Biology subjects

Urabe, J.

Publications and source records attributed to Urabe, J..

3 recordsLinked to original sources

bioRxiv2026

Response diversity inconsistently predicts functional robustness to simulated zooplankton extinctions

1Ecosystem functioning can be maintained in species-rich communities even under fairly severe perturbations. This is because communities with high richness include variation both in species functional roles (functional diversity) and in their responses to environmental changes (response diversity). Response diversity has been proposed as a key mechanism underpinning the stabilising role of biodiversity in variable environments. However, less understood is the role of response diversity in stabilising communities against perturbations and thus preserving ecosystem function. Here, we employ community data from 76 reservoirs across the broad latitudinal gradient of the Japanese archipelago to show that zooplankton assemblages with higher variability in responses to environmental variables can retain functional diversity as species are removed, but that the result depends on the variable examined. We combine empirically derived occurrence data for 47 zooplankton species with biotic and abiotic variables in a joint species distribution model to derive species-specific environmental responses, then measure response diversity to environmental axes including fish community structure and water temperature. We also measure functional trait diversity of zooplankton assemblages and simulate sequential species extinctions, capturing the extinction thresholds beyond which half the functional diversity is lost. Finally, we combine these data streams to show that response diversity can predict higher functional robustness in zooplankton assemblages, but not consistently. The role of response diversity in predicting functional robustness was contingent on the specific metric and environmental variable considered. We found that a balance of positive and negative species responses to water temperature was a significant predictor of robustness, though other metrics and environmental variables mainly yielded non-significant relationships. Overall, we show that response diversity can confer stability to perturbations such as species extinctions, and we demonstrate the utility of species distribution models for measuring response diversity, overcoming mechanistic data limitations and expanding the toolkit available for studying response diversity in natural systems.

ecology↗

bioRxiv2024

Environmental rather than spatial factors determine trait-based community structure: a case study with zooplankton

Ecological community structure, which has traditionally been described in terms of taxonomic units, is driven by a combination of dispersal and environmental filters. Traits have recently been recognized as alternative units for quantifying community parameters, but they may have important differences with taxonomic units. For example, as taxon-based community structures are determined by the identities of individual species, they may be more limited by species dispersal constraints, whereas trait-based community structures may be more regulated by environmental conditions because functional traits should have stronger linkages to habitat types rather than their specific locations. This suggests that the relative importance of dispersal and environmental filters may vary depending on the units employed to define community structure, yet how the contributions of these filters compare remains unclear. Zooplankton in lakes and reservoirs are an ideal system for examining the relative importance of these filters as they have moderate dispersal ability and inhabit communities in isolated habitats. In this study, we examined zooplankton assemblages in 87 artificial reservoirs throughout the Japanese archipelago to test the hypothesis that environmental filters play a more dominant role in determining trait-based community structures than taxon-based structures. To describe trait-based communities, we categorized zooplankton taxa into 12 functional groups using ecologically meaningful traits, including body size, feeding habits and mode, and population growth rate. We then examined the effects of both spatial configuration (reflecting dispersal filters) and environmental variables such as reservoir size and depth, trophic conditions, and fish assemblages for taxon- and trait-based community structures. Although variation in the taxon-based structure was explained equally well by spatial and environmental variables, variation in the trait-based structure explained by environmental variables was nearly twice that of spatial variables. These results support the idea that environmental filters play a more central role in determining trait-based community structures, and show that the relative importance of spatial and environmental filters changes with the way we define community structure. Open research statementAll the data used in this study was obtained from disclosed sources including the Database of Dams in Japan (http://mudam.nilim.go.jp/home) for the location and watershed areas; the Japan Dam Foundation (http://damnet.or.jp/) for the dam specification data; and the River Environmental Database (Red: http://www.nilim.go.jp/lab/fbg/ksnkankyo/index.html) for water chemistry, fish, and zooplankton. Data obtained from local reports of the national reservoir management office, Japan, can be provided by the authors upon request. All analyses were conducted in the R programming language and all functions used in the present study originate from existing packages.

ecology↗

bioRxiv2021

Visualization of ecological successions in lakes subdivided by volcanic eruption at Akan Caldera, Hokkaido, Japan

It is not feasible to continuously observe ecological succession in lakes because of the long time-scales generally involved. Thus, the process has been inductively deduced by comparing many lakes with different succession states, or indirectly simulated by tracking studies of smaller water bodies, experiments using microcosms or mesocosms, and reconstruction of lake history by sediment analysis. However, the reality of succession processes in large lakes with slow succession is not well understood, and new approaches are needed. Theoretically, in a group of large and small lakes of similar ages and with similar initial and watershed environments, the rate of nutrient accumulation in each lake depends on the ratio of watershed area to lake size, and the lakes are predicted to evolve to different trophic levels over time. Here, we tested this hypothesis on the 10 lakes of varying sizes in Akan Caldera, Japan, which were formed thousands of years ago by fragmentation due to volcanic eruptions within the caldera. Topographic and water quality studies showed that the ratio of accumulated watershed area to lake size (area and volume), expressed logarithmically, had a positive linear regression with the total phosphorus concentration, an indicator of trophic level. The trophic levels of the lakes were diverse, including oligotrophic, mesotrophic, and eutrophic types in the traditional "lake type" classification based on total phosphorus and chlorophyll-a concentrations. Furthermore, 21 species of aquatic macrophytes were observed by a diving survey, and the plant species composition was classified into five groups corresponding to the trophic status of the lakes, indicating a conventional "hydrarch succession". The diversity of water quality and aquatic vegetation in a group of lakes with similar origins paves the way for new comparative studies of lakes, including large lakes.

ecology↗