Diversity and deadwood-based interaction networks of saproxylic beetles in remnants of riparian cloud forest

We studied the saproxylic beetle community inhabiting deadwood in remnants of riparian cloud forests in “La Antigua” basin, in central Veracruz (Mexico). We assessed the influence of deadwood features (tree species, trunk position, trunk diameter, trunk volume and decomposition stages) on saproxylic beetle diversity. In order to assess the stability of beetle species-deadwood interactions, we also analyzed the ecological networks structure. A total of 63 deadwood trunks, belonging to four tree species, were sampled by standardized hand-collection throughout well-preserved remnants of riparian cloud forest. We found that tree species and deadwood decay stage are the main drivers that determine the diversity and stability of saproxylic beetle species interactions. Our results indicate that Quercus corrugata is the main tree species in terms of maintaining the significantly highest saproxylic beetle diversity, but with no stable interactions (saproxylic beetle-deadwood). A nested network structure was detected for Clethra mexicana and Liquidambar styraciflua, with a pool of core (generalist) saproxylic beetle species. We observed that beetle diversity from the early and late deadwood stages comprises distinct assemblages and the four stages of decomposition showed a nested network structure. During deadwood succession, community composition and guilds changed among networks; the early successional stage had more specialized xylophagous beetles, while other guilds (mycophagous, saprophagous and zoophagous) arrive later and become the core species in the advanced stages of decomposition networks. Heliscus tropicus (Passalidae) is a key species constituting the core of all of the networks and could be considered an ecosystem engineer in cloud forests. By exploring links between saproxylic beetles and deadwood characteristics, we can further our understanding of species interaction in order to develop management strategies oriented towards the protection of species and their habitats in this threatened ecosystem.

本研究针对墨西哥韦拉克鲁斯州中部"La Antigua"流域内的河岸云雾林残存斑块，开展了针对栖息于枯木中的腐木栖性甲虫（saproxylic beetle）群落的调查。本研究评估了枯木特征（树种、树干位置、胸径、材积与分解阶段）对腐木栖性甲虫多样性的影响；为探究甲虫-枯木物种互作的稳定性，同时分析了生态网络（ecological network）结构。研究通过标准化手采法，在保存完好的河岸云雾林残存斑块中共采集了隶属于4个树种的63根枯树干样本。研究结果显示，树种与枯木腐朽阶段是决定腐木栖性甲虫物种互作多样性与稳定性的核心驱动因子。结果表明，Quercus corrugata是维持腐木栖性甲虫多样性水平最高的关键树种，但其对应的腐木栖性甲虫-枯木互作并不稳定。对于Clethra mexicana与Liquidambar styraciflua，其对应的互作网络呈现嵌套结构，且拥有一组核心（广食性）腐木栖性甲虫类群。研究发现，枯木早期与晚期阶段的甲虫多样性类群组成存在显著差异，且四个分解阶段的互作网络均呈现嵌套结构。在枯木演替过程中，各网络内的群落组成与功能群发生动态变化：演替早期阶段以特化的木食性（xylophagous）甲虫为主，而其他功能群（食真菌性mycophagous、腐食性saprophagous与捕食性zoophagous甲虫）则较晚出现，并在腐木分解后期的网络中成为核心物种。Heliscus tropicus（Passalidae）是构成所有网络核心的关键物种，可被视为云雾林生态系统中的生态系统工程师（ecosystem engineer）。本研究通过解析腐木栖性甲虫与枯木特征间的关联，可深化对物种互作机制的认知，进而为保护这一受威胁生态系统中的物种及其栖息地制定针对性管理策略提供科学依据。