Exotic largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus) are thought to threaten native aquatic organisms worldwide, but few studies have demonstrated their community‐wide impacts, including the interaction between these fish and other exotic organisms. We tested the hypothesis that bass and bluegill in Japanese farm ponds will reduce some native organisms (fish, shrimp, odonates) as well as exotic crayfish (Procambarus clarkii) via top‐down effects, whereas other native organisms (chironomid larvae, oligochaetes, and macrophytes) will increase as a result of trophic cascades. To test this hypothesis, we conducted three types of field experiments. In the first experiment, we estimated predation pressure in ponds with and without bass and bluegills by using predator exclusion cages. This experiment revealed that predation on native odonates and exotic crayfish was greater in ponds with bass or bluegills, whereas predation on chironomids, oligochaetes, and macrophytes was lower in ponds with bass or bluegills. In the second experiment, we estimated the impact of bass and bluegills at the community level using four large mesocosms in a pond. Bass or bluegill were introduced into two mesocosms (treatment), but were absent in the other two mesocosms (control). We found that bass reduced native fish, exotic fish, shrimp, odonates, and exotic crayfish, while chironomids, oligochaetes, and macrophytes increased; however, introducing bluegill reduced only shrimp and odonates. In the third experiment, we established small mesocosms with and without exotic crayfish. This experiment showed that crayfish were responsible for a reduction of macrophytes. All three field experiments supported our hypothesis for bass effects, but not for most of the bluegill effects. The results provide important implications for strategies to eradicate exotic fish; when exotic crayfish are present, bass removal is likely to reduce macrophytes that perform important functions in freshwater ecosystems. To conserve macrophytes we propose that reduction of exotic crayfish should be considered when eliminating bass.

Rice fields provide important habitats for many endemic and endangered species originally dependent on wetlands as habitat. However, the value of rice fields has rarely been evaluated from a multi-scale perspective. We examined abundance of two frogs, the montane brown frog Rana ornativentris and the forest green tree frog Rhacophorus arboreus, that use rice fields as breeding sites, and explored local and landscape-level factors determining their abundance. To determine appropriate spatial scales influencing abundance, we generated different sized buffer circles around a focal rice field, calculated landscape composition in each buffer, and determined the regression model that best explained frog abundance using Akaike's Information criterion (AIC). The montane brown frog and the forest green tree frog exhibited the lowest AIC at buffer sizes of 300 and 1,000 m, respectively. Both species exhibited a higher abundance at intermediate water depths (7-10 cm). At the landscape-level, the montane brown frog showed highest abundance at intermediate forest cover (50%-60%). Forest green tree frogs showed a monotonic increase with forest cover. Because each species responded somewhat differently to spatial scale and landscape composition, context and species dependent outcomes of local restoration practices are required for particular rice fields to achieve cost-effective results.

To evaluate the effects of allochthonous litter input on the population density of invasive red swamp crayfish (Procambarus clarkii) in Japanese farm ponds, we analyzed gut contents, stable isotope ratios, and the correlation between crayfish biomass and environmental factors in the ponds. For our correlation analysis, we used Akaike's information criterion (AIC) corrected for small sample size (AIC C ) to select appropriate models within the generalized linear model. Allochthonous litter input was the most influential variable affecting crayfish biomass, followed by pond area. Gut content analysis demonstrated a positive correlation between the percentage of litter in the crayfish gut and the amount of litter input into the pond from which animals were collected. Crayfish d 13 C became increasingly similar to litter d 13 C as litter input into ponds increased. Nitrogen isotope signature analysis suggested that microorganisms attached to litter may contribute to crayfish diet. The above results obtained by three complementary approaches demonstrated an important influence of allochthonous litter input on crayfish biomass in farm ponds. We propose that the appropriate management of surrounding forests may be effective in controlling the abundance of exotic crayfish with minimized impacts on native communities.

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