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

1. Trait-based approaches represent a promising way to understand how trophic interactions shape animal communities. The approach relies on the identification of the traits that mediate the linkages between adjacent trophic levels, i.e. “trait-matching”. Yet, how trait-matching explains the abundance and diversity of animal communities has been barely explored. This question may be particularly critical in the context of land use intensification, currently threatening biodiversity and associated ecosystem services.
2. We collected a large dataset on plant and grasshopper traits from communities living in 204 sampled grasslands, in an intensively managed agricultural landscape. We used a multi-trait approach to quantify the relative contributions of trait-matching and land use intensification acting at both local and landscape scales on grasshopper functional diversity. We considered two key independent functional traits: incisor strength and body size of grasshopper species. Incisor strength, a resource-acquisition trait, strongly matches grasshopper feeding niche. Body size correlates with mobility traits, and may determine grasshopper dispersal abilities.
3. Plant functional diversity positively impacted the diversity of grasshopper resource-acquisition trait, according to the trait-matching observed between plants and herbivores. However, this positive effect was significantly higher in old grasslands. In addition, the presence of specific habitats in the landscape (i.e. wood and alfalfa) strongly enhanced grasshopper resource-acquisition trait diversity in the focal grassland. Finally, body size increased with landscape simplification, although its response was modulated by local factors such as soil depth.
4. Trait-matching between plants and herbivores was an important driver explaining the abundance and diversity of resource-acquisition traits within grasshopper communities. Herbivore functional diversity in grasslands, however, cannot be understood without taking into account the presence of specific habitats in the surrounding landscape, as well as the age of the grassland. Our study suggests mass effect and assembly time are central mechanisms promoting higher functional diversity within animal communities in highly disturbed anthropogenic system.

1. 基于性状的研究方法是解析营养级互作如何塑造动物群落的极具前景的途径。该方法核心在于识别介导相邻营养级间关联的性状，即“性状匹配（trait-matching）”。然而，性状匹配如何解释动物群落的丰度与多样性，目前仍鲜有探索。在当前正威胁生物多样性及其配套生态系统服务的土地利用集约化（land use intensification）背景下，这一问题显得尤为关键。
2. 本研究在一处集约化管理的农业景观中，从204个调查样地的草原群落中收集了大量植物与蝗虫的性状数据集。我们采用多性状研究方法，量化了在局域与景观尺度上，性状匹配与土地利用集约化分别对蝗虫功能多样性（functional diversity）的相对贡献。本研究选取了两项关键独立功能性状：蝗虫物种的切齿强度（incisor strength）与体型（body size）。其中，切齿强度作为一种资源获取性状（resource-acquisition trait），可与蝗虫的取食生态位（feeding niche）形成强匹配；体型则与移动性状（mobility traits）相关，可决定蝗虫的扩散能力（dispersal abilities）。
3. 基于植物与草食动物（herbivores）间观测到的性状匹配关系，植物功能多样性对蝗虫资源获取性状多样性存在正向影响。但该正向效应在老龄草原中显著更强。此外，景观中特定生境（即林地与苜蓿地）的存在，可显著提升目标草原的蝗虫资源获取性状多样性。最后，蝗虫体型随景观简化（landscape simplification）程度升高而增大，不过这一响应会受局域因子（如土壤深度（soil depth））的调控。
4. 植物与草食动物间的性状匹配，是解释蝗虫群落内资源获取性状丰度与多样性的重要驱动因子。然而，若不考虑周边景观中的特定生境以及草原的发育年限，便无法完整解析草原中的草食动物功能多样性。本研究表明，质量效应（mass effect）与群落组装时间（assembly time）是在受高度干扰的人为系统（anthropogenic system）中，推动动物群落实现更高功能多样性的核心机制。