Influence des perturbations anthropiques sur les communautés de petits mammifères des savanes gabonaises

Les savanes gabonaises connaissent des feux anthropiques récurrents, entraînant des dommages sur cet écosystème. L’influence de ce facteur sur la diversité des micromammifères n’a jamais été étudiée. Une situation préoccupante pour ce taxon qui fait l’objet de très peu de programmes de protection. A travers l’analyse de la distribution spatiale des espèces (Muridés), l’étude vise à mesurer l’empreinte écologique des activités anthropiques dans trois régions du Gabon, présentant des niveaux de perturbations différents. Au total 259 individus appartenant à six espèces de muridés ont été capturés avec un effort de 6220 nuit-pièges. Les rendements de capture varient de 0,5 à 15%. Mus minutoides (62,5%) et Lemniscomys striatus (28.9%) sont les plus abondantes. La richesse spécifique (S) varie de 1 à 4 espèces dans les savanes post -feu, alors qu’elle est de 5 dans les savanes protégées des feux, et de 2 espèces dans les savanes fauchées puis brulées. La diversité la plus élevée a été observée dans les savanes non exposées au feu (H’= 1,10 ; J= 0,68). Ceci atteste que le feu influe sur l’abondance, et lorsqu’il est préalablement associé à la fauche, il agirait à la fois sur la diversité et sur l’abondance d’espèces locales. English title: Influence of human disturbance to the small mammal communities in the Gabonese savannahs In the issue of the use of recurrent fires in Gabon, we carried out an inventory both in the Gabonese savannahs that are regularly burned and in those that are not. The study was carried out in the southern and central savannahs of Gabon during the periods from 2004, 2012 and 2013. A total of 259 individuals representing six species of small savannah rodents were captured over 6,220 trap nights. Trap success was variable (0.5 to 15%). Mus minutoides (62.5%) and Lemniscomys striatus (28.9%) are the most abundant. Small rodent abundance was significantly higher in the savannahs protected from fires. The species richness varies from 1 to 4 species in the post-fire savannahs and up to 5 species in the savannahs protected from fires. The savannahs that were mowing prior to burning have yielded only 2 species. The highest diversity index (H’) is found in savannahs not exposed to fire (H’= 1.10). Bush fires seem to have a direct effect on species abundance. Conversely, when savannahs are mown prior to burning, both the diversity and abundance of local species communities are affected. This study gave an initial idea of the diversity of the rodent population in this the recurrent use to fires.

Rodent host population dynamics drive zoonotic Lyme Borreliosis and Orthohantavirus infections in humans in Northern Europe

Zoonotic diseases, caused by pathogens transmitted between other vertebrate animals and humans, pose a major risk to human health. Rodents are important reservoir hosts for many zoonotic pathogens, and rodent population dynamics affect the infection dynamics of rodent-borne diseases, such as diseases caused by hantaviruses. However, the role of rodent population dynamics in determining the infection dynamics of rodent-associated tick-borne diseases, such as Lyme borreliosis (LB), caused by Borrelia burgdorferi sensu lato bacteria, have gained limited attention in Northern Europe, despite the multiannual abundance fluctuations, the so-called vole cycles, that characterise rodent population dynamics in the region. Here, we quantify the associations between rodent abundance and LB human cases and Puumala Orthohantavirus (PUUV) infections by using two time series (25-year and 9-year) in Finland. Both bank vole (Myodes glareolus) abundance as well as LB and PUUV infection incidence in humans showed approximately 3-year cycles. Without vector transmitted PUUV infections followed the bank vole host abundance fluctuations with two-month time lag, whereas tick-transmitted LB was associated with bank vole abundance ca. 12 and 24 months earlier. However, the strength of association between LB incidence and bank vole abundance ca. 12 months before varied over the study years. This study highlights that the human risk to acquire rodent-borne pathogens, as well as rodent-associated tick-borne pathogens is associated with the vole cycles in Northern Fennoscandia, yet with complex time lags.

Population cycles and outbreaks of small rodents: ten essential questions we still need to solve

Most small rodent populations in the world have fascinating population dynamics. In the northern hemisphere, voles and lemmings tend to show population cycles with regular fluctuations in numbers. In the southern hemisphere, small rodents tend to have large amplitude outbreaks with less regular intervals. In the light of vast research and debate over almost a century, we here discuss the driving forces of these different rodent population dynamics. We highlight ten questions directly related to the various characteristics of relevant populations and ecosystems that still need to be answered. This overview is not intended as a complete list of questions but rather focuses on the most important issues that are essential for understanding the generality of small rodent population dynamics.

Public health implications of rodent-borne zoonotic diseases

Rodents are the most abundant and diversified order of living mammals in the world. Their proximity with human population helps in the transmission of various zoonotic diseases. They are known to transmit around 60 common zoonotic diseases and not only serve as reservoirs of some of the emerging zoonoses but also hosts for a number of infectious diseases. They also provide a nexus between wildlife and humans exposing humans to zoonotic diseases circulating in the natural ecosystem. Rodent populations fluctuate in abundance over both seasonal and multiannual time scales. Rodents are known to be the primary or definitive host for diseases like plague, leptospirosis, Lyme disease, tick-borne relapsing fever, hemorrhagic fever with renal syndrome, leishmaniasis, hymenolepiasis, and moniliformiasis; whereas in other diseases, rodents act as the secondary host. There is an urgent need for field studies of rodent population to determine the likely role of particular rodent species as reservoirs of these diseases and to understand rodent-human interactions. Keywords: Rodents, Zoonotic diseases

Application of normalized difference vegetation index (NDVI) to forecast rodent population abundance in smallholder agro-ecosystems in semi-arid areas in Tanzania

This study aimed to evaluate the potential use of normalized difference vegetation index (NDVI) from satellite-derived remote sensing data for monitoring rodent abundance in semi-arid areas of Tanzania. We hypothesized that NDVI could potentially complement rainfall in predicting rodent abundance spatially and temporally. NDVI were determined across habitats with different vegetation types in Isimani landscape, Iringa Region, in the southern highlands of Tanzania. Normalized differences in reflectance between the red (R) (0.636–0.673 mm) and near-infrared (NIR) (0.851–0.879 mm) channels of the electromagnetic spectrum from the Landsat 8 [Operational Land Imager (OLI)] sensor were obtained. Rodents were trapped in a total of 144 randomly selected grids each measuring 100 × 100 m2, for which the corresponding values of NDVI were recorded during the corresponding rodent trapping period. Raster analysis was performed by transformation to establish NDVI in study grids over the entire study area. The relationship between NDVI, rodent distribution and abundance both spatially and temporally during the start, mid and end of the dry and wet seasons was established. Linear regression model was used to evaluate the relationships between NDVI and rodent abundance across seasons. The Pearson correlation coefficient (r) at p ≤ 0.05 was carried out to describe the degree of association between actual and NDVI-predicted rodent abundances. The results demonstrated a strong linear relationship between NDVI and actual rodent abundance within grids (R2 = 0.71). NDVI-predicted rodent abundance showed a strong positive correlation (r = 0.99) with estimated rodent abundance. These results support the hypothesis that NDVI has the potential for predicting rodent population abundance under smallholder farming agro-ecosystems. Hence, NDVI could be used to forecast rodent abundance within a reasonable short period of time when compared with sparse and not widely available rainfall data.

Modeling and Optimal Control on the Spread of Hantavirus Infection

In this paper, optimal control theory is applied to a system of ordinary differential equations representing a hantavirus infection in rodent and alien populations. The effect of the optimal control in eliminating the rodent population that caused the hantavirus infection is investigated. In addition, Pontryagin’s maximum principle is used to obtain the necessary condition for the controls to be optimal. The Runge–Kutta method is then used to solve the proposed optimal control system. The findings from the optimal control problem suggest that the infection may be eradicated by implementing some controls for a certain period of time. This research concludes that the optimal control mathematical model is an effective method in reducing the number of infectious in a community and environment.

Tibetan sheep grazing modifies rodent density and their interactions effect on GHG emissions of alpine meadow

Digging and mound-building by rodents lead to considerable disturbances in the topsoil and may affect plant composition, soil properties. However, little is known about the effects of these activities on GHG emissions, especially under different grazing management. This paper aimed to measure changes in CO2 and CH4 efflux with varying grazing management during the warm and cold seasons and to relate CO2 and CH4 efflux to pika burrow density and zokor mound density with different grazing management. Results of this study showed that CO2 efflux was significantly affected by the grazing season, whereas CH4 efflux was significantly affected by the grazing system. There were significant relationships between GHG efflux and rodent population density which were regulated by grazing management. CO2 efflux increased linearly with rodent density under seasonal continuous grazing in warm season. CO2 and CH4 efflux and rodent population density showed a significant quadratic convex relationship under rotational grazing at 24 SM/ha in warm and cold seasons and rotational grazing at 48 SM/ha in cold season. Under rotational grazing at light stocking rate (24 SM/ha), appropriate populations of rodents were beneficial for decreasing GHG emissions. This results also used to help drive a best-practices model for grazing practices of local herders.