Annie Ouin

Temporal variability of connectivity in agricultural landscapes: do farming activities help?

In landscapes where natural habitats have been severely fragmented by intensive farming, survival of many species depends on connectivity among habitat patches. Spatio-temporal structure of agricultural landscapes depends on interactions between the physical environment and farming systems, within a socio-economic and historical background. The question is how incentives in agricultural policies may influence connectivity? May they be used to manage the land for biodiversity conservation? We used simulations based on property field maps to compare connectivity on the same landscape during seven years of crop succession for two dairy farming systems, one being representative of conventional systems of western France, the second one representative of systems undergoing intensification of production. Connectivity is a measure of landscape structure and species characteristics based on individual area requirements and dispersal distance. Models used are based on weighed distances, considering differential viscosity for different land uses. The results show that, for a given farming system, physical and field patterns constraints are such that landscape connectivity remains the same over years, while it is significantly different between the two farming systems. This is consistent with the recent input of policies to promote environmentally friendly farming systems, and confirms that policies must encounter the landscape level. The analysis also demonstrates that the localisation of forest patches, resulting from long term land cover changes, plays a central role in connectivity and overrides changes in agricultural land uses.

Spatial dynamics of wood mouse (Apodemus sylvaticus) in an agricultural landscape under intensive use in the Mont Saint Michel Bay (France)

Over the last decades intensification in agricultural use has lead to changes in landscape structure and composition. Seasonal fluctuations of the wood mouse (Apodemus sylvaticus) are well known in cultivated landscapes, but not well explained. The main question relates to the fate of individuals during summer. The hypothesis of a seasonal dispersal of individuals from hedges to crops was investigated in the polder of the Mont Saint Michel Bay (France) at different landscape scales using GIS. Field and landscape scale parameters were analysed in relation to wood mouse abundance in the crops mosaic. The results tend to demonstrate that dilution of the population due to dispersal toward crops could be the main factor explaining the population drops in hedges. Hedgerows act as source habitat in spring whereas field colonisation rate depends on crop quality in summer. The heterogeneity of the crops matrix for the presence of wood mouse has been studied. Variations in vegetation cover of the field plot and its surroundings appear to determine dispersal of mice during summer. Results may have implications in terms of pest management and/or food webs preservation in cultivated landscapes.

Influence of herbaceous elements on butterfly diversity in hedgerow agricultural landscapes

Abstract Landscape factors influencing butterfly diversity in five agricultural landscapes with hedgerows were investigated in western France. Two main questions were addressed: (i) how important are linear (hedge bank, road and lane verge) versus non-linear (grassland) herbaceous elements for butterfly diversity? (ii) Do number and spatial arrangement of these elements influence butterfly diversity? The contribution of each type of herbaceous elements to butterfly diversity was investigated by analyzing diversity at different levels: element, element type (road verge, hedge bank, grassland) and landscape. The spatial arrangement of herbaceous elements was measured by two indices: (i) the mean distance between each grassland and its nearest neighbor (ii) the grain size of the landscape (mean field size). Linear herbaceous elements provided higher butterfly diversity than grasslands. Moreover, butterfly diversity was positively correlated to the surface area in linear herbaceous elements. As they are the remaining low input and lightly managed herbaceous elements in current agricultural landscapes, they contribute greatly to the maintenance of butterfly diversity. Grain size of the landscape was not correlated to butterfly diversity, however, mean distance between nearest grasslands was strongly positively correlated to butterfly diversity. These results show that species movement in the five landscapes was neither prevented by the field size of the studied landscapes nor by the distance between grasslands. The advantages of the landscape heterogeneity measures used in this study and of the method of diversity partitioning, for biodiversity studies in agricultural landscapes, are discussed.

Can the assumption of a non-random search improve our prediction of butterfly fluxes between resource patches?

Abstract.  1. Understanding dispersal patterns that enable small, spatially isolated populations to survive in fragmented landscapes has become an important issue in conservation biology and landscape management. However, for most of the species of interest it is not known whether dispersing individuals navigate or follow systematic search strategies, as opposed to moving randomly.