Population Density Of Rodents Research Articles

Fleas of the Moiynkum Desert and their epizootic significance

The species composition of fleas in the Moiynkum Desert (Chu-Talas interfluve) and indices of their domination on different hosts was established on the basis of long-term observations (1973–2000). The most significant and prolonged changes in the population density of mass flea species (Xenopsylla gerbilli minax and Coptopsylla lamellifer, parasites of the great gerbil) occur in association with changes of the population density of rodents. Changes in the population density of rodents are usually observed year after similar changes in the population density of hosts. The leading role in the transmission of the plague vector belongs to the flea X. gerbilli minax.

Recovery of a rodent community in an agro‐ecosystem after flooding

AbstractThe Dongting Lake region is one of the areas prone to flood disaster in China. Despite the frequent occurrence of flooding in this area, few studies have analysed its effects on rodent communities, especially their recovery after withdrawal of floodwaters. We carried out a study of rodent recovery after flooding of the Dongting Lake region in 1998. Rodent population monitoring in the flooded countryside of the Dongting Lake region was conducted during 1998–2001. The census was conducted in Anzao polder of Anxian County in Hunan Province, where the dike burst in 1998 and thousands of hectares of farmland were flooded from July to October. The results indicate that flood disaster could provide important changes in rodent community structure. Firstly, species abundance in the post‐flood area became less than in the normal area. Striped field mice Apodemus agrarius colonized the flooded area in farmland until March 2000, and Norway rats Rattus norvegicus and house mice Mus musculus occurred in July and December 2000, respectively. The degree of the effect on the rodent community in residential premises is less than that in farmland. However, the rodent community in the flooded area could recover and become similar to the normal community. The recovery of rodent species composition was faster in residential premises than in farmland after flooding. Secondly, there was a similar tendency of the dominant concentration indices between post‐flood and normal areas. Thirdly, inundation for a long period could reduce the species diversity of the rodent community in farmland. The significant difference in abundance was continued to 2000 in post‐flooded farmland; however, the influence on the rodent community in residential premises was less and their diversity indices did not differ in 1999. Similarity indices indicated that variation between post‐flood and normal areas had been gradually becoming low from 1999 to 2001. Finally, the monitoring data showed that rodent populations in the flooded area were less than those in the normal area in the first step after withdrawal of floodwaters. However, the rodent population increased rapidly in the flooded area, and became greater than that in the unflooded area in half a year. The population in the flooded area also increased faster than that in unflooded neighbouring area after the application of rodenticide. Another phenomenon was that the population density of rodents could reach levels greater than the normal area, and may continue for more than 2 years. Flood disasters could reduce population densities and species abundance, species diversity and evenness, while increasing dominant concentration indices of the rodent community. However, after 3 years, the rodent community structure became similar to that in the non‐flooded area, except for high density. The recovery of rodent communities in residential premises was faster than that in farmland for a lesser degree of flooding.

Do farming practices influence population dynamics of rodents? A case study of the multimammate field rats, Mastomys natalensis, in Tanzania

A capture-mark-recapture study was conducted in crop fields in Morogoro, Tanzania, to investigate how the population dynamics of multimammate field rats, Mastomys natalensis, was influenced by the commonly practised land preparation methods and cropping systems. Two land preparation methods (tractor ploughing and slash and burn) and two cropping systems (mono-cropping with maize and inter-cropping with maize and beans) were investigated in a Complete Randomized Design experiment with 2 · 2 factors, and two 0.5 ha replicates per treatment. Mastomys natalensis comprised 97.8% of the abundance of the three rodent species captured in the study area. The slash and burned fields had higher rodent population densities than tractor ploughed fields (P 0.05]. The study shows that land preparation methods should be considered a component of rodent pest management in ecologically based or integrated management practices. In maize fields in Tanzania, the crop is most susceptible to damage by M. natalensis in the first 2 weeks after planting, and therefore, lower densities of rodents will result into lower crop damage in tractor ploughed fields.

Distribution and abundance of rodents in farmlands: a case study in Alleltu Woreda, Ethiopia

A study on the distribution and abundance of rodents was carried out in three live trapping grids in wheat, bean and lentil fields in Alleltu Woreda, Ethiopia. A survey was also conducted in habitats outside the cul tivated fields. A total of 260 rodents were trapped from the cultivated fields during 3087 trap-nights and 61 from outside cultivated areas during 675 trap-nights. The rodents trapped were Mastomys natalensis , Mus mahomet and Arvicanthis abyssinicus . Rodent populations reached their peak when the crops were maturing, and declined after harvest. Distribution and abundance of rodents showed significant temporal variation. M. natalensis was the dominant species in the cultivated fields whereas A. abyssinicus was more outside the cultivated fields. The population density of rodents estimated by Capture - Mark - Recapture method ranged from 120/ha in the lentil field to 379/ha in the wheat field. The total biomass of rodents in wheat, bean and lentil grids was 5019 g, 2200 g and 1520 g, respectively. SINET: Ethiopian Journal of Science Vol. 29(1) 2006: 63–70

Climatic Factors, Reproduction Success and Populations Dynamics in the Montane Vole Microtus Montanus

A variety of hypotheses has been proposed to explain multiannual fluctuations in population density ("cycles") of small rodents (for reviews see Finerty 1980, Taitt and Krebs 1985). Doubtless, such cycles - known since antiquity (Elton 1942) - result from an interaction of a multitude of factors. However, the inability of extant hypotheses, alone or in combination, to explain the causality of cycles rests in no small measure with the fact that long­term studies of the phenomenon are notoriously uncommon.

The use of satellite data in modeling population dynamics and prevalence of infection in the rodent reservoir of Junin virus

We present the first results of a simple numerical model of rodent population dynamics and viral infection for Junin virus, etiologic agent of Argentine hemorrhagic fever (AHF), in its host, Calomys musculinus. In contrast to the more common statistical approach, the model incorporates satellite-derived environmental data in a causal approach. In addition, the model incorporates specific biological characteristics of the host, such as birth rate and longevity. Theoretical and actual rodent population densities are compared with several years of capture data at locations on the Argentine pampas. The model appears to be a good tool for simulating dynamics of populations using remotely sensed data. Results are in agreement with field data showing maximum population densities during the autumn in most localities. The differences between simulated population densities and field observed values indicate that, although computer simulation is useful to obtain some aspects of population dynamics, improvements should be introduced in order to generate more robust results.

Sheep grazing and rodent populations: evidence of negative interactions from a landscape scale experiment

Inter-specific competition, facilitation and predation influence herbivore assemblages, but no study has experimentally explored the interactions between large ungulates and small rodents. In a fully replicated, landscape scale experiment, we manipulated densities of domestic sheep in mountain pastures in Norway. We then determined population growth and densities of rodents by live trapping in each of the areas with different sheep densities. We found that the (summer) population growth rate and autumn density of the field vole (Microtus agrestis) was lower at high sheep density. This provides the first experimental evidence of negative interactions between an ungulate and small rodent species. There was no effect on the bank vole (Clethrionomys glareolus), whose diet differs from sheep. Sheep density, therefore, potentially alters the pattern of inter-specific population synchrony amongst voles. Our study shows that negative interactions between large ungulates and small rodents may be species-specific and negative population consequences for the rodent population appear above threshold ungulate densities.

Climatic Factors, Reproductive Success and Population Dynamics in the Montane Vole Microtus Montanus

A variety of hypotheses has been proposed to explain multiannual fluctuations in population density ("cycles") of small rodents (for reviews see Finerty 1980, Taitt and Krebs 1985). Doubtless, such cycles - known since antiquity (Elton 1942) - result from an interaction of a multitude of factors. However, the inability of extant hypotheses, alone or in combination, to explain the causality of cycles rests in no small measure with the fact that long-term studies of the phenomenon are notoriously uncommon.

A tick-borne encephalitis ceiling in Central Europe has moved upwards during the last 30 years: possible impact of global warming?

The geographic/temporal pattern of cases of tick-borne encephalitis (TBE) registered in the Czech Republic since 1970 was analysed to verify the surmise of a global warming effect. Using a geographic information system, over 8,700 notified places of infection were pin-pointed on a map and overlaid with a digital elevation model to estimate the vertical distribution of the cases. Series of yearly disease ceilings (assessed alternatively as the respective maximum altitude or mean altitudes of the upper 5 or 10 cases) were tested against the null hypothesis of random elevation course and analysed for correlation with concomitant factors (yearly TBE incidence rate, mean yearly temperature, population density of small rodents and roe deer). Statistical tests proved that the TBE ceiling has gradually moved upwards in the course of the last three decades. The average rate of ascension within this period was approx. 5.4 +/- 1.7 m yearly, which corresponds well with concurrent mean temperature rising of approx. 0.036 +/- 0.007 degrees C yearly, and the vertical temperature gradient of 0.0065 +/- 0.0004 degrees C m(-1). The TBE-ceiling estimates significantly correlated with TBE-incidence data and the mean yearly temperature recorded 1-2 years earlier. Although TBE incidence correlated with rodent population density that was observed 1-2 years earlier, the TBE ceiling does not seem to be influenced by rodent population dynamics nor did the population dynamics correlate with mean yearly temperatures. TBE incidence as well as mean altitudes of the upper 10 cases also correlated with official data on harvested roe deer. Overall, the fluctuations of TBE incidence and TBE ceiling proved to be synchronous processes that correspond with temperature changes. Although the dependence of TBE on temperature is not a direct one and various factors could be involved, an impact of climate warming on the vertical disease distribution in Central Europe is evident.

Are Predators Good for Your Health? Evaluating Evidence for Top-down Regulation of Zoonotic Disease Reservoirs

Zoonotic diseases, caused by pathogens transmitted to people from vertebrate reservoirs, take an enormous toll on human health worldwide. Many of these disease agents are harbored in rodent populations, and humans are victims of “accidental” transmission. Here we explore the idea that predatory vertebrates indirectly protect human health by reducing population size of rodent reservoirs of human disease. Research frontiers include the importance of rodent population density to the incidence of human disease, as opposed to behavior or age structure effects; the roles of different types of predators in determining both population dynamics and rodent density per se; and the effects of human-caused environmental change on predators and their rodent prey. A better understanding of these basic ecological issues will inform both environmental and health policy.

Are predators good for your health? Evaluating evidence for top-down regulation of zoonotic disease reservoirs

Zoonotic diseases, caused by pathogens transmitted to people from vertebrate reservoirs, take an enormous toll on human health worldwide. Many of these disease agents are harbored in rodent populations, and humans are victims of “accidental” transmission. Here we explore the idea that predatory vertebrates indirectly protect human health by reducing population size of rodent reservoirs of human disease. Research frontiers include the importance of rodent population density to the incidence of human disease, as opposed to behavior or age structure effects; the roles of different types of predators in determining both population dynamics and rodent density per se; and the effects of human-caused environmental change on predators and their rodent prey. A better understanding of these basic ecological issues will inform both environmental and health policy.

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

A variety of hypotheses has been proposed to explain multiannual fluctuations in population density ("cycles") of small rodents (for reviews see Finerty 1980, Taitt and Krebs 1985). Doubtless, such cycles - known since antiquity (Elton 1942) - result from an interaction of a multitude of factors. However, the inability of extant hypotheses, alone or in combination, to explain the causality of cycles rests in no small measure with the fact that long-term studies of the phenomenon are notoriously uncommon. The objectives of this project are to continue the long-term study of population dynamics of the montane vole, Microtus montanus, in Grand Teton National Park. Earlier observations (Pinter 1986, 1988) indicate that environmental variables might contribute to the population density cycles of these rodents, possibly by influencing their growth and various aspects of their reproduction.

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

A variety of hypotheses have been proposed to explain multiannual fluctuations in population density ("cycles") of small rodents (for reviews see Finerty 1980, Taitt and Krebs 1985). Doubtless, such cycles - known since antiquity (Elton 1942) - result from an interaction of a multitude of factors. However, the inability of extant hypotheses, alone or in combination, to explain the causality of cycles rests in no small measure with the fact that long-term studies of the phenomenon are notoriously uncommon. The objectives of this project are to continue the long-term study of population dynamics of the montane vole, Microtus montanus, in Grand Teton National Park. Earlier observations (Pinter 1986, 1988) indicate that environmental variables might contribute to the population density cycles of these rodents, possibly by influencing their growth and various aspects of their reproduction.

Variations of some physiological and biochemical indices in the population of red-backed vole (Clethrionomys rutilus)

We studied the changes in the population density of the red-backed vole (Clethrionomys rutilus Pall.) on the northern coast of the Sea of Okhotsk (60 degrees N) during three population cycles (1980-1990). A total of 3111 animals were studied, including 1006 alive voles. For evaluation of the population stress and food deficit, a complex of biochemical (blood level of glucose and liver levels of glycogen and lipids) and physiological (blood content of leucocytes, spleen weight, etc.) indices was used. At a high population density, the influence of stress continues during the reproductive period, after its termination, and, supposedly, until the beginning of a new reproductive period, while at a low population density, the consequences of stress were expressed only in the second half of the reproductive period. The signs of starvation were recorded only in some semiadult voles in a high density population. It has been confirmed that stress acts as a mechanism involved in regulation of the population density of small rodents.

Seasonal variation in prevalence of antibody to hantaviruses in rodents from southern Argentina.

We conducted a small mammal trapping study to investigate temporal variation in prevalence of infection in hantavirus reservoir populations in the Patagonian Andes mountain range, Rio Negro province, Argentina. Rodent blood samples collected in natural and periurban habitats and at the home of an hantavirus pulmonary syndrome (HPS) case patient were analysed by enzyme-linked immunosorbent assay. Organ tissue samples were tested by polymerase chain reaction (PCR) and nucleotide sequence analysis. Eight species of 1032 rodents were captured in 15 551 trap nights, giving an overall trap success of 6.6%. Hantavirus antibody was detected in 30 of 555 Oligoryzomys longicaudatus (reservoir of Andes virus), three of 411 Abrothrix longipilis, and one of 10 Loxodontomys micropus. Antibody prevalences in O. longicaudatus were 13.7% in spring 1996, 59.3% in summer 1996, 2.1% in autumn 1997, 12.4% in winter 1997 and 3.1% in spring 1997. A much higher antibody prevalence (33%) was found during trapping around the residence of an HPS case patient. Higher prevalences were found in older male O. longicaudatus. There was no apparent correlation of antibody prevalence with rodent population density, or of rodent population density or antibody prevalence with numbers of human cases. For an HPS case that occurred in our study area in 1997, we identified the probable rodent reservoir and likely site of exposure by matching the genetic sequences of virus obtained from a rodent and the HPS case patient.

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

Multiannual fluctuations in population density ("cycles") of small rodents have been known since antiquity (Elton 1942). Numerous hypotheses have been proposed to explain this phenomenon (for reviews see Finerty 1980, Taitt and Krebs 1985). However, none of these hypotheses, alone or in combination, has been able to explain the causality of cycles, although recently removal of parasites was shown to prevent population cycles in the red grouse, Lagopus lagopus scoticus (Hudson et al. 1998). The objectives of this long-term study are to determine whether environmental variables, possibly acting through reproductive responses, contribute to the multiannual fluctuations of the montane vole, Microtus montanus.

Outbreak of hantavirus infection in the Four Corners region of the United States in the wake of the 1997-1998 El Nino-southern oscillation.

Hantavirus cardiopulmonary syndrome (HCPS), a rodent-borne zoonosis, has been endemic in the Americas for at least several decades. It is hypothesized that the 1991-1992 El Niño-southern oscillation (ENSO) caused increased precipitation that allowed an increase in rodent population densities, thereby increasing the possibility of transmission to humans. The result was a 1993-1994 outbreak of the disease in the Four Corners states of the southwestern United States. A second strong ENSO occurred in 1997-1998, after a period of considerable public education about the risks of hantavirus infection that began during the 1993-1994 outbreak. The caseload of HCPS increased 5-fold above baseline in the Four Corners states in 1998-1999. Regions that had received increased rainfall in 1998 were especially affected. A large majority of the 1998-1999 case patients reported indoor exposure to deer mice. Hantavirus outbreaks can occur in response to abiotic events, even in the face of extensive public education and awareness.

Gut-Associated Lymphoid Tissue in Microtus montanus from Natural Populations

Impaired immunocompetence may contribute to the multiannual fluctuations ("cycles") in population density of arvicoline rodents (Mihok et al. 1985, Pinter 1988, Lochmiller et al. 1993). In a variety of species environmental variables influence at least one component of the immune system, the gut-associated lymphoid system, GALT (Lopez et al. 1985, Li et al. 1995). Preliminary laboratory observations suggest that the development of GALT in Microtus montanus can be influenced by such factors as age and diet (Smith and Pinter 2000). However, these observations are from captive-bred voles, maintained on a synthetic laboratory diet, under strictly controlled laboratory conditions. The complexity and abundance of variables under natural conditions must influence the development and function of GALT- yet, nothing is known about it from Microtus montanus under natural conditions. The purpose of this study was essentially twofold: (1) to describe the morphometries of GALT in wild-caught M. montanus, and (2) to characterize the morphometric changes that occur in GALT of these animals as a function of their age, sex, and the season of the year.

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

Multiannual fluctuations in population density ("cycles") of small rodents have been known since antiquity (Elton 1942). Numerous hypotheses have been proposed to explain this phenomenon (for reviews see Finerty 1980, Taitt and Krebs 1985). However, none of these hypotheses, alone or in combination, has been able to explain the causality of cycles, although recently removal of parasites was shown to prevent population cycles in the red grouse, Lagopus lagopus scoticus (Hudson et al. 1998). The objectives of this long-term study are to determine whether environmental variables, possibly acting through reproductive responses, contribute to the multiannual fluctuations of the montane vole, Microtus montanus.

Statistical sensitivity for detection of spatial and temporal patterns in rodent population densities.

A long-term monitoring program begun 1 year after the epidemic of hantavirus pulmonary syndrome in the U.S. Southwest tracked rodent density changes through time and among sites and related these changes to hantavirus infection rates in various small-mammal reservoir species and human disease outbreaks. We assessed the statistical sensitivity of the program's field design and tested for potential biases in population estimates due to unintended deaths of rodents. Analyzing data from two sites in New Mexico from 1994 to 1998, we found that for many species of Peromyscus, Reithrodontomys, Neotoma, Dipodomys, and Perognathus, the monitoring program detected species-specific spatial and temporal differences in rodent densities; trap-related deaths did not significantly affect long-term population estimates. The program also detected a short-term increase in rodent densities in the winter of 1997-98, demonstrating its usefulness in identifying conditions conducive to increased risk for human disease.