectives of this long term study are essentially threefold. First, to characterize those environmental variables that might affect Microtus montanus in different seasons of the year. Second, to record the growth, maturation and reproductive activity of the voles under natural conditions. Third, to determine the maturational as well as the seasonal pelage changes of these rodents. The data resulting from the execution of the above objectives would be correlated in an attempt to determine the causes underlying the multiannual fluctuations in the population density of these microtine rodents in Grand Teton National Park.

Effects of Environmental Variables on Some Physiological Responses of Microtus montanus under Natural Conditions

Cyclic fluctuations in the population density of microtine rodents have been known since antiquity. However, factors responsible for this phenomenon are not known. The objectives of this long term study are essentially threefold. First, to characterize those environmental variables that might affect Microtus montanus in different seasons of the year. Second, to record the growth, maturation and reproductive activity of the voles under natural conditions. Third, to determine the maturational, as well as the seasonal pelage changes of these rodents. The data resulting from the execution of the above objectives would be correlated in an attempt to determine the causes underlying the multi-annual fluctuations in the population density of these microtine rodents in Grand Teton National Park.

Effects of Environmental Variables on Some Physiological Responses of Microtus montanus Under Natural Conditions

Cyclic fluctuations in the population density of microtine rodents have been known since antiquity. However, factors responsible for this phenomenon are not known. The objectives of this long term study are essentially fourfold. First, to characterize the environmental variables that might affect Microtus in different seasons of the year. Second, to record the growth, maturation and reproductive activity of Microtus montanus under natural conditions. Third, to determine the maturational, as well as, seasonal pelage changes of these rodents. Fourth, the data resulting from the execution of the first three objectives would be correlated in an attempt to determine the causes underlying the multiannual fluctuations in population density of these microtine rodents.

Effects of Environmental Variables on Some Physiolgical Responses of Microtus montanus under Natural Conditions

Cyclic fluctuations in the population density of microtine rodents have been known since antiquity. However, factors responsible for this phenomenon are not known. The objectives of this long term study are essentially fourfold. First, to characterize the environmental variables that might affect Microtus in different seasons of the year. Second, to record the growth, maturation and reproductive activity of Microtus montanus under natural conditions. Third, to determine the maturational as well as seasonal pelage changes of these rodents. Fourth, the data resulting from the execution of the first three objectives would be correlated in an attempt to determine the causes underlying the multiannual fluctuations in population density of these microtine rodents.

Studies on and Related to "Cyclic" Microtus montanus Populations

Multiannual fluctuations in population densities of microtine rodents have attracted much attention from ecologists because they challenge existing hypotheses of population regulation. Yet many aspects of the basic biology of voles and lemmings, even those related to the population cycle, remain wholly or largely uninvestigated.

Microtus Population Densities and Soil Nutrients in Southern Indiana Grasslands.

The sodium hypothesis of Aumann and Emlen (1965) states that peak population densities of microtine rodents are strongly correlated with soil sodium levels. We tested this in southern Indiana with snap-trapping data from 21 grassland areas occupied by Microtus pennsylvanicus and M. ochrogaster. A total of 128,052 trap-nights were expended from 1965 to 1970, and soils from area were analyzed for seven soil parameters including sodium. Soil sodium levels did not correlate with either peak density or mean density levels of either Microtus species. In M. pennsylvanicus 38% of the variation in peak densities could be explained by differences in soil pH and potassium levels. Cover may be an important predictor of peak densities but this was not measured. Microtus pennsylvanicus is not confined to bottomland soils in the Bloomington, Indiana, area and both species of Microtus coexist over a broad range of soil types.

Microtine Abundance and Soil Sodium Levels

A collection of 65 published records of population densities of microtine rodents, including individual studies of 130 populations, reveals a marked difference in peak densities reached according to geographical area. An apparent correlation exists between the relative abundance of sodium in the soil and the peak densities which microtines reach. Densities of over 1,000 per acre are frequently reported from high sodium areas, while they rarely exceed 100 in low sodium areas. Population fluctuations occur regardless of sodium level, but the densities reached at population peaks are characteristically many times higher in regions of high soil sodium than in regions of low soil sodium.