Composition and ecological drivers of the kwongan scrub and woodlands in the northern Swan Coastal Plain,Western Australia

The nature of community patterns and environmental drivers in kwongan mediterranean‐type shrubland on nutrient‐poor soils occurring in Western Australia remain poorly examined. We aimed to determine whether (i) classification of the kwongan vegetation of the northern Swan Coastal Plain would be ecologically informative and (ii) which environmental drivers underpin the plant community patterns. The study area was positioned on the northern Swan Coastal Plain, locality of Cooljarloo (30°39′ S, 115°22′ E), situated 170 km north of Perth, Western Australia. Compositional (518 species × 337 relevés) and environmental data set (29 variables × 87 relevés) describing time since last fire, soil chemical and physical properties, and terrain characteristics were analysed using classification and ordination techniques. OptimClass assisted in the selection of a robust data transformation, resemblance function and clustering algorithm to identify the vegetation patterns. Major ecological drivers of the vegetation patterns were detected using distance‐based redundancy analysis (db‐RDA). Classification revealed major groupings of Wet Heath and Banksia Woodland distinguishable by the high prevalence of myrtyoid and proteoid taxa, respectively. On floristic‐sociological grounds, we recognised four Wet Heath and two Banksia Woodland communities. The Wet Heath was constrained to areas of higher litter depth (db‐RDA axis 1: 9%). Soil chemical and physical properties explained the highest proportion (17%) of the compositional variance, while the terrain‐ and fire‐related variables explained 2% and <0.001%, respectively. While fire explained little compositional variance overall, a separate db‐RDA analysis found that it may play an important pattern‐structuring role within Banksia Woodlands. Fine‐scale compositional patterns correspond only to a small extent to environmental data; the substantial unexplained variance may be due to slow‐acting neutral and stochastic processes.     

Facilitation promotes invasions in plant‐associated microbial communities

While several studies have established a positive correlation between community diversity and invasion resistance, it is less clear how species interactions within resident communities shape this process. Here, we experimentally tested how antagonistic and facilitative pairwise interactions within resident model microbial communities predict invasion by the plant–pathogenic bacterium Ralstonia solanacearum. We found that facilitative resident community interactions promoted and antagonistic interactions suppressed invasions both in the lab and in the tomato plant rhizosphere. Crucially, pairwise interactions reliably explained observed invasion outcomes also in multispecies communities, and mechanistically, this was linked to direct inhibition of the invader by antagonistic communities (antibiosis), and to a lesser degree by resource competition between members of the resident community and the invader. Together, our findings suggest that the type and strength of pairwise interactions can reliably predict the outcome of invasions in more complex multispecies communities.     

滇东南地区的蚂蚁物种多样性

为了全面揭示云南蚂蚁多样性规律,采用样地调查法研究了滇东南地区的蚂蚁物种多样性。结果表明:在滇东南地区5个垂直带共采获蚂蚁7亚科57属202种;各样地蚂蚁群落主要指标为:物种数目6～49种(平均24种),个体密度0.7～5 943.6头/m~2(平均560.5头/m~2),多样性指数0.1693～2.6382(平均1.6574),均匀度指数0.0771～0.8022(平均0.5468),优势度指数0.0012～0.9031(平均0.2733);蚂蚁群落间相似性系数0.0333～0.3810,处于极不相似至中等不相似水平。结论认为,滇东南地区栖息着丰富的蚂蚁种类,在生态系统功能和生物多样性保护中具有重要价值。垂直带上蚂蚁物种的丰富度和多样性主要受气温制约,具体表现为纬度和海拔对蚂蚁群落的影响。该地区蚂蚁群落主要指标普遍表现出多域效应现象,除了地形和森林结构因素外,主要受到人类干扰影响,应当结合天然林保护工程对该地区蚂蚁群落加以保护,以便充分发挥其生态功能。     

Indirect effect of nitrogen enrichment modified invertebrate herbivory through altering plant community composition in an alpine meadow

Aims Nitrogen enrichment may affect ‘community invertebrate herbivory’ (hereafter ‘herbivory’) directly by changing plant species’ specific herbivory, or indirectly by altering the composition of natural plant communities. Here, we investigated how community composition altered the community herbivory in natural ecosystems and compared the relative importance of direct and indirect effects of nitrogen addition on community herbivory.