Agricultural practices, Predators, Preys, Grassland voles and Biodiversity

Abstract : In the context of major socio-economic, technological and environmental changes from agricultural revolutions, mountainous areas are often considered favorable for biodiversity and agricultural practices that respect the environment. Yet these territories suffer a real human pressure through agriculture or forestry leading to fundamental issues of the coming century on the alteration of natural resources. Those new farming systems have led to the emergence or increase of abundance of species considering as agricultural pests. Due to food production losses, chemical control and damage to non-target wildlife, zoonosis tanks or as they represent key link of food webs, micro-mammals and their outbreaks represent a field of study of primary importance in ecology. Agricultural policies that led to a specialization in agricultural practices to grassland production have helped to foster the emergence of outbreaks of grassland voles (montane water vole and common vole) through increased vegetal production and homogenization of farming landscape in the Jura Mountains and Central Mountains. While some small predators such as weasels specialize in the consumption of these micro-mammals. Other predators, considered generalists, have a functional response by adapting their diet to the availability of the resource. This functional response can cause a diet switching on alternative prey to micro-mammals. Of all these species, small game species and endangered species are currently management issues and marked conservation. This thesis aims to compare two geographic areas (Alpine valley of the Haute-Romanche and the Jura Mountains) with a degree different from knowledge about grassland vole outbreak. We, through this work, compared the overgrowth phenomenon observed in Haute-Romanche with current knowledge of the Jura Mountains. We also have, through the analysis of long-term monitoring data and establishment of field experiments, tried to provide information about the relationship between prey and predators in a grassland vole outbreaking system in temperate environments. The objective is to attempt a comparison as possible between the two geographic areas to improve the management of these ecosystems. Our first task was to analyze the data collected between 1998 and 2010 to characterize the spatio-temporal variation of the montane water vole population in Haute-Romanche. We also faced this data to the agricultural history of the valley between 1810 and 2003 at the parcel scale. At first we found the similar agricultural historical scenario between the valley of the Haute-Romanche and other European mountainous areas with emphasis on grassland production, with direct effect as the virtual disappearance of the plowed areas, the cantonment of mowing areas in the valley bottoms and expansion of pasture areas. Based on these data, we were able to show a correlative link between the current land-use and the intensity of outbreaks of water vole. The grazing areas have presented a range of montane water vole abundance less important than mowed areas. The current agricultural land-use is directly dependent on the agricultural history of the valley, it appears likely that agricultural specialization towards grassland production in this valley is, as in the Jura Mountains, at the origin of the development of this episode of the montane water vole outbreak. Apart from the cyclical nature of the phenomenon that remains to be seen given its new appearance in this valley, there are great similarities with previous knowledge in the Jura Mountains and the Auvergne. Thus, the development of the outbreak at the parcel scale shows a process spread over about five years with at least one peak period and a period of decline and a period of low abundance. From a spatial point of view, the episode of outbreaks showed a spatial distribution in the form of a wave of colonization channeled through the relief, leaving the Northwest and then up the Romanche valley to the east. In the Doubs department, after taking into account time trend data and the impact of rodenticide treatments on our study area, it appears that there is a negative statistical relationship between the relative abundance of European hare and the red fox one. At the same time there is also a positive relationship between relative abundance of European hare and the montane water vole one. The latter can be considered as an indication of a potential diet switching of the red fox on the European hare. However this finding as a major present limits of never include diet analysis of red fox in the same period necessary to strengthen the hypothesis of diet switching of this species in particular. By working on the harvest of red fox faeces in Haute-Romanche, we observed that on fixed routes we harvested 4-5 times more faeces in autumn than in the summer and during the autumn faeces were located closer to inhabited areas. Regarding the latter observation, hypothesis proposed is the reduction or disappearance of summer food resources and the degradation of climatic conditions in altitude forcing red foxes to descend into the valley. We observed a high occurrence of insects (especially Orthoptera) in the diet of the fox. The montane water vole and voles of the genus Microtus are micro-mammals with the highest occurrence in red fox faeces. It seems that two types of food response exist for the red fox in our Alpine system. The first is characterized by opportunistic behavior of the red fox with increase in certain food resources simply linked to their seasonal availability. At the same time, when the montane water vole abundance decreases, the occurrence of other food items increases (fruits, meso or macro-mammals, indeterminate small mammals and Microtus spp.). It is difficult to conclude on diet switching of red fox on food resources presented above. Also on these two areas of study, we developed an experimental approach to predation by baiting camera traps. The predators observed are composed of 50% by mammals dominated by red foxes and domestic animals (cats and dogs), 40% by the predatory birds dominated by corvids and in 10% of cases by non-identified predators. This device allowed us to see a lure survival difference depending on the type of predator. Thus predatory birds discover more quickly meat lures than most land predators (domestic cats with the same answer as avifauna). The categorization into two main types of landscape did not allow us to detect effects lure survival. Using an approach by satellite data analysis, we found a positive effect of the increase in plant biomass on the survival of meat lure advocating the assumption of a protective effect of plant density. However the explained variance seen little and we must remain cautious about this observation. The positive statistical relationship between the abundance of some predators (red fox, carrion crow, red kite) and montane water vole abundance advocate for considering a partial numerical response of predators via spatial mobility from an area overgrowth to another. This result is emerging as a new information in temperate systems like our mountainous areas. We have shown a positive relationship between survival of lure and relative abundance in montane water vole. This result is again an indication of the potential existence of a diet switching in our experiment. The renewal of this experiment in the Alpine valley of the Haute-Romanche brought us similar observations. This allowed us to strengthen our conclusions regarding the body of evidence arguing for a diet switching and therefore a functional response of predators. However, the low proportion of variance explained in each of our analyzes in the two areas questions the importance of the phenomenon in relation to other sources of variation in this kind of system with multiple food resources and many possible interactions. In terms of technical output, this finding therefore leads to a reflection on how to limit this potential diet switching on species whose conservation status is already weakened. One result is the possible presence of a positive effect qualifiable of "refuge" effect of plant biomass on lure survival. The conclusion of this thesis reinforces the idea that we must tackle the global problem of water vole at source by working on a landscape rediversification. Regarding predation, regulatory tools must be used after consultation with the various institutional bodies due to economic, ethical and health issues they raise. To strengthen field actions, the first action is the strengthening of observation systems for wildlife over the long term and over large spatial scales to measure the potential effects of corporate management actions.
Keywords : water vole
Document type :
Theses
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Submitted on : Thursday, January 21, 2016 - 3:48:33 PM
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Guillaume Halliez. Agricultural practices, Predators, Preys, Grassland voles and Biodiversity. Life Sciences [q-bio]. école doctorale environnement santé université de bourgogne franche comté, 2015. English. ⟨tel-01259687⟩

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