Population Density Of Rodents Research Articles

Nonlinear scaling of foraging contacts with rodent population density

Density‐dependent shifts in population processes like territoriality, reproduction, dispersal, and parasite transmission are driven by changes in contacts between individuals. Despite this, surprisingly little is known about how contacts change with density, and thus the mechanisms driving density‐dependent processes. A simple linear contact–density function is often assumed, but this is not based on a sound basis of empirical data. We addressed this question using a replicated, semi‐natural experiment in which we measured contacts at feeding stations between multimammate mice,Mastomys natalensis, across ten distinct, linearly increasing densities between 10 and 272 animals/ha. Unexpectedly, unique contacts increased not linearly but sigmoidally with density, which we attribute to the species’ scramble competition mating system, small‐scale dominance/avoidance and absence of territoriality. These results provide new insights into how species’ characteristics can relate to density‐dependent changes in contacts, and the unexpected shape of the contact–density function warrants that density‐dependence in ecological models, such as parasite transmission models, must be parameterized with care.

Distribution and Population Density of Rodents and Chigger Mites in Gokseong-gun of Jeollanam-do, Korea

Distribution and Population Density of Rodents and Chigger Mites in Gokseong-gun of Jeollanam-do, Korea

The Effect of Aluminum Exposure on Reproductive Ability in the Bank Vole (Myodes glareolus)

Human impact on the environment is steadily increasing the amounts of aluminum in the ecosystems. This element accumulates in plants and water, potentially exposing herbivores to its harmful effect. In heavily polluted sites, a decrease in the density of small rodent populations has been observed. This decline may be caused by many factors, including decreased fertility. The aim of the presented research was to determine how aluminum, administered at concentrations similar to those recorded in industrial districts (Al I = 3 mg/l, Al II = 200 mg/l), affects the reproductive abilities of small rodents. As the indicators of reproductive abilities, body weight, weight of the testes and accessory sex glands of males, and uterus weight of females were estimated. In females, the number of matured follicles (types 6, 7, and 8) was analyzed, while in males, the quantity and quality (matured, viable, swollen, motile, head abnormalities) of epididymal sperm cells were assessed. Moreover, the development of testes, measured by spermatogenic index, was determined. The model species was the bank vole. Our results have proven that aluminum impairs adult individuals’ reproductive abilities by decreasing the quality and quantity of sperm cells and by causing morphologically abnormal development of the gonads. However, no difference in male organometric parameters was found, and only in females treated with 3 mg/l Al, the uterus weight was higher than control. No differences were found in the total number of matured follicles. These results suggest that the decline in rodent numbers in industrial districts is due, at least in part, to poorer males’ reproductive abilities, resulting from exposure to aluminum contamination.

Dynamics of Rodent and Rodent-borne Disease during Construction of the Three Gorges Reservoir from 1997 to 2012

ObjectiveTo investigate the impact of impoundment and active public health interventions on rodent populations and rodent-borne diseases in the Three Gorges reservoir region from 1997 to 2012. MethodsSurveillance data from 1997 to 2012 were extracted from the Public Health Surveillance System of The Three Gorges established in 1997. Temporal changes in the incidences of hemorrhagic fever with renal syndrome (HFRS) and leptospirosis, rodent density, pathogen-carrying rates, and their correlations were analyzed. ResultsThe average indoor and outdoor rodent densities decreased overall from 1997 to 2012. The average densities decreased by 47.72% (from 4.38% to 2.29%) and 39.68% (from 4.41% to 2.66%), respectively, after impoundment (2003-2012) compared with before impoundment (1997-2002). The average annual incidence rates of HFRS and leptospirosis were 0.29/100,000 and 0.52/100,000, respectively, and decreased by 85.74% (from 0.68/100,000 to 0.10/100,000) and 95.73% (from 1.47/100,000 to 0.065/100,000), respectively, after impoundment compared with before impoundment. Incidences of HFRS and leptospirosis appear to be positively correlated with rodent density in the reservoir area. ConclusionThis study demonstrated that rodent density and incidences of rodent-borne diseases decreased and were maintained at low levels during construction of the Three Gorges dam. Measures that reduce rodent population densities could be effective in controlling rodent-borne diseases during large-scale hydraulic engineering construction.

English

An ecological study on population structure of rodents was conducted in Alage, Southern Ethiopia. Sherman live traps were used to capture rodents in four habitats and trapping sessions. A total of 684 rodents that represented 11 species were captured. Regarding population size and density, Mastomys natalensis was the dominant species followed by Arvicanthis dembeensis while the least was observed in Graphiurus murinus in the study period. The highest biomass was recorded in A. dembeensis (6771.43 g/ha) followed by M. natalensis (6246.63 g/ha) and M. erythroleucus (3257.14 g/ha) while the least was recorded for G. murinus (10.2 g/ha) followed by Mus musculus (35.36 g/ha).The largest and lowest biomasses per habitat type were recorded for M. natalensis and M. musculus, respectively from bushland. There was variation in the population size, density and biomass among trapping sessions and habitats with the highest estimate in the second trapping session and bushland habitat type. All age groups were represented in the population with seasonal and age group variation. In conclusion, there was variation in population size, density and biomass of rodents among habitats and seasons. These population fluctuations might be mostly due to variation in rainfall, habitat heterogeneity, vegetation cover, reproductive patterns, quality and quantity of food and water.   Key words: Age, biomass, density, population, rodents

Recent increase in prevalence of antibodies to Dobrava-Belgrade virus (DOBV) in yellow-necked mice in Northern Italy.

Dobrava-Belgrade virus (DOBV) is the most pathogenic hantavirus in Europe with a case-fatality rate of up to 12%. To detect changes in risk for humans, the prevalence of antibodies to DOBV has been monitored in a population of Apodemus flavicollis in the province of Trento (northern Italy) since 2000, and a sudden increase was observed in 2010. In the 13-year period of this study, 2077 animals were live-trapped and mean hantavirus seroprevalence was 2·7% (s.e.=0·3%), ranging from 0% (in 2000, 2002 and 2003) to 12·5% (in 2012). Climatic (temperature and precipitation) and host (rodent population density, rodent weight and sex, and larval tick burden) variables were analysed using Generalized Linear Models and multi-model inference to select the best model. Climatic changes (mean annual precipitation and maximum temperature) and individual body mass had a positive effect on hantavirus seroprevalence. Other possible drivers affecting the observed pattern need to be studied further.

Experimental Infection of voles with Francisella tularensis indicates their amplification role in tularemia outbreaks.

Tularemia outbreaks in humans have been linked to fluctuations in rodent population density, but the mode of bacterial maintenance in nature is unclear. Here we report on an experiment to investigate the pathogenesis of Francisella tularensis infection in wild rodents, and thereby assess their potential to spread the bacterium. We infected 20 field voles (Microtus agrestis) and 12 bank voles (Myodes glareolus) with a strain of F. tularensis ssp. holarctica isolated from a human patient. Upon euthanasia or death, voles were necropsied and specimens collected for histological assessment and identification of bacteria by immunohistology and PCR. Bacterial excretion and a rapid lethal clinical course with pathological changes consistent with bacteremia and tissue necrosis were observed in infected animals. The results support a role for voles as an amplification host of F. tularensis, as excreta and, in particular, carcasses with high bacterial burden could serve as a source for environmental contamination.

Effect of copper exposure on reproductive ability in the bank vole (Myodes glareolus).

The amount of copper in natural ecosystems is steadily increasing, due to human activities. It accumulates in plants, posing a threat to herbivores. In polluted areas the population density of small rodents is observed to be lower. The decline in rodent numbers may be caused by increased mortality or diminished fertility. This study examined the effect of copper on the reproductive activity of the bank vole (Myodes glareolus), a small rodent which during foraging often wanders into fields where it might be exposed to pollution. The animals were treated with solutions of 0, 150 or 600 ppm Cu. After 12 weeks of exposure the quality and quantity of the male's sperm was tested. To assess morphological development we compared the experimental groups for body weight, the weight of the male's testes and accessory sex glands, the female's uterus, and the number of matured ovary follicles in tested females. At both doses, copper administration led to lower sperm count and caused sperm head anomalies. The higher dose compromised sperm tail membrane integrity, viability and motility. No effect of copper on morphological development was observed in males, and only the lower dose increased testes weight. In females the higher dose had a negative effect on morphological development, and the lower dose increased uterus weight. No effect of copper on ovarian follicle number was found. For the first time, the morphology of the most typical ovarian follicles of the bank vole is presented.

Sources of variation in small rodent trophic niche: new insights from DNA metabarcoding and stable isotope analysis

Intraspecific competition for food is expected to increase the trophic niche width of consumers, defined here as their diet diversity, but this process has been little studied in herbivores. Population densities of small rodents fluctuate greatly, providing a good study model to evaluate effects of competition on trophic niche. We studied resource use in five arctic small rodent populations of four species combining DNA metabarcoding of stomach contents and stable isotope analysis (SIA). Our results suggest that for small rodents, the most pronounced effect of competition on trophic niche is due to increased use of secondary habitats and to habitat-specific diets, rather than an expansion of trophic niche in primary habitat. DNA metabarcoding and SIA provided complementary information about the composition and temporal variation of herbivore diets. Combing these two approaches requires caution, as the underlying processes causing observed patterns may differ between methodologies due to different spatiotemporal scales.

Deratization Activities in the Jewish Autonomous Region in the Post-Flooding Period

Represented is a quantitative characteristic of the objects and facilities in the Jewish Autonomous Region exposed to the flooding-2013. Justified is the necessity for implementation of preventive measures against increase in the activity of HFRS natural foci; showed are the data on disinfestation organization for the prevention of natural-focal infection during the high water and post-flooding period in 2013. Displayed are the results of deratization efficacy control in various administrative units of the entity, calculated using Abbot formula, as well as results of investigation of small rodent population density at the natural stations and substantiation of the barrier disinfestation carrying out. Specified are the areas of the continuous and barrier disinfestation, indicators of Hanta Virus contamination of the rodents caught while performing control over efficacy of deratization works.

Analysis of an Outbreak of Hemorrhagic Fever with Renal Syndrome in College Students in Xi’an, China

The aim of the present study was to analyze an outbreak of hemorrhagic fever with renal syndrome (HFRS), caused by a Hantavirus, in college students in the northern urban area of Xi’an in 2012. The outbreak affected six students and included two deaths. The epidemiological survey revealed that both of the deceased cases were misdiagnosed initially, and treatment was delayed. Furthermore, a higher rodent population density and lower HFRS vaccine coverage were observed in the affected area, which indicates a possible role in the outbreak. Rattus norvegicus (Rn) and Mus musculus (Mm) were the predominant host populations in the area. Genotyping revealed that all HVs from patients and rodents were Hantaan virus (HTNV). Sequence analysis of the S segments revealed that the HTNVs reported in this study had high similarity with strains reported in 2011 and 1985, but these viruses diverged from a strain isolated in 1984 and the HTNV prototype strain 76-118. Detection of anti-HV IgG and amplification of the S segment of HTNV from a non-natural HTNV reservoir indicates that further investigations by increased rodent trapping are necessary.

Is quantity or quality of food influencing the reproduction of rice-field rats in the Philippines?

Context Asynchronous or aseasonal planting of rice crops can extend the period when high-quality food is available to rodents. Consequently, rodents may extend their breeding season, increasing population densities. An improved understanding of the effects of food availability and quality on rodent reproduction may enable better forecasts of high rodent population densities in response to asynchronous or aseasonal planting of crops. Aim The present study examined the association between the quality and quantity of food and the reproductive success of female rice-field rats, Rattus tanezumi and Rattus argentiventer, in a lowland rice landscape in the Philippines. Methods We evaluated the main dietary components of female rats on two different islands through a cropping season during the 2010 wet season. The breeding performance of 60 female R. tanezumi and 60 R. argentiventer individuals was measured. Key results Our findings indicated the following: (1) the main dietary items for females of both rodent species during the main breeding season (the booting stage to harvest) were rice panicles and rice seeds; (2) the high protein content of the rice crop at the tillering stage triggered the onset of the main breeding season, leading to the highest rates of conception during the booting and ripening stages; (3) the quantity of food available at the stubble stage provided sufficient nutrient to maintain pregnancy and lactation by females; and (4) asynchronous planting and poor harvest technology could extend the breeding season of rice-field rats. Conclusions We contend that the extension of the growing season by 3–4 weeks provides high-quality food for rodents, which in turn provides sufficient conditions for higher population densities. The availability of spilled rice grain at the stubble stage is a source of good-quality food for pregnant and lactating females, allowing extension of the breeding season. Implications Synchronous planting (within 2 weeks) with good post-harvest management of rice stubble are important to prevent high population densities of rice-field rats in lowland rice landscapes in the Philippines.

Evaluation of Chemical and Mechanical Control to Reduce Active Burrows for Arvicanthis Niloticus in Sohag Governorate, Egypt

Two rodenticides, Supercaid %0.004 and Zinc phosphide %3 and three mechanical control methods including handing destroy, deep irrigation and traps were evaluated for their efficacy for rodent control under field conditions. In the chemical control the high efficacy of rodenticides bait was obtained when applied inside burrow method, the percent of reduce in active rodent population by using Supercaid %66.60 and %83.20 for Zinc phosphide. Mechanical control methods achieved great success in rodent control as compared to chemical control. the percent of reduction in rodent active burrows population by using mechanical control methods ranged between %93.20 in deep irrigation , %87.20 in handing destroy and %52.60 in trap methods. This method is safe to the environment and higher than reduced rodent population density.

Habitat fragmentation and the population status of rodents in Abayum forest, Ikom, Cross River State, Nigeria

The threat to wildlife population is attributed to various anthropogenic activities. The main objective of this study was to identify the influence of fragment size on the population density of rodents in the study area. Fourteen (14) out of forty (40) fragments existing in the area were randomly sampled. The parameters used for the study were number, size of fragments and the corresponding population distribution of rodents in the study area. Fifty hunters in the area were also interviewed. The fragments were stratified into first, second and third order fragments on the basis of their sizes and randomly selected for the study. Indirect method of wildlife census was carried out through the observation of droppings, trail or tract, burrows, eating habits and noise. Fragment growth rate was 18 to 40 (87.5%) in 7 years. Anthropogenic perturbations in the form of cultivation of permanent cropland, settlement expansion, bush burning, timber exploitation and new settlements in areas previously thinly settled or not accessible to outsiders have resulted in disjointed ecosystems. The population density of rodents correlated with fragment size was highly significant ((P < 0.05) r = 0.9). It was then concluded that fragment size greatly influenced the population and diversity of rodent species. It was recommended that the remaining large fragments in the study area should be protected by law from further fragmentation.

The Food of the Imperial Eagle (Aquila heliaca) in Slovakia

Abstract In this work we assess the data on the food of the Imperial Eagle (Aquila heliaca) in two separate nesting populations: one in Western Slovakia (21 pairs), the other in Eastern Slovakia (30 pairs). In Western Slovakia between 1978 and 2005 we recorded a total of 562 food items, consisting of 33 species of animal. The species predominantly featuring in the food were the brown hare Lepus europaeus (40.2%), common pheasant Phasianuscolchicus (17.3%), feral pigeon Columba livia domestica (11.7%) and the common hamster Cricetus cricetus (11.6%). In Eastern Slovakia between 1971 and 2005 we identified a total of 524 food items, made up of 30 animal species with slightly varying predominance of the same principal kinds of prey: L. europaeus (29.0%), C. cricetus (27.7%), P. colchicus (8.4%) and Columba sp. (8.2%). Imperial Eagles nesting in Slovakia are affected by the consequences of a marked reduction in population density of steppe-type rodents, especially ground squirrels (Spermophilus citellus) and hamsters (C. cricetus) and have become dependent for their food mainly on the prevalence of other small animals (L. europaeus, P. colchicus) and pigeons (C. livia domestica). Pairs nesting in neighbouring Hungary had similar prey, but a different order of predominance of the species (Haraszthy et al. 1996): C. cricetus (51.0%), L. europaeus (12.0%), P. colchicus (11.6%) and S. citellus (7.4%).

Comparison of the Prevalence of Salmonella Infection in Layer Hens from Commercial Layer Farms with High and Low Rodent Densities

A comparison on the prevalence of Salmonella infection in layer hens from commercial layer farms with high and low rodent densities was investigated. Out of 280 laying hens sampled from three commercial layer farms with high rodent densities, Salmonella enterica subsp. enterica serovar Enteritidis (Salmonella Enteritidis) was isolated from 20 (7.14%) hens and Salmonella enterica subsp. enterica serovar Infantis (Salmonella Infantis) from three (1.07%) hens. In contrast, layer hens sampled from four commercial layer farms with low rodent densities were negative for any salmonellae. Significant differences (P < 0.05) in the isolation rates of Salmonella from various organs of infected layer hens were also noted. For Salmonella Enteritidis, liver (55.0%) and the oviduct (55.0%) had the highest isolation rates while all Salmonella Infantis isolates were from the oviduct. Pulsed field gel electrophoresis (PFGE) analysis of BlnI-digested chromosomal DNA of Salmonella Enteritidis isolated from layer hens and rodents showed similar patterns. PFGE analysis of Salmonella Infantis isolated from layer hens, rodents, eggs, and the environment yielded identical patterns. In this study, the significantly higher prevalence rate (P < 0.05) of Salmonella Enteritidis and Salmonella Infantis in layer hens from high rodent density farms could be attributed to the high rodent population density. The persistent Salmonella Enteritidis and Salmonella Infantis infection inside layer houses may have been amplified by the increasing numbers in the rodent population over the years, which increased the opportunity for environment-rodent-chicken interaction and the transmission of salmonellae to chickens. Monitoring of salmonellae from rodents inside poultry premises is recommended to be an effective additional tool in the assessment of the Salmonella status of layer flocks.

An ecological study on rodents of natural vegetation and farm lands in Siltie, Central Ethiopia

An ecological study on species composition, distribution, relative abundance and habitat association of rodents was conducted in Siltie natural vegetation and nearby farmlands during July 2008 - March 2009. Five habitat types, three from natural and two from agricultural fields were randomly selected based on representation of the main vegetation zones. In each habitat type, one representative grid was selected for live trapping. In addition, rodents were also snap-trapped from these habitats. A total of 562 captures was made in 2940 live-trap nights and 87 in 1200 snap-trap nights. Species of small mammals trapped were Mastomys natalensis (33.3%), Arvicanthis dembeensis (23.0%), Mastomys erythroleucus (12.1%), Stenocephalemys albipes (8.4%), Desmomys harringtoni (6.0%), Mus mahomet (5.9%) , Tatera robusta (5.1%) , Lophuromys flavopunctatus (2.8%) , Rattus rattus (2.5%) and Arvicanthis niloticus (0.9%). The trap success varied significantly from habitat to habitat. Population density of rodents was high in the bush land and forest habitats. Plant matters were the most common food items revealed from the stomach contents of snap-trapped individuals. A. dembeensis , M. Mahomet , D. harringtoni and M. natalensis were recorded as major pests in the study area. Breeding was seasonal for most of the species trapped. The number of embryos varied both within and among species.An ecological study on species composition, distribution, relative abundance and habitat association of rodents was conducted in Siltie natural vegetation and nearby farmlands during July 2008 - March 2009. Five habitat types, three from natural and two from agricultural fields were randomly selected based on representation of the main vegetation zones. In each habitat type, one representative grid was selected for live trapping. In addition, rodents were also snap-trapped from these habitats. A total of 562 captures was made in 2940 live-trap nights and 87 in 1200 snap-trap nights. Species of small mammals trapped were Mastomys natalensis (33.3%), Arvicanthis dembeensis (23.0%), Mastomys erythroleucus (12.1%), Stenocephalemys albipes (8.4%), Desmomys harringtoni (6.0%), Mus mahomet (5.9%) , Tatera robusta (5.1%) , Lophuromys flavopunctatus (2.8%) , Rattus rattus (2.5%) and Arvicanthis niloticus (0.9%). The trap success varied significantly from habitat to habitat. Population density of rodents was high in the bush land and forest habitats. Plant matters were the most common food items revealed from the stomach contents of snap-trapped individuals. A. dembeensis , M. Mahomet , D. harringtoni and M. natalensis were recorded as major pests in the study area. Breeding was seasonal for most of the species trapped. The number of embryos varied both within and among species.

Genetic estimates of immigration and emigration rates in relation to population density and forest patch area in Peromyscus leucopus

An emerging pattern is that population densities of generalist rodents are higher in small compared to large forest patches in fragmented landscapes. We used genetically based measures of migration between patches to test two dispersal-based hypotheses for this negative density-area relationship: (1) emigration rates from small patches should be relatively lower compared to large patches (“inhibited dispersal hypothesis”), or (2) immigration rates should be higher into small than large patches (“immigration hypothesis”). Neither hypothesis was supported using data on dispersal inferred from eight microsatellite loci for 12 populations of Peromyscus leucopus in six small (1.3–2.7 ha) and six large (8–150 ha) forest patches. Emigration rates were not lower from and immigration rates were not higher into small than large patches. In fact, contrary to both hypotheses, emigration rates were higher from populations of P. leucopus in small compared to large patches. Based on a combination of genetic and field data, we speculate that higher reproduction in smaller patches resulted in higher densities which led to higher emigration rates from those patches. Rates of reproduction (presumably driven by better habitat conditions in smaller patches), rather than dispersal, seems to drive density differences in forest patches. We conclude that smaller forest patches within an agricultural matrix act as a source of individuals, and that migration rates are fairly high among forest patches regardless of size.

Molecular characterization of two hantavirus strains from different rattus species in Singapore

BackgroundHantaviruses cause human disease in endemic regions around the world. Outbreaks of hantaviral diseases have been associated with changes in rodent population density and adaptation to human settlements leading to their proliferation in close proximity to human dwellings. In a parallel study initiated to determine the prevalence of pathogens in Singapore's wild rodent population, 1206 rodents were trapped and screened. The findings established a hantavirus seroprevalence of 34%. This paper describes the molecular characterization of hantaviruses from Rattus norvegicus and Rattus tanezumi, the predominant rodents caught in urban Singapore.MethodologyPan-hanta RT-PCR performed on samples of Rattus norvegicus and Rattus tanezumi indicated that 27 (2.24%) of the animals were positive. sequence analysis of the S and M segments established that two different hantavirus strains circulate in the rodent population of Singapore. Notably, the hantavirus strains found in Rattus norvegicus clusters with other Asian Seoul virus sequences, while the virus strains found in Rattus tanezumi had the highest sequence similarity to the Serang virus from Rattus tanezumi in Indonesia, followed by Cambodian hantavirus isolates and the Thailand virus isolated from Bandicota indica.ConclusionsSequence analysis of the S and M segments of hantavirus strains found in Rattus norvegicus (Seoul virus strain Singapore) and Rattus tanezumi (Serang virus strain Jurong TJK/06) revealed that two genetically different hantavirus strains were found in rodents of Singapore. Evidently, together with Serang, Cambodian and Thailand virus the Jurong virus forms a distinct phylogroup. Interestingly, these highly similar virus strains have been identified in different rodent hosts. Further studies are underway to analyze the public health significance of finding hantavirus strains in Singapore rodents.

Impacts of differential prey dynamics on the potential recovery of endangered arctic fox populations

1. The arctic fox Vulpes lagopus in Fennoscandia was heavily decimated in the early 20th century and has failed to recover despite full protection during the last 70 years. On the contrary, since the 1970s the population has declined even further and the species is now on the verge of regional extinction. 2. The most recent population decline of the arctic fox in Fennoscandia has coincided with some distinct changes in the cyclic population dynamics of its key prey, lemmings and voles. Although this coincidence of events and the tight trophic connection between foxes and rodents suggest that the two phenomena are causally linked, the effects of spatio-temporal small rodent dynamics on the viability of arctic fox populations have not been fully explored. 3. Here we address how the mean, temporal variance and the periodicity of small rodent population density cycles impact long-term stochastic growth rate of arctic fox populations. We do this in a modelling framework where the vital rates of the fox are linked to realistic, quantitative realizations of small rodent density dynamics. 4. Arctic fox population growth rate was found to be highly sensitive to the temporal mean and to some extent to the variance in small rodent density cycles, whereas cycle period in the observed range of 3- to 5-year cycles was surprisingly of minor importance. 5. Synthesis and applications. Our analysis shows that small rodent population dynamics characterized by low-amplitude density cycles (irrespective of their average cycle period), provide little scope for positive population growth, and thus recovery, of the arctic fox. Thus, we advise that management actions such as re-introductions and red fox Vulpes vulpes control should be conducted in mountain tundra regions where regular, high-amplitude cycles, of any period, with recurrent high spring densities of rodents still prevail. In order to properly identify geographic areas with the highest potential for arctic fox recovery, the emphasis of current monitoring programmes of small rodent dynamics needs to consider more quantitative metrics than they currently employ.