Estimation d’abondance des criquets (Orthoptera: Acrididae) dans les écosystèmes prairiaux

Abstract

Abstract. Estimation of grashopper abundance in grassland ecosystems (Orthoptera: Acrididae). Grasshoppers form an important component of the trophic chain and are considered as good indicators of agricultural change and its environmental consequences. They are among the major inhabitants of grasslands and are thought to decline in intensive agricultural landscape due to habitat fragmentation and loss, as well as agricultural practices. Estimates of acridid population parameters are essential in ecological studies and in management strategies, especially for implementation of conservation schemes. In this paper we describe a sampling technique and a sampling plan to estimate grasshopper densities in grassland ecosystems. We used a 7-yr data set consisting in grasshopper surveys in 916 grasslands in a 450-km² study site located in an intensive agricultural landscape. We establish that a 1 m² cage sampler provides robust estimates of grasshopper densities in regard to temperature during sampling operations. Moreover, we provide sampling plans based on count data to estimated grasshopper densities per m². A random sampling plan can be used to estimate grasshopper densities based on variance-mean relationships. Relative precisions that could be reached, when using sample size of 15 replicates, range between 50% when acridid densities are lower than 1/m² and 20% when they are higher than 7/m². The importance of taking into account population dynamics in the sampling process is discussed.Résumé. Les criquets représentent un taxon central dans les chaînes alimentaires et sont de bons indicateurs à la fois des caractéristiques des milieux et des perturbations de leurs habitats. Associés exclusivement aux habitats herbacés pérennes, ils sont menacés dans les zones d'agriculture intensive. Du fait de leur importance dans les réseaux trophiques, notamment comme ressources alimentaires pour un grand nombre d'espèces aviaires, ils font l'objet d'une attention croissante des écologistes et des gestionnaires des milieux dans le cadre d'études de conservation pour évaluer quantitativement leurs populations. L'objectif de cette étude est de décrire une technique d'échantillonnage et un plan d'échantillonnage destinés à estimer la densité de criquets dans les milieux prairiaux. Cette étude se base sur 7 années d'observations de terrain, menées sur un vaste site d'étude en plaine agricole intensive. Nous montrons que le biocénomètre d'1 m² de base est une technique robuste vis-à-vis des conditions de température durant l'échantillonnage. L'étude établit pour l'ensemble des espèces et pour deux espèces particulières, Pezotettix giornae et Calliptamus italicus, la relation qui lie la variance et la moyenne des effectifs par m². C'est grâce à cette relation qu'on peut établir les tailles d'échantillons qui permettent d'atteindre des objectifs de précision choisis pour les estimateurs de la densité. Nous montrons que la réalisation de 15 lancers aléatoirement par parcelle permet d'obtenir des estimations de la densité de criquets/m² d...

Trait‐matching and mass effect determine the functional response of herbivore communities to land‐use intensification

“…Similarly, artificial grasslands dominated by alfalfa, a plant characterised by soft leaves (Deraison et al . ), can support large populations of Calliptamus italicus (Badenhausser ), a grasshopper species with weak incisors (Deraison et al . ).…”

“…Grasshoppers were sampled by removal trapping with a one square metre cage sampler (Badenhausser et al 2009) randomly thrown 10 times within the grassland field. The survey was conducted during the day from 10.00 to 16.00 h and when temperatures were >10°C (Badenhausser 2012). Rain that occurred during sampling survey was noted as it may influence grasshopper activity.…”

“…Grasshopper morphological traits were measured on the fifteen dominant species in the study area that represented more than 90% of all individuals trapped since 2004 (Badenhausser 2012). We measured grasshopper incisor strength, a trait related to resource-acquisition which is an accurate predictor of grasshopper feeding niche (Ibanez et al 2013a;Deraison et al 2015a).…”

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

“…). In this study, we selected the six numerically dominant grasshopper species, that is those accounting for 80% of the individuals recorded from 2003 to 2011 in the study area (Badenhausser ): Chorthippus biguttulus L., Chorthippus dorsatus Zett, C. italicus , Euchorthippus elegantulus Zeuner , P. giornae and Pseudochorthippus parallelus Zett. These species are characterized by contrasted size and habitat preferences (Badenhausser ).…”

“…Since 2003, grasshopper species richness and density in grasslands have been surveyed annually within the LTER site (Badenhausser 2012). Thirty grasshopper species (Caelifera) have been recorded in the study area, and among them the genera Chorthippus (Gomphocerinae) and Euchorthippus (Gomphocerinae) dominate (Badenhausser 2012). Species from these genera are mostly considered grass feeders (Bernays & Chapman 1970).…”