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The potential environmental impacts of engineered cerium oxide nanoparticles (CeO2 NPs) on aquatic organisms have remained largely unknown. Therefore, the laboratory study featured herein was performed to determine the fate of CeO2 NPs in an aquatic environment and their toxicity towards 14 different ciliated protist species at a specified population level. An investigation of 48 h aggregation kinetics in the Dryl's solution showed the CeO2 NPs to be relatively stable. The pH values in three test medium were too far away from PZC, which explained the stability of CeO2 NPs. CeO2 NPs generally elicited more toxicity with increasing NP concentration, following certain dose-response relationships. Nano-CeO2 resulted in greater toxicity in a particle state than when added as bulk material. LC50 values showed a negative correlation with the surface-to-volume ratio for these protists, suggesting that surface adsorption of CeO2 NPs might contribute to the observed toxicity. Additionally, acute toxic responses of 14 ciliated protist species to CeO2 NPs were not significantly phylogenetically conserved. The results of these observations provide a better insight into the potential risks of CeO2 NPs in an aquatic environment.

Degrees of aging on hot-mix asphalt mixture depend on the processes utilized on producing, transporting and paving operations. Rotated thin film oven (RTFOT) and/or thin film oven test (TFOT) tests were commonly used to determine the performance of asphalt aging in the laboratory. In this paper, the samples from the field (through actual mixing, transporting, and placing) were tested and compared with the samples from the lab (through RTFOT simulation). Through the analyses of the test results, it is concluded that the degrees of aging are much higher for asphalt samples from the field than those samples from lab aging simulations (i.e. RTFOT test).

Ample evidence suggests that ecological communities can exhibit historical contingencies. However, few studies have explored whether differences in assembly history can generate alternative local community states in metacommunities in which local communities are linked by dispersal. In a protist microcosm experiment, we examined the influence of species colonization history on metacommunity assembly under homogeneous environmental conditions, by manipulating both the sequence of species colonization into local communities and the rate of dispersal among local communities. Whereas the role of dispersal in structuring local communities decreased over time and became non-significant towards the end of the experiment, species colonization history significantly influenced local communities throughout the experiment. Local communities, regardless of the rate of dispersal among them, exhibited two alternative states characterized by the dominance of different species. The alternative community states, however, emerged in the absence of priority effects that were often associated with alternative community states found in other assembly studies. Rather, they were driven by variation in species interaction strength among local communities with different assembly histories. These results suggest that dispersal among local communities may not necessarily reduce the role of species colonization history in shaping metacommunity assembly, and that differences in species colonization history need to be explicitly considered as an important factor in causing heterogeneous community states in metacommunities.

Despite considerable research on the environmental impacts of nanomaterials, we know little about how they influence interactions between species. Here, we investigated the acute (12 d) and chronic (64 d) toxicities of cerium oxide nanoparticles (CeO2 NPs) and bulk particles (0–200 mg/L) to three ciliated protist species (Loxocephalus sp., Paramecium aurelia, and Tetrahymena pyriformis) in single-, bi-, and multispecies microcosms. The results show that CeO2 NPs strongly affected the interactions between ciliated protozoan species. When exposed to the highest CeO2 NPs (200 mg/L), the intrinsic growth rates of Loxocephalus and Paramecium were significantly decreased by 18.87% and 88.27%, respectively, while their carrying capacities declined by more than 90%. However, CeO2 NP exposure made it difficult to predict outcomes of interspecific competition between species. At higher NP exposure (100 and 200 mg/L), competition led to the extinction of both species in the Loxocephalus and Paramecium microcosms that survived in the absence of competitors or CeO2 NPs. Further, the presence of potential competitors improved the survival of Loxocephalus to hundreds of individuals per milliliter in microcosms with Tetrahymena where Loxocephalus would otherwise not be able to tolerate high levels of NP exposure. This result could be attributed to weakened NP adsorption on the cell surface due to competitor-caused reduction of NP surface charge (from −18.52 to −25.17 mV) and intensified NP aggregation via phagocytosis of NPs by ciliate cells. Our results emphasize the need to explicitly consider species interactions for a more comprehensive understanding of the ecological consequences of NP exposure.

Aims The relationship between biodiversity and ecological stability is a long-standing issue in ecology. Current diversity–stability studies, which have largely focused on species diversity, often report an increase in the stability of aggregate community properties with increasing species diversity. Few studies have examined the linkage between phylogenetic diversity, another important dimension of biodiversity, and stability. By taking species evolutionary history into account, phylogenetic diversity may better capture the diver sity of traits and niches of species in a community than species diversity and better relate to temporal stability. In this study, we investigated whether phylogenetic diversity could affect temporal stability of community biomass independent of species diversity. Methods We performed an experiment in laboratory microcosms with a pool of 12 bacterivorous ciliated protist species. To eliminate the possibility of species diversity effects confounding with phylogenetic diversity effects, we assembled communities that had the same number of species but varied in the level of phylogenetic diversity. Weekly disturbance, in the form of short-term temperature shock, was imposed on each microcosm and species abundances were monitored over time. We examined the relationship between temporal stability of community biomass and phylogenetic diversity and evaluated the role of several stabilizing mechanisms for explaining the influence of phylogenetic diversity on temporal stability. Important Findings Our results showed that increasing phylogenetic diversity promoted temporal stability of community biomass. Both total community biomass and summed variances showed a U-shaped relationship with phylogenetic diversity, driven by the presence of large, competitively superior species that attained large biomass and high temporal variation in their biomass in both low and high phylogenetic diversity communities. Communities without these species showed patterns consistent with the reduced strength of competition and increasingly asynchronous species responses to environmental changes under higher phylogenetic diversity, two mechanisms that can drive positive diversity–stability relationships. These results support the utility of species phylogenetic knowledge for predicting ecosystem functions and their stability.

The relationship between environmental productivity and species richness often varies among empirical studies, and despite much research, simple explanations for this phenomenon remain elusive. We investigated how phytoplankton and zooplankton coevolution shapes productivity-richness relationships in both phytoplankton and zooplankton, using a simple nutrient-phytoplankton-zooplankton model that incorporates size-dependent metabolic rates summarized from empirical studies. The model allowed comparisons of evolved species richness across productivity levels and at different evolutionary times. Our results show that disruptive selection leads to evolutionary branching of phytoplankton and zooplankton. Both the time required for evolutionary branching and the number of evolved species in phytoplankton and zooplankton tend to increase with productivity, producing a transient unimodal or positive productivity-richness relationship but followed by a positive productivity-richness relationship for both groups over long enough evolutionary time. Our findings suggest that coevolution between phytoplankton and zooplankton can drive the two common forms (unimodal and positive) of productivity-richness relationships in nature.

Whether plant communities in a given region converge towards a particular stable state during succession has long been debated, but rarely tested at a sufficiently long time scale. By analysing a 50-year continuous study of post-agricultural secondary succession in New Jersey, USA, we show that the extent of community convergence varies with the spatial scale and species abundance classes. At the larger field scale, abundance-based dissimilarities among communities decreased over time, indicating convergence of dominant species, whereas incidence-based dissimilarities showed little temporal tend, indicating no sign of convergence. In contrast, plots within each field diverged in both species composition and abundance. Abundance-based successional rates decreased over time, whereas rare species and herbaceous plants showed little change in temporal turnover rates. Initial abandonment conditions only influenced community structure early in succession. Overall, our findings provide strong evidence for scale and abundance dependence of stochastic and deterministic processes over old-field succession.

To better understand the potential impacts of engineered metal oxide nanoparticles (NPs) in the ecosystem, we investigated the acute toxicity of seven different types of engineered metal oxide NPs against Paramecium multimicronucleatum, a ciliated protozoan, using the 48 h LC(50) (lethal concentration, 50%) test. Our results showed that the 48 h LC(50) values of these NPs to Paramecium ranged from 0.81 (Fe(2)O(3) NPs) to 9269 mg/L (Al(2)O(3) NPs); their toxicity to Paramecium increased as follows: Al(2)O(3)TiO(2)CeO(2)ZnOSiO(2)CuOFe(2)O(3) NPs. On the basis of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, interfacial interactions between NPs and cell membrane were evaluated, and the magnitude of interaction energy barrier correlated well with the 48 h LC(50) data of NPs to Paramecium; this implies that metal oxide NPs with strong association with the cell surface might induce more severe cytotoxicity in unicellular organisms.

One of the oldest ecological hypotheses, proposed by Darwin, suggests that the struggle for existence is stronger between more closely related species. Despite its long history, the validity of this phylogenetic limiting similarity hypothesis has rarely been examined. Here we provided a formal experimental test of the hypothesis using pairs of bacterivorous protist species in a multigenerational experiment. Consistent with the hypothesis, both the frequency and tempo of competitive exclusion, and the reduction in the abundance of inferior competitors, increased with increasing phylogenetic relatedness of the competing species. These results were linked to protist mouth size, a trait potentially related to resource use, exhibiting a significant phylogenetic signal. The likelihood of coexistence, however, was better predicted by phylogenetic relatedness than trait similarity of the competing species. Our results support phylogenetic relatedness as a useful predictor of the outcomes of competitive interactions in ecological communities.

Ecologists have long recognized the roles of competition and disturbance in shaping ecological communities, and the combinatorial effects of these two factors have been the subject of substantial ecological research. Nevertheless, it is still unclear whether competition remains as an important structuring force in habitats strongly influenced by disturbance. The conventional belief remains that the importance of competition decreases with increasing disturbance, but limited theory suggests otherwise. Using protist communities established in laboratory microcosms, we demonstrate that disturbance does not diminish the importance of competition. Interspecific competition significantly increased rates of species extinction over a broad disturbance gradient, and increasing disturbance intensities increased, rather than decreased, the tempo of competitive exclusion. This community-level pattern is linked to the species-level pattern that interspecific competition led to most frequent extinctions of each species at the highest level of disturbance that the species can tolerate. Consequently, despite a strong tradeoff between competitive ability and disturbance tolerance across the competing species, species diversity generally declined with disturbance. The consistent structuring role of competition throughout the disturbance gradient underscores the need to understand competitive interactions and their consequences even in highly disturbed habitats.

One of the oldest ideas in invasion biology, known as Darwin's naturalization hypothesis, suggests that introduced species are more successful in communities in which their close relatives are absent. We conducted the first experimental test of this hypothesis in laboratory bacterial communities varying in phylogenetic relatedness between resident and invading species with and without a protist bacterivore. As predicted, invasion success increased with phylogenetic distance between the invading and the resident bacterial species in both the presence and the absence of protistan bacterivory. The frequency of successful invader establishment was best explained by average phylogenetic distance between the invader and all resident species, possibly indicating limitation by the availability of the unexploited niche (i.e., organic substances in the medium capable of supporting the invader growth); invader abundance was best explained by phylogenetic distance between the invader and its nearest resident relative, possibly indicating limitation by the availability of the unexploited optimal niche (i.e., the subset of organic substances supporting the best invader growth). These results were largely driven by one resident bacterium (a subspecies of Serratia marcescens) posting the strongest resistance to the alien bacterium (another subspecies of S. marcescens). Overall, our findings support phylogenetic relatedness as a useful predictor of species invasion success.

Much of our knowledge on biodiversity and ecosystem functioning comes from studies examining the effects of biodiversity on biomass production within a trophic group. A large number of these studies have found that increasing biodiversity tends to increase biomass production, leading many ecologists to believe that there exists a general positive relationship between biodiversity and ecosystem functioning. Here we argue that such a positive relationship may not be general, particularly for ecosystem functions other than biomass. Our argument centers on the potential importance of the negative selection effect, which operates where competitively dominant species do not contribute significantly to the function of interest. We suggest that negative selection effects may be potentially common for non-biomass functions, for which species competitive ability may often be a poor indictor of its functional impact. We conclude that diverse (positive, negative, and neutral) BEF relationships are possible for non-biomass functions and that for a particular function, the exact form of the BEF relationship may depend on how species functional impacts relate to their competitive abilities in the community.

A central goal of invasion biology is to elucidate mechanisms regulating community invasibility. Darwin's naturalization hypothesis, one of the oldest hypotheses in invasion biology, emphasizes the importance of phylogenetic relatedness (PR) between resident and invader species for predicting invasibility. Alternatively, a recent extension of the diversity-invasibility hypothesis predicts that phylogenetic diversity (PD) of resident communities influences invasibility. Neither of these hypotheses has undergone rigorous experimental testing, and the relative contributions of PR and PD to community invasibility are unknown, in part because their effects tend to be confounded with each other. Here we consider both perspectives together by independently manipulating PR and PD in laboratory bacterial assemblages. We found that, although invader abundance decreased significantly as PR increased, it was unaffected by PD. Likewise, we found that resident-invader functional similarity, not functional diversity of resident communities, was a significant predictor of invader abundance. Nevertheless, invader abundance was better predicted by PR than by functional similarity. These results highlight the importance of considering species evolutionary relationships, especially the PR between resident and invader species, for the prediction, prevention, and management of biological invasions.

Comparing elevational gradients across a wide spectrum of climatic zones offers an ideal system for testing hypotheses explaining the altitudinal gradients of biodiversity. We document elevational patterns of lizard and snake species richness, and explore how land area and climatic factors may affect species distributions of lizards and snakes. Our synthesis found 42 lizard species and 94 snake species known from the Hengduan Mountains. The lizards are distributed between 500 and 3500 m, and the snakes are distributed between 500 and 4320 m. The relationship between species richness and elevation for lizards and snakes is unimodal. Land area explains a significant amount of the variation in lizard and snake species richness. The cluster analysis reveals pronounced distinct assemblages for lizards and snakes to better reflect the vertical profiles of climate in the mountains. Climatic variables are strongly associated with lizard and snake richness along the elevational gradient. The data strongly implicate water availability as a key constraint on lizard species richness, and annual potential evapotranspiration is the best predictor of snake species richness along the elevational gradient in the Hengduan Mountains.

We studied frog biodiversity along an elevational gradient in the Hengduan Mountains, China. Endemic and non-endemic elevational diversity patterns were examined individually. Competing hypotheses were also tested for these patterns. Species richness of total frogs, endemics and non-endemics peaked at mid-elevations. The peak in endemic species richness was at higher elevations than the maxima of total species richness. Endemic species richness followed the mid-domain model predictions, and showed a nonlinear relationship with temperature. Water and energy were the most important variables in explaining elevational patterns of non-endemic species richness. A suite of interacting climatic and geometric factors best explained total species richness patterns along the elevational gradient. We suggest that the mid-domain effect was an important factor to explain elevational richness patterns, especially in regions with high endemism.

Darwin's naturalization hypothesis (DNH), which predicts that alien species more distantly related to native communities are more likely to naturalize, has received much recent attention. The mixed findings from empirical studies that have tested DNH, however, seem to defy generalizations. Using meta-analysis to synthesize results of existing studies, we show that the predictive power of DNH depends on both the invasion stage and the spatial scale of the studies. Alien species more closely related to natives tended to be less successful at the local scale, supporting DNH; invasion success, however, was unaffected by alien–native relatedness at the regional scale. On the other hand, alien species with stronger impacts on native communities tended to be more closely related to natives at the local scale, but less closely related to natives at the regional scale. These patterns are generally consistent across different ecosystems, taxa and investigation methods. Our results revealed the different effects of invader–native relatedness on invader success and impact, suggesting the operation of different mechanisms across invasion stages and spatial scales.

Darwin's naturalization hypothesis (DNH), which predicts that alien species more distantly related to native communities are more likely to naturalize, has received much recent attention. The mixed findings from empirical studies that have tested DNH, however, seem to defy generalizations. Using meta-analysis to synthesize results of existing studies, we show that the predictive power of DNH depends on both the invasion stage and the spatial scale of the studies. Alien species more closely related to natives tended to be less successful at the local scale, supporting DNH; invasion success, however, was unaffected by alien–native relatedness at the regional scale. On the other hand, alien species with stronger impacts on native communities tended to be more closely related to natives at the local scale, but less closely related to natives at the regional scale. These patterns are generally consistent across different ecosystems, taxa and investigation methods. Our results revealed the different effects of invader–native relatedness on invader success and impact, suggesting the operation of different mechanisms across invasion stages and spatial scales.

Species immigration history can structure ecological communities through priority effects, which are often mediated by competition. As competition tends to be stronger between species with more similar niches, we hypothesize that species phylogenetic relatedness, under niche conservatism, may be a reasonable surrogate of niche similarity between species, and thus influence the strength of priority effects. We tested this hypothesis using a laboratory microcosm experiment in which we established bacterial species pools with different levels of phylogenetic relatedness and manipulated the immigration history of species from each pool into microcosms. Our results showed that strong priority effects, and hence multiple community states, only emerged for the species pool with the greatest phylogenetic relatedness. Community assembly also resulted in a significant positive relationship between bacterial phylogenetic diversity and ecosystem functions. Interestingly, these results emerged despite a lack of phylogenetic conservatism for most of the bacterial functional traits considered. Our results highlight the utility of phylogenetic information for understanding the structure and functioning of ecological communities, even when phylogenetically conserved functional traits are not identified or measured.

One of the oldest ecological hypotheses, proposed by Darwin, suggests that the struggle for existence is stronger between more closely related species. Despite its long history, the validity of this phylogenetic limiting similarity hypothesis has rarely been examined. Here we provided a formal experimental test of the hypothesis using pairs of bacterivorous protist species in a multigenerational experiment. Consistent with the hypothesis, both the frequency and tempo of competitive exclusion, and the reduction in the abundance of inferior competitors, increased with increasing phylogenetic relatedness of the competing species. These results were linked to protist mouth size, a trait potentially related to resource use, exhibiting a significant phylogenetic signal. The likelihood of coexistence, however, was better predicted by phylogenetic relatedness than trait similarity of the competing species. Our results support phylogenetic relatedness as a useful predictor of the outcomes of competitive interactions in ecological communities.

The question of how species diversity affects ecological stability has long interested ecologists and yet remains largely unresolved. Historically, attempts to answer this question have been hampered by the presence of multiple potentially confounding stability concepts, confusion over responses at different levels of ecological organization, discrepancy between theoretical predictions, and, particularly, the paucity of empirical studies. Here we used meta-analyses to synthesize results of empirical studies published primarily in the past 2 decades on the relationship between species diversity and temporal stability. We show that the overall effect of increasing diversity was positive for community-level temporal stability but neutral for population-level temporal stability. There were, however, striking differences in the diversity-stability relationship between single- and multitrophic systems, with diversity stabilizing both population and community dynamics in multitrophic but not single-trophic communities. These patterns were broadly equivalent across experimental and observational studies as well as across terrestrial and aquatic studies. We discuss possible mechanisms for population stability to increase with diversity in multitrophic systems and for diversity to influence community-level stability in general. Overall, our results indicate that diversity can affect temporal stability, but the effects may critically depend on trophic complexity.