村上 正志

Abstract Polyphagous insect herbivores feed on multiple host‐plant species and face a highly variable chemical landscape. Comparative studies of polyphagous herbivore metabolism across a range of plants is an ideal approach for exploring how intra‐ and interspecific chemical variation shapes species interactions. We used polyphagous caterpillars of Lymantria mathura (Erebidae, Lepidoptera) to explore mechanisms that may contribute to its ability to feed on various hosts. We focused on intraspecific variation in polyphenol metabolism, the fates of individual polyphenols, and the role of previous feeding experience on polyphenol metabolism and leaf consumption. We collected the caterpillars from Acer amoenum (Sapindaceae), Carpinus cordata (Betulaceae), and Quercus crispula (Fagaceae). We first fed the larvae with the leaves of their original host and characterized the polyphenol profiles in leaves and frass. We then transferred a subset of larvae to a different host species and quantified how host shifting affected their leaf consumption and polyphenol metabolism. There was high intraspecific variation in frass composition, even among caterpillars fed with one host. While polyphenols had various fates when ingested by the caterpillars, most of them were passively excreted. When we transferred the caterpillars to a new host, their previous experience influenced how they metabolized polyphenols. The one‐host larvae metabolized a larger quantity of ingested polyphenols than two‐host caterpillars. Some of these metabolites could have been sequestered, others were probably activated in the gut. One‐host caterpillars retained more of the ingested leaf biomass than transferred caterpillars. The pronounced intraspecific variation in polyphenol metabolism, an ability to excrete ingested metabolites and potential dietary habituation are factors that may contribute to the ability of L. mathura to feed across multiple hosts. Further comparative studies can help identify if these mechanisms are related to differential host‐choice and response to host‐plant traits in specialist and generalist insect herbivores.

Understanding the process underlying the spatial gradients in biodiversity is a fundamental issue in ecology. Altitudinal gradients are ideal systems for examining the community assembly process because they represent rapid changes in environmental conditions over relatively short distances. The functional and phylogenetic approaches allow a deeper mechanistic understanding of the underlying assembly process. However, whether community assembly from montane to alpine zones is driven more by ecological constraints or human settlement patterns is not fully resolved and may vary by system. Here, we examined the phylogenetic and trait-based functional structures from the montane to alpine zones and clarified the effects of natural environmental factors and human-induced landscape transformation on the breeding bird assemblage on Mount Norikura, central Japan. Breeding birds from 700 to 3026 m a.s.l. were surveyed in 2016–2017. Bird community structures were examined based on species richness, functional and phylogenetic structures. A null modelling approach was performed to examine functional and phylogenetic cluster/overdispersion structures; clustering and overdispersion imply species elimination by environmental filters and limiting similarity as a corollary of competitive exclusion of species, respectively. Furthermore, we examined the relative effect of natural environments and human disturbance. Bird species richness was high in the mountain base to mid-elevation, then decreased with elevation. We found a contrasting pattern in the phylogenetic and functional structures in the alpine zone: phylogenetic overdispersion and functional clustering. In contrast, the functional and phylogenetic structures were clustered in the upper parts of the subalpine zone. The functional and phylogenetic clusterings in the lower parts of the subalpine and montane zones were negligible with the weak effects of the environmental filtering. Single-trait analysis showed that the high abiotic tolerance and foraging or nesting capabilities in treeless environments were clustered in the alpine zone, and mobility was clustered in the subalpine zones. Natural environments strongly affected bird community structures, but human disturbance added species to assemblages in the mountain base to mid-elevation and changed the functional and phylogenetic structures. Our findings highlight that filtering by severe natural environments is a fundamental community assembly process in high mountain regions, whereas filtering effects can be weaker at lower elevations. Furthermore, the filtering effect should differ between the alpine and the upper parts of the subalpine zones because of different combinations of clustered traits. Climate change and landscape transformation pressures may strongly impact biodiversity in the alpine and subalpine zones, respectively.

We collected seven fixed pairs of Rhyacophila lezeyi during mating copulation and observed four different states of copulation. We investigated the underlying mechanism for the variations in the morphology of each copulating device, based on the copulation state. Notably, the male anal sclerites underwent considerable changes from the early stages of copulation. Initially, the female segment VIII approached the male anal sclerites, which were pushed downwards by the female VIII and IX segments, extending from IX. With the progression of mating stage, the distended end of the female’s segment VIII covered the anal sclerites, pushing them further down. The male parameres were initially folded in bellows-like shapes under the aedeagus before copulation initiation. However, as the copulation stage advanced, they extended to about 3.2 times of their original length. Distended ends of both parameres adhered to the position of the spiracles at the anterior margin of the lateral part of the female’s VII abdominal sternite. The attachment site was the external surface of the hair bulb of the male parameres. During the middle stage of copulation, movements involving the opening and closing of the male gonopods started. The gonoslylus made strong contact with the female’s abdominal segment VIII, resulting in the deformation of segment VIII due to the contact pressure.

Abstract As one of the unique owl-wing morphologies, trailing-edge (TE) fringes are believed to play a critical role in the silent flight of owls and have been widely investigated using idealized single/tandem airfoils. However, the effect of TE fringes and associated mechanisms on the aeroacoustics of owl wings, which feature curved leading edges, wavy TEs, and several feather slots at the wingtips, have not yet been addressed. In this study, we constructed two 3D owl wing models, one with and one without TE fringes, based on the geometric characteristics of a real owl wing. Large-eddy simulations and the Ffowcs Williams‒Hawkings analogy were combined to resolve the aeroacoustic characteristics of the wing models. Comparisons of the computed aerodynamic forces and far-field acoustic pressure levels demonstrate that the fringes on owl wings can robustly suppress aerodynamic noise while sustaining aerodynamic performance comparable to that of a clean wing. By visualizing the near-field flow dynamics in terms of flow and vortex structures as well as flow fluctuations, the mechanisms of TE fringes in owl wing models are revealed. First, the TE fringes on owl wings are reconfirmed to robustly suppress flow fluctuations near the TE by breaking up large TE vortices. Second, the fringes are observed to effectively suppress the shedding of wingtip vortices by mitigating the flow interaction between feathers (feather-slot interaction). These complementary mechanisms synergize to enhance the robustness and effectiveness of the TE fringe effects in owl wing models, in terms of aerodynamic force production and noise suppression. This study thus deepens our understanding of the role of TE fringes in real owl flight gliding and points to the validity and feasibility of employing owl-inspired TE fringes in practical applications of low-noise fluid machinery.

Abstract Radioactive cesium-bearing microparticles (CsMPs) are glassy particles containing large amounts of radioactive cesium (Cs, i.e., ¹³⁴Cs and ¹³⁷Cs). Because Cs in CsMPs is covered with insoluble glass, CsMPs may not release Cs into the liquid phase of river water. Previous studies have shown that CsMPs may drive overestimation of Cs transfer between the solid and liquid phases in rivers. In this study, we investigated the contribution of CsMPs to Cs concentrations in forest soil and river water in the Takase River watershed to explore the migration of CsMPs from a forest catchment and their effect on the distribution coefficient in the river water. The Cs concentration derived from CsMPs as a proportion of that in the bulk soil and particulate Cs in the river water was not large; therefore, CsMPs did not have a significant effect on the distribution coefficient. In forest soil, variation in the distribution of CsMPs in soil was greater than that in the distribution of Cs adsorbed onto soil particle. This variation might cause the Cs concentration derived from CsMPs flowing into rivers to vary more than the particulate Cs concentration. To elucidate CsMPs migration and its effects on the Cs concentration in the river, further research such as soil sampling to assess the spatial distribution of CsMPs in the watershed is needed.

Partial mycoheterotrophic i.e., mixotrophic, plants are the species which partially depend on mycorrhizal fungi for its nutrients. Although some of these plants are known to show plasticity in the degree of fungal dependence induced by the changes in light condition, the genetic background of this plasticity is largely unsolved. Here, we investigated the relationships between environmental conditions and nutrient sources based on 13C and 15N enrichment in mixotrophic orchid Cymbidium goeringii. We also shaded them for 2 months and evaluated the effect of light condition on the nutrient sources based on the abundance of 13C and 15N and the gene expressions by RNA-seq based de novo assembly. The shading had no effect on isotope enrichment, possibly because of the translocation of carbon and nitrogen from the storage organs. Gene expression analysis showed the upregulation of genes involved in jasmonic acid response in leaves of the shaded plants, which suggests that the jasmonic acid played an important role in regulation of degree of dependence against the mycorrhizal fungi. Our results suggest that mixotrophic plants might be controlling their dependency against the mycorrhizal fungi by a common mechanism with the autotrophic plants.

The bird assemblages in high mountain ecosystems exhibit dramatic seasonal changes in community structure following the sequential arrival of species during the pre-breeding season. The investigation of this process should offer the great interest because of the vulnerability of alpine bird assemblages under climate change. In the present study, the mechanisms underlying the seasonal dynamics of a passerine bird assemblage in alpine and subalpine zones were investigated on Mount Norikura in central Japan. We empirically determined the arrival dates of 18 bird species and collected data on 6 traits: the number of food types and foraging methods, body mass, the lowest temperature in the northernmost wintering area, and the foraging and nesting strata. We analyzed the effects of these traits on the arrival date and found that the species with a lower temperature in the northernmost wintering area arrived earlier. We also found that species with smaller food types arrived earlier when the long-distance migratory species were excluded from the analysis. In addition, the annual dynamics of the assemblage and environments were examined. We found that temperature and snowpack were significantly associated according to the species composition changes. The functional properties of the assemblage became simpler in winter. Our findings suggest that bird assemblage dynamics from winter to summer are driven by the sequential arrival of species according to their abilities—behavioral and/or thermophysiological adaptations to cold temperatures in an environment characterized by lacking readily available food. Furthermore, cold temperatures and deep snowpack should restrict species inhabitance in winter.

Herbivorous insects have evolved counteradaptations to overcome the chemical defences of their host plants. Several of these counteradaptations have been elucidated at the molecular level, in particular for insects specialized on cruciferous host plants. While the importance of these counteradaptations for host plant colonization is well established, little is known about their microevolutionary dynamics in the field. In particular, it is not known whether and how host plant diversity shapes diversity in insect counteradaptations. In this study, we examine patterns of host plant use and insect counteradaptation in three Pieris butterfly species across Japan. The larvae of these butterflies express nitrile-specifier protein (NSP) and its paralogue major allergen (MA) in their gut to overcome the highly diversified glucosinolate–myrosinase defence system of their cruciferous host plants. Pieris napi and Pieris melete colonize wild Brassicaceae whereas Pieris rapae typically uses cultivated Brassica as a host, regardless of the local composition of wild crucifers. As expected, NSP and MA diversity was independent of the local composition of wild Brassicaceae in P. rapae. In contrast, NSP diversity correlated with local host plant diversity in both species that preferred wild Brassicaceae. Both P. melete and P. napi revealed two distinct major NSP alleles, which shaped diversity among local populations, albeit with different evolutionary trajectories. In comparison, MA showed no indication for local adaptation. Altogether, MA appeared to be evolutionary more conserved than NSP, suggesting that both genes play different roles in diverting host plant chemical defence.

The community composition of insect herbivores is largely shaped by host–plant phylogeny and functional traits. These effects differ between herbivores due at least in part to varying levels of diet specialisation. Distinguishing between herbivores with differing specialisation is therefore necessary to understand the roles of host phylogeny and traits in shaping complex insect communities. We surveyed the complete plant–caterpillar food web in a 0.2 ha plot of a lowland cool-temperate deciduous forest. We measured leaf nutrients, physical traits and polyphenols of the hostplants and analysed the effects of leaf traits and phylogeny on Lepidoptera caterpillars with differing levels of host specialisation. We sampled 190 species from 16 433 individual caterpillars on 20 host plant species. These included 102 species of specialists using confamilial hostplant species, 17 species of conservative generalists using allofamilial but phylogenetically close hostplant species and 71 species of non-conservative generalists using phylogenetically distant hostplant species. The species composition of non-conservative generalists associated with the polyphenol protein precipitation capacity and overall leaf trait dissimilarity; conservative generalists were weakly associated with polyphenol oxidative activity. In contrast, the composition of specialist assemblages showed no correlation with leaf traits. Our results demonstrate that host phylogeny and traits play variable roles in structuring communities of herbivores, based on the phylogenetic specialisation of herbivores. Understanding the factors that shape the community structures of various herbivores traditionally classified as ‘generalists’ is important as they account for a large proportion of herbivore species while showing differential responses to traits of hosts.

Latitude is correlated with environmental components that determine the distribution of biodiversity. In combination with geographic factors, latitude-associated environmental variables are expected to influence speciation, but empirical evidence on how those factors interplay is scarce. We evaluated the genetic and environmental variation among populations in the pair of sister species Dioon sonorense–D. vovidesii, two cycads distributed along a latitudinal environmental gradient in northwestern Mexico, to reveal their demographic histories and the environmental factors involved in their divergence. Using genome-wide loci data, we determined the species delimitation, estimated the gene flow, and compared multiple demographic scenarios of divergence. Also, we estimated the variation of climatic variables among populations and used ecological niche models to test niche overlap between species. The effect of geographic and environmental variables on the genetic variation among populations was evaluated using linear models. Our results suggest the existence of a widespread ancestral population that split into the two species ~829 ky ago. The geographic delimitation along the environmental gradient occurs in the absence of major geographic barriers, near the 28th parallel north, where a zonation of environmental seasonality exists. The northern species, D. vovidesii, occurs in more seasonal environments but retains the same niche of the southern species, D. sonorense. The genetic variation throughout populations cannot be solely explained by stochastic processes; the latitudinal-associated seasonality has been an additive factor that strengthened the species divergence. This study represents an example of how speciation can be achieved by the effect of the latitude-associated factors on the genetic divergence among populations.

Herbivorous insects are thought to have evolved counteradaptations to conquer chemical defenses in their host plants in a stepwise co-evolutionary process. Papilio butterflies use CYP6B gene family members to metabolize furanocoumarins in their Rutaceae or Apiaceae host plants. CYP6Bs have functionally diverged among Papilio species to be able to metabolite diverse types of furanocoumarins in their host plants. In this study, we examined the diversification and selection patterns of CYP6B among nine Papilio species in Japan (eight Rutaceae specialists and one Apiaceae specialist) and their association with host plant spectra and furanocoumarin profiles. We compared host plant spectrum of eight Rutaceae feeding Papilio species and also performed a furanocoumarin profiling of their host plants. In addition, we reconstructed CYP6B gene phylogeny and performed selection analysis based on the transcriptome data of those nine Papilio species. Among Rutaceae-feeding Papilio species, host plant spectrum differences were correlated with their furanocoumarin profiles. However, all tested Papilio species had similar duplicated sets of CYP6B, with no apparent lineage-specific or host plant-specific pattern of CYP6B diversification. Selection analysis showed a signature of positive selection on a CYP6B branch. The positively selected sites located at predicted substrate recognition sites and we also found that these CYP6B genes were observed only in Rutaceae-feeding species. These findings indicate that most CYP6B diversification occurred in ancestral species of these Papilio species, possibly in association with specific host plant chemical defenses and subsequent gene loss due to host specialization. These processes would have shaped the complex diversification patterns of the CYP6B gene family in Papilio butterflies. Our results also show potentially important CYP6B clades among Papilio species which likely to have diverged functions and associated with host plant phytochemicals in ancestral Papilio species.

Assemblages of insect herbivores are structured by plant traits such as nutrient content, secondary metabolites, physical traits, and phenology. Many of these traits are phylogenetically conserved, implying a decrease in trait similarity with increasing phylogenetic distance of the host plant taxa. Thus, a metric of phylogenetic distances and relationships can be considered a proxy for phylogenetically conserved plant traits and used to predict variation in herbivorous insect assemblages among co-occurring plant species. Using a Holarctic dataset of exposed-feeding and shelter-building caterpillars, we aimed at showing how phylogenetic relationships among host plants explain compositional changes and characteristics of herbivore assemblages. Our plant–caterpillar network data derived from plot-based samplings at three different continents included >28,000 individual caterpillar–plant interactions. We tested whether increasing phylogenetic distance of the host plants leads to a decrease in caterpillar assemblage overlap. We further investigated to what degree phylogenetic isolation of a host tree species within the local community explains abundance, density, richness, and mean specialization of its associated caterpillar assemblage. The overlap of caterpillar assemblages decreased with increasing phylogenetic distance among the host tree species. Phylogenetic isolation of a host plant within the local plant community was correlated with lower richness and mean specialization of the associated caterpillar assemblages. Phylogenetic isolation had no effect on caterpillar abundance or density. The effects of plant phylogeny were consistent across exposed-feeding and shelter-building caterpillars. Our study reveals that distance metrics obtained from host plant phylogeny are useful predictors to explain compositional turnover among hosts and host-specific variations in richness and mean specialization of associated insect herbivore assemblages in temperate broadleaf forests. As phylogenetic information of plant communities is becoming increasingly available, further large-scale studies are needed to investigate to what degree plant phylogeny structures herbivore assemblages in other biomes and ecosystems.

Niche conservatism is the tendency of lineages to retain the same niche as their ancestors. It constrains biological groups and prevents ecological divergence. However, theory predicts that niche conservatism can hinder gene flow, strengthen drift and increase local adaptation: does it mean that it also can facilitate speciation? Why does this happen? We aim to answer these questions. We examined the variation of chloroplast DNA, genome-wide single nucleotide polymorphisms, morphological traits and environmental variables across the Dioon merolae cycad populations. We tested geographical structure, scenarios of demographic history, and niche conservatism between population groups. Lineage divergence is associated with the presence of a geographical barrier consisting of unsuitable habitats for cycads. There is a clear genetic and morphological distinction between the geographical groups, suggesting allopatric divergence. However, even in contrasting available environmental conditions, groups retain their ancestral niche, supporting niche conservatism. Niche conservatism is a process that can promote speciation. In D. merolae, lineage divergence occurred because unsuitable habitats represented a barrier against gene flow, incurring populations to experience isolated demographic histories and disparate environmental conditions. This study explains why cycads, despite their ancient lineage origin and biological stasis, have been able to diversify into modern ecosystems worldwide.

Networks of direct and indirect biotic interactions underpin the complex dynamics and stability of ecological systems, yet experimental and theoretical studies often yield conflicting evidence regarding the direction (positive or negative) or magnitude of these interactions. We revisited pioneering data sets collected at the deciduous forested Horonai Stream and conducted ecosystem-level syntheses to demonstrate that the direction of direct and indirect interactions can change depending on the timescale of observation. Prior experimental studies showed that terrestrial prey that enter the stream from the adjacent forest caused positive indirect effects on aquatic invertebrates during summer by diverting fish consumption. Seasonal and annual estimates of secondary production and organic matter flows along food web pathways demonstrate that this seasonal input of terrestrial invertebrate prey increases production of certain fish species, reversing the indirect effect on aquatic invertebrates from positive at the seasonal timescale to negative at the annual timescale. Even though terrestrial invertebrate prey contributed 54% of the annual organic matter flux to fishes, primarily during summer, fish still consumed 98% of the aquatic invertebrate annual production, leading to top-down control that is not revealed in short-term experiments and demonstrating that aquatic prey may be a limiting resource for fishes. Changes in the direction or magnitude of interactions may be a key factor creating nonlinear or stabilizing feedbacks in complex systems, and these dynamics can be revealed by merging experimental and comparative approaches at different scales.

Adaptive traits that enable organisms to conquer novel niches and experience subsequent diversification are ecologically and evolutionarily important. The larvae of Pieris butterflies express nitrile-specifier proteins (NSPs), a key innovation for overcoming the glucosinolate (GLS)-myrosinase-based defence system of their Brassicales host plants. Nitrile-specifier proteins are a member of the NSP-like gene family, which includes the major allergen (MA) protein, a paralog of NSP with a GLS-disarming function, and a single domain major allergen (SDMA) protein, whose function is unknown. The arms-race between GLS-based defences and the NSP-like gene family is suggested to mediate diversification in both Pierid butterflies and Brassicales plants. Here, we tested whether the expected strong selection on NSP-like gene family correlates with shifts in host plant spectra among Pierid butterflies. We combined feeding experiments using 25 Brassicaceae plants and five Pieris species with larval transcriptome data to investigate the patterns of selection acting on NSP-like gene family members. Although we observed significantly elevated nonsynonymous to synonymous substitution rate ratios in NSPs on branches associated with changes in patterns of host plant usage, no such pattern was observed in MAs or SDMAs. Furthermore, we found evidence for positive selection of NSP at a phylogenetic branch which reflects different host plant spectra. Our data indicate that the NSP-related gene members have evolved differently: NSPs have accumulated more amino acid changes in response to shifting preferences for host plants, whereas MAs and SDMAs appear to be more conserved. Further detailed functional assays of these genes would provide important insights to understand their role in the chemical arms-race between Pieris butterflies and their Brassicales host plants.

Research on canopy arthropods has progressed from species inventories to the study of their interactions and networks, enhancing our understanding of how hyper-diverse communities are maintained. Previous studies often focused on sampling individual tree species, individual trees or their parts. We argue that such selective sampling is not ideal when analyzing interaction network structure, and may lead to erroneous conclusions. We developed practical and reproducible sampling guidelines for the plot-based analysis of arthropod interaction networks in forest canopies. Our sampling protocol focused on insect herbivores (leaf-chewing insect larvae, miners and gallers) and non-flying invertebrate predators (spiders and ants). We quantitatively sampled the focal arthropods from felled trees, or from trees accessed by canopy cranes or cherry pickers in 53 0.1 ha forest plots in five biogeographic regions, comprising 6,280 trees in total. All three methods required a similar sampling effort and provided good foliage accessibility. Furthermore, we compared interaction networks derived from plot-based data to interaction networks derived from simulated non-plot-based data focusing either on common tree species or a representative selection of tree families. All types of non-plot-based data showed highly biased network structure towards higher connectance, higher web asymmetry, and higher nestedness temperature when compared with plot-based data. Furthermore, some types of non-plot-based data showed biased diversity of the associated herbivore species and specificity of their interactions. Plot-based sampling thus appears to be the most rigorous approach for reconstructing realistic, quantitative plant-arthropod interaction networks that are comparable across sites and regions. Studies of plant interactions have greatly benefited from a plot-based approach and we argue that studies of arthropod interactions would benefit in the same way. We conclude that plot-based studies on canopy arthropods would yield important insights into the processes of interaction network assembly and dynamics, which could be maximised via a coordinated network of plot-based study sites.

We have investigated the redistribution dynamics of radiocesium deposited after the nuclear power station accident in March 2011 in a forested catchment located in North Fukushima over a four-year period (2012-2015). At the catchment scale, 137 Cs accumulation decreased drastically by 50% of the estimated initial accumulation during the first 2 years. Cs-137 accumulation in the forest floor occurred in the litter layers and the surface part of mineral soils and have accounted for about 90% of the total catchment scale accumulation. The internal 137Cs cycle among the soil-plant system was also identified as a retention mechanism and was biologically dynamic. Monitoring the decreasing and retaining mechanisms of radioactivity at the ecosystem scale will be required for effective forest and water resource management.

The effects of the Japanese horned beetle larvae on the transfer of 137Cs from a contaminated leaf litter to the leaf vegetable, komatsuna (Brassica rapa var. perviridis) was studied. Feces of the larvae which were fed 137Cs-contaminated leaf litter were added to a potting mix in which komatsuna plants were cultivated. The presence of feces increased the harvest yield of komatsuna, suggesting that feces provided nutrients for the plant growth. In addition, the amount of exchangeable 137Cs in leaf litter was experimentally confirmed to be enhanced by the presence of feces which were excreted by larvae feeding. However, there was no difference in the soil-to-plant transfer factor of 137Cs for the presence and absence of feces. Interactions between clay minerals and exchangeable 137Cs in the soil beneath the litter layer may diminish the root uptake of 137Cs. From these results, it was concluded that the effect of exchangeable 137Cs released from feces was limited for the transfer of 137Cs to plants if plant roots were not present in litter layers.

The article “A paradox of latitudinal leaf defense strategies in deciduous and evergreen broadleaved trees”, written by Saihanna Saihanna, Tomoe Tanaka, Yu Okamura, Buntarou Kusumoto, Takayuki Shiono, Toshihide Hirao, Yasuhiro Kubota, and Masashi Murakami, was originally published electronically on the publisher’s internet portal (currently SpringerLink) on 01 June 2018 without open access.

The classical “low latitude–high defense” hypothesis is seldom supported by empirical evidence. In this context, we tested latitudinal patterns in the leaf defense traits of deciduous broadleaved (DB) and evergreen broadleaved (EGB) tree species, which are expected to affect herbivore diversity. We examined the co-occurrence of leaf defense traits (tannin and phenol content, leaf mechanical strength, leaf dry matter content, leaf mass per area, and leaf thickness) in 741 broadleaved tree species and their correlations with species geographical range in East Asian island flora. We discovered contrasting latitudinal defense strategy gradients in DB and EGB tree species. DB species employed chemical defenses (increasing tannin and phenol content) at higher latitudes and physical defenses (softer and thinner leaves) at lower latitudes, whereas EGB tree species exhibited opposite latitudinal defense patterns. The “low latitude high defense” hypothesis included a paradoxical aspect in chemical and physical defense traits across broadleaved tree species. To reconcile paradoxical defense strategies along the latitudinal gradient, we conclude that interactive correlations among leaf traits are controlled by leaf longevity, which differs between DB and EGB tree species.

Insects tend to feed on related hosts. The phylogenetic composition of host plant communities thus plays a prominent role in determining insect specialization, food web structure, and diversity. Previous studies showed a high preference of insect herbivores for congeneric and confamilial hosts suggesting that some levels of host plant relationships may play more prominent role that others. We aim to quantify the effects of host phylogeny on the structure of quantitative plant-herbivore food webs. Further, we identify specific patterns in three insect guilds with different life histories and discuss the role of host plant phylogeny in maintaining their diversity. We studied herbivore assemblages in three temperate forests in Japan and the Czech Republic. Sampling from a canopy crane, a cherry picker and felled trees allowed a complete census of plant-herbivore interactions within three 01ha plots for leaf chewing larvae, miners, and gallers. We analyzed the effects of host phylogeny by comparing the observed food webs with randomized models of host selection. Larval leaf chewers exhibited high generality at all three sites, whereas gallers and miners were almost exclusively monophagous. Leaf chewer generality dropped rapidly when older host lineages (5-80myr) were collated into a single lineage but only decreased slightly when the most closely related congeneric hosts were collated. This shows that leaf chewer generality has been maintained by feeding on confamilial hosts while only a few herbivores were shared between more distant plant lineages and, surprisingly, between some congeneric hosts. In contrast, miner and galler generality was maintained mainly by the terminal nodes of the host phylogeny and dropped immediately after collating congeneric hosts into single lineages. We show that not all levels of host plant phylogeny are equal in their effect on structuring plant-herbivore food webs. In the case of generalist guilds, it is the phylogeny of deeper plant lineages that drives the food web structure whereas the terminal relationships play minor roles. In contrast, the specialization and abundance of monophagous guilds are affected mainly by the terminal parts of the plant phylogeny and do not generally reflect deeper host phylogeny.

Plants defend themselves against herbivores not only by a single trait but also by diversified multiple defense strategies. It remains unclear how these multiple defense mechanisms are effectively organized against herbivores. In this study, we focused on Brassicaceae plants, which have one of the most diversified secondary metabolites, glucosinolates (GSLs), as a defense against herbivores. By analyzing various defense traits including GSL profiles among 12 species (11 genera) of Brassicaceae plants, it is revealed that their defense strategies can be divided into three categories as multiple defenses. The GSL profiles differed between these three categories: (i) high nutritional level with long-chain aliphatic GSLs; (ii) low nutritional level and high physical defenses with short-chain aliphatic GSLs; and (iii) high nutritional level and low defense. The feeding experiment was conducted using two types of herbivores, Pieris rapae (Lepidoptera: Pieridae) as a specialist herbivore and the Eri silkmoth Samia cynthia ricini (Lepidoptera: Saturniidae) as a generalist, to assess the ability of each plant in multiple defense strategy. It was observed that the Eri silkmoth's performance differed according to which defense strategy it was exposed to. However, the growth rate of P. rapae did not vary among the three categories of defense strategy. These results suggest that the diversified defense strategies of Brassicaceae species have evolved to cope with diversified herbivores.

© The Author(s) 2016. The accident at the Fukushima Daiichi Nuclear Power Plant in March 2011 emitted 1.2 × 1016 Bq of cesium-137 (137 Cs) into the surrounding environment. Radioactive substances, including 137 Cs, were deposited onto forested areas in the northeastern region of Japan. 137 Cs is easily adsorbed onto clay minerals in the soil; thus, a major portion of 137 Cs can be transported as eroding soil and particulate organic matter in water discharge. Dissolved 137 Cs can be taken up by microbes, algae, and plants in soil and aquatic systems. Eventually, 137 Cs is introduced into insects, worms, fishes, and birds through the food web. To clarify the mechanisms of dispersion and export of 137 Cs, within and from a forested ecosystem, we conducted intensive monitoring on the 137 Cs movement and storage in a forested headwater catchment in an area approximately 50 km from the Nuclear Power Plant. Two major pathways of 137 Cs transport are as follows: (1) by moving water via dissolved and particulate or colloidal forms and (2) by dispersion through the food web in the forest-stream ecological continuum. The 137 Cs concentrations of stream waters were monitored. Various aquatic and terrestrial organisms were periodically sampled to measure their 137 Cs concentrations. The results indicate that the major form of exported 137 Cs is via suspended matter. Particulate organic matter may be the most important carrier of 137 Cs. High water flows generated by a storm event accelerated the transportation of 137 Cs from forested catchments. Estimation of 137 Cs export from the forested catchments requires precise evaluation of the high water flow during storm events. The results also suggested that because the biggest pool of 137 Cs in the forested ecosystem is the accumulated litter and detritus, 137 Cs dispersion is quicker through the detritus food chain than through the grazing food chain.

Since the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011, large areas of the forests around Fukushima have become highly contaminated by radioactive nuclides. To predict the future dynamics of radioactive cesium (Cs-137) in the forest catchment, it is important to measure each component of its movement within the forest. Two years after the accident, we estimated the annual transportation of Cs-137 from the forest canopy to the floor by litterfall, throughfall and stemflow. Seasonal variations in Cs-137 transportation and differences between forests types were also determined. The total amount of Cs-137 transported from the canopy to the floor in two deciduous and cedar plantation forests ranged between 3.9 and 11.0 kBq m(-2) year(-1). We also observed that Cs-137 transportation with litterfall increased in the defoliation period, simply because of the increased amount of litterfall. Cs-137 transportation with throughfall and stemflow increased in the rainy season, and Cs-137 flux by litterfall was higher in cedar plantation compared with that of mixed deciduous forest, while the opposite result was obtained for stemflow. (C) 2015 Elsevier Ltd. All rights reserved.

AimTo examine the roles of geohistorical and ecological factors in the development of butterfly assemblages on continental islands with multiple source pools. LocationThe Ryukyu Islands, Japan. This arc of continental islands is located between two source islands, Kyushu and Taiwan, and contains two major straits, the Tokara and Kerama gaps. MethodsA total of 489 butterfly species were identified on 59 islands, including the two source islands. The influences on species richness and rarity of latitude, area, elevation, and distances from the nearest source and from the nearest larger island were analysed using generalized linear models. The relationships between differences in area, elevation, and distance and dissimilarity between island butterfly faunas were evaluated by multiple regressions on distance matrices. The relationships between area, elevation, and distance from the source and dissimilarity to the source fauna were examined using linear models. The dissimilarity was based on the SOrensen index and its nestedness and turnover components. ResultsLatitude, area and isolation determined species richness and rarity, whereas differences in elevation and distance regulated species turnover between islands. The gaps between islands were associated with nestedness between island faunas. Area consistently had a negative relationship with the total dissimilarity to source fauna. The overall dissimilarity to Kyushu decreased with the distance from Kyushu, whereas dissimilarity to Taiwan increased with distance from Taiwan. Main conclusionsBoth environmental filtering and dispersal limitation determine the geographical patterns of butterfly assemblages in the Ryukyus. The present study focuses on the unique pattern wherein migration from Kyushu is facilitated on islands farther from Kyushu, while migration from Taiwan is inhibited on islands farther from Taiwan. The two source islands have contrasting roles that affect butterfly distributions unidirectionally. This study highlights the importance of resolving dissimilarity into nestedness and turnover components to elucidate the formation of island biota.

Capsule The distribution and abundance of waterfowl species were surveyed at artificial water reservoirs in Japan. The species richness and the species-specific abundances of most of species were positively related to the extent of shallow areas within reservoirs.

Although patch isolation and patch size have long been considered the two primary parameters affecting metapopulation processes, patch quality is now recognized as a third factor. The extent to which patch quality influences between-patch migration processes and local population sizes, however, is poorly understood. Using a mark–recapture survey for the butterfly Minois dryas, which inhabits grasslands in a fragmented landscape, we investigated factors affecting immigration and emigration of female individuals between patches. For patch quality, we assessed the proportion of forest-edge length along the patch periphery, as well as nectar resource availability, as the former is known to provide shelter from heat stress for grassland butterflies in midsummer. Results revealed that immigration into patches was largely determined by patch quality represented by forest–grassland adjacency, in addition to patch isolation. Emigration was lower from patches with high-quality measured by nectar resource availability as well as the amount of surrounding forest. These results suggest that a forest–grassland boundary is important, even for grassland-dwelling butterflies, in fragmented landscapes, and that conservation priorities should be given to habitats having this structural feature, as well as large patch size and high connectivity.

1. The pattern of host utilisation by congeneric Caloptilia caterpillars on 14 different species of Acer (maple) was investigated in temperate mixed forests of central Japan. A multi-filtering model of host plant utilisation was proposed to address how phylogenetically related herbivore assemblages are constructed on phylogenetically related host plant species. 2. Two hypotheses were examined. The first questioned whether a negative relationship exists between the phylogenetic distance of plants from the most suitable host species and the abundance of herbivorous insects on the host. Regarding the second, it was investigated whether the assemblage dissimilarity of herbivorous insects among host plant species increases with increasing distance of plant phylogeny and traits. 3. Mantel and partial Mantel tests were used to measure the relationship between assemblage dissimilarity of Caloptilia species and the distance of plant phylogeny and leaf traits. 4. Both hypotheses were confirmed, clearly suggesting that the utilisation and suitability of hosts for Caloptilia caterpillars were strongly influenced by phylogenetic relatedness and leaf trait similarity among Acer species. This implies that phylogenetic distance is an integrated measure of phenotypic and ecological attributes of congeneric Acer species that can be used to explain specialisation and constraints of host utilisation of congeneric herbivore species even on a short evolutionary timescale.

Understanding variation in resource specialization is important for progress on issues that include coevolution, community assembly, ecosystem processes, and the latitudinal gradient of species richness. Herbivorous insects are useful models for studying resource specialization, and the interaction between plants and herbivorous insects is one of the most common and consequential ecological associations on the planet. However, uncertainty persists regarding fundamental features of herbivore diet breadth, including its relationship to latitude and plant species richness. Here, we use a global dataset to investigate host range for over 7,500 insect herbivore species covering a wide taxonomic breadth and interacting with more than 2,000 species of plants in 165 families. We ask whether relatively specialized and generalized herbivores represent a dichotomy rather than a continuum from few to many host families and species attacked and whether diet breadth changes with increasing plant species richness toward the tropics. Across geographic regions and taxonomic subsets of the data, we find that the distribution of diet breadth is fit well by a discrete, truncated Pareto power law characterized by the predominance of specialized herbivores and a long, thin tail of more generalized species. Both the taxonomic and phylogenetic distributions of diet breadth shift globally with latitude, consistent with a higher frequency of specialized insects in tropical regions. We also find that more diverse lineages of plants support assemblages of relatively more specialized herbivores and that the global distribution of plant diversity contributes to but does not fully explain the latitudinal gradient in insect herbivore specialization.

Historical, niche-based, and stochastic processes have been proposed as the mechanisms that drive community assembly. In plant-herbivore systems, these processes can correspond to phylogeny, leaf traits, and the distribution of host plants, respectively. Although patterns of herbivore assemblages among plant species have been repeatedly examined, the effects of these factors among co-occurring congeneric host plant species have rarely been studied. Our aim was to reveal the process of community assembly for herbivores by investigating the effects of phylogeny, leaf traits, and the altitudinal distribution of closely related host plants of the genus Acer. We sampled leaf functional traits for 30 Acer species in Japan. Using a newly constructed phylogeny, we determined that three of the six measured leaf traits (leaf thickness, C/N ratio, and condensed tannin content) showed a phylogenetic signal. In a field study, we sampled herbivore communities on 14 Acer species within an elevation gradient and examined relationships between herbivore assemblages and host plants. We found that herbivore assemblages were significantly correlated with phylogeny, leaf traits, phylogenetic signals, and the altitudinal distribution of host plants. Our results indicate that the interaction between historical and current ecological processes shapes herbivore community assemblages.

Understandings of the effect of host plant phylogeny on the structure of herbivore assemblage is useful for estimating global species richness of herbivores. Here we test the relationship between host plant phylogeny and two assemblages including ambrosia beetle assemblage that have been considered to be the lowest host specificity among plant-dependent guilds. These results of local scale were used for estimating regional species richness by extrapolating to the number of plant order and species in Japan. The estimated numbers were compared with the numbers of described species in Japan. Tree trunks of 17 plant species representing 17 orders of all major lineages of Japanese tree flora were exposed for collecting wood boring beetle species. A total of 12 ambrosia and four bark beetle species were collected. Similarity of both ambrosia and bark beetle assemblages showed a significant negative trend with phylogenetic distance between focal host plant species. The regression model for this relationship was well fit by a linear model whereas previous studies used a semi-log model, which suggests a difference in mechanism of host utilization with host taxonomic levels. Our results showed a broader host range of ambrosia beetle assemblage in temperate forest than to a comparable study in tropical rainforests. Species richness estimated is lower than the described species in Japan, suggesting the need for more samples along the altitudinal gradients for accurate estimation for the Japanese fauna.

Radionuclides, including Cs-137, were released from the disabled Fukushima Daiichi Nuclear Power Plant and had been deposited broadly over forested areas of north-eastern Honshu Island, Japan. In the forest, Cs-137 was highly concentrated on leaf litters deposited in autumn 2010, before the accident. Monitoring of the distribution of Cs-137 among functional groups clearly showed the role of the detrital food chain as the primary channel of Cs-137 transfer to consumer organisms. Although many studies have reported the bioaccumulation (or dilution) of radioactive materials through trophic interactions, the present results highlight the importance of examining multiple possible pathways (e.g., grazing vs. detrital chains) in the proliferation of Cs-137 through food webs. These results provide important insight into the future distribution and transfer of Cs-137 within forest ecosystems.

Species abundance distributions of moth and beetle assemblages, in addition to beetle feeding guilds, were examined using data collected by light traps in a cool-temperate deciduous forest at Hokkaido, Japan. Four types of species abundance distributions with a continuous shift in shape (broken stick, log-normal, power function, and dispersal-limited multinomial) were fitted and compared, and then the deviation of observed data from that expected for the neutral model (dispersal-limited multinomial distribution) was tested using species evenness and richness. Significantly better fits were obtained for the neutral model than for the other models for all assemblages and all beetle guilds. This result implies that the better fits of the neutral model might be characteristic of transient assemblages having an excess of rare species. The evenness of species abundance distributions for assemblages and guilds, except for moths associated with the understorey and predatory beetles, significantly deviated from that expected by the neutral model. The departure of beetle guilds (detritivores, herbivores, and xylophages) from the neutral model suggests their microhabitat dependence. The neutral model may prove to be a viable null hypothesis for examining the species abundance distributions of insect assemblages. In this study, we found that although stochastic dynamics appeared to have an increasing influence on insect community assembly, there are also complex biological processes still likely to be present. The fits of the neutral model suggest that habitat connectivity and microhabitat diversity are potentially important for conserving moth and beetle diversity in a temperate forest. © 2012 The Royal Entomological Society.

Determining the way in which spatial distribution and diversity of forest-dwelling mammals varies with natural disturbance is essential to understanding the spatial dynamics of mammal assemblages in forests. Bats are the only forest-dwelling mammals capable of true flight. At a local scale, bat flight ability, which may be related to ecomorphological traits, is an important factor influencing spatial distribution. We tested two postulates: (1) the spatial distribution of bats is affected by sizes of forest gaps created by natural disturbances and (2) species-specific responses can be predicted from bat ecomorphological traits (aspect ratio (AR) and wingtip shape index (WT)) that influence bat flight ability. We found that sizes of forest gaps affected the occurrence of each bat species and species richness of bats at local scales: species-specific responses were related to the ecomorphological traits of individual species. Bat species with high AR and low WT were not affected by variation in canopy gap size. In contrast, bat species with low AR and high WT responded negatively to gap size, and those with intermediate AR and WT responded positively to canopy gap size at sites with small-sized gaps but responded negatively to large-sized gaps. Overall bat species richness responded negatively to gap size. Thus, ecomorphological traits may be important determinants of bat spatial distributions and species diversity at local scales in disturbed habitats. In this study, forest edges might have been undersampled due to the location of bat detectors. However, this potential undersampling should not have affected the interpretation of occurrence patterns of bat species responding to gap size. Our results imply that bat conservation efforts in forest lands should take into consideration specific responses related to ecomorphological traits of species inhabiting an area. The results also suggest that quantifying the effects of natural disturbances on bat assemblages may provide a knowledge base for forest management to minimize the impacts of unavoidable anthropogenic disturbances on bat species diversity. Rare or infrequent natural disturbances can provide models for forest management aimed at maintaining bat species diversity. (C) 2011 Elsevier B.V. All rights reserved.

Quantifying the roles of historical versus contemporary constraints in determining species diversity is a central issue in island biogeography, and the phylogenetic beta diversity between islands is an essential measure specifying the influence of historical barriers on insular assemblages. In this study, using phylogenetic information for 513 tree species on 26 islands in the subtropical Ryukyu Archipelago, phylogenetic beta diversity between islands was calculated, and effects of historical factors (gaps as surrogate measures of historical barriers) and current ones (distance, area and elevation) on the phylogenetic structure of tree assemblages were examined. The pattern of phylogenetic beta diversity demonstrated that the Tokara Gap and geographical distance were consistently important for characterizing tree assemblages in the Ryukyus relative to other historical and current factors, which suggests that the Tokara Gap and distance-limited dispersal from the two adjacent source islands have left a deep imprint on the phylogenetic structure of the current tree flora of the islands.

Aim Anolis lizard invasions are a serious threat world-wide, and information about how this invasive predator affects the diversity of prey assemblages is important for many strategic conservation goals. It is hypothesized that these predators reduce the slope of species-area relationships (SARs) of their prey assemblages. The effects of island area and predation by anolis lizards on the species richness of insular insect assemblages were investigated. Location Twenty-four isles around Staniel Cay, Exuma Cays, Bahamas. Methods Flying insects were sampled using half-sized Malaise traps for three consecutive days on each island in May 2007. First, the effect of island area on the probability of lizard presence was evaluated. Then, the effects of the presence-absence of predatory lizards on SARs were analysed for the overall insect assemblage and for the assemblages of five dominant insect orders. Results Our results indicated that anolis lizards occurred primarily on larger islands. The species richness of the overall insect assemblage and five dominant insect orders significantly increased with island area. The interaction between island area and predator presence-absence significantly affected the overall insect assemblage and Diptera and Hymenoptera assemblages (but not Coleoptera, Hemiptera and Lepidoptera assemblages). The presence of predators caused decreases in the slope of the SARs. Main conclusions The presence of predatory lizards strongly affects species richness of insular insect assemblages with the island area being a crucial determinant of the species richness. Therefore, the slope of the SAR can serve as a measure of the consequence of invasive predatory species on native insect assemblages.

1. Ecological assemblages frequently show nestedness patterns of species distribution. Despite the common occurrence, the causality for nestedness patterns remains unclear. The effects of environmental and spatial factors on the patterns of insect species distributions were examined on 28 small islands in central Exuma, Bahamas. 2. Flying insects on each island were surveyed by Malaise traps, island area and vegetation height being used as environmental factors, and the degree of island isolation as a spatial factor. Body and relative wing length, and abundance of insect species were also considered as species traits which, together with environmental and spatial factors, determine insect distributions. 3. Island isolation was determined from distance to the mainland, greatest distance in a stepping-stone pathway, distance to the nearest island, and the island area within 250, 500 and 1000 m of each island's perimeter. 4. The pattern of island-insect nestedness was examined for the overall insect assemblage and those of five dominant insect orders on the islands. The order of island ranking in the nested matrix was tested relative to area, isolation and vegetation height, the rank order of insect species then being examined relative to body and wing length, and abundance of species. 5. Significant nestedness was found in all assemblages. Significant contributions of environmental factors were found in Diptera and Hemiptera assemblages, whereas relatively large contributions of spatial factors were found in Lepidoptera and Hymenoptera assemblages. These results illustrated the need to include spatial factors in analyses on the assembly of insular insect assemblages.

P>1. Although a latitudinal gradient in species diversity has been observed for various taxa, the factors generating the latitudinal gradient at broad spatial scales are difficult to identify because several candidate factors change simultaneously with latitude. We investigated latitudinal gradients in stream invertebrate assemblages in 30 headwater streams in Hokkaido Island, Japan, focusing on the regional scale to discount historical factors and to extract the effects of environmental factors on latitudinal gradients in diversity. 2. Taxon diversity (Shannon index) and taxon richness (number of taxa per unit area) increased with latitude. Abundance showed a similar latitudinal gradient, whereas evenness (Delta(1)) did not. Hence, we conclude that the observed latitudinal gradient in taxon richness was generated by directional variation in abundance (passive accumulation), leading to that in taxon diversity. 3. Precipitation, which is strongly related to flood disturbances, decreased with latitude and was an important factor explaining variation in taxon diversity, taxon richness and abundance. The probability of a taxon being present tended to increase from south to north, suggesting that the higher taxon richness observed in northern sites may be because of the presence of rare species. These findings indicate that flood disturbance varying with latitude may influence abundance and local extinction rates of rare species, consequently affecting taxon richness and taxon diversity. 4. By detecting the effects of an environmental factor (precipitation) on the latitudinal gradients in taxon diversity and taxon richness without interference by historical factors, this study demonstrates processes that can produce latitudinal gradients in the diversity of stream invertebrate assemblages.

1. Streams are highly connected to their landscapes and so are easily altered by multiple stressors that affect both uplands and riparian zones, and the streams themselves. These include dams and diversions, channelisation, deforestation, water pollution, biological invasions and climate change. 2. We review research conducted in Hokkaido Island, northern Japan, which measured the effects of many of these stressors on both stream food webs and fluxes of invertebrates to and from the riparian zone that feed aquatic and terrestrial consumers. About half the energy that sustains fish falls directly into streams as terrestrial invertebrates, and a quarter of the energy needs for riparian birds is supplied by adult aquatic insects emerging from the stream. 3. Single stressors in these Hokkaido streams, including deforestation, channelisation, erosion-control dams, biological invasions and climate change, have drastic effects on stream food webs, the fishes they support and riparian predators (spiders, birds, and bats). Most stressors caused 30-90% declines in foraging, growth, or abundance of aquatic or terrestrial predators. Indirect effects of stressors also cascaded throughout stream food webs and across the aquatic-terrestrial boundary. 4. Effects of individual stressors were largely concordant across spatial scale, through time during years of different productivity and among different food web components. 5. Two studies of multiple stressors revealed that each stressor alone reduced food web components like abundance of stream benthos or riparian spiders to low levels (35-83% reduction; mean 59%), beyond which an additional stressor had little effect. Synergism and antagonism are less relevant when individual stressors have such large effects. 6. Thematic implications: small streams in Hokkaido are highly sensitive to many individual stressors and have little resistance or resilience to their effects. Moreover, each stressor alone can reduce biota strongly, indicating that restoration will need to consider all simultaneously to protect biotic diversity.

The vertical stratification of lepidopteran and coleopteran communities in a cool-temperate deciduous forest in Japan was examined to evaluate the hypothesis of an expected uniform distribution of mobile flying insects between the canopy and understory of temperate forests. Lepidopteran and coleopteran insects were trapped using light traps at three sites in each of the canopy and understory for three consecutive nights each month from April to October 2001. For Lepidoptera, species richness, abundance, and family richness were significantly higher in the understory than in the canopy. For Coleoptera, only abundance was larger in the canopy relative to the understory; species and family richness did not differ between the strata. The beta diversity of the lepidopteran community was larger between the strata than among sites, but the coleopteran community showed an inverse pattern. These results imply the presence of vertical stratification within the lepidopteran community, but not within the coleopteran community, in the temperate forest. The understory contributes more than the canopy to lepidopteran diversity in the temperate forest, although this stratification may be relatively weak because, in contrast to the situation in tropical forests, the canopy and understory assemblages share many species.

Empirical studies have shown that temporally fluctuating inputs of resource subsidies can indirectly increase or decrease the abundance of in situ resources by affecting generalist consumers that feed on both subsidies and in situ resources. By mathematical modeling, we develop a theoretical framework that can explain these variable consumer-mediated indirect effects. We show that the hierarchy of timescales among fluctuations in the subsidy input rate and consumers' reproductive and aggregative numerical responses predict the signs of the indirect effects. These predictions are consistent with field observations from a variety of natural systems. Our results suggest that the timescale hierarchy of ecological processes is fundamentally important for understanding and predicting indirect effects in nonequilibrium food web dynamics.

The dispersal of organisms among patches affects community structure in spatially heterogeneous habitats. The enhancement of dispersal frequency among patches can be expected to increase potential interaction between organisms in food webs. However, it has been difficult to fairly evaluate the effects of dispersal on the food web structure because the quantification of actual dispersal is difficult. In this study, in order to manipulate the dispersal frequency, two oak plantations (each with 100 oak trees) were established as high-patch connectivity (1-m interval) and low-patch connectivity (3-m interval) plots. Quantitative food webs of herbivores and their parasitoids were constructed for the high- and low-connectivity plots, and quantitative measures of food web metrics as indices of structure were calculated for both webs to examine dispersal effects on food web complexity. In the entire web, 86 herbivore species (Lepidoptera and Coleoptera) were attacked by 50 parasitoid species (Hymenoptera and Diptera). As a result, although we found no significant difference in herbivore abundance between high- and low-connectivity plots, a higher parasitism rate and greater complexity in web structure were observed in many food web metrics for the high-connectivity plot. Furthermore, the parasitoid overlap diagram showed a higher potential for indirect interactions among herbivore species in the high-connectivity plot. These results imply that the increase in dispersal frequency among habitat patches facilitates food web complexity, and the role of dispersal as a determinant of food web structure should be considered in food web ecology.

Community dynamics in local habitats are affected by landscape characteristics such as the area and connectivity of surrounding habitats at a functional spatial scale where the community responds to landscape structure. However, the functional spatial scale at which community composition is affected by landscape structure has never been explored. We assessed the functional spatial scales of composition change in birds and in three types of arthropod communities (canopy, forest-floor and flying ones) with regard to landscape heterogeneity resulting from a large typhoon in a temperate forest of Japan. We examined the effects of tree-fall disturbance on the communities at various spatial scales, with special attention to compositional evenness. The spatial scale of the best-fitting model, which was selected from models fitted to the disturbance area at stepwise spatial scales, was interpreted as the community-specific functional spatial scale. The composition of all communities studied was all significantly dependent on gap area. The functional spatial scale was highest in birds (370 m in radius), intermediate in flying arthropods (90 m) and lowest in canopy and forest-floor arthropods (10 m). This result may reflect typical dispersal ability and the spatial range of resource use in the community. Compositional changes in each community were consistent with theory regarding traits and responses of component taxa, although the enhancement of evenness was observed only in the arthropod communities. These results imply that management and reserve selection based on functional spatial scales can be effective in the conservation of biodiversity and ecosystem services at the community level.

1. Light traps have been widely used for surveying insect community structure, but some biases are known to occur under certain meteorological conditions. 2. In addition to weather factors, we raise the novel hypothesis that if the daily movement distance of focal insects is shorter than the effective range of the light trap, then the species richness and abundance of the daily captures will increase during the course of the night. 3. This study examined the daily attraction patterns of Lepidoptera and Coleoptera to light traps and the factors affecting the attraction of these communities. Light traps were run for three consecutive nights in each month from April to October 2001 in a cool-temperate forest in Japan. 4. The species richness and abundance of Coleoptera increased during trap nights, whereas lepidopteran captures remained constant. Meteorological factors influenced the capture of both communities throughout the sampling season, but the daily increment in Coleoptera was not explained by the daily trends in weather conditions. 5. We argue that the daily augmentation of Coleoptera capture rate results from the daily movement distance of Coleoptera being generally shorter than the effective and perceivable range of the light traps. These results suggest that consideration of the typical daily movement of a focal taxon is required when conducting biological monitoring using light trap sampling.