Herbivore effect traits and their impact on plant community biomass: an experimental test using grasshoppers

1. Using trait-based approaches to study trophic interactions may represent one of the most promising approaches to evaluate the impact of trophic interactions on ecosystem functioning. To achieve this goal, it is necessary to clearly identify which traits determine the impact of one trophic level on another.2. Using functionally contrasting grasshopper species, we tested the ability of multiple traits (morphological, chemical and biomechanical) to predict herbivore impact on the biomass of a diverse plant community. We set up a cage experiment in an old species rich grassland field and evaluated how multiple candidate grasshopper effect traits mediated herbivore impact on plant biomass.3. Grasshoppers had different impact on plant community biomass (consuming up to 60 % of plant community biomass). Grasshopper impact was positively correlated with their incisive strength while body size or grasshopper C:N ratio exhibited low predictive ability. Importantly, the strong relationship between the incisive strength and the impact was mediated by the grasshopper feeding niche, which was well predicted in our study by two simple plant traits (leaf dry matter content, leaf C:N ratio). Feeding niche differences between grasshoppers were explained by differences in incisive strength, highlighting the fundamental linkage between grasshopper effect traits and their niche.4. Our study contributes to the development of the trait-based approach in the study of trophic interactions by providing a first experimental test of the relationship between herbivore effect traits, their impact on plant community biomass, and in a larger extent on ecosystem functioning. By comparing the relative importance of multiple interacting grasshopper traits, our study showed that incisive strength was a key effect trait which determined grasshopper feeding niche and its relative impact on plant community biomass

Landscape effects on the population dynamics of small mammal communities: A preliminary analysis of prey-resource variations

This study aims at estimating the effect of landscape composition on the availability of small mammal preys (in terms of biomass) to predators on a sectorial scale (n x 1 km2). Four study sites, representative of different stages of agriculture intensification, were selected in eastern France according to landscape composition. The population dynarnics of Microtus arvalis, Arvicola terrestris, Clethrionomys glareolus and Apodemus sp. were monitored from 1992 to 1996 by using index methods and trapping. M. arvalis and A. terrestris population biomasses were stable in landscapes with low percentage of permanent grassland. M. arvalis populations displayed greater biomass variations with sharp declines in the sites where the proportion of permanent grassland to farmland was greater than 50 %. A. terrestris populations were very unstable in one study site where the proportion of permanent grassland to farmland was greater than 85 %. Synchronic patterns between M. arvalis populations and the populations of hedgerow rodents were suspected at sites with large fluctuations of M. arvalis: every decline of the populations of hedgerow rodents was concomitant with the M. arvalis decline. These results suggest that two kinds of ecological systems in terms of prey-resource variations for mammalian predators can be distinguished: (i) stable in landscapes with lower proportion of permanent grassland, and (ii) unstable, with grassland species crashes and synchronous declines of the rodent community, in landscapes with higher proportion of permanent grassland. Moreover, the population dynamics of small mammals were asynchronous between the four sites situated at relatively short distance (some tens kilometres)L'objectif de cette étude est d'estimer l'effet de la composition du paysage sur les variations de disponibilité en biomasse de micro-mammifères pour les prédateurs, à l'échelle sectorielle (n × 1 km2), Quatre sites d'étude représentatifs d'un gradient d'intensification agricole ont été choisis dans l'est de la France en fonction de la composition du paysage. Les fluctuations de biomasses de Microtus arvalis et Arvicola terrestris (espèces prairiales), de Clethrionomys glareolus et Apodemus sp. (espèces de milieux fermés) ont été suivies de 1992 à 1996 par méthodes indiciaires et piégeage. Les synchronies entre les populations de M. arvalis et celles de rongeurs de milieux fermés ont été recherchées. Les fluctuations de biomasse de M. arvalis et A. terrestris sont stables dans les sites où la proportion de prairie permanente est la plus faible. Les populations de M. arvalis présentent les plus larges amplitudes de variation de biomasse et les déclins les plus prononcés dans les sites où la proportion de prairie permanente sur la surface agricole est supérieure à 50 %. Les populations d'A. terrestris ne sont instables que dans un site, là où la proportion de prairie permanente sur surface agricole est supérieure à 85 %. Les déclins de populations de rongeurs de milieux fermés (Clethrionomys glareolus et Apodemus sp.) sont concomitants de ceux de M. arvalis dans les sites à fortes variations de biomasse de cette dernière espèce. Ces résultats suggèrent deux types de fonctionnement, en terme de variation de disponibilité en proies pour les prédateurs: (i) stable dans les paysages à faible proportion de prairie permanente, et (ii) instable, avec des déclins prononcés et rapides des populations d'espèces prairiales, entraînant des déclins synchrones du peuplement de micro-mammifères étudié, dans les paysages à forte proportion de prairie permanente. Aucune synchronie dans les dynamiques de population de ces micro-mammifères n'est observée entre les sites d'étude, éloignés de quelques dizaines de kilomètres seulement

Diffusion à l'échelle régionale d'une pullulation de campagnols terrestres (Arvicola terrestris Scherman)

National audienc

Relations entre composition/structure du paysage et pullulation des rongeurs prairiaux

National audienc

Estimation of water vole abundance by using surface indices

International audienc

Population dynamics of fossorial water vole (Arvicola terrestris scherman): A land use and landscape perspective

International audienc

La lutte contre les campagnoles champêtres. Enjeux et perspectives

National audienc

La lutte contre les campagnoles champêtres. Enjeux et perspectives

National audienc

Population dynamics of fossorial water vole (Arvicola terrestris scherman): A land use and landscape perspective

International audienc

Communautés parasitaires et cinétiques démographiques des populations de rongeurs

National audienc