Abstract Recent studies have revealed that biotic interactions in ecological communities vary over time, possibly mediating community responses to anthropogenic disturbances. This study investigated the heterogeneity of such variability within a real community and its impact on population stability in the face of pesticide application, particularly focusing on density-dependence of the interaction effect. Using outdoor mesocosms with a freshwater community, we found considerable heterogeneity in density-dependent interaction variability among links in the same community. This variability mediated the stability of recipient populations, with negative density-dependent interaction variability stabilizing whereas positive density-dependence and density-independent interaction variability destabilizing populations. Unexpectedly, the mean interaction strength, which is typically considered crucial for stability, had no significant effect, suggesting that how organisms interact on average is insufficient to predict the ecological impacts of pesticides. Our findings emphasize the multifaceted role of interaction variability in predicting the ecological consequences of anthropogenic disturbances such as pesticide application.

Abstract Root-colonizing fungi, such as mycorrhizal fungi and dark septate endophyte fungi, are often found on pioneer plant species during early primary succession. However, little is known about which fungal species are responsible for the establishment of pioneer plants when these symbionts colonize simultaneously. We investigated the root-colonizing fungal communities of Pinus thunbergii that established prior to lichens, bryophytes, and short-lived herbaceous plants in a primary successional volcanic mudflow site on Kuchinoerabu Island, Japan. We collected a total of 54 current-year and 1- to 2-year-old seedlings. The colonization of root fungi was evaluated by direct observation of key structures (e.g., mantle, arbuscule, microsclerotia, and hyphae) and molecular analysis. Of the 34 current-year seedlings collected, only 12 individuals were colonized by ectomycorrhizal (ECM) fungi. By contrast, all 1- to 2-year-old seedlings were colonized by ECM fungi. Seedlings colonized by pine-specific ECM fungi, specifically Rhizopogon roseolus and Suillus granulatus, showed higher nitrogen and phosphorus contents in their needles compared to non-ECM seedlings. Arbuscular mycorrhizal fungi and dark septate endophyte fungi were found in only two and three individuals, respectively. The high density of mycophagous deer on Kuchinoerabu-jima may contribute to the favored dispersal of ECM fungi over other root-colonizing fungi. In conclusion, the seedling establishment of P. thunbergii at the volcanic mudflow may be largely supported by ECM fungi, with negligible effects of arbuscular mycorrhizal fungi and dark septate endophytes.

Abstract Invasive ants pose a risk to human well-being and social/ecosystem stability. Linepithema humile Mayr is among the most damaging invasive ants worldwide. Most L. humile populations invade ports/wharfs isolated from surrounding landscapes, but unfortunately, a new population was discovered in an inland urban area (Nara Prefecture) of Japan in 2021. In this study, first, the supercolony type of the Nara L. humile population was identified via a hostility test, and then its distribution pattern was characterized. In aggression tests between L. humile from Nara and four supercolonies (haplotypes LH1, LH2, LH3, LH4), this ant showed extremely strong hostility against all supercolonies exept LH2, which was detected only in Japan in its introduced range. In Nara, L. humile was abundant in and around the urban river. Simulations revealed that using this environment for movement/dispersal increased the annual dispersal ability by 14 times compared with that achieved via ground (125 m), as mentioned in the literature. Therefore, river channels can serve as major pathways of long-distance dispersal for L. humile invading inland urban areas. Since applying chemical strategies around rivers is problematic, preventing L. humile from moving to rivers from initial invasion sites is crucial.

Recent studies have uncovered that biotic interaction strength varies over time in real ecosystems intrinsically and/or responding to anthropogenic disturbances. Little is known, however, about whether such interaction variability strengthens or weakens community resistance against disturbances. Here, we examine how the change in interaction strength after pesticide application mediates disturbance impacts on a freshwater community using outdoor mesocosms. We show that the change in interaction strength buffered the disturbance impact but amplified it once the disturbance severity exceeded a certain threshold. Importantly, we also show that interactions fluctuating more temporally under no disturbances were more changeable in response to pesticide applications. Our findings suggest that a severe disturbance may have a surprise impact on a biological community amplified by their own interaction variability, but the possibility still remains that we can predict the consequences of the disturbance by measuring the interaction variability before the disturbance occurs.

Strategic responses to invasive Latrodectus widow spiders are a global challenge due to the risks they pose to health and ecosystems. Chemical strategies involving the use of pyrethroids are effective against adult spiders, but as their populations rebound, chemical control becomes costly and unsustainable for eradication. A major obstacle is the inefficacy of insecticides against eggs, which are covered by a protective silk egg sac. Eradication of invasive spiders must focus on destroying progeny. Here, the responses of eggs in egg sacs of two invasive Latrodectus spiders in Japan (Latrodectus hasseltii (Thorell) and Latrodectus geometricus (C.L. Koch)) to short-term dry-heat exposure were examined. To test whether the dry-heat tolerance of the egg sacs of both spider species differed, lethal temperature (LT) was determined based on the hatching rate of eggs from egg sacs subjected to a range of temperatures. Hatching in both species failed completely when the egg sacs were exposed to temperatures of 55°C and above for 10 min, but the LT to reduce hatching by 90% (LT90) differed significantly between L. hasseltii (50. 9°C) and L. geometricus (52. 8°C). Our study highlights the efficacy of dry heat in suppressing hatching and thus shows the possibility for effective extermination of these noxious invasive pests. Further exploration and investigation of the effects of humidity and heat exposure time on egg sacs under field conditions are needed to guide Latrodectus spider control strategies.

The Argentine ant, Linepithema humile Mayr, has spread to almost all continents. In each introduced region, L. humile often forms a single large colony (supercolony), the members of which share the haplotype "LH1", despite the presence of other supercolonies with different genetic structures. However, the mechanisms underlying the successful invasion of LH1 ants are unclear. Here, we examined whether diet breadth differs between more successful (LH1) and less successful (LH2, LH3, LH4) L. humile supercolonies in Japan to better understand the processes responsible for invasion success. The standard ellipse areas (SEAs) of δ13C and δ15N and their ranges (CR and NR) were used as diet breadth indices. The SEAs of LH1 were much larger than those of the less successful supercolonies despite no differences in the baseline SEAs of arthropods within the supercolony habitats, indicating that the invasion success of a supercolony is associated with its diet breadth. Furthermore, LH1 had a broader CR than the other supercolonies, suggesting that which might be derived from superior resource exploitation ability. Our study highlights the importance of focusing on intraspecific differences in diet breadth among supercolonies when assessing organisms that can potentially invade and become dominant in new habitats.

Among invasive species, aquatic plants pose serious threats to local biodiversity and ecosystem functions. Spartina alterniflora Loisel. (Poaceae), native to the eastern United States, was introduced unintentionally into Japan (Aichi and Kumamoto Prefectures) at around 2010. This invasive species could easily and rapidly spread to estuarine areas of Japan via vigorous trade and transport, making the prediction of its future invasion necessary. Here, the distribution and structure of the genetic variation of S. alterniflora in Japan were examined using chloroplast DNA (cpDNA) and microsatellite genotyping analyses for clarifying its invasion route and process. According to the cpDNA analysis, S. alterniflora populations in Japan had a single haplotype (haplotype C4) that is the most dominant genotype around the Florida Peninsula, the region of its origin, and is also widely found in the introduced populations in the East Asia. Microsatellite analysis also showed a loss of genetic diversity in Japanese S. alterniflora populations (allelic richness (A R) = 1.20-1.39) compared with that in its native region (A R = 4.58-4.59), suggesting a founder effect on S. alterniflora that might have occurred after invasion of the species into Japan. The principal coordinate analysis and The STRUCTURE analysis indicated that no gene mixing among Japanese local populations (Aichi, northern and southern Kumamoto) was observed, indicating that Spartina invasion occurred independently into these regions. Among the three regions, trading between the ports of northern Kumamoto and the U.S. was obviously lower than trading with China. We concluded that invasive S. alterniflora might have independently invaded Japan at different times through an East Asia route, particularly via China (i.e., secondary introduction). Therefore, it is important to strengthen the quarantine control on the importation of commodities, especially of transport vehicles at potential donor spots (i.e., border control/border biosecurity system), and to share information networks on invasive species between each region/port for minimizing further risks of biological species such as Spartina.

Several experiments were carried out to investigate morphology and germination trait of achene in Rumex nipponicus, endangered species, for understanding basic characteristics of this species for its conservation. In our experiments on the germination trait, stratification (low and/or high temperature) and dry-dark treatment were performed; R. nipponicus achene consists of three pieces of perianth with long spines in their edge like R. obtusifolius. However, the former possesses a protuberance in each perianth unlike the latter, which has just one in total. On the other hand, achene of R. nipponicus would not be likely to have deep dormancy because, for instance, the effects of stratification and dry-dark treatment on their germination were not indicated.

The effects of two successive annual treatments of imidacloprid and fipronil on dragonfly nymph communities, which are one of the best-known bioindicators in Japanese agroecosystems, were monitored in experimental paddies. The abundance of dragonfly nymphs was lower in both insecticides-treated fields than it was in the controls, particularly following fipronil treatments. Residues of both insecticides were found in the soil throughout the two years, and imidacloprid persisted in water up to three months following each treatment. A Principal Response Curve analysis (PRC) showed that the second annual treatments caused greater structural changes in dragonfly nymph communities than the initial treatments caused, particularly for fipronil. The community structures continued to change even after the insecticides dissipated from the water. This suggests that ecological impacts, and therefore risks, of imidacloprid and fipronil on dragonfly nymph communities depend more on soil residues than they do on waterborne residues. As expected, susceptibility of dragonfly nymphs to these two insecticides differed among species.

In Japan, assessments of the ecological impacts of pesticides on aquatic organisms are generally based on laboratory single-species acute toxicity tests carried out in accordance with OECD guidelines. Because biodiversity conservation in agroecosystems is very important, pesticide exposure effects should be assessed using a tiered system. Here, we review techniques for assessing the ecological risks of pesticides at the multi-species or community level, and discuss the future of effective pesticide risk management with regard to biodiversity. Laboratory toxicity data can be used to predict community recovery after pesticide contamination when using the species sensitivity distribution (SSD) approach. However, SSD cannot detect impacts on species-interactions and long-term effects on communities. One solution to this problem is the use of model ecosystems under real-world conditions. In particular, mesocosms are effective tools for predicting potential impacts of pesticides on biocenosis, and they can help validate toxicity risks identified by laboratory tests and SSD. However, ecological impacts on long-living species would be underestimated if post-exposure monitoring periods in mesocosms are too short. It is indispensable to integrate laboratory toxicity tests, SSD, and long-term mesocosm studies as an evaluation package to obtain more realistic ecological risk assessments for pesticides.

The ecological risk assessment has become incleaseingly an important issue of the conservation of biodiversity. Many countries including Japan have introduced the test guideline maintained by OECD, in which the ecological risk of each chemicals is assessed based on the acute toxicity test of the three water organism species, that is algae, water flea, and fish, in the laboratory. However, there is little in the studies regarding whether such toxicity data reflect the ecological impacts of each chemical in the actual field. We have promoted the paddy field masocosm test for assessing how insecticides influence the communities of organisms in paddy fields, which is difficult to predict by laboratory tests. We tested the ecological impacts caused by the 2 systemic insecticides, imidacroprid and fipronyl, widely used in the Japanese paddy fields by the paddy field masocosms sice 2010 to 2012. In each the year, we conventionarily applied the chemical into the experimental paddy fields and researched the occurrence of water organism species. As result, we could detect that the insecticides severely influenced the population dynamics of some species even under the standard concentration for the environmental safety provided by the OECD test guideline. And also it was discovered that the divergence of community components of the insecticide applied paddy fields from those of non-chemical paddy filelds increased as years go by because of accumulation of the insecticides residues. We aim to construct and spread a standard method for mesocosm test to each region in Japan for assessing the ecological impact of pesticide to each regional ecosystem.

In order to work out the basic data for future coastal management and coastal sand-dune vegetation conservation, vegetation patterns on dry coastal sand dunes along the Shonan Coast of Kanagawa Prefecture were investigated phytosociologically and relationships to environmental factors were analyzed. In this study, coastal vegetation was classified into four classes, nine associations and six communities including two communities unknown in the higher units. Results from principal components analysis showed that vegetation habitats clearly differed in soil nutrients, other soil properties, frequency of cleaning and number of visitors. Salsoletea komarovii, Glehnietea littoralis and Viticetea rotundifoliae appear under low soil nitrogen content and anthropogenic disturbances, and Plantaginetea maioris and communities unknown in the higher units occur on soils with high content of fine gravel and high nitrogen content Communities of Cynodon dactylon and Oenothera laciniata occurred widely on the Shonan Coast, but their habitats differ from each other. These results could be found on coastal sand dunes under strong human activity elsewhere in Japan. Based on these results, strict limitation to human activity on sand dunes is recommended for conservation of coastal vegetation. As all vegetation types of Shonan Coast were found in Hiratsuka City and Oiso Town, coastal vegetation in these two areas should be conserved carefully (strictly).

本研究は、農薬の曝露拠点であり、かつ生物・生態系サービスのホットスポットである水田をモデルに、複合影響要因や地理的影響を操作・比較可能な野外・開放系実験を主軸として、①汎用的な生態系把握のためのコア機能群（共通の特性をもつ生物種や個体群の集合）や相互作用の特定と、②実用的な生態系機能の指標（生態系レジリエンス指標）の検討に取り組み、もって化学物質による群集・生態系への実効性のある影響評価手法を検討するものである。 令和3年度は全国的なコロナ禍の猛威により、現地調査や出張自体がままならず、思うような進捗は達成できなかったが、各サブテーマで以下のような成果が得られた。 サブテーマ①の成果：加温と農薬曝露に対する生物群集の組成についてモニタリングした結果、農薬曝露単独処理区の群集組成は時間経過とともに無処理区と近似する傾向にある一方、複合処理の群集組成は常に無処理区と異なる傾向にあった。一方で、加温単独処理の組成は、時間経過とともに無処理と乖離した。つまり、複合処理では、農薬の影響と加温の影響が入れ替わるように群集に作用したことで、生態影響が長期化した可能性が示唆された。また、各生物群の密度に着目すると、農薬処理による捕食性昆虫の密度低下にともない餌生物種の密度が増加するといった、生物間相互作用を介した間接効果を示唆する結果も得られた。 サブテーマ②の成果：野外操作実験区における生物の個体数モニタリングデータにもとづいて、多数の生物間で構成される相互作用ネットワークの定量化を試みた。その上で、ネットワークの中心性や連結性などのトポロジー構造や、相互作用強度や強度の時間変動などの定量的な性質など、実験処理として与える人為かく乱に対する生物群集の応答に影響を及ぼすことが想定される生物間相互作用ネットワークの特性値を算出・定量化した。

本研究は、2015年に鹿児島県口永良部島で発生した噴火直後の特異な現象、すなわち一次遷移の一般的な先駆植物に先立ってクロマツを主体とした「樹木」が広域に侵入したメカニズムを解明するにあたり、地上部－地下部の関係性から議論することを目指すものである。 研究2年目は、前年度に引き続き、撹乱跡地における植生（植物種子を含む）、菌根菌および種子・菌根菌散布者等の調査を実施した。なお、コロナ禍で当初計画を達成したとは言い難い。各項目の成果は以下の通りである。 1）植生（植物種子を含む）調査および地形測量： 森林域において、森林を対象として植生調査と埋土種子調査を行った。照葉樹二次林、スギ植林、火砕流跡地の各林分間で、植物の種組成と種多様性を比較した。結果、火砕流攪乱後の植生回復過程では、シカの不嗜好種である低木とシダ植物の優占度が著しく大きいことが明らかになった。同様の傾向は埋土種子集団でもみられ、火砕流による攪乱が種多様性、特に均等度の低下を引き起こしている可能性が示唆された． 2）菌根菌調査： 火山泥流跡地に生育する1-4年生クロマツの外生菌根菌群集を調査した。その結果、マツ科樹木に特異性の高いショウロ属・ヌメリイグチ属やアテリア科が高頻度で検出された。 3）種子・菌根菌散布者（主に節足動物）調査： 引き続き、火砕流跡地およびその周辺で土壌動物調査を行った。前年度と同様、火砕流跡地で土壌動物があまり得られなかったことから、火砕流跡地のような未成熟土壌は、土壌動物の生息環境としては不適、または侵入できても定着できにくい場である可能性が示唆された。 4）群集解析等： 口永良部島における既存の生物データを用いて、群集組成におよぼす噴火前の植生履歴と火山攪乱のタイプの効果について予備解析を行った。その結果、植生履歴と火山攪乱のタイプの双方が群集組成に影響をおよぼす可能性が示唆された。

令和元年度は、１と２の課題であるアルゼンチンアリと在来アリとの餌獲得能力および消費量の違い、さらには３の課題の一部であるアルゼンチンアリの分配能力の違いについて研究を行った。１と２の課題研究の結果、アルゼンチンアリは、在来アリ類（トビイロシワアリ、クロヒメアリ等）に比べ，単位時間あたりにベイト剤へと動員するワーカー個体数が多かった．一方で，餌発見に要する時間，喫食した餌重量，および個体あたりの喫食した餌重量において，種間で明確な差は確認できなかった．アルゼンチンアリの３つのスーパーコロニー（J.main、神戸A、神戸B）間での比較では、スーパーコロニー間で餌資源の獲得能力は異なり、世界および日本で最も広域の分布域を獲得している集団J.mainが、少ない個体数で最大限の資源獲得を行っていることが示唆された。 ３の研究課題に関しては、次年度から行う予定であったが、これを繰上げ、本研究において新たなチャレンジングとなり研究の核ともなりうる、安定同位体を用いた餌分配能力の定量化についての研究、についての研究に着手した。これはアルゼンチンアリ及び在来アリ類のコロニーを採集し、ワーカーおよびブルードの安定同位体比を測定し、両者の値の違いから、餌分配の証拠を得ようというものである。現在、アルゼンチンアリのみ安定同位体比分析を実施することができている。結果、ワーカーの安定同位体比のばらつきに比べ、ブルードの安定同位体比のばらつきは小さくなることが判明した。これは、ワーカー1個体あたりが複数のブルードに餌を分配していることを示唆するものであり、餌の分配能力を定量化するための指標となりうると考えられる。

Examinations on the stable isotope revealed that the 4 super-colonies of Argentina ants in Japan have wide range of food habits, especially in the wide-distributed super colony, but have no correlation with their strength of aggressiveness. large numbers of Argentina ants were collected from Rhaphiolepis indica var. umbellate and Morella rubra as a provider of food and wintering nests. In contrary, the abundaces of the ants collected from the trees, Cinnamomum camphora and Juniperus chinensis cv. Pyramidalis and shrubs, Imperata cylindrica and Zoysia pacifica were significantly smaller than those of the other two wood and shrub species. These results suggested that creating of the green space by planting wood and shrub species that are hard to utilize by the invasive ants may also play a role in restraint efficacy against their invasion.