Hiroyuki Togashi
Kyoto University
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Featured researches published by Hiroyuki Togashi.
Oecologia | 2014
Naoto Ishikawa; Yoshikazu Kato; Hiroyuki Togashi; Mayumi Yoshimura; Chikage Yoshimizu; Noboru Okuda; Ichiro Tayasu
The stable N isotopic composition of individual amino acids (SIAA) has recently been used to estimate trophic positions (TPs) of animals in several simple food chain systems. However, it is unknown whether the SIAA is applicable to more complex food web analysis. In this study we measured the SIAA of stream macroinvertebrates, fishes, and their potential food sources (periphyton and leaf litter of terrestrial C3 plants) collected from upper and lower sites in two streams having contrasting riparian landscapes. The stable N isotope ratios of glutamic acid and phenylalanine confirmed that for primary producers (periphyton and C3 litter) the TP was 1, and for primary consumers (e.g., mayfly and caddisfly larvae) it was 2. We built a two-source mixing model to estimate the relative contributions of aquatic and terrestrial sources to secondary and higher consumers (e.g., stonefly larva and fishes) prior to the TP calculation. The estimated TPs (2.3–3.5) roughly corresponded to their omnivorous and carnivorous feeding habits, respectively. We found that the SIAA method offers substantial advantages over traditional bulk method for food web analysis because it defines the food web structure based on the metabolic pathway of amino groups, and can be used to estimate food web structure under conditions where the bulk method cannot be used. Our result provides evidence that the SIAA method is applicable to the analysis of complex food webs, where heterogeneous resources are mixed.
Ecology | 2016
Naoto F. Ishikawa; Hiroyuki Togashi; Yoshikazu Kato; Mayumi Yoshimura; Yukihiro Kohmatsu; Chikage Yoshimizu; Nanako O. Ogawa; Nobuhito Ohte; Naoko Tokuchi; Naohiko Ohkouchi; Ichiro Tayasu
Long-term monitoring of ecosystem succession provides baseline data for conservation and management, as well as for understanding the dynamics of underlying biogeochemical processes. We examined the effects of deforestation and subsequent afforestation of a riparian forest of Japanese cedar (Cryptomeria japonica) on stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) and natural abundances of radiocarbon (Δ¹⁴C) in stream biota in the Mt. Gomadan Experimental Forest and the Wakayama Forest Research Station, Kyoto University, central Japan. Macroinvertebrates, periphytic algae attached to rock surfaces (periphyton), and leaf litter of terrestrial plants were collected from six headwater streams with similar climate, topography, and bedrock geology, except for the stand ages of riparian forests (from 3 to 49 yr old in five stands and > 90 yr old in one reference stand). Light intensity and δ¹³C values of both periphyton and macroinvertebrates decreased synchronously with forest age in winter. A Bayesian mixing model indicates that periphyton contributions to the stream food webs are maximized in 23-yr-old forests. Except for grazers, most macroinvertebrates showed Δ¹⁴C values similar to those of terrestrial leaf litter, reflecting the influence of modern atmospheric CO₂ Δ¹⁴C values. On the other hand, the Δ¹⁴C values of both periphyton and grazers (i.e., aquatic primary consumers) were significantly lower than that of modern atmospheric CO₂, and were lowest in 23-yr-old forest stands. Previous studies show that root biomass of C. japonica peaks at 15-30 yr after planting. These evidences suggest that soil CO₂ released by root respiration and dispersed by groundwater weathers carbonate substrata, and that dissolved inorganic carbon (DIC) with low Δ¹⁴C is incorporated into stream periphyton and some macroinvertebrates. The ecological response in the studied streams to clear-cutting and replanting of Japanese cedar is much slower (~20 yr) than the chemical response (< 5 yr). More than 50 yr is required for the food web structure to completely recover from clear-cutting. The ecological delay is attributed to several biogeochemical factors, the understanding of which is critical to integrated management of forest-stream continuum and the prediction of ecosystem resilience in response to environmental change.
Scientific Reports | 2017
Naoto F. Ishikawa; Yoshito Chikaraishi; Naohiko Ohkouchi; Aya R. Murakami; Ichiro Tayasu; Hiroyuki Togashi; Jun-ichi Okano; Yoichiro Sakai; Tomoya Iwata; Michio Kondoh; Noboru Okuda
The relationship between biodiversity and ecosystem functioning is an important theme in environmental sciences. We propose a new index for configuration of the biomass pyramid in an ecosystem, named integrated trophic position (iTP). The iTP is defined as a sum of trophic positions (i.e. the average number of steps involved in biomass transfer) of all the animals in a food web integrated by their individual biomass. The observed iTP for stream macroinvertebrates ranged from 2.39 to 2.79 and was negatively correlated with the species density and the Shannon–Wiener diversity index of the local community. The results indicate a lower efficiency of biomass transfer in more diverse communities, which may be explained by the variance in edibility hypothesis and/or the trophic omnivory hypothesis. We found a negative effect of biodiversity on ecosystem functioning.
Ecology Letters | 2018
Yoshikazu Kato; Michio Kondoh; Naoto Ishikawa; Hiroyuki Togashi; Yukihiro Kohmatsu; Mayumi Yoshimura; Chikage Yoshimizu; Takashi F. Haraguchi; Yutaka Osada; Nobuhito Ohte; Naoko Tokuchi; Noboru Okuda; Ichiro Tayasu
Japan Geoscience Union | 2014
Abigail Cid; Uhram Song; Ichiro Tayasu; Jun-ichi Okano; Hiroyuki Togashi; Naoto Ishikawa; Aya R. Murakami; Takuya Hayashi; Tomoya Iwata; Ken'ichi Osaka; Shin-ichi Nakano; Noboru Okuda
Journal of Applied Ichthyology | 2018
Satoshi Takahashi; Yutaka Kurita; Hiroyuki Togashi; Takeshi Tomiyama
Ecosphere | 2018
Yu Saitoh; Takanori Nakano; Ki-Cheol Shin; Jun Matsubayashi; Yoshikazu Kato; Hiroshi Amakawa; Yutaka Osada; Chikage Yoshimizu; Noboru Okuda; Yosuke Amano; Hiroyuki Togashi; Yutaka Kurita; Ichiro Tayasu
水産研究・教育機構研究報告 = Bulletin of Japan Fisheries Research and Education Agency | 2017
Yuki Minegishi; Minoru Ikeda; Yutaka Kurita; Hiroyuki Togashi; Yukinori Nakane; Akihiro Kijima
Japan Geoscience Union | 2017
Chia-Ying Ko; Tomoya Iwata; Jun-Yi Lee; Aya R. Murakami; Jun-ichi Okano; Naoto Ishikawa; Yoichiro Sakai; Ichiro Tayasu; Masayuki Itoh; Uhram Song; Hiroyuki Togashi; Shinich Nakano; Nobuhito Ohte; Noboru Okuda
Japan Geoscience Union | 2017
Yu Saitoh; Jun Matsubayashi; Hiroyuki Togashi; Hiroshi Amakawa; Ki-Cheol Shin; Takanori Nakano; Ichiro Tayasu