There is a long history of humans either intentionally or accidentally moving plant species to areas outside of their native ranges. In novel environments, populations of many of these plant species exhibit explosive population growth and spread, in part due to the absence of coevolved enemies such as herbivorous insects. However, over time such enemies can ‘catch up' with their host and re‐establish host–herbivore relationships. Though this phenomenon has been documented in several systems, little evidence exists on how this re‐assembly of enemies results in increased levels of herbivory. In this study we focus on the case of black locust Robinia pseudoacacia, a sparsely populated tree species when growing on undisturbed sites in its limited native range in the eastern USA but a highly invasive species, especially in disturbed environments, in most temperate world regions. We recorded folivore damage on invasive populations in five continents, including both native and invaded portions of North America. Here, we investigated 1) how total foliage damage and damage caused by different groups of folivores differs among regions; 2) how seasonal development of folivore damage differs among regions; 3) how folivory varies with distance from the native range within North America; and 4) how the number of recorded specialist folivores correlates with the amount of folivory. We observed strong differences among regions in the amount and type of folivore damage, with the native range experiencing the highest damage, especially that caused by the native chrysomelid beetle Odontota dorsalis, which is limited to the native and invaded North American range of R. pseudoacacia. Among world regions, total folivory is negatively associated with the distance from the native range and positively associated with the number of established R. pseudoacacia specialist folivore species, supporting the hypothesis that global patterns of herbivore invasions are associated with diminished enemy release.

ワサビ(Wasabia japonica)は、アブラナ科ワサビ属に属する日本料理に欠かせない植物である。多年生植物であり、1年を通して葉を落としながら新しい葉に生え変わることを繰り返すため、通年出荷が可能な作物である。基本的に重量が重く大きいものほど単価は高くなる傾向があり、その他辛味や風味が良いもの、くびれがないものや色合いが良い物ほど品質が良いとされている。品質が悪いものは加工食品に利用され、1あたりの重さが100gを上回るようなものは高級料亭用に取引される。ワサビは栽培方法によって沢ワサビと畑ワサビに分類されるが、いずれも生育時に窒素やカリウム、石灰などを多く吸収する。よってそれらを豊富に含む流水が利用できる地域では一般的に沢ワサビとして栽培され、水量が少ない地域ではそのまま耕土に植える畑ワサビが栽培される。沢ワサビの方が形、色合いや辛味などが畑ワサビを上回るため、市場価値は沢ワサビのほうが高い。沢ワサビは主に長野や静岡など山間部の多い地域74橋本敏一・松野裕・八丁信正・河内香織で栽培されている。沢ワサビの栽培に必要な水は豊富な養分に加え、水温が8～19℃の間であり、12～13℃の問が最適とされている。もし水温が8～19℃の範囲を外れると生育停止がおこる。また水温が高くなると墨入病や軟腐病などの病害が発生するので栽培の際には水温に注意する必要がある。ワサビは半陰性の植物で直射日光に弱く、環境によっては栽培時に遮光するなどの工夫が必要となる。植えつけの時期は生育停止するような夏期や冬期を避け、春植え(3～5月)もしくは秋植え(9～10月)が一般的で、秋植えの方が生育がよいとされる。

Most studies of the effects of litter mixing have focused on decomposition in mixtures of senescent leaves of different plant species. In temperate forests, substantial quantities of green leaves fall in spring and summer, and previous research has shown that stream detritivores can benefit from the combined use of senescent and green leaves. We conducted a litterbag experiment to test the hypothesis that mixtures of senescent and green leaves of different species decomposed more rapidly, mediated by increased detritivore colonization, than leaves of each type in isolation. The observed abundances of 2 detritivore species, the amphipod Sternottioera rhyaca and the caddisfly Lepidostoma complication, were 3 to 6x higher in mixtures of senescent oak and green alder leaves than expected based on litter patches consisting of each species alone. Lepidostoma complication also responded positively to mixtures of senescent oak and green maple leaves, but S. rhyaca did not. These results verify that caddisfly behavior can reflect benefits gained from the combined use of senescent and green leaves. In contrast, the extent of the advantage to amphipods depends on the specific combination of senescent and green leaves. Despite the synergistic effect of mixed senescent oak and green alder leaves on detritivore colonization, observed leaf mass loss in mixtures was not higher than expected. Changes in the chemical properties of senescent oak and green alder leaves in mixtures might decrease feeding rates of detritivores because of preferential or compensatory feeding. Mixtures of senescent and green leaves did not alter leaf decomposition of each component in spring and summer, but might enhance leaf decomposition in autumn and winter by augmenting detritivore populations.

In forested streams, surrounding riparian forests provide essential supplies of organic matter to aquatic ecosystems. We focused on two pathways of particulate organic matter inputs: direct input from upper riparian forests and indirect lateral input from bank slopes, for which there are limited quantitative data. We investigated the inputs of coarse particulate organic matter (CPOM) and carbon and nitrogen in the CPOM into the uppermost reaches of a headwater stream with steep bank slopes in Hokkaido, Japan. CPOM collected by litter traps was divided into categories (e.g., leaves, twigs) and weighed. Monthly nitrogen and carbon inputs were also estimated. The annual direct input of CPOM (ash-free dry mass) was 472 g m(-2), a common value for temperate riparian forests. The annual lateral CPOM input was 353 g m(-1) and 941 g m(-2) when they were converted to area base. This value surpassed the direct input. Organic matter that we could not separate from inorganic sediments contributed to the total lateral input from the bank slopes (124 g m(-1)); this organic matter contained relatively high amounts of nitrogen and carbon. At uppermost stream reaches, the bank slope would be a key factor to understanding the carbon and nitrogen pathways from the surrounding terrestrial ecosystem to the aquatic ecosystem.

2つの体サイズに応じた幼生の微生息場選択性を明らかにすることを目的として，石狩川水系尾白利加川において，カワヤツメ(Lethenteron japonicum)幼生の採集と環境要因を測定した．また，幼生の餌資源利用を議論するために，餌資源の取りこみ実験と安定同位体分析を行った．大型群(5-15cm)の幼生では河床有機物(DOM)と底質硬度，小型群(1-5cm)では底質硬度・流速・底質組成(シルト質)が最良モデルとして選ばれ，これらの要因がカワヤツメ幼生の出現個体数を規定することが明らかとなった．またカワヤツメ幼生の成長と餌資源の取り込みを調べるために飼育実験を行ったところ，落葉リターを与えた処理は体長，湿重量ともに有意に増加することが示された．加えて実験の終了した個体の窒素，炭素安定同位体比分析を行ったところ，実験で用いた幼生が餌資源として与えた落葉リターと藻類の同位体比に誘導され，特に落葉リターにおいてその度合いが高かった．このことから，カワヤツメ幼生はデトリタスを栄養として吸収することが示唆された．以上の野外調査・室内実験から，体サイズの小さなカワヤツメ幼生は自発的に生息環境を選択することができないため，生息河川に柔らかな河床と成長するために落葉リターのような餌資源が最初から必要となる．一方，サイズの大きな幼生は自発的に生息環境を選択し，特に底質中の有機物が多い場所に生息することが明らかとなった．そのためカワヤツメ幼生の生息する河川には，柔らかい泥土が堆積できる多様な河川地形と餌資源の供給源となる河畔林の存在，およびそのような環境が連続して存在することが重要であると推察された．

We investigated the distribution patterns of senescent and green leaf litter patches on a streambed to evaluate the hypothesis that the different immersion times of senescent leaves in long-term benthic storage and newly retained green leaves affect streambed distribution patterns in summer (June, July, and August). We counted all the leaf litter patches in the streambed of the study reach, comparing the physical condition of patches and classifying the trapping obstacles associated with each patch type. The distribution patterns of senescent and green leaf litter patches differed. Green leaf litter patches were more numerous at every sampling date, with most trapped by cobbles, whereas senescent leaf litter patches were retained by twig obstacles, backwaters, and cobbles. In June and July, senescent leaf litter patches were located in significantly deeper stream areas than were green leaf litter patches. The distribution of senescent leaves would be primarily determined during spring snowmelt-driven floods. We speculate that senescent leaves were originally located at the edges of pools in the main flow pathway of the channel, which overflowed in the floods. We conducted flume experiments to clarify the transport characteristics of senescent and green painted maple and manchurian alder leaves in the water column. Our hypothesis was that the transport characteristics of each leaf type differ when they first enter the water, because of differing leaf properties. The flume experiments showed that duration of surface flotation differed for senescent and green leaves and for the two tree species. These differences in the duration of leaves on the streambed and in the floating time of green leaves of different trees ensure varied food resources for macroinvertebrates in various physical conditions.

森林域から河口域に流下した粗大有機物が、沿岸に生息するトンガリキタヨコエビ（Anisogammarus pugettensis）の隠れ場所や食物資源としてはたす役割を明らかにするために飼育実験を行った。1、粒径と量の異なる落ち葉だまり内において、クロガシラガレイ若齢魚を捕食者として24時間後のトンガリキタヨコエビの生残率を測定した。ヨコエビの生残率はどの粒径においても量が多い場合に最大であった。2、落葉と海藻（ホソメコンブ）を食物資源としてトンガリキタヨコエビの飼育実験を行い、成長速度と炭素安定同位体比を調べた。ヨコエビの安定同位体比からは、海藻に加え、体内に落葉も取り込んでいる事が示された。トンガリキタヨコエビは、落葉を主に隠れ場所として利用するが、予備的に食物資源としても利用していると推察され、河口域の落葉だまりは、低次消費者の涵養の場として重要な役割を果たしていると考えられた。

We conducted a decomposition experiment using green and senescent maple and alder leaves in a coastal headwater stream in Hokkaido, northern Japan, during June and July 2000. We estimated whether shredder colonization on the leaves and leaf breakdown differed between green and senescent leaves during the experimental period. Late-instar Lepidostoma complicatum (Trichoptera) and Sternomoera rhyaca (Amphipoda) were the predominant shredder taxa among the macroinvertebrates that colonized litterbags. There was no significant difference in shredder colonization between green and senescent leaves although we found a significant difference between maple and alder leaves. The colonization patterns of large individuals of L. complicatum and S. rhyaca differed from those of small individuals. All decomposition coefficients of green and senescent leaves were high. During the experiment, decomposition was significantly faster in maple than in alder leaves, although no significant difference was found between green and senescent leaves. However, the fragmented nitrogen portion was higher in green leaves than in senescent leaves during the experiment. Higher nitrogen release (2-2.5 times more) as particulate organic matter in green than in senescent leaves indicates that green leaves may be a potentially valuable food resource for other macroinvertebrate collector-gatherer species.

The brackish waters along the Hokkaido coast contain a mixture of plant material of both marine and terrestrial origin that provide food and habitat sources for many macroinvertebrates. Field and laboratory experiments were used to investigate the amount of breakdown of seaweed (kelp) and terrestrial oak leaves (green, senescent, and stream-water soaked ('conditioned')). In addition, the consumption and growth rates of Anisogammarus pugettensis were compared for the different leaf treatments. The breakdown of kelp was greater than that of terrestrial leaves. Among the three types of oak leaves, the amount of breakdown of green leaves was smallest and the breakdown of conditioned senescent oak leaves was 1.5 times greater than that of senescent leaves. Conditioning of leaves in fresh water enhances leaf decomposition in brackish water. The growth rates of A. pugettensis were similar and fastest when fed seaweed and a seaweed-leaf mixture (0.035 +/- 0.009 and 0.043 +/- 0.013 mg mg(-1) day(-1), respectively). The rapid colonisation of oak, despite its low nutritional value, suggests that leaves are important as a habitat, rather than as a food resource. Availability of both seaweed and terrestrial leaves as food resources and habitat would yield benefits for seawater-inhabiting macroinvertebrates.

The effects of salmon carcasses on dissolved nutrients, epilithic production, leaf decomposition rates. and aquatic invertebrates were examined using 10-m-long, artificial channels fed by an adjacent natural stream in Hokkaido, northern Japan. Bags containing maple leaf litter were placed in nine channels, each of which was assigned to one of three treatments with three replicates, for 6 weeks in fall 2002. The three treatments were: (1) salmon carcasses+invertebrates, (2) invertebrates only. and (3) control (no salmon carcasses or invertebrates added). Nutrient concentrations, biomass of epilithic algae (chlorophyll), leaf weight loss, abundance and biomass of invertebrates in the leaf packs were compared among the three treatments at 14, 27, and 40 days after the beginning of the experiment. The NH4+ in stream water and chlorophyll concentrations of epilithic algae were higher in the salmon treatment than the other treatments, and the maple leaves decomposed faster in the salmon treatment than in the other treatments. Moreover. the N content of the leaves was highest and the C/N ratio was lowest in the salmon treatment. although not significantly so. The abundance and biomass of the dominant leaf-shredding invertebrate Goerodes satoi did not differ between the first two treatments. However, the stable N isotope ratio in G. satoi was nearly 3 parts per thousand higher in the salmon treatment, suggesting that around 20% of salmon-derived N was taken up by this shredder. Our results indicate that salmon carcasses affect stream ecosystems directly by enhancing primary production, indirectly by accelerating woody leaf decomposition, and finally by incorporating into the food web primary consumers that utilize fertilized woody leaves.

1. Freshly fallen green leaves and flowers of terrestrial plants enter temperate streams in spring and summer, when senescent leaf litter is often scarce. These resources appear to provide good supplementary food for macroinvertebrate shredders, but have some potential shortcomings as food or case material for caddisflies. 2. To compare suitability of green leaves or flowers and senescent leaves for the growth and development of stream shredders, we reared the caddisfly Lepidostoma complicatum in the laboratory with treatments that provided larvae with senescent (oak) and green (oak or maple) leaves separately, and also together, in case the combined use of both types of leaf may benefit the shredder. 3. Larvae supplied with green leaves alone grew at 65% of the rate of those provided with senescent leaves alone, due to their lower consumption rate. No individuals given green leaves alone developed into adults, whereas 70% of the individuals given senescent leaves alone did. Green leaves may inhibit larval consumption due to their high phenol content, or they may be unsuitable for case material because they are less tough than senescent leaves. 4. Larvae supplied with both senescent and green leaves (or flowers) had a higher growth rate and developed faster, than those given senescent leaves alone, whereas the proportions of successfully emerged individuals did not differ. Lepidostoma probably benefits from the higher nitrogen content of the green leaves when used together with senescent leaves. 5. These results suggest that green leaves (or flowers) cannot serve as an alternative food resource to senescent leaves, but that they can enhance the growth and development of a Lepidostoma stream shredder if senescent leaves are also available.

通し回遊型サクラマスの炭素・窒素安定同位体比を生活史ステージに沿って測定し、餌生物の安定同位体比との関係から濃縮係数およびターンオーバータイムを推定した。サクラマス卵の安定同位体比はその親魚と同等の高い値を示し、海洋での餌生物由来の物質を親魚から受け継いだことが示された。サクラマス幼魚の安定同位体比は、河川生活の開始直後においては卵と同様に高い値を示した。河川生活の進展に伴い幼魚の安定同位体比は河川での餌生物の値に近づくように低下したが、河川生活の開始およそ120日後以降変化が認められなくなった。この時点での安定同位体比は河川での餌生物の平均値と比べ、炭素で2.1‰、窒素で4.0‰高い値を示した。これらの値がサクラマス幼魚におけるそれぞれの元素の濃縮係数に相当し、ターンオーバータイムは120日程度であると考えられた。

We investigated the amounts and types of organic matter that entered a coastal forest stream in Hokkaido, northern Japan. Organic matter input from the riparian forest was collected using litter traps, and benthic organic matter was collected from the streambed. Plant parts were weighed, and monthly nitrogen and carbon inputs were calculated. Organic matter input was highest in October, accounting for 58 % of the total annual amount, whereas input between May and August comprised only 22 % of the total amount. Frass and various plant parts, Such as flowers and green leaves, contributed nitrogen from May to August, and the total input during this period accounted for 39 % of the annual input, which was comparable to the input recorded in October. In May and June, senescent leaves accounted for 30-40 % to the total standing crop although only green leaves entered the stream during this period. To explore the relationship between benthic organic matter and stream macroinvertebrate density, we collected the two dominant summer growing shredder species (Goerodes complicatus [Trichoptera] and Sternomoera rhyaca [Gammaridea]). Densities of S. rhyaca were significantly related to the standing crop of detritus; G. complicatus showed the same trend, although the relationship was not significant. During spring and summer, plant matter that contained high levels of nitrogen contributed to increased nutrient resources in the stream. This organic matter probably affected the growth and development of stream macroinvertebrates when resources were scarce during early summer.

大気中の二酸化炭素濃度は特にここ数十年上昇を続けており、二酸化炭素濃度の上昇に伴う温暖化によって、さまざまな生態系への影響が懸念されている。温暖化の影響は、陸上だけではなく、湖沼や河川、海洋など、水中にも及ぶと考えられている。河川では水面に周囲の渓畔林から落葉や落枝などの陸上由来の有機物が流入することにより河川生態系に取り込まれ、河川に生息する底生生物や魚類などの生息場所や食物資源を提供している。このように、河川生態系は陸上生態系と密接につながっており、温暖化が河川生態系に与える影響を考えるうえで、直接的な温度上昇だけではなく化学的反応や陸域生態系を介した影響など、さまざまな要素について検討する必要がある。申請者は、22年度は、河川生態系における知見の整理を中心として研究を行った。その一環として、22年3月に開催された日本生態学会東京大会で申請者が企画した「河川上流・中流・沿岸における粒状有機物の移動と水生生物による利用-各場の特性と流域スケールでの理解に向けて」をもとにした特集号のとりまとめと執筆を行った。粒状有機物の移動や、生物特に底生動物による粒状有機物の利用について、それぞれの場の特性と共通点を理解し、そこから河川全体を捉える概念にフィードバックすることをめざし、河川上流域から沿岸海域までを対象とする申請者を含む研究者が自身の研究を紹介しつつ国内外の研究のレビューを行った。これらの論文は日本生態学会誌61巻1号に掲載されている。

ダム構造物が流域の物質循環や生態系に与える影響に関する解明と生態系を修復する手法を開発した.ダムが物質循環に及ぼす影響に関してはダムの背後に貯留される落葉が嫌気化して分解がされにくい過程を解明できた.また遡河回遊魚がダムによって遡上を阻まれる実態についてヤツメウナギやサクラマスで明らかにし,そのことが河畔の陸上生態系に与える影響に関して窒素安定同位体比分析で明らかにすることができた.こうしたダムの弊害を緩和する手法としてダムのスリット化が挙げられ,既存のダムの切り下げ試験を行政との共同で行い,その有効性について実証できた.さらに高落差のコンクリート構造物ではなく現地発生の木材を利用して防災的機能を発揮させつつも,魚類の生息場としても機能できるログダム,デブリキャッチャーなどの構造物を開発した.またアメリカ・カリフォルニア州でダム撤去の現場を実際に訪れ,技術的な問題点や行政的な課題などの情報収集を行った.

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