Plant traits, which are often species specific, can serve as environmental filtering for community assembly on plants. At the same time, the species identity of the initially colonizing arthropods would vary between plant individuals, which would subsequently influence colonizing arthropods and community development in the later stages. However, it remains unclear whether interindividual divergence due to priority effects is equally important as plant trait-specific environmental filtering in the initial stages. In this study, we propose that plant volatile organic compounds (PVOCs) may play a crucial role as an environmental filter in the initial stages of community assembly, which can prevent the community assembly process from being purely stochastic. To test this hypothesis, we conducted short term but highly frequent monitoring (19 observations over 9 days) of arthropod community assembly on intact individuals of six willow species in a common garden. PVOC compositions were analyzed before starting the experiment and compared with arthropod compositions occurring on Days 1-2 of the experiment (earliest colonizer community) and those occurring on Days 8-9 of the experiment (subsequent colonizer community). Unintentionally, deer herbivory also occurred at night of Day 2. Distance-based statistics demonstrated that PVOC compositions were plant species specific, but neither the earliest colonizer nor the subsequent colonizer community composition could be explained by plant species identity. Rather, Procrustes analysis showed that both the PVOC composition and that of the earliest colonizer community can be used to explain the subsequent colonizer community. In addition, the linkage between PVOCs and the subsequent colonizer community was stronger on individuals with deer herbivory. These findings indicate that PVOCs have widespread effects on initial community assembly, as well as priority effects brought on by stochastic immigration, and that plant species identity only has weak and indirect effects on the actual composition of the community.
植物の形質は多くの場合種特異的であり，植物上の群集集合における環境フィルタリングとして機能すると考えられる.同時に，最初に植物上に移入してくる節足動物は植物個体間で種が異なるであろうことが予想される.したがって，どの種が最初に移入してくるかは，その後に移入してくる節足動物の種類と形成される群集の発展過程に影響すると考えられる.しかし，群集集合の最初期においても，先住効果によって引き起こされる植物個体間での群集組成の多様化が，植物種特異的な環境フィルタリングと同程度に顕著であるかは未解明なままである.本研究では，植物の揮発性有機化合物(PVOC)が最初期の群集集合において環境フィルタリングとして機能し，節足動物の移入が完全に確率的に決まるのではないとの仮説を提案する.この仮説を検証するため，実験圃場において6種の健全ヤナギ個体上で，節足動物の群集集合を短期間・高頻度でモニタリングした(9日間で19の観測).実験開始前にPVOC組成を分析し，実験開始1‐2日目に形成された節足動物組成(「最初期移入者」群集)と実験開始8‐9日目に形成された節足動物組成(「二次移入者」群集)とを比較した.また，予期せず2日目の夜間にシカによる食害も発生した.距離ベースの多変量解析の結果，植物個体間のPVOC組成の違いは，ヤナギ樹種の違いによって説明された.一方，最初期移入者群集と二次移入者群集の植物個体間での組成の違いはどちらもヤナギ樹種の違いでは説明できなかった.むしろ，Procrustes解析により，PVOC組成と最初期移入者群集の組成の両方が，二次移入群集の組成を説明できることが示された。また，Procrustes解析の残差に注目すると，PVOCと二次移入群集との関連性は，シカの食害が起きた個体ほど強いことが示された.これらの結果は，非決定論的な初期移入が発端となる先住者効果に加えて，PVOCは初期の群集集合に広く影響を与えたことを示す一方，植物種間の違いは群集集合に対して弱く間接的な影響しか持たないことを示唆している.
Keywords: community assembly; plant‐arthropod feedback; plant–animal interaction.
© 2023 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.