Preference for natural borders in rice paddies by two treefrog species

In the Republic of Korea, one of the biggest threats to amphibians is habitat modification such as urbanisation and land conversion. With the loss of natural habitats, rice paddies play an important role as substitute habitats for amphibians that originally inhabited wetlands. However, since the 70’s, traditional rice agriculture has been modernised, leading to an increase in the number of concrete ditches and roads bordering rice paddies. This modernisation could have affected the distribution and density of amphibians. In this study, we investigated the preferred position, based on the advertisement calls for two treefrog species (Dryophytes japonicus and D. suweonensis), in relation to different types of borders such as natural ditch, concrete ditch, one-lane dirt road and vegetation. The results show that treefrogs seem to avoid rice paddies with concrete ditches, and with no ditch, which provided no resting microhabitat. The sides of the paddies preferred by the two treefrog species were the ones with vegetation of 30?cm wider or higher, while the two species seemed to avoid the side of paddies with roads. Our results are important for the conservation of anuran species in rice paddies in general as it highlights the need for vegetated areas, preferentially along natural ditches.     

Spider predation on a mirid pest in Japanese rice fields

Spiders are common generalist predators, and understanding their potential in biological control is important for the development of integrated pest management programs. In this study, predation by three groups of spiders on the mirid bug Stenotus rubrovittatus (Hemiptera: Miridae) in rice paddies was investigated using DNA-based gut-content analysis. A laboratory feeding study revealed that the detection half-lives of bug DNA in the spider gut at 25 °C was 3.4 days for Lycosidae and 1.5 days for Tetragnathidae. Individual spider predation on the mirid bug was investigated by detecting DNA of prey in field-collected spiders. In total, 1199 spiders were assayed from three spider groups: Pirata subpiraticus (Lycosidae), Tetragnatha spp. (Tetra-gnathidae), and Pachygnatha clercki (Tetra-gnathidae), which each differ in their preferred microhabitat as well as their predatory habits. Detection rates of prey DNA in spiders increased significantly with the density of prey across all spider groups. P. subpiraticus and Tetragnatha spp. predation showed a better fit to a saturated response curve to increasing prey density, while P. clercki showed a simple linear relationship with prey density. Densities of alternative prey species did not affect the detection rates of mirids. These results suggest that predation on pests by generalist predators in an agroecosystem is affected not only by prey abundance but also by predator preference for specific prey. Predator preference is therefore an important factor to consider when estimating the role of natural enemies as biological control agents.     

Multiple spatial scale factors affecting mirid bug abundance and damage level in organic rice paddies

Mirid bugs, major insect pests in rice production, have dramatically expanded their range in Japan, resulting in increased economic losses especially for organic rice farmers. In this study, the within-field and landscape-scale factors affecting the bug and its damage to crops were examined in organic rice farms. Bug densities and crop damage levels showed significant positive relationships with weed densities (Schoenoplectus juncoides and Echinochloa crus-galli) within individual fields. Bug densities were negatively associated with Tetragnatha spp. and Pachygnatha clercki densities, indicating that these spiders act as biological control agents that help to decrease crop damage levels. At the landscape scale, bug densities increased with the proportion of the area that was fallow within a 400-m radius around focal fields. Fallows represent important source habitat for the bug and the spatial extent at which bug abundance was affected indicates the mobility of these insects. These results suggest that the combination of biological control by natural enemies, and weed management within individual paddies and surrounding landscapes inside a buffer zone of less than half a kilometre may be effective in controlling mirid bugs and the damage they cause in organic paddy fields.     

Carbon isotope composition of CH4 from rice paddies in Japan

Carbon isotope ratios (¹³C) for bubble CH₄ in a submerged paddy soil were studied in Yokohama, Japan, throughout a growing period, and its variation was found. Bubble CH₄ collected from other 33 paddy fields in Japan was also measured for its ¹³C and the results agreed with Yokohama. Furthermore, the variation occurred irrespective of the amount and the type of supplied organic substances to the fields (whole rice straw, rice stubble, or compost). The ¹³C value (average value of -55.9 ± 4.24) from these paddy fields was higher than those of the CH₄ emitted from African and North American paddies. The higher value was little affected by their difference in the supplied organic substances. CH₄ oxidation likely occurs for bubble CH₄ in the shallow paddy fields. A rough estimate of the total CH₄ production, using isotope mass balance, showed that 17 to 22% of organic carbon supplied to Japanese paddies transforms to CH₄.     

Divergent landscape effects on population connectivity in two co-occurring amphibian species

The physical and environmental attributes of landscapes often shape patterns of population connectivity by influencing dispersal and gene flow. Landscape effects on movement are typically evaluated for single species. However, inferences from multiple species are required for multi‐species management strategies increasingly being applied in conservation. In this study, I compared the spatial genetic patterns of two amphibian species across the northeastern United States and estimated the influence of specific landscape features on the observed genetic structure. The spotted salamander (Ambystoma maculatum) and wood frog (Rana sylvatica) share many ecological attributes related to habitat use, phenology and site fidelity. However, I hypothesized that important differences in their movement patterns and life history would create distinct genetic patterns for each species. Using 14 microsatellite loci, I tested for differences in the level of genetic differentiation between the two species across 22 breeding ponds. The effects of eight landscape features were also estimated by evaluating 32 landscape resistance models. Spotted salamanders exhibited significantly higher genetic differentiation than wood frogs. Different landscape features were also identified as potential drivers of the genetic patterns in each species, with little overlap in model support between species. Collectively, these results provide strong evidence that these two amphibian species interact with the landscape in measurably different ways. The distinct genetic patterns observed are consistent with key differences in movement ability and life history between A. maculatum and R. sylvatica. These results highlight the importance of considering more than one species when assessing the impacts of the landscape matrix on population connectivity, even for ecologically similar species within the same habitats.     

Monogamy and polygamy in two species of mirid bugs: a functional-based approach

Multiple mating in females is widespread among insects in spite of the risk of predation, disease acquisition and/or physical injury that may occur. One common consequence of female polyandry is competition among sperm from two or more males within the female to fertilize the ova. This competition is an evolutionary driving force that determines a series of adaptations in both males and females. In this work, we examine some behavioral, morphological and physiological characteristics of males and females of two Heteropteran species that are related to their monoandrous/polyandrous mating behavior. Females of Macrolophus pygmaeus (Het. Miridae), the monoandrous species, were coy about accepting a male partner, spent a short time in copula, and received only a small volume of ejaculate. Even so, with only one mating event, they received enough sperm to fertilize most of their ova (21 days after mating all females were still fertile). In contrast, females of Nesidiocoris tenuis (Het. Miridae), the polyandrous species, readily accepted any mating partner, spent a long time in copula and received a large volume of ejaculate. However, these latter females soon ran out of sperm and needed to mate periodically in order to maintain a sufficient sperm supply to fertilize their eggs. As predicted, based on current theory (Simmons, 2001b), an increased investment in spermatogenesis was detected in N. tenuis with relation to M. pygmaeus. The males of the polyandrous species had larger accessory reproductive glands, seminal vesicles, testes and sperm cells than those of the monoandrous species.     

Prediction of species composition of plant communities in a rural landscape based on species traits

The species composition of a community is a subset of the regional species pool, and predicting the species composition of a community from ecological traits of organisms is an important objective in ecology. If such a prediction can be made feasible, we could assess the risk of invasion of locally new species (alien species and genetically modified species) into natural communities. We developed and tested statistical models to predict a community’s species composition from ecological traits of the species pool. Various types of communities (forest, meadow, and weed communities) exist in a small area of traditional rural landscape in Japan, and have been maintained by human activities. These communities and the tracheophytes species pool in the 1-km² research area were considered. We used logistic regression and decision-tree analysis to construct predictive models of community species composition based on plant traits, using the presence or absence of species in a community as the dependent variable and ecological traits as independent variables. Plant traits were grouped by cluster analysis, and the average in each trait group was used for model building to avoid multiple collinearity. Statistical prediction models were significant in all communities. About 60–75% of species composition could be predicted from the measured plant traits in forest communities, but 33–56% in the meadow and weed communities. Our results showed the possibility of predicting the species composition of plant communities from the ecological traits of the plant species together with the information on local species pool.     

转cry1 Ab基因粳稻对稻田节肢动物群落的影响

在将稻田节肢动物群落按营养关系分为植食类、寄生类、捕食类、腐食类和其他类等5个功能团的基础上,从功能团优势度、群落结构参数及群落相异性等方面,经2年3点的调查就2个转cry1Ab基因粳稻（Bt粳稻）品系KMD1和KMD2对稻田节肢动物群落结构的影响做了评价。结果表明：在大多数情况下,Bt粳稻与对照间各功能团优势度、群落结构参数[物种丰富度（S）、Shannon-Wiener多样性指数（H′）、均匀性指数（J）、优势集中性指数（C）]及其时间动态无明显差异;Bt粳稻与对照间植食类、寄生类、捕食类亚群落,及整个节肢动物群落的相似性也较高。综合分析认为,Bt粳稻对稻田节肢动物群落结构无明显的负面影响。     

Ecological impacts of the 2011 Tohoku Earthquake Tsunami on aquatic animals in rice paddies

The 2011 Tohoku Earthquake Tsunami hit the Pacific coast of eastern Japan on March 11, 2011 and disturbed various ecosystems, including rice paddies along the coast. In Miyagi Prefecture, located in the Tohoku Region, a total of 12685 ha, or about 11.5 % of the rice paddies, were inundated and damaged by the tsunami. Although rice paddies are artificially constructed, they have long been used by many kinds of aquatic animals as habitats. To assess impacts of the 2011 Tohoku Earthquake Tsunami on aquatic animals inhabiting the rice paddies, census surveys were conducted at inundated and non-inundated rice paddies at six sites along the coast of Miyagi Prefecture from June to July 2012. This was 30–60 days after the first transplanting of rice seedling in inundated rice paddies following the tsunami. In the surveys a total of 100 aquatic animal taxa, 72 from inundated and 86 from non-inundated rice paddies, were found. Although the taxonomic richness and composition differed among the sites, the total number of observations of walk dispersers and obligatory aquatic animals without resting stages were significantly lower in inundated than in non-inundated rice paddies. However, no notable difference was detected in taxonomic richness and the total number of observations of flight dispersers and obligatory aquatic animals with resting stages between inundated and non-inundated rice paddies. The results showed that the tsunami had a substantial impact on freshwater animals but that restoration of the paddies for rice cultivation enhanced rapid recolonization by aquatic animals with high dispersal abilities and resting stages.     

Production, oxidation and emission of methane in rice paddies

Abstract Production and emission of methane from submerged paddy soil was studied in laboratory rice cultures and in Italian paddy fields. Up to 80% of the CH₄ produced in the paddy soil did not reach the atmosphere but was apparently oxidized in the rhizosphere. CH₄ emission through the rice plants was inhibited by an atmosphere of pure O₂ but was stimulated by an atmosphere of pure N₂ or an atmosphere containing 5% acetylene. Gas bubbles taken from the submerged soil contained up to 60% CH₄, but only < 1% CH₄ after the bubbles had passed the soil-water interface or had entered the intercellular gas space system of the rice plants. CH₄ oxidation activities were detected in the oxic surface layer of the submerged paddy soil. Flooding the paddy soil with water containing > 0.15% sea salt (0.01% sulfate) resulted in a strong inhibition of the rates of methanogenesis and a decrease in the rates of CH₄ emission. This result explains the observation of relatively low CH₄ emission rates in rice paddy areas flooded with brackish water.     

Grazer species effects on epilithon nutrient composition

1. Field and laboratory experiments were conducted to investigate the excretion stoichiometry of nitrogen (N) and phosphorus (P) of two benthic macroinvertebrate grazers, the crayfish Orconectes propinquus and the snail Elimia livescens, that differ in body stoichiometry (mean body molar N : P 18 and 28, respectively). Crayfish excretion had a significantly higher ammonium : soluble reactive phosphorus (SRP) ratio in the laboratory and in three natural streams than did snails, as predicted by ecological stoichiometry theory. 2. In greenhouse recirculating artificial streams, treatments consisting of crayfish, snails, or no grazers were used to examine responses in dissolved nutrient concentrations and epilithon nutrient composition and limitation. SRP concentrations depended upon the grazer species, with the snail treatment having a higher SRP concentration than other treatments (P < 0.05). Dissolved inorganic N was not affected by grazers, but appeared to be rapidly incorporated in epilithon. 3. Epilithon N content was dependent upon the grazer species present, with the crayfish treatment having a significantly higher N content than other treatments (P = 0.001). No grazer species effects on epilithon P content were found. However, both grazer treatments had significantly lower epilithon P content than the no‐grazer treatment. 4. Traditionally, studies have focused on how grazer‐induced structural changes to epilithon can alter epilithon nutrient dynamics, but this structural mechanism could not solely explain differences in epilithon nutrient contents and ratios in the present study. Our results rather suggest that benthic grazers can alter epilithon nutrient composition and limitation via nutrient excretion. Consequently, macroinvertebrate grazers may serve as ‘nutrient pumps’ that partly regulate the availability of nutrients to algae in stream ecosystems.     

Processes involved in formation and emission of methane in rice paddies

The seasonal change of the rates of production and emission of methane were determined under in-situ conditions in an Italian rice paddy in 1985 and 1986. The contribution to total emission of CH₄ of plant-mediated transport, ebullition, and diffusion through the flooding water was quantified by cutting the plants and by trapping emerging gas bubbles with funnels. Both production and emission of CH₄ increased during the season and reached a maximum in August. However, the numbers of methanogenic bacteria did not change. As the rice plants grew and the contribution of plant-mediated CH₄ emission increased, the percentage of the produced CH₄ which was reoxidized and thus, was not emitted, also increased. At its maximum, about 300 ml CH₄ were produced per m² per hour. However, only about 6% were emitted and this was by about 96% via plant-mediated transport. Radiotracer experiments showed that CH, was produced from H₂/CO₂. (30–50%) and from acetate. The pool concentration of acetate was in the range of 6–10 mM. The turnover time of acetate was 12–16 h. Part of the acetate pool appeared to be not available for production of CH₄ or CO₂     

Combined effects of landscape composition and heterogeneity on farmland avian diversity

Conserving biodiversity on farmland is an essential element of worldwide efforts for reversing the global biodiversity decline. Common approaches involve improving the natural component of the landscape by increasing the amount of natural and seminatural habitats (e.g., hedgerows, woodlots, and ponds) or improving the production component of the landscape by increasing the amount of biodiversity‐friendly crops. Because these approaches may negatively impact on economic output, it was suggested that an alternative might be to enhance the diversity (compositional heterogeneity) or the spatial complexity (configurational heterogeneity) of land cover types, without necessarily changing composition. Here, we develop a case study to evaluate these ideas, examining whether managing landscape composition or heterogeneity, or both, would be required to achieve conservation benefits on avian diversity in open Mediterranean farmland. We surveyed birds in farmland landscapes of southern Portugal, before (1995–1997) and after (2010–2012) the European Union's Common Agricultural Policy (CAP) reform of 2003, and related spatial and temporal variation in bird species richness to variables describing the composition, and the compositional and configurational heterogeneity, of the natural and production components of the landscape. We found that the composition of the production component had the strongest effects on avian diversity, with a particularly marked effect on the richness of farmland and steppe bird species. Composition of the natural component was also influential, mainly affecting the richness of woodland/shrubland species. Although there were some effects of compositional and configurational heterogeneity, these were much weaker and inconsistent than those of landscape composition. Overall, we suggest that conservation efforts in our area should focus primarily on the composition of the production component, by striving to maximize the prevalence of biodiversity‐friendly crops. This recommendation probably applies to other areas such as ours, where a range of species of conservation concern is strongly associated with crop habitats.     

Impacts of forest fragmentation on species composition and forest structure in the temperate landscape of southern Chile

Aim Few studies have explicitly examined the influence of spatial attributes of forest fragments when examining the impacts of fragmentation on woody species. The aim of this study was to assess the diverse impacts of fragmentation on forest habitats by integrating landscape‐level and species‐level approaches. Location The investigation was undertaken in temperate rain forests located in southern Chile. This ecosystem is characterized by high endemism and by intensive recent changes in land use. Method Measures of diversity, richness, species composition, forest structure and anthropogenic disturbances were related to spatial attributes of the landscape (size, shape, connectivity, isolation and interior forest area) of forest fragments using generalized linear models. A total of 63 sampling plots distributed in 51 forest fragments with different spatial attributes were sampled. Results Patch size was the most important attribute influencing different measures of species composition, stand structure and anthropogenic disturbances. The abundance of tree and shrub species associated with interior and edge habitats was significantly related to variation in patch size. Basal area, a measure of forest structure, significantly declined with decreasing patch size, suggesting that fragmentation is affecting successional processes in the remaining forests. Small patches also displayed a greater number of stumps, animal trails and cow pats, and lower values of canopy cover as a result of selective logging and livestock grazing in relatively accessible fragments. However, tree richness and β‐diversity of tree species were not significantly related to fragmentation. Main conclusions This study demonstrates that progressive fragmentation by logging and clearance is associated with dramatic changes in the structure and composition of the temperate forests in southern Chile. If this fragmentation process continues, the ability of the remnant forests to maintain their original biodiversity and ecological processes will be significantly reduced.     

Interspecific relationship between the Japanese horned beetle and two Japanese stag beetle species

The Japanese horned beetle Trypoxylus dichotomus septentrionalis and the Japanese stag beetles Lucanus maculifemoratus maculifemoratus and Prosopocoilus inclinatus inclinatus generally occur syntopically and aggregate on oak tree surfaces that exude sap. Securement of these sap sites might be directly linked to male reproductive success. Among the three species, it is likely that males of T. d. septentrionalis are dominant in occupation of feeding sites because of their larger body size. However, there is no clear evidence of this superiority. Moreover, if T. d. septentrionalis is dominant, the mechanism by which the two stag beetle species secure the feeding sites remains unclear. In the present study, I used body mass to compare the body size among males of T. d. septentrionalis, L. m. maculifemoratus and P. i. inclinatus. Further, to clarify the interspecific relationship between the horned beetle and the two stag beetles, I investigated the seasonality of emergence pattern of males at the feeding sites in the field. Comparison of body mass and observation of fighting behavior revealed that males of T. d. septentrionalis have an apparent superiority over males of the two stag beetle species. The seasonal emergence patterns of the two stag beetle species at the feeding sites showed bimodal distributions, and avoided the peak of emergence in T. d. septentrionalis. My results suggest that the two stag beetle species exhibit mate‐securing tactics by emerging at the feeding sites early and late during the breeding season, in order to avoid encountering T. d. septentrionalis.     

Influence of island geography,age and landscape on species composition in different animal groups

Aim To study the importance of ecological and geographical factors in explaining arthropod species composition on islands. Location The Aeolian Islands, a volcanic archipelago in the central Mediterranean, near Sicily. Methods The influence of island area, age, distance to the mainland, distance to the nearest island and land cover categories on species composition of arthropod groups was analysed using canonical correspondence analysis (CCA). The use of multiple animal groups in the same archipelago allowed the development of two complementary approaches based on CCA – a ‘taxon‐focused’ approach and an ‘island‐focused’ approach – to elucidate, respectively, how different taxa respond to the same environmental factors, and which factors are mainly responsible for the composition of the faunas in different locations. Results Island area was an important factor in explaining species composition in Chilopoda, Orthoptera and Tenebrionidae. Distance to the mainland was important mainly for Carabidae. Distance to the closest island was important for many groups. By contrast, island age exerted a significant influence only on the species composition of Orthoptera. Various groups were influenced by a combination of broad‐leaved forest and natural grassland. Main conclusions The example of the arthropods of the Aeolian Islands indicates that the influence of a given island characteristic on species composition varies among groups, although measures of inter‐island isolation were typically more important for taxa than isolation from the mainland source. This suggests that colonization of islands may occur mostly by stepping‐stone dispersal.     

不同种植方式下转Bt基因水稻对稻田节肢动物群落的影响

如何设置庇护所使其在转基因作物靶标害虫抗性治理中达到更高的效率,就此,本文 研究了Bt水稻与非Bt水稻不同种植方式对Bt稻田节肢动物群落的影响。结果表明,整体上,块块种植和列列混栽方式对Bt稻田节肢动物群落多样性、均匀度和优势集中性无显著影响;但混栽方式下的Bt稻田节肢动物群落个体密度和物种丰富度显著偏低。在水稻发育中期,混栽方式下Bt稻田节肢动物群落季节动态与块块种植方式下的明显不同,其多样性、均匀度、优势集中性指数均类似于同种植方式下非Bt稻上各参数的季节动态。混栽方式下的庇护所效应更明显。