Taku Kadoya

Dragonfly species richness on man-made ponds: effects of pond size and pond age on newly established assemblages

We studied the abundance and species richness of adult dragonflies in 11 artificial ponds which were recently established (within 2 years). We found that the adult dragonfly assemblage patterns were influenced by pond size as well as pond age. The species richness was positively correlated with the pond size, which was because the distributional patterns of species were significantly nested according to pond area. The species richness was highly correlated with pond age in association with the vegetation cover within ponds. It was suggested that the species richness was enhanced by the increasing immigration rate of species which favor well-vegetated ponds.

Assessing functional connectivity using empirical data

The potential for connectivity to impact populations in heterogeneous landscapes, and the obvious implications for conservation biology, has led to increasing interest in connectivity and a proliferation of connectivity measures. Despite the pivotal role of this measure in ecology, however, there is no generally accepted and employed formal definition of connectivity. In addition, despite the strong desire from conservationists, who are increasingly asked to design and implement corridor plans, empirically determining measures of movement and dispersal, and assessing connectivity from field data remain challenging tasks in spatial ecology. Here I summarize the current use of connectivity concepts in terms of both metapopulation and landscape ecology, and present recently developed promising techniques in spatial ecology, such as graph theory, pattern-oriented modeling, and state–space modeling, which will help to improve assessment of species-centered or functional connectivity based on empirical data.

The sensitivity of dragonflies to landscape structure differs between life-history groups

Contrasting life-history strategies of long versus short pre-reproductive phases are known in adult dragonflies (Odonata) of temperate regions. Because the long-phase species spend a longer time in terrestrial habitats such as grasslands or woodlands during their pre-reproductive phase, we hypothesized that long-phase species would be more sensitive to landscape structure than short-phase species. To test this hypothesis, we conducted periodic censuses of adult dragonflies at small man-made ponds. We compared the two above functional groups in terms of the degree to which species occurrence depended on landscape structure. The difference among the two groups was not significant, but occurrence of long-phase species tended to depend on landscape structure. Long-phase species responded to landscape structure at larger spatial scales and showed stronger spatial autocorrelation in their occurrence among sampling ponds than short-phase species.

Global legume diversity assessment : concepts, key indicators, and strategies

While many plant species are considered threatened under anthropogenic pressure, it remains uncertain how rapidly we are losing plant species diversity. To fill this gap, we propose a Global Legume Diversity Assessment (GLDA) as the first step of a global plant diversity assessment. Here we describe the concept of GLDA and its feasibility by reviewing relevant approaches and data availability. We conclude that Fabaceae is a good proxy for overall angiosperm diversity in many habitats and that much relevant data for GLDA are available. As indicators of states, we propose comparison of species richness with phylogenetic and functional diversity to obtain an integrated picture of diversity. As indicators of trends, species loss rate and extinction risks should be assessed. Specimen records and plot data provide key resources for assessing legume diversity at a global scale, and distribution modeling based on these records provide key methods for assessing states and trends of legume diversity. GLDA has started in Asia, and we call for a truly global legume diversity assessment by wider geographic collabora- tions among various scientists.

Impacts of weeping lovegrass (Eragrostis curvula) invasion on native grasshoppers: responses of habitat generalist and specialist species

We investigated invasion impacts of a grass species (Eragrostis curvula) on native grasshoppers by periodic censuses of these insects on gravelly floodplains of the Kinu River, Japan. Our hypothesis was that there are greater impacts on natives when they are habitat specialists, as opposed to habitat generalists. The study area comprised two main habitat types: gravelly areas and riparian grasslands. Among 12 grasshopper species identified, five were more abundant in one of the habitat types and all of them were significantly negatively affected by coverage of weeping lovegrass, whereas seven occurred at the both habitat types simultaneously and a significantly smaller portion of species (two of the seven) was negatively affected by the alien plants. The results suggest that habitat specificity is related to the grasshopper species’ sensitivity to the plant, indicating that habitat specialist herbivores living on open gravelly floodplains are likely highly vulnerable to this plant invasion.

IsoWeb: A Bayesian Isotope Mixing Model for Diet Analysis of the Whole Food Web

Quantitative description of food webs provides fundamental information for the understanding of population, community, and ecosystem dynamics. Recently, stable isotope mixing models have been widely used to quantify dietary proportions of different food resources to a focal consumer. Here we propose a novel mixing model (IsoWeb) that estimates diet proportions of all consumers in a food web based on stable isotope information. IsoWeb requires a topological description of a food web, and stable isotope signatures of all consumers and resources in the web. A merit of IsoWeb is that it takes into account variation in trophic enrichment factors among different consumer-resource links. Sensitivity analysis using realistic hypothetical food webs suggests that IsoWeb is applicable to a wide variety of food webs differing in the number of species, connectance, sample size, and data variability. Sensitivity analysis based on real topological webs showed that IsoWeb can allow for a certain level of topological uncertainty in target food webs, including erroneously assuming false links, omission of existent links and species, and trophic aggregation into trophospecies. Moreover, using an illustrative application to a real food web, we demonstrated that IsoWeb can compare the plausibility of different candidate topologies for a focal web. These results suggest that IsoWeb provides a powerful tool to analyze food-web structure from stable isotope data. We provide R and BUGS codes to aid efficient applications of IsoWeb.

Dispersal of larvae of Margaritifera laevis by its host fish

Abstract: Local aggregations of unionoids (mussel beds) represent subpopulations constituting a riverine metapopulation and are presumed to be linked by dispersal of parasitic mussel larvae (glochidia) on host fishes. We examined movement patterns of Masu Salmon (Oncorhynchus masou masou), the obligate host fish for the freshwater pearl mussel Margaritifera laevis, during the mussels parasitic period to determine the dispersal potential of glochidia via host fish in the Shubuto River system, Hokkaido, Japan. We conducted a mark—recapture study in a 650-m river section to describe the distance and directionality of host fish movement, and we used fyke net sampling to quantify the number of host fish moving from mainstem rivers to tributaries. Most individuals of Masu Salmon captured in the study were infected with glochidia of M. laevis. The displacement distance of infected fishes ranged from 37.5 m downstream to 512.5 m upstream (mean = 36.5 m upstream from marking location). The dispersal kernel based on a diffusion—advection model represented a leptokurtic distribution with a fat-tailed upstream bias, but most recaptured fish remained near the initial capture location. Movement of fish from mainstem rivers to tributaries was strongly affected by differences in water temperature among tributaries. Most individuals moved to cooler tributaries, but tributaries did not support populations of M. laevis. These results suggest that glochidial dispersal via host fish is important for local recruitment and upstream dispersal, but dispersal to tributaries may be a source of mortality for M. laevis.

Invasion of weeping lovegrass reduces native food and habitat resource of Eusphingonotus japonicus (Saussure)

To examine the relative importance and interactions of trophic and non-trophic effects of plant invasions on herbivores, we investigated how the invasion of weeping lovegrass Eragrostis curvula impacted Eusphingonotus japonicus, a food generalist grasshopper endemic to gravelly floodplains with sparse vegetation in Japan. Field observations and laboratory experiments showed that the grasshopper fed mainly on herbs endemic to the gravelly floodplains, which were negatively impacted by the alien grass. The alien grass was not consumed as food. Field censuses also showed that the abundance of the grasshopper was positively correlated with the coverage of endemic herbs in a plot where weeping lovegrass was not dominant. Dominance of the grass (i.e., habitat modification for E. japonicus) negatively impacted the grasshopper and weakened the positive relationship between the grasshopper and endemic herbs. These results suggest that an understanding of the relationship between non-trophic and trophic effects is essential to predict the impacts of plant invasions on herbivores.

Development of a National Land-Use/Cover Dataset to Estimate Biodiversity and Ecosystem Services

Land-use/cover data are essential to estimate biodiversity and ecosystem services. Although many data and maps have been produced in Japan, there is significant variation in their characteristics, such as publication year, spatial resolution, and land-use/cover classification categories because the purposes of the data and maps differ (e.g., resource inventory). Unfortunately, little attention has so far been paid to biodiversity and ecosystem services, which require preparation of new land-use/cover data. First, we searched existing public national data in Japan published by government sectors and researchers and evaluated their characteristics. Second, we briefly reviewed user needs (e.g., temporal coverage, spatial resolution, and classification categories) to estimate biodiversity and ecosystem services. We then integrated the information, and we present herein a procedure to prepare a new national land-use/cover dataset from existing datasets to bridge the gaps between data producers and users by determining the temporal coverage needed to reveal historic change, determining the spatial resolution suitable for estimation, and setting classification categories needed for estimation. The resultant land-use/cover data could contribute significantly to research and management related to conservation of biodiversity and provision of ecosystem services.

Crisis of Japanese vascular flora shown by quantifying extinction risks for 1618 taxa

Although many people have expressed alarm that we are witnessing a mass extinction, few projections have been quantified, owing to limited availability of time-series data on threatened organisms, especially plants. To quantify the risk of extinction, we need to monitor changes in population size over time for as many species as possible. Here, we present the worlds first quantitative projection of plant species loss at a national level, with stochastic simulations based on the results of population censuses of 1618 threatened plant taxa in 3574 map cells of ca. 100 km2. More than 500 lay botanists helped monitor those taxa in 1994–1995 and in 2003–2004. We projected that between 370 and 561 vascular plant taxa will go extinct in Japan during the next century if past trends of population decline continue. This extinction rate is approximately two to three times the global rate. Using time-series data, we show that existing national protected areas (PAs) covering ca. 7% of Japan will not adequately prevent population declines: even core PAs can protect at best <60% of local populations from decline. Thus, the Aichi Biodiversity Target to expand PAs to 17% of land (and inland water) areas, as committed to by many national governments, is not enough: only 29.2% of currently threatened species will become non-threatened under the assumption that probability of protection success by PAs is 0.5, which our assessment shows is realistic. In countries where volunteers can be organized to monitor threatened taxa, censuses using our method should be able to quantify how fast we are losing species and to assess how effective current conservation measures such as PAs are in preventing species extinction.