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Agrochemical-free rice farming has attracted interest for restoring paddy field biodiversity and producing safe food. Odonata are commonly used as a biodiversity indicator in these low-input farms. However, the effect of agrochemical-free rice farming on odonate diversity has rarely been assessed over the entire emergence period of these insects. We investigated whether different farming practices, such as conventional or natural (agrochemical-and fertilizer-free) cultivation, and associated water management strategies affect the emergence rates of Odonata in paddy field landscapes in central Japan. Weekly exuviae sampling in 2017 and 2019 suggested that odonate assemblages differed between conventional and natural paddy fields, with a higher number of taxa emerging from natural paddy fields. Contrary to expectations, conventional paddy fields had equivalent or higher emergence rates of all Odonata and two numerically dominant Sympetrum species. Peak emergence periods for numerically dominant taxa differed between the farming types, with the emergence of three Sympetrum species peaking in late June in conventional paddy fields and that of S. frequens peaking in early to mid-July in natural paddy fields. Our findings suggest that both conventional and natural paddy fields are important habitats for Odonata in Japan.

In Japan, farm ponds retain water throughout the year while rice fields are continuously inundated for no more than 2 months, usually from spring to early summer. Although the zooplankton fauna in artificial water bodies would be expected to vary according to differences in inundation periods, scientific confirmation of this relation is largely lacking. Due to its ubiquity, the cladoceran Moina is a suitable target for studying habitat-related differences in the planktonic fauna, but its taxonomy remains unresolved, making morphological identifications potentially uncertain. We thus applied integrative taxonomy with both morphological and genetic evaluations for reliable species delimitation to Moina samples collected primarily in Japan (with smaller collections from Taiwan). This approach increased the alpha diversity of Moina species in Japan from three (in previous studies) to seven. It also revealed different habitat preferences among Moina species, with the smaller species being distributed mostly in farm ponds (followed by natural lakes), and the larger species mostly in rice fields. We argue that the phenological match/mismatch with inundation period of rice fields was a major factor for this strong trend of spatial species turnover, with differing degrees of fish predation pressure among the habitat types being another factor.

In lowland areas of the world and high-altitude European mountains, the species compositions, body sizes, and wing forms of carabid beetles are known to change according to vegetation structures. However, little is known regarding the assemblage structure and habitat associations of carabid beetles in Japanese alpine-subalpine areas. We surveyed carabid beetles in four habitats (snow beds, alpine meadows, Pinus scrub, and fell-fields) in the alpine-subalpine zone on Mt. Hakusan, Japan. We surveyed carabid beetles six times between mid-July and late September. Nonmetric multidimensional scaling (NMDS) and analysis of similarities (ANOSIM) revealed three distinct carabid beetle assemblages in snow beds and alpine meadows, Pinus scrub, and fell-fields. The carabid beetle assemblages in the four habitats consisted predominantly of small and/or wingless species with differential spatiotemporal variability in abundance. Biota-environment (BIO-ENV) analyses showed that the percentage coverage by Pinus scrub, soil water content, and ground surface temperature were among the most significant variables affecting carabid beetle compositions. Given their small sizes and reduced wings, which are characteristic traits for limited mobility, and high-level habitat specificity, carabid beetles in the alpine-subalpine zone may serve as an important target group to monitor the impacts of global environmental change on mountain ecosystems.

金沢大学環日本海域環境研究センター, Latrine sites, or areas where otters scent-mark and deposit feces, are a habitat feature that serve an important role in communication for many otter species. The small-clawed otter (Aonyx cinereus) inhabits both natural and rice field landscapes in Southeast Asia. However, latrine site use by small-clawed otters in rice field landscapes is largely unknown. Based on a 53-week field survey and landscape analyses, we investigated latrine site use by small-clawed otters in rice field landscapes in West Sumatra, Indonesia. Using land use and/or local environmental variables as predictors, we performed generalized linear model analyses to explain the spatial patterns of latrine site occurrence and otter visitation frequency to latrine sites. We determined that small-clawed otters use some latrine sites repeatedly over time; 10 latrine sites were still in use more than 7 years after their initial discovery. Generalized linear model analyses revealed that an intermediate number of rice field huts was the single most important predictor of latrine site occurrence, whereas distance to the nearest settlement, distance to the river, and mean water depth of the rice field adjacent to the latrine site were important predictors of otter visitation frequency to latrine sites. These results indicate that the latrine site preferences of small-clawed otters in rice field landscapes are strongly associated with intermediate levels of rice farming activities. Indonesian rice fields are being degraded or disappearing at an accelerated rate because of land conversion and modernization of agriculture. We emphasize an urgent need for design and implementation of otter-friendly rice farming to conserve small-clawed otters. © 2017 The Ecological Society of Japan, Embargo Period 12 months

金沢大学環日本海域環境研究センター, Farm ponds are among the most biodiverse anthropogenic freshwater habitats because of their small size, shallow water depth, and aquatic vegetation. Land-use changes, such as converting riparian vegetation to human use or changing the management practices of farm ponds, are assumed to be major factors that change such ecosystems from a clear-water state to a turbid state, leading to deterioration of water quality and biodiversity in such ponds. Using the database of a large-scale pond survey, we evaluated the effects of surrounding land use (landscape factors and modern pond management practices), fish abundance, and other environmental variables on total phosphorus concentration and taxonomic richness patterns of six biological indicators associated with changes in the trophic state. Local- and landscape-level vegetation structure associated with land use and total fish abundance were among the factors influencing the total phosphorus concentration of farm ponds, a main driver of trophic state changes. In addition, a transition from a clear-water state to a turbid state was associated with lower taxonomic richness of aquatic plants, macroinvertebrates, and adult Odonata, and a higher taxonomic richness of phytoplankton and fish. Based on these results, we discuss potential land-use and pond management strategies for conserving and/or restoring the water quality and biodiversity of farm ponds through maintenance of a clear-water state. © 2017 Elsevier B.V., Embargo Period 24 months

Invasive alien species and climate change are two of the most serious global environmental threats. In particular, it is of great interest to understand how changing climates could impact the distribution of invaders that pose serious threats to ecosystems and human activities. 2. In this study, we developed ensemble species distribution models for predicting the current and future global distribution of the signal crayfish Pacifastacus leniusculus and the red swamp crayfish Procambarus clarkii, two of the most highly problematic invaders of freshwater ecosystems worldwide. We collected occurrence records of the species, from native and alien established ranges worldwide. These records in combination with averaged observations of current climatic conditions were used to calibrate a set of 10 distinct correlative models for estimating the climatic niche of each species. We next projected the estimated niches into the geographical space for the current climate conditions and for the 2050s and 2070s under representative concentration pathway 2.6 and 8.5 scenarios. 3. Our species distribution models had high predictive abilities and suggest that annual mean temperature is the main driver of the distribution of both species. Model predictions indicated that the two crayfish species have not fully occupied their suitable climates and will respond differently to future climate scenarios in different geographic regions. Suitable climate for P. leniusculus was predicted to shift poleward and to increase in extent in North America and Europe but decrease in Asia. Regions with suitable climate for P. clarkii are predicted to widen in Europe but contract in North America and Asia. 4. This study highlights that invasive species with different thermal preference are likely to respond differently to future climate changes. Our results provide important information for policy makers to design and implement anticipated measures for the prevention and control of these two problematic species.

Successful invasion by nonindigenous species is often attributed to high propagule pressure, yet some foreign species become widespread despite showing reduced genetic variation due to founder effects. The signal crayfish (Pacifastacus leniusculus) is one such example, where rapid spread across Japan in recent decades is believed to be the result of only three founding populations. To infer the history and explore the success of this remarkable crayfish invasion, we combined detailed phylogeographical and morphological analyses conducted in both the introduced and native ranges. We sequenced 16S mitochondrial DNA of signal crayfish from across the introduced range in Japan (537 samples, 20 sites) and the native range in western North America (700 samples, 50 sites). Because chela size is often related to aggressive behavior in crayfish, and hence, their invasion success, we also measured chela size of a subset of specimens in both introduced and native ranges. Genetic diversity of introduced signal crayfish populations was as high as that of the dominant phylogeographic group in the native range, suggesting high propagule pressure during invasion. More recently established crayfish populations in Japan that originated through secondary spread from one of the founding populations exhibit reduced genetic diversity relative to older populations, probably as a result of founder effects. However, these newer populations also show larger chela size, consistent with expectations of rapid adaptations or phenotypic responses during the invasion process. Introduced signal crayfish populations in Japan originate from multiple source populations from a wide geographic range in the native range of western North America. A combination of high genetic diversity, especially for older populations in the invasive range, and rapid adaptation to colonization, manifested as larger chela in recent invasions, likely contribute to invasion success of signal crayfish in Japan. © 2016 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.

In lowland areas, carabid beetles show diurnal or nocturnal activity patterns depending on habitat type. However, the diel activity patterns of carabid beetles in alpine areas are poorly understood. We conducted field studies in the alpine area of Mt. Hakusan in central Japan to determine the diel activity patterns of carabid beetles according to habitat type and ground surface temperature. Using baited pitfall traps, we collected samples every three hours over a 24-hour period in the summers of 2015 and 2016 in Pinus scrub, snowbed, and fellfield sites. In both years, the numerically dominant species were Pterostichus janoi Jedlicka, 1952 in the Pinus scrub, Bembidion sp. in the snowbed, and Bembidion sp. and Colpodes xestus (Bates, 1883) in the fellfield. Carabid beetles on alpine Hakusan showed activity patterns that varied depending on habitat type or ground surface temperature. Bembidion sp. showed diurnal activity patterns in the snowbed but nocturnal activity patterns in the fellfield when the diurnal temperature range was large. However, this species was active throughout the day and night in these habitats when the diurnal temperature range was small. By contrast, P. janoi in the Pinus scrub and C. xestus in the fellfield were mainly active nocturnally in both years, regardless of temperature fluctuations. Because alpine areas are generally characterized by harsh and changeable climates, some alpine carabids such as Bembidion sp. are probably adapted to show versatile activity patterns in response to changeable microclimatic conditions.

Tropical rice fields with asynchronous growth stages provide a good model to investigate the effects of landscape heterogeneity on the use of agricultural landscapes by wildlife. The small-clawed otter (Aonyx cinereus) uses rice fields as latrine sites in Southeast Asia. Through a 53-week survey of latrine sites, we analyzed the spatiotemporal patterns of latrine-site use by small-clawed otters in an asynchronous rice field in West Sumatra, Indonesia. Based on a generalized linear mixed model incorporating local environmental factors, otter latrine-site visitation was positively associated with the vegetative stage of rice cultivation and the biomass of a major prey item, the golden apple snail (Pomacea canaliculata). The vegetative stage of rice cultivation and golden apple snail biomass were closely associated with deep water in rice fields; therefore, water availability in rice fields is likely important in determining the spatiotemporal patterns of small-clawed otter latrine-site use in the asynchronous rice field landscape. To consistently provide latrine sites for small-clawed otters, we recommend that asynchronous rice cultivation be maintained, or zoning of synchronous and asynchronous rice cultivation areas be planned in the region.

I performed a field experiment to test the hypotheses that omnivorous crayfish both promote breakdown of leaves (basal resources) and decouple any potential trophic cascade by simultaneously affecting intermediate consumers as well as their basal resource. Leaf packs were placed inside in situ artificial channels, which excluded or allowed access to crayfish. During a 4-week period, crayfish greatly promoted leaf processing, with decomposition rates among the fastest ever recorded from temperate streams. Crayfish also affected invertebrate abundance in the leaf packs. As a result of resource consumption, predation and bioturbation, crayfish treatments contained significantly lower densities of invertebrates. In contrast, exclusion of crayfish did not promote leaf decay via increased colonisation by detritivores, primarily because of the conspicuous lack of shredder insects in New Zealand streams. The results support the hypothesis that omnivorous top consumers decouple cascading chains through simultaneous direct and indirect effects on intermediate consumers and basal resources. Decapod consumers, which have been largely ignored in leaf decomposition studies, can be key leaf processors in temperate streams where shredder insects are poorly represented.

Farm ponds have high conservation value because they contribute significantly to regional biodiversity and ecosystem services. In Japan pond draining is a traditional management method that is widely believed to improve water quality and eradicate invasive fish. In addition, fishing by means of pond draining has significant cultural value for local people, serving as a social event. However, there is a widespread belief that pond draining reduces freshwater biodiversity through the extirpation of aquatic animals, but scientific evaluation of the effectiveness of pond draining is lacking. We conducted a large-scale field study to evaluate the effects of pond draining on invasive animal control, water quality, and aquatic biodiversity relative to different pond-management practices, pond physicochemistry, and surrounding land use. The results of boosted regression-tree models and analyses of similarity showed that pond draining had little effect on invasive fish control, water quality, or aquatic biodiversity. Draining even facilitated the colonization of farm ponds by invasive red swamp crayfish (Procambarus clarkii), which in turn may have detrimental effects on the biodiversity and water quality of farm ponds. Our results highlight the need for reconsidering current pond management and developing management plans with respect to multifunctionality of such ponds. Efectos del Drenado de Estanques sobre la Biodiversidad y la Calidad del Agua en Estanques de Cultivo.

ERIC R. LARSON*, CATHRYN L. ABBOTT , NISIKAWA USIO ‡, § , NORIKO AZUMA , KIMBERLY A. WOOD*, LEIF-MATTHIAS HERBORG** AND JULIAN D. OLDEN* *School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA, U.S.A. Pacific Biological Station, Fisheries and Oceans Canada, Nanaimo, BC, Canada Center for Transdisciplinary Research, Niigata University, Nishi-ku, Niigata, Japan Center for Toki and Ecological Restoration, Niigata University, Niibokatagami, Sado, Japan Center for Environmental Biology and Ecosystem Studies, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba City, Ibaraki, Japan **BC Ministry of the Environment, Victoria, BC, Canada

The role of resource subsidies across ecosystem boundaries has emerged as an important concept in contemporary ecology. For lake ecosystems, this has led to interest in quantifying the contribution of terrestrial allochthonous carbon to aquatic secondary production. An inverse relationship between habitat area and the role of allochthonous subsidies has been documented on marine islands and assumed for lakes, yet there have been no tests of this pattern among benthic (lake bottom) consumers. Here, we used carbon stable isotopes to trace terrestrial allochthonous and benthic autochthonous carbon use by the crayfish Pacifastacus leniusculus over a gradient of lake area, productivity and urbanization. Consistent with findings from terrestrial islands, habitat size dictated the importance of allochthonous subsidies, as P. leniusculus transitioned from using predominantly terrestrial carbon in small lakes to an increased reliance on autochthonous production in larger lakes. However, shoreline urbanization interacted with this pattern, particularly for small lakes where greater urbanization resulted in reduced use of allochthonous resources. As such, we provide, to our knowledge, the first confirmation of the predicted relationship between habitat size and importance of allochthonous subsidies to lake benthic consumers, but found that urbanization can interfere with this pattern.

Whether a species niche is conserved or shifts across space and time is a question of heightened interest in ecology and evolution. Considerable scientific inquiry into this topic has used invasive species to evaluate conservatism of the Grinnellian climatic niche while generally neglecting the Eltonian functional niche. By contrast, we report here on the first simultaneous reciprocal comparison of both the Grinnellian and Eltonian niches for the globally invasive signal crayfish Pacifastacus leniusculus between its native (Pacific Northwest of North America) and non‐native ranges (Japan). Using multivariate statistics and the Maxent machine‐learning algorithm, we found strong evidence for a climatic niche shift between geographic regions for P. leniusculus. Pacifastacus leniusculus shifted from warmer temperatures with strong precipitation seasonality in western North America to cooler temperatures with less precipitation seasonality in Japan. However, analysis of stable isotopes of carbon and nitrogen revealed conservatism of the functional niche of P. leniusculus between multiple lakes in the native and non‐native ranges. We found that trophic position and niche width of P. leniusculus were equivalent between regions, and that niche attributes including reliance on autochthonous or allochthonous energy sources and ontogenetic shifts were comparable regardless of origin. Our finding of functional niche conservatism contrasts with the results of some recent studies evaluating the Grinnellian niche for invasive species, as well as our own climatic niche comparison, and raises the question of whether Grinnellian or Eltonian niches are more prone to shifts or conservatism. We hypothesize that the Grinnellian niche may be more labile than the Eltonian niche in general, but argue that resolving this question will require more reciprocal comparisons of Eltonian niches to keep pace with the recent increase in Grinnellian niche studies.

Despite the existence of well‐established international environmental and nature conservation policies (e.g., the Ramsar Convention and Convention on Biological Diversity) ponds are largely missing from national and international legislation and policy frameworks. Ponds are among the most biodiverse and ecologically important freshwater habitats, and their value lies not only in individual ponds, but more importantly, in networks of ponds (pondscapes). Ponds make an important contribution to society through the ecosystem services they provide, with effective conservation of pondscapes essential to ensuring that these services are maintained. Implementation of current pond conservation through individual site designations does not function at the landscape scale, where ponds contribute most to biodiversity. Conservation and management of pondscapes should complement current national and international nature conservation and water policy/legislation, as pondscapes can provide species protection in landscapes where large‐scale traditional conservation areas cannot be established (e.g., urban or agricultural landscapes). We propose practical steps for the effective incorporation or enhancement of ponds within five policy areas: through open water sustainable urban drainage systems in urban planning, increased incentives in agrienvironment schemes, curriculum inclusion in education, emphasis on ecological scale in mitigation measures following anthropogenic developments, and the inclusion of pondscapes in conservation policy.

The invasive signal crayfish ( Pacifastacus leniusculus ) may undergo ontogenetic diet shifts with increasing size, but the consequences of crayfish size–structure changes for aquatic food webs are little known. We evaluated size-dependent impacts of signal crayfish on a littoral marsh food web using in-situ enclosures in a northern Japanese marsh. During the 60-day experiment, large crayfish ( 30 mm) appeared after more time had passed. Benthic algal biomass was reduced in the presence of large crayfish but was affected little by small crayfish, suggesting that large crayfish were significant bioturbators. On the other hand, total invertebrate biomass was reduced while total invertebrate density was enhanced in the presence of both crayfish size classes. Potential crayfish impacts on invertebrates are: (1) predation on large vulnerable taxa such as Trichoptera and predatory invertebrates, (2) mechanical destruction of macrophytes, thereby reducing microhabitats for invertebrates, (3) heightened emigration of invertebrates in response to bioturbation and/or (4) predation or competition release on small invertebrates as a result of crayfish reducing their predators/competitors. Invertebrate taxa richness was nearly halved in the presence of large crayfish, probably reflecting reductions of rare taxa. Overall, functional roles of signal crayfish as omnivores and ecosystem engineers remained similar during the ontogenetic stage but the magnitude and rate of crayfish impacts intensified with increasing crayfish size. Thus, removal of large invasive crayfish alone may reduce detrimental impacts on aquatic biodiversity.

Japan’s only native crayfish species Cambaroides japonicus has been declining dramatically in the past few decades. For the purpose of conservation planning, twenty-two coastal streams were surveyed to investigate summer distributions of crayfish in relation to stream and riparian environment. Classification and regression trees were used to predict the occurrence and abundance of crayfish. The classification tree model with stream variables as predictors showed that crayfish would occur in swift or high gradient streams (correct classification rate = 91%). Within those streams, however, crayfish only inhabited depositional microhabitats, in which the areas are limited in availability. Crayfish were not found in gentle, low gradient streams containing abundant depositional microhabitats. This paradoxical distribution pattern was attributed to availability of boulder substrates in swift or high gradient streams. The regression tree model indicated that crayfish abundance was determined primarily by the percentage of boulder substrates and the presence of fish (observed vs. predicted r = 0.64). The classification tree model using only riparian variables indicated that the total woody plant (mainly broadleaf species) density followed by the percentage of early successional species such as alder and willow determined the splits of the tree model (correct classification rate = 95%). A leaf processing experiment on 10 riparian plant species suggested that crayfish preferred high nitrogen (or low C/N) leaves. These results suggest that swift or high gradient fishless streams associated with abundant cover in dense broadleaf forest serve conservation areas for this endangered crayfish, and that consideration of riparian composition may facilitate conservation efforts.

We manipulated through an enclosure experiment the presence and absence of small common carp (Cyprinus carpio, L) and their sediment access using a mesh net. The aims of the experiment were to determine carp effects on nutrient dynamics and community composition, and partially separate bioturbation effects from the remaining carp effects such as excretion and predation. During the two months, carp influenced water quality and nutrient dynamics, altered phytoplankton biomass and composition and decreased submerged macrophyte biomass independently of sediment access, indicating that nutrient excretion was the primary mechanism for the carp effects. However, Secchi depth decreased while the concentration of suspended solids increased when carp access to the sediments was allowed, suggesting that bioturbation by carp influenced water transparency. Increase in phytoplankton (dominated by cyanobateria) and suspended solids resulted in reduced submerged macrophyte biomass through reduction of light availability. Zooplankton, numerically dominated by rotifers, increased in carp enclosures. In addition, benthic macroinvertebrates decreased in carp enclosures, regardless of the presence and absence of the netting. Because direct predation effects were not evident, carp probably affected benthic macroinvertebrates through reduction of submerged macrophytes. These results indicate that carp can have dramatic direct and indirect impacts on nutrient dynamics and littoral community structure through excretion and bioturbation. Ecosystem engineering by carp may therefore trigger a shift from a clear water state dominated by submerged macrophytes to a turbid water state dominated by phytoplankton.

In northern Japan, an alien crayfish species (signal crayfish; Pacifastacus leniusculus) is replacing Japan's only native crayfish species (Cambaroides japonicus) that is endemic to the country. We tested experimentally if these two crayfish species had similar roles in terms of ecosystem functioning in stream habitats. Experiments were performed to examine the impacts of alien and endemic crayfish on detritus-based food webs. During the experiment, neither crayfish species affected rates of breakdown of microbially conditioned oak leaves. In contrast, the amphipod Jesso-gammarus jesoensis, which dominated the non-crayfish invertebrate biomass, was significantly reduced in the presence of the two crayfish species. Thus, effects of crayfish on leaf breakdown were probably masked by the leaf processing activities of these large amphipods in the absence of crayfish. Overall, per-unit biomass impacts of Pacifastacus on leaf processing and invertebrate colonisation of leaves were comparable to those by Cambaroides. Laboratory experiments were performed to test whether rates of leaf processing of 10 riparian plant species, particulate organic matter (POM) production and nutrient excretion differed between crayfish species in the absence of other invertebrates. Although POM production rates did not differ between crayfish species, crayfish impacts on leaf processing differed depending on plant species reflecting differential leaf preference. Comparisons of individual nutrient excretion rates revealed that ammonia and phosphate excretion rates were higher in Cambaroides compared with Pacifastacus. Further, ammonia excretion rates were proportional to crayfish biomass in Cambaroides but not in Pacifastacus. Taken together, the two crayfish species had similar roles in stream food webs when biomass was similar. However, their roles as leaf processors and excretion rates of nutrients differed when there was a choice among different riparian species as sources of leaf litter. Species replacement between alien and endemic crayfish may therefore result in differential consequences for ecosystem processes.

Summer distributions of the invasive signal crayfish (Pacifastacus leniusculus) were investigated in relation to physicochemistry in a Kusiro Moor marsh and its inflows and outflows in northern Japan. Maximum crayfish abundance and biomass were 1.04 individuals/m2 and 3.56 g dry mass (DM)/m2 in littoral marsh habitats, and 5.84 individuals/m2 and 13.48 g DM/m2 in stream habitats. Classification tree analysis was used to predict crayfish occurrence at 102 sites from all habitats (i.e. littoral marsh, pelagic marsh and stream) while regression tree analyses were used to predict crayfish abundance at littoral marsh and stream sites separately. The classification tree showed that crayfish occurrence was primarily determined by undercut bank volume regardless of habitat identity. When undercut bank volume was 0.61 m3, and moderately high when dissolved oxygen was >9.09 mg/l and undercut bank volume was

Two field experiments were performed to examine the impacts on stream invertebrates of crayfish (Paranephrops zealandicus) as predators and bioturbators. A den- sity manipulation experiment involved three treatments with different crayfish densities in streamside channels (0, 5, and 10 crayfish/m2) in which accrual of fine sediment, leaf decomposition, and associated invertebrates were measured. During the 50-d experiment, leaf decomposition was not affected by the presence of crayfish, whereas fine sediment was reduced to similar extents in both crayfish treatments. Some invertebrates followed a similar pattern to that of sediment accrual, suggesting that removal of fine sediment by crayfish was a primary mechanism underlying differences in invertebrate densities. Medium (4-6 mm body length) and large (-7 mm) Tanypodinae were rare in crayfish treatments, probably as a result of selective predation. Conversely, crayfish appeared to facilitate Deleatidium mayflies, as predicted by a trophic cascade (large Tanypodinae predator removal) or shred- der-collector facilitation (fine particulate organic matter production). In many cases, the response of dependent variables was equally strong at both crayfish densities. In a sediment flush experiment, sediment removal treatments were established, along with no-crayfish control and crayfish treatments, to assess the relative impacts of predation and sediment removal on each invertebrate taxon. Crayfish had little impact on leaf decomposition, although decomposition rate was significantly faster than in sediment flush treatments, where collector-scraper invertebrates were reduced as a result of sediment removal. Despite the fact that fine sediment was similarly reduced in crayfish and flush treatments, the response of invertebrates to treatments differed according to invertebrate taxon and size class. Overall, large Tanypodinae were selectively preyed upon; Orthocladiinae, Oribatei, and Oligochaeta responded primarily to sediment removal; Deleatidium were indirectly facilitated; and Chi- ronominae, Ostracoda, and Cyclopoida were relatively unaffected. These results are likely to be relevant at various levels of local scale in the natural environment, but not at the catchment scale. Crayfish are therefore considered to play important roles in determining local distribution of invertebrates through both trophic and nontrophic effects.

Heterogeneity of species interactions in food webs can result from characteristics of substrates as well as attributes of top consumers. We performed a streamside channel experiment to evaluate the impact of crayfish on lower trophic levels in detritus-based (leaf packs) and algal-based food webs (hard-bottoms). After 43 days, both male and female crayfish had dramatically promoted leaf decomposition, with males processing material at a faster rate. However, the difference in leaf processing rates was not related to a greater level of male activity. Despite the sex-related difference in residual leaf dry mass, densities of invertebrates in leaf packs were similarly low in the presence of crayfish of either sex, due to resource consumption, physical dislodgment (bioturbation) and/or predation. No trophic cascade was evident in the leaf pack assemblage. In the hard-bottom assemblage, the results confirmed circumstantial field evidence that crayfish reduce predatory Tanypodinae and indirectly increase collector-gatherer Chironominae following the prediction of a trophic cascade. However, no other taxa were indirectly facilitated, because of strong direct effects of crayfish on algal abundance (through direct consumption and bioturbation). Overall, impacts of crayfish on lower trophic levels were more pronounced in the structurally complex, detritus-based assemblages than in its hard-bottom, algal-based counterpart. This conflicts with the expectation that net predation effects should be weaker where structural complexity is greater but is mainly a consequence of the profound engineering effects of crayfish in reducing colonisable substrate when they shred and disturb detrital material. Effects of crayfish may therefore propagate differently and with varying strength depending on substrate. Moreover, engineering activities and predation by crayfish appear to have been of overwhelming significance with subtle sex differences in leaf processing rates failing to lead to differences in invertebrate densities.

Paddy fields are important as alternative wetland habitats for a range of aquatic and semi-aquatic wildlife that once inhabited floodplain habitats. However, depopulation and aging in rural communities have led to the loss of biodiversity across rural areas of Japan. In Japan, wildlife-friendly farming is typically implemented using charismatic wildlife as an icon, and much attention has been given as a means for restoring paddy field biodiversity. Sado Island in central Japan is among the leading areas for such wildlife-friendly farming in terms of the implemented area. Nevertheless, scientific evaluation is largely lacking for the effectiveness of wildlife-friendly farming on paddy field biodiversity. Using four aquatic macroinvertebrate taxa as indicator groups, we surveyed over 300 paddy fields in winter and summer across Sado Island. In winter, although most indicator groups were significantly associated with the percentage of water coverage in paddy fields, winter flooding had limited effects on aquatic macroinvertebrate abundance or richness, because of large variations in water coverage among paddy fields. In contrast, implementing diversion ditches provided additional habitats for aquatic macroinvertebrates that prefer deep-water habitats, resulting in the separation of macroinvertebrate composition between paddy fields and their adjacent ditches in both winter and summer. Furthermore, agrochemical reduction and fallow flooding were effective in enhancing aquatic macroinvertebrate abundance and richness in summer. Overall, diverse practices of wildlife-friendly farming contributed to the enhancement of aquatic macroinvertebrate diversity on Sado Island.

A laboratory experiment was conducted to test the hypothesis that leaf processing by Japanese crayfish (Cambaroides japonicus de Haan) enhances the growth and reduces the mortality of collector amphipods (Sternomoera yezoensis Ueno) through fine particulate organic matter (FPOM) production. Two treatments (crayfish shredding, no shredding control) were established using flow-through artificial streams and permitting differential FPOM production rates. An amphipod enclosure, associated with juvenile amphipods and preconditioned leaf packs, was placed at the downstream end of each channel. During a 4-week period, shredding by crayfish greatly increased the amount of drifting FPOM compared to that in the control channels, in which only shredder-independent FPOM occurred. Despite the substantial contribution of crayfish to FPOM production, amphipods in both treatments grew during the 4-week period and neither amphipod survival nor growth differed between the two treatments. Furthermore, the residual leaf mass in the amphipod enclosures did not differ between the two treatments. However, residual leaf mass in amphipod enclosures was about 20% less than that expected from the processing rates of the leaf packs in the absence of invertebrate shredding. It is likely that amphipods were directly utilizing leaf packs as their food source regardless of FPOM abundance. These results indicate that juvenile amphipods, despite their classification as collectors, were plastic in their foraging habits, and that the FPOM produced by crayfish was not critical for amphipod growth or survivorship.

Despite their prevalence in headwater streams, crayfish are largely ignored in most leaf decomposition studies. We conducted a field survey in 30 pools along a headwater stream to document the biomass of various shredder invertebrate species and subsequently compared their leaf processing and particulate organic matter (POM) production rates in a laboratory experiment. The crayfish Paranephrops zealandicus dominated the shredder functional feeding group, comprising 99% on average of the total biomass of shredder invertebrates. This was followed by the stonefly Austroperla cyrene, which made up only 0.62%. A laboratory experiment, using stoneflies and two size classes of crayfish, showed that processing rates of large crayfish (normalised by body weight) were lower than those of small crayfish and stoneflies. However, large crayfish had the greatest impact on leaf decomposition and POM production. It is their large body size and dominance of invertebrate biomass that determines the significance of...

In eastern Hokkaido, Japan, the native crayfish Cambaroides japonicus de Haan has been declining rapidly while the exotic crayfish Pacifastacus leniusculus Dana has been expanding its range. We speculated that the observed displacement of Cambaroides by Pacifastacus is partly due to an interference interaction for shelter between the two species. We studied the impacts of Pacifastacus on Cambaroides by testing experimentally whether intensity of interference, the outcome of dominance order and shelter occupancy differed between single- and mixed-species combinations of the two species. Pacifastacus showed less defensive behaviours towards Cambaroides than to conspecifics. In contrast, Cambaroides exhibited more defensive behaviours towards Pacifastacus than to conspecifics. Pairwise comparison of agonistic behaviours in mixed species groups revealed that Pacifastacus exhibiting frequently more aggressive attacks while Camaboides showing more defensive behaviours to their respective counterparts. Dominance in aggressive encounter generally dictated shelter occupancy in mixed-species and Pacifastacus pairs but not in Cambaroides pairs. Because shelter utilization, when these are not limited in supply, was much more frequent in Cambaroides than Pacifastacus, Cambaroides suffered interference from both conspecifics and heterospecifics when they competed for a single shelter. Pacifastacus, however, did not show any change in shelter occupancy in the presence or absence of conspecics or heterospecifics. Inferiority in aggressive interactions and shelter occupancy can therefore be a critical disadvantage for Cambaroides if shelters are limited in natural situations.

Summer distributions of the crayfish Paranephrops zealandicus White, and of potential predators and prey, were investigated in 30 pools along a stream in Otago, New Zealand. Environmental variables were regarded as independent and invertebrates as dependent variables for young‐of‐the‐year (YOY) and adult crayfish. YOY and adults were negatively associated with trout presence and suspended solid concentrations, and positively with wood cover. Adults were further negatively associated with current velocity and positively with depth, leaf cover, and percentage sand. In contrast, YOY were positively associated with coarse substrates. The results are consistent with hypotheses that crayfish are vulnerable to sedimentation and trout predation. Furthermore, coarse substrate and cover may be important because they provide shelter from predation and cannibalism. Deep habitat, however, may act as a refuge from terrestrial predators and/or provide detritus storage for adult crayfish. Densities of adults wer...

Aggressive interactions, foraging behaviour and microhabitat use were observed among four sympatric stream fishes inhabiting the water column: ayu (Plecoglossus altivelis), white-spotted charr (Salvelinus leucomaenis), masu salmon (Oncorhynchus masou) and Japanese dace (Tribolodon hakonensis), each species being categorised into five body-size classes (species-size groups; SSG's). Aggressive interactions were observed between most pairs of SSG's, an almost linear dominance order being apparent throughout the three-month study period. Ayu were relatively subordinate in June, but became the second most dominant in July and the most dominant in August, as a consequence of a reversal in dominance order with salmon. In contrast, smaller-sized dace, which continually suffered from intra- and interspecific aggression, occupied the most subordinate ranks throughout the study period. Intensive aggression was observed among various SSG's, exhibiting same microhabitat propensity throughout the three months. The direction and frequency of aggressive interactions varied month by month due to a reversal in dominance order between ayu and masu salmon, and/or changes in density, body size and resource use of the component members. Opponent selectivity was higher within SSG's, where resource use was assumed to be highly overlapping, rather than among SSG's throughout the study period. Correlation analysis indicated that opponent selectivity in aggressive interactions among SSG's was positively correlated with similarity in microhabitat selectivity in June, but not in other months or with that in foraging habits, suggesting that intensive aggressive behaviour reflected overlapping habitat use among assemblage members during a certain period.

Intra-specific genetic diversity is important not only because it influences population persistence and evolutionary potential, but also because it contains past geological, climatic and environmental information. In this paper, we show unusually clear genetic structure of the endangered Japanese crayfish that, as a sedentary species, provides many insights into lesser-known past environments in northern Japan. Over the native range, most populations consisted of unique 16S mtDNA haplotypes, resulting in significant genetic divergence (overall F_[ST] = 0.96). Owing to the simple and clear structure, a new graphic approach unraveled a detailed evolutionary history; regional crayfish populations were comprised of two distinct lineages that had experienced contrasting demographic processes (i.e. rapid expansion vs. slow stepwise range expansion) following differential drainage topologies and past climate events. Nuclear DNA sequences also showed deep separation between the lineages. Current ocean barriers to dispersal did not significantly affect the genetic structure of the freshwater crayfish, indicating the formation of relatively recent land bridges. This study provides one of the best examples of how phylogeographic analysis can unravel a detailed evolutionary history of a species and how this history contributes to the understanding of the past environment in the region. Ongoing local extinctions of the crayfish lead not only to loss of biodiversity but also to the loss of a significant information regarding past geological and climatic events.

Invasion by common carp (Cyprinus carpio) and red swamp crayfish (Procambarus clarkii) in shallow lakes have been followed by stable-state changes from a macrophyte-dominated clear water state to a phytoplankton-dominated turbid water state. Both invasive carp and crayfish are, therefore, possible drivers for catastrophic regime shifts. Despite these two species having been introduced into ecosystems world-wide, their relative significance on regime shifts remains largely unexplored. We compared the ecological impacts of carp and crayfish on submerged macrophytes, water quality, phytoplankton, nutrient dynamics, zooplankton and benthic macroinvertebrates by combining an enclosure experiment and a meta-analysis. The experiment was designed to examine how water quality and biological variables responded to increasing carp or crayfish biomass. We found that even at a low biomass, carp had large and positive impacts on suspended solids, phytoplankton and nutrients and negative impacts on benthic macroinvertebrates. In contrast, crayfish had a strong negative impact on submerged macrophytes. The impacts of crayfish on macrophytes were significantly greater than those of carp. The meta-analysis showed that both carp and crayfish have significant effects on submerged macrophytes, phytoplankton, nutrient dynamics and benthic macroinvertebrates, while zooplankton are affected by carp but not crayfish. It also indicated that crayfish have significantly greater impacts on macrophytes relative to carp. Overall, the meta-analysis largely supported the results of the experiment. Taken as a whole, our results show that both carp and crayfish have profound effects on community composition and ecosystem processes through combined consequences of bioturbation, excretion, consumption and non-consumptive destruction. However, key variables (e.g. macrophytes) relating to stable-state changes responded differently to increasing carp or crayfish biomass, indicating that they have differential ecosystem impacts.