Aridity-dependent shifts in biodiversity-stability relationships but not in underlying mechanisms.

Climate change will affect the way biodiversity influences the stability of plant communities. Although biodiversity, associated species asynchrony, and species stability could enhance community stability, the understanding of potential nonlinear shifts in the biodiversity-stability relationship across a wide range of aridity (measured as the aridity index, the precipitation/potential evapotranspiration ratio) gradients and the underlying mechanisms remain limited. Using an 8-year dataset from 687 sites in Mongolia, which included 5496 records of vegetation and productivity, we found that the temporal stability of plant communities decreased more rapidly in more arid areas than in less arid areas. The result suggests that future aridification across terrestrial ecosystems may adversely affect community stability. Additionally, we identified nonlinear shifts in the effects of species richness and species synchrony on temporal community stability along the aridity gradient. Species synchrony was a primary driver of community stability, which was consistently negatively affected by species richness while being positively affected by the synchrony between C3 and C4 species across the aridity gradient. These results highlight the crucial role of C4 species in stabilizing communities through differential responses to interannual climate variations between C3 and C4 species. Notably, species richness and the synchrony between C3 and C4 species independently regulated species synchrony, ultimately affecting community stability. We propose that maintaining plant communities with a high diversity of C3 and C4 species will be key to enhancing community stability across Mongolian grasslands. Moreover, species synchrony, species stability, species richness and the synchrony between C3 and C4 species across the aridity gradient consistently mediated the impacts of aridity on community stability. Hence, strategies aimed at promoting the maintenance of biological diversity and composition will help ecosystems adapt to climate change or mitigate its adverse effects on ecosystem stability.

Dryland sensitivity to climate change and variability using nonlinear dynamics.

Primary productivity response to climatic drivers varies temporally, indicating state-dependent interactions between climate and productivity. Previous studies primarily employed equation-based approaches to clarify this relationship, ignoring the state-dependent nature of ecological dynamics. Here, using 40 y of climate and productivity data from 48 grassland sites across Mongolia, we applied an equation-free, nonlinear time-series analysis to reveal sensitivity patterns of productivity to climate change and variability and clarify underlying mechanisms. We showed that productivity responded positively to annual precipitation in mesic regions but negatively in arid regions, with the opposite pattern observed for annual mean temperature. Furthermore, productivity responded negatively to decreasing annual aridity that integrated precipitation and temperature across Mongolia. Productivity responded negatively to interannual variability in precipitation and aridity in mesic regions but positively in arid regions. Overall, interannual temperature variability enhanced productivity. These response patterns are largely unrecognized; however, two mechanisms are inferable. First, time-delayed climate effects modify annual productivity responses to annual climate conditions. Notably, our results suggest that the sensitivity of annual productivity to increasing annual precipitation and decreasing annual aridity can even be negative when the negative time-delayed effects of annual precipitation and aridity on productivity prevail across time. Second, the proportion of plant species resistant to water and temperature stresses at a site determines the sensitivity of productivity to climate variability. Thus, we highlight the importance of nonlinear, state-dependent sensitivity of productivity to climate change and variability, accurately forecasting potential biosphere feedback to the climate system.

Differential responses and mechanisms of productivity following experimental species loss scenarios.

Experiments that simulate nonrandom species loss from natural communities can offer a fundamentally different understanding of the impacts of species loss on ecosystem function and their underlying mechanisms compared to seeding experiments where species are randomly assembled from a local species pool. We examined the mechanisms underlying changes in primary productivity following experimental species loss scenarios in Mongolian grassland. The range of species loss scenarios was based on natural patterns of species abundance that reflect the species' contributions to ecosystem processes. We found a clear reduction in productivity due to species loss only when species were lost randomly. Grassland productivity was relatively robust following nonrandom species loss scenarios. Even in the context of density compensation, the decrease in dominant trait values for leaf height would explain the reduction in productivity with random species loss. In contrast, the maintenance of dominant trait values of key productivity traits such as leaf dry matter content and leaf height might contribute to the maintenance of productivity in response to nonrandom species loss. Our experiment demonstrated that the responses and mechanisms of primary productivity to species loss differ according to the scenarios of species loss in natural grassland communities. The effects of diversity on productivity might be weak in mature natural systems when species loss is nonrandom. Understanding the consequences of realistic species loss on ecosystem functioning based on field-based removal experiments will give insights into real conservation strategies in the face of global biodiversity change.

A global meta-analysis of the relative extent of intraspecific trait variation in plant communities.

Recent studies have shown that accounting for intraspecific trait variation (ITV) may better address major questions in community ecology. However, a general picture of the relative extent of ITV compared to interspecific trait variation in plant communities is still missing. Here, we conducted a meta-analysis of the relative extent of ITV within and among plant communities worldwide, using a data set encompassing 629 communities (plots) and 36 functional traits. Overall, ITV accounted for 25% of the total trait variation within communities and 32% of the total trait variation among communities on average. The relative extent of ITV tended to be greater for whole-plant (e.g. plant height) vs. organ-level traits and for leaf chemical (e.g. leaf N and P concentration) vs. leaf morphological (e.g. leaf area and thickness) traits. The relative amount of ITV decreased with increasing species richness and spatial extent, but did not vary with plant growth form or climate. These results highlight global patterns in the relative importance of ITV in plant communities, providing practical guidelines for when researchers should include ITV in trait-based community and ecosystem studies.

Relationship between pastoralists' evaluation of rangeland state and vegetation threshold changes in Mongolian rangelands.

Applying the threshold concept to rangeland management is an important challenge in semi-arid and arid regions. Threshold recognition and prediction is necessary to enable local pastoralists to prevent the occurrence of an undesirable state that would result from unsustainable grazing pressure, but this requires a better understanding of the pastoralists' perception of vegetation threshold changes. We estimated plant species cover in survey plots along grazing gradients in steppe and desert-steppe areas of Mongolia. We also conducted interviews with local pastoralists and asked them to evaluate whether the plots were suitable for grazing. Floristic composition changed nonlinearly along the grazing gradient in both the desert-steppe and steppe areas. Pastoralists observed the floristic composition changes along the grazing gradients, but their evaluations of grazing suitability did not always decrease along the grazing gradients, both of which included areas in a post-threshold state. These results indicated that local pastoralists and scientists may have different perceptions of vegetation states, even though both of groups used plant species and coverage as indicators in their evaluations. Therefore, in future studies of rangeland management, researchers and pastoralists should exchange their knowledge and perceptions to successfully apply the threshold concept to rangeland management.

Response diversity determines the resilience of ecosystems to environmental change.

A growing body of evidence highlights the importance of biodiversity for ecosystem stability and the maintenance of optimal ecosystem functionality. Conservation measures are thus essential to safeguard the ecosystem services that biodiversity provides and human society needs. Current anthropogenic threats may lead to detrimental (and perhaps irreversible) ecosystem degradation, providing strong motivation to evaluate the response of ecological communities to various anthropogenic pressures. In particular, ecosystem functions that sustain key ecosystem services should be identified and prioritized for conservation action. Traditional diversity measures (e.g. 'species richness') may not adequately capture the aspects of biodiversity most relevant to ecosystem stability and functionality, but several new concepts may be more appropriate. These include 'response diversity', describing the variation of responses to environmental change among species of a particular community. Response diversity may also be a key determinant of ecosystem resilience in the face of anthropogenic pressures and environmental uncertainty. However, current understanding of response diversity is poor, and we see an urgent need to disentangle the conceptual strands that pervade studies of the relationship between biodiversity and ecosystem functioning. Our review clarifies the links between response diversity and the maintenance of ecosystem functionality by focusing on the insurance hypothesis of biodiversity and the concept of functional redundancy. We provide a conceptual model to describe how loss of response diversity may cause ecosystem degradation through decreased ecosystem resilience. We explicitly explain how response diversity contributes to functional compensation and to spatio-temporal complementarity among species, leading to long-term maintenance of ecosystem multifunctionality. Recent quantitative studies suggest that traditional diversity measures may often be uncoupled from measures (such as response diversity) that may be more effective proxies for ecosystem stability and resilience. Certain conclusions and recommendations of earlier studies using these traditional measures as indicators of ecosystem resilience thus may be suspect. We believe that functional ecology perspectives incorporating the effects and responses of diversity are essential for development of management strategies to safeguard (and restore) optimal ecosystem functionality (especially multifunctionality). Our review highlights these issues and we envision our work generating debate around the relationship between biodiversity and ecosystem functionality, and leading to improved conservation priorities and biodiversity management practices that maximize ecosystem resilience in the face of uncertain environmental change.

Robustness of trait distribution metrics for community assembly studies under the uncertainties of assembly processes.

Numerous studies have revealed the existence of nonrandom trait distribution patterns as a sign of environmental filtering and/or biotic interactions in a community assembly process. A number of metrics with various algorithms have been used to detect these patterns without any clear guidelines. Although some studies have compared their statistical powers, the differences in performance among the metrics under the conditions close to actual studies are not clear. Therefore, the performances of five metrics of convergence and 16 metrics of divergence under alternative conditions were comparatively analyzed using a suite of simulated communities. We focused particularly on the robustness of the performances to conditions that are often uncertain and uncontrollable in actual studies; e.g., atypical trait distribution patterns stemming from the operation of multiple assembly mechanisms, a scaling of trait-function relationships, and a sufficiency of analyzed traits. Most tested metrics, for either convergence or divergence, had sufficient statistical power to distinguish nonrandom trait distribution patterns without uncertainty. However, the performances of the metrics were considerably influenced by both atypical trait distribution patterns and other uncertainties. Influences from these uncertainties varied among the metrics of different algorithms and their performances were often complementary. Therefore, under the uncertainties of an assembly process, the selection of appropriate metrics and the combined use of complementary metrics are critically important to reliably distinguish nonrandom patterns in a trait distribution. We provide a tentative list of recommended metrics for future studies.

Isolation of a phomoxanthone A derivative, a new metabolite of tetrahydroxanthone, from a Phomopsis sp. isolated from the mangrove, Rhizhopora mucronata.

From the rice culture of Phomopsis sp. IM 41-1, isolated from the mangrove plant, Rhizhopora mucronata, two dimeric tetrahydroxanthones, phomoxanthone A (1) and 12-O-deacetyl-phomoxanthone A (2) were obtained. Their structures were determined by spectroscopic and spectrometric methods. Both compounds exhibited antimicrobial activities.

[A case of advanced gastric cancer with recurrence-free long survival showing disappearance of distant lymph node metastases by S-1/docetaxel therapy followed by curative resection].

A screening CT of a 78-year-old man suffering from a laryngeal foreign body revealed multiple lymph nodes swelling at the left subclavicular, mediastinal, perigastric, and paraaortic space. He was diagnosed as advanced gastric cancer. After five courses of S-1/docetaxel therapy, the primary tumor became flat and lymph nodes became undetectable. After seven courses, he received operation(total gastrectomy and D2 lymph nodes dissection)because of tumor bleeding and severe adverse effects. The pathological chemotherapeutic effect was Grade 1b for the primary tumor and Grade 3 for lymph nodes. He received S-1 maintenance therapy for three years afterward, and is now still in good condition without recurrence 53 months after the first administration. S-1/docetaxel therapy was thought to be a useful optional regimen for highly advanced gastric cancer.

Dominant species, rather than diversity, regulates temporal stability of plant communities.

A growing body of empirical evidence suggests that the temporal stability of communities typically increases with diversity. The counterview to this is that dominant species, rather than diversity itself, might regulate temporal stability. However, empirical studies that have explicitly examined the relative importance of diversity and dominant species in maintaining community stability have yielded few clear-cut patterns. Here, using a long-term data set, we examined the relative importance of changes in diversity components and dominance hierarchy following the removal of a dominant C4 grass, Bouteloua gracilis, in stabilizing plant communities. We also examined the relationships between the variables of diversity and dominance hierarchy and the statistical components of temporal stability. We found a significant negative relationship between temporal stability and species richness, number of rare species, and relative abundance of rare species, whereas a significant positive relationship existed between temporal stability and relative abundance of the dominant species. Variances and covariances summed over all species significantly increased with increasing species richness, whereas they significantly decreased with increasing relative abundance of dominant species. We showed that temporal stability in a shortgrass steppe plant community was controlled by dominant species rather than by diversity itself. The generality of diversity-stability relationships might be restricted by the dynamics of dominant species, especially when they have characteristics that contribute to stability in highly stochastic systems. A clear implication is that dominance hierarchies and their changes might be among the most important ecological components to consider in managing communities to maintain ecosystem functioning.

Two-phase functional redundancy in plant communities along a grazing gradient in Mongolian rangelands.

The concept of functional redundancy is at the core of theory relating changes in ecosystem functioning to species loss. However, few empirical studies have investigated the strength and form of the relationship between species and functional diversity (i.e., the presence of functional redundancy in ecological communities) in this context. In particular, we know little about how local extinctions in real communities might impact functional diversity. Here, we examined the relationship between species and functional diversity in plant communities along a grazing gradient across Mongolian rangeland ecosystems. We applied a recently described measure of functional diversity that incorporates species' dissimilarities defined from plant functional traits and tested several hypothesized forms of the relationship between species and functional diversity using linear and nonlinear modeling techniques. We found a significant sigmoid logistic relationship between species richness and functional diversity in relatively benign environmental conditions. This indicates high functional redundancy at low levels of species richness followed by a rapid increase at intermediate levels, until functional diversity reaches an asymptote at high levels (i.e., two-phase functional redundancy). In contrast, we generally observed a positive linear relationship between these parameters in relatively harsh environmental conditions, indicating low functional redundancy. Observed functional redundancy probably resulted from two factors, intrinsic redundancy in species' functional traits and extrinsic redundancy caused by nonrandom compositional change that is nonrandom with respect to functional traits. Lack of either intrinsic or extrinsic redundancy may result in low functional redundancy. Two-phase functional redundancy suggests that functional traits are abruptly lost from a community below a certain level of species richness, and a community then shifts into a contrasting state that has a few limited functional groups characterized by disturbance-resistant traits, as a consequence of disturbances such as livestock grazing. This study represents a major step forward in predicting the consequences of livestock grazing on the functioning of Mongolian rangeland ecosystems.

Management applicability of the intermediate disturbance hypothesis across Mongolian rangeland ecosystems.

The current growing body of evidence for diversity-disturbance relationships suggests that the peaked pattern predicted by the intermediate disturbance hypothesis (IDH) may not be the rule. Even if ecologists could quantify the diversity-disturbance relationship consistent with the IDH, the applicability of the IDH to land management has rarely been addressed. We examined two hypotheses related to the generality and management applicability of the IDH to Mongolian rangeland ecosystems: that the diversity-disturbance relationship varies as a function of landscape condition and that some intermediate scales of grazing can play an important role in terms of sustainable rangeland management through a grazing gradient approach. We quantified the landscape condition of each ecological site using an ordination technique and determined two types of landscape conditions: relatively benign and harsh environmental conditions. At the ecological sites characterized by relatively benign environmental conditions, diversity-disturbance relationships were generally consistent with the IDH, and maximum diversity was observed at some intermediate distance from the source of the grazing gradient. In contrast, the IDH was not supported at most (but not all) sites characterized by relatively harsh environmental conditions. The intermediate levels of grazing were generally located below the ecological threshold representing the points or zones at which disturbance should be limited to prevent drastic changes in ecological conditions, suggesting that there is little "conundrum" with regard to intermediate disturbance in the studied systems in terms of land management. We suggest that the landscape condition is one of the primary factors that cause inconsistencies in diversity-disturbance relationships. The ecological threshold can extend its utility in rangeland management because it also has the compatibility with the maintenance of species diversity. This study thus suggests that some intermediate scales of grazing and ecological thresholds are mutually supportive tools for sustainable management of Mongolian rangelands.