村上 正志

The specialization of herbivores among tree species is poorly understood despite its fundamental importance as a factor regulating diversity. To examine the effect of tree species on larval community structure, the larval communities in 10 temperate deciduous tree species that differed in leaf emergence pattern (flush- vs. intermediate-type) were seasonally surveyed. The newly developed soft, nitrogen-rich leaves of all species became tough and nitrogen-poor as the season progressed. Following the changes in leaf quality, two distinct seasonal lepidopteran larval communities emerged, with a marked turnover in early July. The beta diversity, or dissimilarity, of species composition in the larval communities among tree species was higher in summer than in spring. These results imply that the lepidopteran larval communities as a whole were supported by alpha diversity in spring and by beta diversity in summer, demonstrating that the plant diversity of this forest could support a caterpillar community. We examined the importance of spatio-temporal variations in leaf quality within and among tree species in promoting herbivore diversity, although other factors, such as tree species phylogeny and predators, may also have a large effect on lepidopteran larval communities.

Quantitative food webs were constructed to explore the community structure of leaf-mining moths in the family Gracillariidae and their parasitoid wasps in a deciduous forest in Hokkaido, Japan. A whole food web was constructed from data collected from June to October 2001. In the web, 16 leafminer species on seven tree species were attacked by 58 species of hymenopteran parasitoid; 376 links between leafminers and parasitoids were observed. Leafminers were specialist herbivores, but most parasitoids were generalists. Five webs were constructed for the seasonal prevalence of leafminers over the one-year period to reveal the temporal dynamics in community structure. Among the seasonal webs, the first web in June was distinctive because two tree species, Japanese umbrella tree Magnolia obovata and Japanese magnolia M. kobus, supported the community. Second to fourth webs from July to September were dominated by the leafminer species on Japanese oak Quercus crispula, and the fifth web was marked by that on Carpinus cordata. The extent of potential apparent competition among leafminers was evaluated using quantitative parasitoid overlap diagrams. These diagrams suggested that abundant host species are likely to have large indirect effects on less abundant species. Moreover, the potential for apparent competition between leafminer species inhabiting different host tree species can occur, although leafminers sharing the same tree species are prone to interact via shared parasitoids. In this system, particular leafminer species, acting as potential sources of apparent competition, can affect other species as sinks, and control whole-community dynamics. Directed apparent competition may potentially occur around oak trees.

The effect of disturbance on local communities may operate within the context of the spatial landscape. We examined the scale-dependent effects of windthrow disturbance caused by a large typhoon on three arthropod communities in a temperate forest of Japan. Canopy arthropods were collected by beating foliage, forest-floor arthropods were collected by sweeping the vegetation, and flying arthropods were collected in Malaise traps. To assess the "functional spatial scale" at which arthropods responded to tree-fall disturbance, the gap rate was quantified at different spatial scales by sequentially enlarging the radius of a circular landscape sector in 10-m increments from 10 to 500 m. We then analyzed the responses of order richness and abundance to the gap rate for each arthropod community. The spatial scale of the significant best-fitting model, which was selected from the models fitted to the gap rate at stepwise spatial scales, was regarded as the arthropod-specific functional spatial scale. Arthropod order richness was not dependent on the gap rate. In contrast, arthropod order abundance depended significantly on the gap rate in many orders, but varied in the response direction and functional spatial scale. These order-specific, scale-dependent responses to tree-fall gaps could complicate interactions among organisms, leading to complex community organization. An understanding of the spatial processes that link the use of space by organisms with the spatial scale at which ecological processes are experienced is required to elucidate the responses of populations, communities, and biotic interactions to disturbances in a spatial landscape context.

Community structure is expected to be affected by spatial heterogeneity in a landscape. We examined the spatial-scale-dependent effects of windthrow caused by a large typhoon on a forest bird community. Typhoon events of this magnitude are rare in Hokkaido, Japan, occurring only once or twice a century. To assess the "functional spatial scale" at which bird groups (community, species, body-size class, and foraging guild) specifically responded to landscape heterogeneity, the canopy gap rate (CGR, gap percentage) was evaluated at different spatial scales by varying the radius of a circular landscape sector from 100 to 500m stepwise by 10m. We then analysed bird community responses, in terms of species richness and abundance, to CGR, Bird species richness did not significantly depend on CGR. In contrast, abundance was significantly dependent on CGR. Bird species richness did not significantly depend on CGR. In contrast, abundance was significantly dependent on CGR in many groups (species, body-size class, and foraging guild). The guild-level response was clearer than the species-level response, which suggests that the integration and filtration of species traits by guild can reveal a clear response of bird abundance to the extent of canopy gaps. For example, the scale dependence of responses to disturbance clearly varied among body-size classes, where larger birds had larger functional spatial scales. These results reveal that different groups of organisms have different functional spatial scales at which they respond to habitat heterogeneity. Our results also suggest that monitoring only a small number of species could be misleading for conserving biodiversity at the landscape level. (c) 2007 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved.

1. The enormous diversity of phytophagous insects in forest canopies is hypothesised to be supported by the number of herbivorous species per host tree species or host specificity. It is therefore necessary to examine the effect of host plant species on compositional changes in the herbivore communities. 2. The lepidopteran larval communities were examined in the canopies of 10 tree species in a temperate deciduous forest of Japan. The phylogeny and leaf flush phenology of host plant species were taken into account as factors affecting the herbivore community assembly. 3. Examination of seasonal changes in the larval community structures on each tree species showed that larval species richness, abundance, and evenness decreased significantly from spring to summer. Larval species richness and abundance were characterised by family-level phylogenetic differences among tree species, whereas evenness was determined at a higher taxonomic level. 4. Compositional changes in the larval communities among tree species showed a remarkable pattern, with a phylogenetic effect at a high taxonomic level in spring, similar to evenness, but a phenological effect in summer. This suggests that host specificity could support the lepidopteran larval diversity in spring. 5. These results suggest that the differences in host utilisation of the herbivore, which reflects the phylogenetic effect of the host plants, can be important as a factor affecting the diversity of lepidopteran larval communities in temperate forests.

1. Forest entomofauna retain high diversity, and examining beta diversity, or species turnover, among assemblages in a forest community is vital to elucidate the source of this diversity. 2. Under the DIVERSITAS in Western Pacific and Asia-International Biodiversity Observation Year (DIWPA-IBOY) project for simultaneously documenting biodiversity throughout the Western Pacific and Asian Region, 892 lepidopteran species (51 742 specimens) and 355 coleopteran species (11 633 specimens) were collected in 2001 by light traps in a cool-temperate forest in northern Japan. 3. This study evaluated the beta diversity of lepidopteran and coleopteran communities by ecological categories (i.e. trap location, forest strata, sampling days, and months), and assessed the habitat preferences of lepidopteran and coleopteran species. 4. ANOVA-like additive apportioning models were used to quantify the beta diversity among the categories. The models simultaneously provide assessments of whether species distributions are biased in favour of particular habitats. 5. Significantly high beta diversity was observed among months for both Lepidoptera and Coleoptera. The category of months corresponded fairly well to the number of specialist species detected in the category, although a remarkably large number of significant specialists in Coleoptera were observed on strata. 6. The high beta diversity and number of specialist species among strata in both communities indicate that stratification between canopy and ground, and seasonal variation, played major roles in species composition and the rich entomofauna in the forest. Highly mobile adults were influenced by the vertical spatial scale, as previously suggested for larvae.

Movements of prey organisms across ecosystem boundaries often subsidize consumer populations in adjacent habitats. Human disturbances such as habitat degradation or non-native species invasions may alter the characteristics or fate of these prey subsidies, but few studies have measured the direct effects of this disruption on the growth and local abundance of predators in recipient habitats. Here we present evidence, obtained from a combined experimental and comparative study in northern Japan, that an invading stream fish usurped the flux of allochthonous prey to a native fish, consequently altering the diet and reducing the growth and abundance of the native species. A large-scale field experiment showed that excluding terrestrial invertebrates that fell into the stream with a mesh greenhouse reduced terrestrial prey in diets of native Dolly Varden charr (Salvelinus malma) by 46-70%, and reduced their growth by 25% over six weeks. However, when normative rainbow trout (Oncorhynchus mykiss) were introduced, they monopolized these prey and caused an even greater reduction of terrestrial prey in charr diets of 82-93%, and reduced charr growth by 31% over the same period. Adding both greenhouse and rainbow trout treatments together produced similar results to adding either alone. Results from a comparative field study of six other stream sites in the region corroborated the experimental findings, showing that at invaded sites rainbow trout usurped the terrestrial prey subsidy, causing a more than 75% decrease in the biomass of terrestrial invertebrates in Dolly Varden diets and forcing them to shift their foraging to insects on the stream bottom. Moreover, at sites with even low densities of rainbow trout, biomass of Dolly Varden was more than 75% lower than at sites without rainbow trout. Disruption of resource fluxes between habitats may be a common, but unidentified, consequence of invasions, and an additional mechanism contributing to the loss of native species.

Seasonal fluctuation of allochthonous subsidies influences food web structure and dynamics in recipient communities. This study investigated whether aquatic subsidies influence the dynamics of insectivorous birds in entire catchment. We estimated the prey biomass and bird density in riparian and upland habitats in three catchments in temperate deciduous forests in Hokkaido, Japan. Aquatic prey was found only in riparian forests and the biomass peaked in early spring, while terrestrial prey was equally distributed between habitats and increased in biomass in late spring. Bird density was higher in riparian than in upland forests before bud break, when the biomass of aquatic insects peaked, but was similar in both forests during the rest of the seasons. These results suggest that aquatic prey subsidies are used not only by birds inhabiting riparian forests, but also by birds associated with upland forests. Aquatic prey subsidies may be particularly important in the spring as a critical food resource for survival and the breeding activities of birds, thereby, influencing the population dynamics of bird communities.

河畔林に生息する鳥は，河川から羽化する水生昆虫を利用し，河川生態系に依存していることが知られている。このような河川から森林へのエネルギーの移動は，森林に生息する鳥類群集に影響すると考えられる。本研究では，静岡県清水町を流れる，柿田川，および，近隣の狩野川を対象として，河川から羽化する水生昆虫の季節消長と，河畔に生息する鳥類の群集との関係を調査した。柿田川は湧水河川であり，流量と水温が通年安定しているのに対し，狩野川の流量は大きく変動し，また，水温も顕著な季節変化を示す。このような両河川の特性の違いが，河川からの羽化水生昆虫の羽化量に影響していた。羽化量は，狩野川と比較して，柿田川においては11月から3月まで継続して多かった。4月以降は両調査河川で羽化量が増加し，両調査地点間で差は見られなかった。柿田川，狩野川は両調査地点において，鳥類の個体数と種数は，水生昆虫の羽化量に対応した変化を示した。4月から10月には，両調査地点でともに鳥類は少なく，また，調査地点間の差は見られなかった。しかし，11月から3月にかけては鳥類の生息個体数，種数は両地点ともに増大し，この期間，柿田川において，個体数で3倍，種数でも約2倍の鳥類が観察された。これらの結果から，柿田川が鳥類の越冬場所として非常に重要であることが示された。しかし同時に，夏の生息個体数が，過去の調査と比較して少なかったことから，夏期，柿田川河畔林は，繁殖地としては十分に機能していないようだった。これは，柿田川の河畔林が孤立した森林であることと関係すると思われる。このような結果は，今後の柿田川の河畔林も含めた保全に対して重要な示唆を与えるものである。

An international project, DIWPA-IBOY, took place for simultaneously observing biodiversity throughout the Western-Pacific and Asian regions in 2001-2003, as one of the core projects for International Biodiversity Observation Year, a crosscutting network activity of DIVERSITAS (an international programme of biodiversity science). DIWPA-IBOY provides extensive data on species diversity obtained by the standardized method. Under this project, 51,742 individuals of Lepidoptera and 11,633 of Coleoptera were collected by light traps from the Tomakomai Experimental Forest of Hokkaido University, one of the core DIWPA-IBOY sites, in the cool-temperate region of northern Japan. Based on these data, this study examined the relative abundance distribution (RAD) to evaluate the amount of rare species in the Lepidoptera and Coleoptera communities. The beta diversities between sampling seasons, forest strata, and trap sites were also assessed to evaluate the spatio-temporal variability of species composition in these communities. In the analysis of the RAD, the best-fit model was selected from the log-Normal, Zipf-Mandelbrot, and Zipf models differing in the tail length of the RAD, i.e., the proportion of rare species. To explore the beta diversity between samples, the abundance-based Jaccard index with an unseen species estimator was calculated, and then a hierarchical clustering analysis was conducted. As a result of RAD analysis, the Coleoptera community was regarded as containing a larger proportion of rare species than the Lepidoptera community. The seasonal compartmentalization of the community, deduced from the beta-diversity analysis, was finer in Lepidoptera (seven assemblages recognized) than in Coleoptera (three assemblages). The spatial (vertical and horizontal) compartmentalization was negligible in both communities. The coincidence of the larger proportion of rare species and the lower beta diversity between seasons in the Coleoptera community was explained by the longer life spans of beetles compared to moths, based on the assumption that the length of life span acts as a temporal agent for mass effect on the analogy of the migration rate as a spatial agent for mass effect.

1. Riparian zones serve several ecological functions for bats. They provide a source of prey and likely provide favourable structural habitats and shelter from predators. Many studies have shown that bats use the space above streams, ponds or riparian vegetation as feeding habitat. These studies, however, have never distinguished between the effects of habitat structure and prey availability on the foraging activities of bats. Such effects can only be distinguished by an experimental approach. We predicted that bat activity along a stream is influenced by the number of emerged aquatic insects. 2. We evaluated the response of terrestrial consumers, insectivorous bats, to changes in the abundance of emergent aquatic insects by conducting a manipulative field experiment. In a deciduous riparian forest in Japan, aquatic insect flux from the stream to the riparian zone was controlled with an insect-proof cover over a 1.2 km stream reach. 3. We estimated the abundance of emergent aquatic and flying terrestrial arthropods near the treatment and control reaches using Malaise traps. The foraging activity of bats was evaluated in both treatment and control reaches using ultrasonic detectors. 4. The insect-proof cover effectively reduced the flux of emergent aquatic insects to the riparian zone adjacent to the treatment reach. Adjacent to the control reach, adult aquatic insect biomass was highest in spring, and then decreased gradually. Terrestrial insect biomass increased gradually during the summer at both treatment and control reaches. 5. Foraging activity of bats was correlated with insect abundance. In spring, foraging activity of bats at the control reach was significantly greater than at the treatment reach, and increased at both sites with increasing terrestrial insect abundance. 6. Our result suggests that the flux of aquatic insects emerging from streams is one of the most important factors affecting the distribution of riparian-foraging bats. As is the case with other riparian consumers, resource subsidies from streams can directly enhance the performance or population density of riparian-dependent bats. To conserve and manage bat populations, it is important to protect not only forest ecosystems, but also adjacent aquatic systems such as streams.

1. Lepidoptera larval abundance and diversity in the canopies of oak (Quercus crispula) trees and saplings were surveyed in a cool-temperate, deciduous broadleaf forest in northern Japan. 2. In general, newly developed leaves were soft, rich in water and nitrogen, and low in tannin, whereas they became tough, poor in water and nitrogen, and high in tannin as the season proceeded. Leaf quality also varied among forest strata, such variations resulting in seasonal and among-strata differences in the structure of the Lepidoptera larval assemblage. 3. The greater Lepidoptera larval abundance and species richness may related to the higher leaf quality on spring foliage compared with summer foliage. On the other hand, diversity (Shannon's H′) and evenness (Pielou's J′) were greater on summer foliage than on spring foliage. Strengthened defences of the host plants against herbivory may cause these differences by filtering the larvae of Lepidoptera species and by constraining the super-dominance of a few species on summer foliage. 4. Canonical Correspondence Analysis (CCA) ordination also revealed a stratified structure of the Lepidoptera larval assemblage in the forest. In both spring and summer, the assemblage composition was more similar between sunlit and shaded canopies than between canopies and saplings. Such assemblage stratification was highly correlated with toughness and tannin content (in spring and summer) or water content (in summer). 5. This study emphasised the importance of spatio-temporal variations in leaf quality, even within the same host plant species, for promoting herbivore diversity in forests. © 2005 Royal Entomological Society.

1. We examined effects of water temperature on the community structure of a three trophic level food chain (predatory fish, herbivorous caddisfly larvae and periphyton) in boreal streams. We used laboratory experiments to examine (i) the effects of water temperature on feeding activities of fish and caddisfly larvae and on periphyton productivity, to evaluate the thermal effects on each trophic level (species-level experiment), and (ii) the effects of water temperature on predation pressure of fish on abundance of the lower trophic levels, to evaluate how temperature affects top-down control by fish (community-level experiment). 2. In the species-level experiment, feeding activity of fish was high at 12 °C, which coincides with the mean summer temperature in forested streams of Hokkaido, Japan, but was depressed at 3 °C, which coincides with the mean winter temperature, and also above 18 °C, which coincides with the near maximum summer temperatures. Periphyton productivity increased over the range of water temperatures. 3. In the community-level experiments, a top-down effect of fish on the abundance of caddisfly larvae and periphyton was clear at 12 °C. This effect was not observed at 3 and 21 °C because of low predation pressure of fish at these temperatures. 4. These experiments revealed that trophic cascading effects may vary with temperature even in the presence of abundant predators. Physiological depression of predators because of thermal stress can alter top-down control and lead to changes in community structure. 5. We suggest that thermal habitat alteration can change food web structure via combinations of direct and indirect trophic interactions. © 2005 Blackwell Publishing Ltd.

1. 本稿は, 群集集合の一般的な枠組みについて, そのメカニズムとプロセス, 結果として生成される群集構造の関係を包括的にまとめたものである.2. 群集集合とは, ある群集が形成されること, または形成されていることである.群集集合は, 種プールの制約, 分散の制約, 環境の制約, および集合規則に制約される.また, 群集集合が確率論的に決まるとする考え方もある.3. 群集は局所群集とメタ群集の階層的構造をもち, 階層的なα多様性, β多様性, γ多様性によって記述される.また, 群集集合の帰結として, 群集構造が分岐する多重安定状態が観察される.4. 種プールのサイズが大きくなるとともに, α多様性, β多様性, γ多様性がそれぞれ増大する.生息場所タイプの頻度をもとに種プールサイズと種多様性を関連づけた種プール仮説がある.5. 分散率が大きくなるとともに, α多様性は単峰形となるが, β多様性とγ多様性は減少する.種の移入順序は群集構造の収斂と分岐, すなわちα, β, γ多様性それぞれに影響を及ぼす.また, 分散を主要なメカニズムとして, メタ群集で種の入れ子分布による構造化が観察される.6. 一次生産性が大きくなるとともに, α多様性は単峰形となるが, β多様性とγ多様性は増大する.撹乱率が大きくなるとともに, α多様性は単峰形となるが, β多様性とγ多様性は減少する.種の特性に基づいて, 環境の制約には環境フィルターとしての作用がある.また, 環境勾配に基づいて, メタ群集で群集の空間的回転による構造化が観察される.7. 群集集合において作用する内部の制約として, 栄養段階内と栄養段階間において5つの集合規則が一般的に考えられる.これらの集合規則のほとんどは群集における資源動態や空間動態に基づくものである.8. すべての種個体が繁殖と死亡において同等であり, それぞれの種個体数が確率論的に増減することを仮定している中立理論では, その予測性や仮定がテストされている.決定論的プロセスと確率論的プロセスのどちらで現実的なデータに当てはまりがよいかは不明である.9. 群集集合における今後の研究では, 制約間の相互作用と時空間スケールの考慮が必要である.また, 食物網で群集構造を記載することによって, 群集集合と生態系機能に関する研究の統合を図ることが課題である.

Brown trout, Salmo trutta, and rainbow trout, Oncorhynchus mykiss, have been introduced to freshwaters in Hokkaido, Japan. Today, it is recognized that these introduced salmonids have negative impacts on native salmonids such as white-spotted charr, Salvelinus leucomaenis, and masu salmon, O. masou. In particular, interspecific competition may be an important mechanism that could contribute to the exclusion for native salmonids. In this study, experimental pairwise contests were conducted to compare interference competitive ability between native and introduced salmonids. We demonstrated that brown trout were competitively superior to white-spotted charr and masu salmon whereas rainbow trout were superior to white-spotted charr. We suggest that introduced brown trout negatively impact both white-spotted charr and masu salmon, and introduced rainbow trout negatively impact white-spotted charr.

Food webs driven by energy from the oxidation of methane are now recognized to be omnipresent in terrestrial and freshwater ecosystems (e.g. lakes, soils and peat bogs), as well as in deep-sea hydrothermal vents and cold seeps. However, the incorporation of methane-derived carbon into stream food webs has never been reported. Here we present the first circumstantial evidence from stable carbon and nitrogen isotope ratios that a stream food web composed of aquatic macroinvertebrates is partly sustained by methanotrophs or chemoautotrophs that gain carbon respired by methane-oxidizing bacteria. Methane-derived carbon seems to enter stream communities around anoxic habitats such as backwater pools and hyporheic zones. Because these reductive habitats exist in many streams, food webs partly sustained by methane-derived carbon are likely to be ubiquitous in lotic ecosystems.

Forestry activities in riparian areas are known to affect stream communities considerably. Not only do riparian deforestation resulting from agriculture or urbanization developments affect stream communities but extensive commercial plantation and forestry practices can alter stream environments adjacent to remaining, intact or secondary forests. Because forestry often includes the construction of logging roads through the riparian zone, this can directly degrade stream environments. Twelve streams in the Shiretoko Peninsula, Hokkaido were investigated so as to determine the effects of forestry practices on stream temperature, periphyton biomass, grazer (benthic invertebrates) biomass and Dolly Varden (Salvelinus malma Walbaum) biomass. The greater the proportion of planted area in the catchment, the higher the stream temperature. Stream temperature directly affects periphyton biomass and Dolly Varden biomass negatively. Neither stream temperature nor periphyton biomass predicted grazer biomass, whereas a positive correlation was found between grazer biomass and Dolly Varden biomass that forage on invertebrates. The overall results indicated that Dolly Varden in the Shiretoko streams were negatively affected by forestry practices and the resultant stream temperature increases. Without effective future riparian forest management, the complex effects of both riparian disturbance and ongoing global warming could further reduce Dolly Varden populations in the region.

Habitat alteration and biotic invasions are the two leading causes of global environmental change and biodiversity loss. Recent innovative experiments have shown that habitat disturbance can have drastic effects that cascade to adjacent ecosystems by altering the flow of resource subsidies from donor systems. Likewise, exotic species invasions could alter subsidies and affect distant food webs, but very few studies have tested this experimentally. Here we report evidence from a large-scale field experiment in northern Japan that invasion of nonnative rainbow trout (Oncorhynchus mykiss) interrupted reciprocal flows of invertebrate prey that drove stream and adjacent riparian forest food webs. Rainbow trout usurped terrestrial prey that fell into the stream, causing native Dolly Varden charr (Salvelinus malma) to shift their foraging to insects that graze algae from the stream bottom. This indirectly increased algal biomass, but also decreased biomass of adult aquatic insects emerging from the stream to the forest. In turn, this led to a 65% reduction in the density of riparian-specialist spiders in the forest. Thus, species invasions can interrupt flows of resources between interconnected ecosystems and have effects that propagate across their boundaries, effects that may be difficult to anticipate without in-depth understanding of food web relationships.

Adult aquatic insects emerging from streams are a fundamental resource sustaining riparian bird communities in broad-leaved deciduous forests. We investigated how stream geomorphology affects the aquatic insect flux and insectivorous bird abundance in 26 riparian-forest plots during spring season in northern Japan. Lateral dispersal of emergent aquatic insects into the riparian forest exponentially decreased with distance from the stream. Similar to aquatic insect distribution, flycatchers and gleaners concentrated their foraging attacks around the stream channel, preying intensively upon emergent aquatic insects. In contrast, bark probers consumed fewer emergent aquatic insects. The abundance of flycatchers and gleaners was closely related to stream geomorphology, whereas that of bark probers was associated with snag density in the study plots. A path analysis showed that the study plots with longer stream channels had greater aquatic insect abundance. This can be interpreted as a consequence of the increased amount of both stream edge and stream surface, where emergent aquatic insects readily penetrate. The increased flux of aquatic insects by stream meanders elevated gleaner abundance in the study plots. In addition, their abundance was directly affected by stream length per se. On the other hand, flycatcher abundance was only directly affected by stream length. Flycatchers, which mainly consumed emergent aquatic insects in the air, may have increased in response to the increase in suitable foraging sites (i.e., open spaces adjacent to perches) accompanying longer stream channels. Although the causal links affecting bird abundance differed among guilds, meandering streams apparently support abundant insectivorous birds in riparian forests. Therefore, to conserve riparian bird communities, it will be necessary to maintain the functions of stream geomorphology that affect the magnitude of energy transfer across the forest-stream interface.

Resource subsidies from external habitats can substantially affect the food web dynamics of local habitats. In this paper, we explore a mathematical model that is tailored for a stream food web, studied by Nakano and colleagues, in which consumers, in situ prey and subsidies all show seasonal fluctuation. The model reveals that the food web dynamics are stabilized if subsidies increase in summer when in situ productivity is low. Consumer dynamics are stabilized because subsidies complement seasonal resource deficiency. In situ prey dynamics are stabilized because subsidies indirectly balance the predation pressure by consumers, with seasonal change in prey carrying capacity. In summer when prey carrying capacity is low, seasonally abundant subsidies indirectly decrease predation pressure, whereas in winter, with high prey carrying capacity, scarce subsidies increase the predation pressure. Our results suggest that temporal productivity differences between spatially linked habitats are important to promote the stability of food web dynamics in a landscape context.

Temporal changes in the foraging habitat of four forest bird species and the distribution pattern of arthropod populations were investigated. The abundance and distribution of arthropods changed drastically with the season within the forest. Lepidoptera larvae were most abundant in the canopy in the first three weeks after budbreak; their numbers decreased rapidly during mid-June. In contrast, on the forest floor, the larvae were abundant from early to late June. The foraging height of the Narcissus Flycatcher Ficedula narcissina changed in parallel with the distribution pattern of Lepidoptera larvae. Three other species, the Great Tit Parus major, Marsh Tit P. palustris, and Eastern Crowned Warbler Phylloscopus coronatus, however, did not change their foraging heights; they continued to forage in the canopy. These differences are probably due to the greater preference of the flycatcher for Lepidoptera larvae compared with the other three species. The three other species switched from feeding on Lepidoptera larvae to spiders or other arthropods in mid June, when the number of Lepidoptera larvae decreased in the canopy. The results of this study suggest that the abundance and distribution of arthropods and differences in foraging tactics among bird species considerably affect avian foraging habitat. The foraging behavior of three species of forest birds revealed species-specific responses to spatiotemporal fluctuations in the distribution of resources. © 2002, The Ornithological Society of Japan. All rights reserved.

A manipulative field experiment was performed to determine the effect of birds, subsidized by aquatic insect emergence, on the insect herbivores in a riparian deciduous forest. Insectivorous birds were observed more frequently in the riparian forest than in upland forest away from the stream, utilizing both herbivorous insects feeding on the riparian vegetation and aquatic insects emerging from the stream as their prey. Field experiments revealed that the insect herbivore population in the riparian forest was more depressed by bird predation than that in the upland forest. This suggests that allochthonous prey input to the in situ prey population was responsible for a modification in the interaction between birds and herbivorous insects, resulting in a heterogeneous food web structure in the forest.

Understanding the induced resistance to herbivory in plants is important in elucidating plant life-history traits. Resistance to herbivory takes two basic forms: defense and tolerance. Induced defense plays an important role in the ecology and evolution of plant-herbivore interactions. It has become increasingly clear that induced defenses to herbivory are complex traits involving the interaction of intrinsic and extrinsic factors. In this study, we investigated the effects of herbivory and the availability of light on induced resistance in Quercus crispula saplings, and the relation between defense and tolerance involving photosynthesis and growth. We conducted field experiments with herbivorous insects under two light conditions. As an induced defense, the leaf mass per area increased with herbivory regardless of the amount of light available, and the concentration of condensed tannin was significantly higher when light was plentiful. On the other hand, as induced tolerance, the photosynthetic rate decreased with herbivory under conditions of ample light. In conclusion, we found that both the availability of light and herbivory affected defense and tolerance in Q. crispula. In addition, we suggest that the interaction between defense and tolerance was noticeable when much light was available because of the photosynthetic reduction caused by herbivory.

河畔林(riparian forest)は野生生物の生育•生息環境として非常に重要である.鳥類についても数多くの研究が河畔林における高い生息密度や種多様度を示しているが,その高い多様性を説明する要因としては,(1) 河畔林の複雑な植生構造,(2)河川-河畔林-後背林という景観の多様性,(3)コリドーとしての機能(4) 境界における生物間相互作用の複雑さ,(5) 後背林からの栄養塩の供給による河畔林における生産性の高さ,(6)河川からのエネルギーの移流があげられる.とくに近年は,水域と陸域の境界面としての河畔林の機能が注目されている.しかし,わが国においては鳥類の群集研究,とくに景観生態学的な視点を組み入れた研究は極あて少ない.鳥類の多様性保全における河畔林さらには景観の多様性の機能解明に向け,今後このような研究が必要とされるであろう.

Mutual trophic interactions between contiguous habitats have remained poorly understood despite their potential significance for community maintenance in ecological landscapes. In a deciduous forest and stream ecotone, aquatic insect emergence peaked around spring, when terrestrial invertebrate biomass was low. In contrast, terrestrial invertebrate input to the stream occurred primarily during summer, when aquatic invertebrate biomass was nearly at its lowest. Such reciprocal, across-habitat prey flux alternately subsidized both forest birds and stream fishes, accounting for 25.6% and 44.0% of the annual total energy budget of the bird and fish assemblages, respectively. Seasonal contrasts between allochthonous prey supply and in situ prey biomass determine the importance of reciprocal subsidies.

In riparian forest, insectivorous birds are largely dependent on aquatic preys. However, the contribution made by aquatic preys to bird diets varies considerably among bird species. In the present study, bird foraging behaviors were observed in order to examine the relationship between bird foraging method and the variation in the contribution of aquatic preys. The great tit, the black-faced bunting, and the wren are largely dependent on aquatic preys by capturing them on the ground. Sallyers, the brown flycatcher, the pale-legged willow warbler, and the narcissus flycatcher are also largely dependent on aquatic preys and capture them mostly during flight. The narcissus flycatcher frequently utilises aquatic invertebrates dwelling on the ground. The leaf and branch gleaner, the crowned willow warbler, does not depend on aquatic prey as much. Although both the pygmy woodpecker and nuthatch are branch and trunk gleaners, the nuthatch utilises aquatic preys frequently by capturing them on the ground as well as during flight, but the pygmy woodpecker does not depend on aquatic preys. The marsh tit also does not depend on aquatic preys but carefully searches terrestrial prey that hide in the vegetation. The differential dependence on aquatic preys among species can lead to the heterogeneous distribution of birds within a riparian forest, suggesting that the indirect effect of aquatic preys on a forest ecosystem via birds can vary within a forest-stream ecotone.

Bird functions in a forest-canopy food web were evaluated by a large-scale field experiment using 'canopy' enclosures. By controlling the presence of two bird species, great tits (Parus major; foliage gleaner) and nuthatches (Sitta europaea; trunk gleaner), in the enclosures, their effect on predatory insects (ants), herbivorous insects (Lepidoptera larvae) and producers (oak trees) was quantified. Great tits reduced the density of Lepidoptera larvae and, indirectly, leaf damage, but had no impact on ants. Nuthatches decreased the density of ants but did not influence either Lepidoptera larvae or leaf damage. These results highlight species-specific functions of birds in the maintenance of forest ecosystems.

The acorn-producing oak Quercus crispula Blume is shade-tolerant and its seedlings were found to be underdispersed on the forest floor, forming seedling aggregations near fertile canopy trees. However, 84.4% of the seedlings were dead within 2 years, with the highest mortality near the adult canopy trees of Q. crispula. This was mostly due to the high levels of herbivory by lepidopteran larvae. The most serious damage was caused by spring consumers, which fed on the leaves of canopy trees in June and, when the food quality of the leaves declined, fell down to the forest floor to consume the juveniles, including the seedlings. Contrary to the expectation of the herbivore-host arms race theory, most of the herbivores were polyphagous. The most dominant spring consumer Telorta edentata (Leech) was also polyphagous, and its distribution on the forest floor showed a high level of association with the distribution of dead oak seedlings.

Manipulative field experiments were performed in a northern Japanese deciduous forest to determine the role of avian predation in the survival of three leaf-rolling lepidopterous larvae (Homonopsis foedenratana, Archips viola, and Zeiraphera corpulentana) on Japanese lilac (Syringa reticulata) trees. When all leaf rolls on the lilacs were experimentally removed, the visitation rate of birds declined, indicating that the leaf rolls served as a visual cue for the birds. In a second experiment in which birds were excluded from the lilac trees, the survival of H. foedenratana larvae was improved, whereas the mortality of the other two Lepidoptera stayed the same. This is probably the result of differences in the shape of leaf rolls; larvae of H. foedenratana alter the leaf form to a greater extent, which may facilitate the detection of the rolls by birds. The high predation rate on the tight leaf rolls of H. foedenratana may be offset by enhanced resistance against other predators and better food quality for the enclosed larvae.

The migratory behavior of moth larvae feeding on oak (Quercus crispula) leaves in spring was investigated with reference to seasonal changes in the quality of the canopy and current-year seedling leaves. After budbreak, the leaf toughness and tannin content of canopy trees increased, while the nitrogen and water contents decreased. These changes in leaf quality appeared to force the moth larvae to migrate from the canopy to the forest floor. A rearing experiment showed that moth (Conistra unimacula (Noctuidae)) larvae could not grow up to the sixth (mature) instar rearing only on canopy leaves. However, when the food material was changed from canopy leaves to seedling leaves after the fourth instar, 72% of the larvae could survive through the fifth instar, and 30% pupated. Seedling leaves were softer, fresher, and more nutritious than canopy leaves. These differences in leaf quality improved the performance of larvae reared with seedling leaves. Our findings suggest that moth larvae migrate from oak canopies to the forest floor in late spring not only to pupate in the ground but also to seek alternative food resources on the forest floor. The latter may have a great impact on the survival of seedlings under the crowns of mother trees.