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Papers 【 display / non-display 】

• Local-manifold-distance-based regression: an estimation method for quantifying dynamic biological interactions with empirical time series

  Kazutaka Kawatsu

  Royal Society Open Science   11 ( 7 )   2024.7

  DOI CiNii Research

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  Language：The in addition, foreign language   Publishing type：Research paper (scientific journal)   Publisher：The Royal Society   Single Work  

  <jats:p>Quantifying species interactions based on empirical observations is crucial for ecological studies. Advancements in nonlinear time-series analyses, particularly S-maps, are promising for high-dimensional and non-equilibrium ecosystems. S-maps sequentially perform a local linear model fitting to the time evolution of neighbouring points on the reconstructed attractor manifold, and the coefficients can approximate the Jacobian elements corresponding to interaction effects. However, despite that the advantages in nonlinear forecasting with noise-contaminated data, these methodologies have a limitation in the Jacobian estimation accuracy owing to non-equidistantly stretched local manifolds in the state space. Herein, we therefore introduced a local manifold distance (LMD) concept, a non-equidistant measure based on the multi-faceted state dependency. By integrating LMD with advanced computation techniques, we presented a robust and efficient analytical method, LMD-based regression (LMDr). To validate its advantages in prediction and Jacobian estimation, we analysed synthetic time series of model ecosystems with different noise levels and applied it to an experimental protozoan predator–prey system with established biological information. The robustness to noise was the highest for LMDr, which also showed a better correspondence to expected predator–prey interactions in the protozoan system. Thus, LMDr can be applied to study complex ecological networks under dynamic conditions.</jats:p>

• Monitoring and prediction of the spongy moth (Lymantria dispar) outbreaks in Mountain’s landscape using a combination of Sentinel-2 images and nonlinear time series model

  Natsumi Mori, Kazutaka Kawatsu, Suzuki Noriyuki, Aleksey Kosilov, Vyacheslav Martemyanov, Megumi Ya … Show more authors

  Forest Ecology and Management   563   121975   2024.7

  DOI CiNii Research

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  Language：The in addition, foreign language   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV   Joint Work  

• Unraveling emergent network indeterminacy in complex ecosystems: A random matrix approach

  Kazutaka Kawatsu

  Proceedings of the National Academy of Sciences   121 ( 27 )   2024.6

  DOI CiNii Research

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  Language：The in addition, foreign language   Publishing type：Research paper (scientific journal)   Publisher：Proceedings of the National Academy of Sciences   Single Work  

  <jats:p>Indeterminacy of ecological networks—the unpredictability of ecosystem responses to persistent perturbations—is an emergent property of indirect effects a species has on another through interaction chains. Thus, numerous indirect pathways in large, complex ecological communities could make forecasting the long-term outcomes of environmental changes challenging. However, a comprehensive understanding of ecological structures causing indeterminacy has not yet been reached. Here, using random matrix theory (RMT), we provide mathematical criteria determining whether network indeterminacy emerges across various ecological communities. Our analytical and simulation results show that indeterminacy intricately depends on the characteristics of species interaction. Specifically, contrary to conventional wisdom, network indeterminacy is unlikely to emerge in large competitive and mutualistic communities, while it is a common feature in top–down regulated food webs. Furthermore, we found that predictable and unpredictable perturbations can coexist in the same community and that indeterminate responses to environmental changes arise more frequently in networks where predator–prey relationships predominate than competitive and mutualistic ones. These findings highlight the importance of elucidating direct species relationships and analyzing them with an RMT perspective on two fronts: It aids in 1) determining whether the network’s responses to environmental changes are ultimately indeterminate and 2) identifying the types of perturbations causing less predictable outcomes in a complex ecosystem. In addition, our framework should apply to the inverse problem of network identification, i.e., determining whether observed responses to sustained perturbations can reconstruct their proximate causalities, potentially impacting other fields such as microbial and medical sciences.</jats:p>

• Dynamics‐based characterization and classification of biodiversity indicators

  Yuri Otomo, Reiji Masuda, Yutaka Osada, Kazutaka Kawatsu, Michio Kondoh

  Ecology and Evolution   13 ( 7 )   2023.7

  DOI PubMed CiNii Research

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  Language：The in addition, foreign language   Publishing type：Research paper (scientific journal)   Publisher：Wiley   Joint Work  

  <jats:title>Abstract</jats:title><jats:p>Various biodiversity indicators, such as species richness, total abundance, and species diversity indices, have been developed to capture the state of ecological communities over space and time. As biodiversity is a multifaceted concept, it is important to understand the dimension of biodiversity reflected by each indicator for successful conservation and management. Here we utilized the responsiveness of biodiversity indicators' dynamics to environmental changes (i.e., environmental responsiveness) as a signature of the dimension of biodiversity. We present a method for characterizing and classifying biodiversity indicators according to environmental responsiveness and apply the methodology to monitoring data for a marine fish community under intermittent anthropogenic warm water discharge. Our analysis showed that 10 biodiversity indicators can be classified into three super‐groups based on the dimension of biodiversity that is reflected. Group I (species richness and community mean of latitudinal center of distribution (cCOD)) showed the greatest robustness to temperature changes; Group II (species diversity and total abundance) showed an abrupt change in the middle of the monitoring period, presumably due to a change in temperature; Group III (species evenness) exhibited the highest sensitivity to environmental changes, including temperature. These results had several ecological implications. First, the responsiveness of species diversity and species evenness to temperature changes might be related to changes in the species abundance distribution. Second, the similar environmental responsiveness of species richness and cCOD implies that fish migration from lower latitudes is a major driver of species compositional changes. The study methodology may be useful in selecting appropriate indicators for efficient biodiversity monitoring.</jats:p>

• Time series analysis showing how different environmental conditions affect the interspecific interactions of <i>Callosobruchus maculatus</i> and <i>Callosobruchus chinensis</i>

  Takanori Kawase, Daisuke Kyogoku, Kazutaka Kawatsu, Noboru Katayama, Takeshi Miki, Michio Kondoh

  Population Ecology   66 ( 1 )   6 - 21   2023.6

  DOI CiNii Research

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  Language：The in addition, foreign language   Publishing type：Research paper (scientific journal)   Publisher：Wiley   Joint Work  

  <jats:title>Abstract</jats:title><jats:p>Environmental changes alter the strength of interspecific interactions. However, because it is difficult to quantify interaction strength, empirical evidence remains limited on the relationships among environmental change, interaction strength, and consequences on population dynamics. Here, we evaluated how the interactions of two species of <jats:italic>Callosobruchus</jats:italic> seed beetles changed with increasing the cage size of the experiments and then affected the coexistence period as a property of population dynamics. Specifically, competition experiments were conducted on <jats:italic>Callosobruchus maculatus</jats:italic> (<jats:italic>C. maculatus</jats:italic>) and <jats:italic>Callosobruchus chinensis</jats:italic> (<jats:italic>C. chinensis</jats:italic>) using cages of different sizes, which altered the density of adults. We focused on two modes of interspecific interactions between these two species: larval resource competition and adult reproductive interference. Convergent cross mapping (CCM) was implemented to the experimental time series of the two species to assess how environmental change altered their interaction strength and the coexistence period (as a proxy of population dynamics). In most replications, <jats:italic>C. maculatus</jats:italic> persisted, whereas <jats:italic>C. chinensis</jats:italic> became extinct. The coexistence periods were longer with increasing cage size. However, there was no statistically significant relationship between cage size and interaction strength. Nevertheless, the stronger (or weaker) interaction strength of the competitively inferior (superior) species on competitively superior (inferior) was associated with longer coexistence periods. Overall, this study demonstrated that interaction strength affected population dynamics; however, changing interaction strength by altering environmental conditions did not necessarily mean that increasing habitat size reduces competition strength.</jats:p>

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Grant-in-Aid for Scientific Research 【 display / non-display 】

Grant-in-Aid for Scientific Research 【 display / non-display 】

• 生態学と制御理論の融合による可制御キーストーンの提案とその創発メカニズムの解明

  Grant number：26K09469  2026.4 - 2029.3

  Grant-in-Aid for Scientific Research(C)

  Investigator(s)：川津一隆

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  Authorship：Principal investigator  Grant type：Competitive

• 下水道における上流から下流への生態系変遷と薬剤耐性細菌定着の実態解明

  Grant number：24K03094  2024.4 - 2027.3

  Grant-in-Aid for Scientific Research(B)

  Investigator(s)：松井一彰

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  Authorship：Coinvestigator(s)  Grant type：Competitive

• 土壌微生物機能発揮の鍵となる群集・メタゲノム構造の特定

  Grant number：21H05315  2021.4 - 2026.3

  Investigator(s)：近藤倫生

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  Authorship：Coinvestigator(s)  Grant type：Competitive

• ワンヘルスアプローチの具現化に向けた下水管における薬剤耐性菌の動態解明

  Grant number：20H04348  2020.4 - 2023.4

  Grant-in-Aid for Scientific Research(B)

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  Authorship：Coinvestigator(s)  Grant type：Competitive

• 沿岸生態系における構造転換：高度観測と非線形力学系理論に基づく実証アプローチ

  Grant number：19H05641  2019.4 - 2024.3

  Grant-in-Aid for Scientific Research(S)

  Investigator(s)：近藤倫生

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  Authorship：Coinvestigator(s)  Grant type：Competitive

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Charge of on-campus class subject 【 display / non-display 】

Charge of on-campus class subject 【 display / non-display 】

• 2026   Advanced workshop in nature and human society Ⅱ

  Graduate School of Environment and Information Sciences

• 2026   Advanced workshop in nature and human society I

  Graduate School of Environment and Information Sciences

• 2026   Workshop in nature and human society Ⅱ

  Graduate School of Environment and Information Sciences

• 2026   Workshop in nature and human society I

  Graduate School of Environment and Information Sciences

• 2026   生態レジリエンスのデータ科学Ⅱ

  Graduate School of Environment and Information Sciences

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