Response trait diversity and species asynchrony underlie the diversity-stability relationship in Romanian bird communities.

Multi-year nitrogen accumulation weakens the stabilizing effect of species asynchrony on drought resistance in a Tibetan alpine meadow

Aims Long-term heavy grazing reduces plant diversity and ecosystem function by intensifying nitrogen (N) and water limitation. In contrast, the absence of biomass removal can cause species loss by elevating light competition and weakening community stability, which is exacerbated by N and water enrichment. Hence, how to maintain species diversity and community stability is still a huge challenge for sustainable management of worldwide grasslands. Methods We conducted a 4-year manipulated experiment in six long-term grazing blocks to explore combination of resource additions and biomass removal (increased water, N and light availability) on species richness and community stability in semiarid grasslands of Inner Mongolia, China. Important Findings In all blocks treated with the combination of resource additions and biomass removal, primary productivity increased and species richness and community stability were maintained over 4 years of experiment. At both species and plant functional group (PFG) levels, the aboveground biomass of treated plants remained temporally stable in treatments with the combination of N and/or water addition and biomass removal. The maintenance of species richness was primarily caused by the biomass removal, which could increase the amount of light exposure for grasses under resource enrichment. Both species asynchrony and stability of PFGs contributed to the high temporal stability observed in these communities. Our results indicate that management practices of combined resource enrichment with biomass removal, such as grazing or mowing, could not only enhance primary productivity but also maintain plant species diversity, species asynchrony and community stability. Furthermore, as overgrazing-induced degradation and resource enrichment-induced biodiversity loss continue to be major problems worldwide, our findings have important implications for adaptive management in semiarid grasslands and beyond.

Atmospheric nitrogen (N) deposition includes inorganic N (IN) and organic N (ON). IN enrichment trends to reduce species richness greater than ON, likely lowering ecosystem stability, as species richness and ecosystem stability are usually positively related. However, previous field experiments evaluating N deposition effects on ecosystem stability used either IN or ON additions, likely biasing results. We assessed the effects of IN:ON ratios (0:10, 3:7, 5:5, 7:3, and 10:0) at 10 g N m-2 yr-1 on the temporal stability of plant community productivity in a temperate meadow grassland using 6-year (2017-2022) data from a long-term N addition experiment established in 2014. Species richness, species asynchrony, population stability, and dominant species stability were investigated to explore mechanisms underlying community stability changes. We found that IN:ON ratio showed no significant effect on community stability, although all N addition significantly reduced community stability (averaged 26.7% reduction). However, IN decreased species richness more than ON (54.1% reduction in 10:0 versus 31.8% reduction in 0:10). IN:ON ratio showed no significant effect on species asynchrony, population stability or dominant species stability. Species asynchrony and dominant species stability were both positively related to community stability, while population stability showed no significant association. It implies that species asynchrony and dominant species stability maintained community stability across IN:ON ratios. Overall, our findings suggest that, despite IN reducing species richness greater than ON, it may be reasonable to assess N deposition effects on ecosystem stability using either IN or ON addition.

Global nitrogen enrichment has been identified as a major environmental problem that poses a threat to ecosystem functioning. However, there is no consensus on the impact of enriched nitrogen on ecosystem stability or the underlying mechanisms driving that impact. We conducted a 5-year multi-level nitrogen addition experiment in Inner Mongolia grassland. We determined plant diversity, species asynchrony, population stability, functional group stability and dominant stability, focusing on investigating the impact of nitrogen enrichment on stability and the driving mechanisms. Community stability responded negatively to nitrogen enrichment. Added nitrogen decreased plant diversity, and had a direct negative effect on species asynchrony, graminoid functional group stability, population stability, and dominant stability; all of these showed tight associations with reduced community stability. In addition, community stability showed no significant response at nitrogen addition rate ≤ 1.01 g N m−2 year−1, and saturated at ≥9.17 g N m−2 year−1. Nitrogen-induced reduction in diversity, together with alterations in species asynchrony, graminoid functional group stability, population stability and dominant stability, worked concurrently leading to deceased stability in the Inner Mongolia grassland. In addition, an effect threshold and saturation rate for added nitrogen was observed.

Winter warming alleviates the severely negative effects of nitrogen addition on ecosystem stability in a Tibetan alpine grassland

There is now ample evidence that biodiversity stabilizes aggregated ecosystem functions, such as primary production, in changing environments. In primary producer systems, this stabilizing effect is found to be driven by higher functional resistance (i.e., reduced changes in functions by environmental changes) rather than through higher functional resilience (i.e., rapid recovery following environmental changes) in more diverse systems. The stability of aggregated ecosystem functions directly depends on changes in species composition and by consequence their functional contributions to ecosystem functions. Still, it remains only theoretically explored how biodiversity can stabilize ecosystem functions by affecting compositional stability. Here, we demonstrate how biodiversity effects on compositional stability drive biodiversity effects on functional stability in diatom communities. In a microcosm experiment, we exposed 39 communities of five different levels of species richness (1, 2, 4, 6, and 8 species) to three concentrations of a chemical stressor (0, 25, and 250μg/L atrazine) for four weeks, after which all communities were transferred to atrazine-free medium for three more weeks. Biodiversity simultaneously increased, increasing functional and compositional resistance, but decreased functional and compositional resilience. These results confirm the theoretically proposed link between biodiversity effects on functional and compositional stability in primary producer systems, and provide a mechanistic underpinning for observed biodiversity-stability relationships. Finally, we discuss how higher compositional stability can be expected to become increasingly important in stabilizing ecosystem functions under field conditions when multiple environmental stressors fluctuate simultaneously.

Understanding the relationship between biodiversity and ecosystem stability is a central goal of ecologists. Recent studies have concluded that biodiversity increases community temporal stability by increasing the asynchrony between the dynamics of different species. Theoretically, this enhancement can occur through either increased between-species compensatory dynamics, a fundamentally biological mechanism; or through an averaging effect, primarily a statistical mechanism. Yet it remains unclear which mechanism is dominant in explaining the diversity-stability relationship. We address this issue by mathematically decomposing asynchrony into components separately quantifying the compensatory and statistical-averaging effects. We applied the new decomposition approach to plant survey and experimental data from North American grasslands. We show that statistical averaging, rather than compensatory dynamics, was the principal mediator of biodiversity effects on community stability. Our simple decomposition approach helps integrate concepts of stability, asynchrony, statistical averaging, and compensatory dynamics, and suggests that statistical averaging, rather than compensatory dynamics, is the primary means by which biodiversity confers ecological stability.

Adaptation of communities to environmental fluctuations can emerge from different facets of biodiversity, which may impact ecosystem functioning differently. Previous work in the field of biodiversity–ecosystem functioning (BEF) examined how ecosystem functions can be influenced by two sources of adaptive potential: sorting – i.e. changes in community composition due to fitness differences – can occur when multiple species or groups are present (richness), and trait adaptability – i.e. trait adjustments within species or functional groups – can emerge from genetic or phenotypic diversity. However, their effect is typically studied separately, and often in the context of only one trophic level. Therefore, we used a trait‐based, multispecies predator–prey model to investigate how sorting and trait adaptability, at one or two trophic levels, separately or jointly shape ecosystem functions and properties, such as total biomass, production, biomass‐weighted mean trait, relative top–down control and synchrony. We found that the adaptive potential emerging from any facet of diversity induced changes in trophic interactions, in turn affecting biomass distributions within and across trophic levels, dynamical behaviour, and synchrony of biomass dynamics within a trophic level. Particularly, sorting and trait adaptability could contribute to a similar degree and at a similar time to temporal changes in ecosystem functions, but their respective contribution depended on the speed of trait adaptation, the trait range between similar functional groups and trophic interactions. We thus suggest to consider multiple facets of diversity and their corresponding sources of adaptive potential to deepen our mechanistic understanding of BEF relationships, especially in the context of rapid biodiversity change.

EDITORIAL article Front. Microbiol., 26 September 2014Sec. Terrestrial Microbiology Volume 5 - 2014 | https://doi.org/10.3389/fmicb.2014.00497

Human-induced changes in external nutrient loading affect the phytoplankton community and abundance directly by changing the amount of nutrients available, but also indirectly through changes in the zooplankton (that is, grazer) community structure, mediated in part by changes in the fish community structure and biomass. Such shifts affect the species dynamics and community succession of lake phytoplankton communities, and they may ultimately influence community stability. However, the relative importance of different biotic mechanisms influencing the community stability of phytoplankton along nutrient and associated zooplankton grazing pressure gradients remains unclear. Here, we evaluated the importance of four potential stabilizing biotic metrics—taxon richness, synchrony, community dominance and biomass of phytoplankton to the seasonal stability over two decades of re-oligotrophication in 20 Danish lakes. We found no clear temporal patterns in seasonal stability across lakes but considerable variations in the individual lakes. Total phosphorus (TP) affected the seasonal stability of the phytoplankton communities either directly or indirectly through changes in community dominance. Total nitrogen (TN) influenced the seasonal stability indirectly via changes in phytoplankton taxon richness, synchrony, and community dominance. Grazer richness (that is, zooplankton taxa richness) impacted the seasonal stability indirectly through changes in phytoplankton taxon richness and synchrony. Grazing pressure, using the biomass ratio of zooplankton:phytoplankton as a proxy, had an indirect effect on seasonal stability via changes in synchrony and community dominance. Compensatory dynamics (as indicated by the synchrony of phytoplankton) exerted dominant control of phytoplankton seasonal stability at high TN and high grazer richness and pressure, while the portfolio effect (as indicated by taxon richness) contributed to phytoplankton seasonal stability at low TN and high grazer richness. However, a strongly negative selection effect (as indicated by community dominance of phytoplankton) was observed at high nutrient levels and low grazer richness. Grazer richness and grazing pressure had stronger stabilizing effects on the seasonal succession of the phytoplankton communities than did TP and TN. Our results highlight how various biotic mechanisms (for example, compensatory dynamics and portfolio effect) can change in their importance in maintaining the seasonal stability of phytoplankton communities subjected to nutrient and grazer control.

SummaryTo quantify the major environmental drivers of stream bacterial population dynamics, we modelled temporal differences in stream bacterial communities to quantify community shifts, including those relating to cyclical seasonal variation and more sporadic bloom events. We applied Illumina MiSeq 16S rRNA bacterial gene sequencing of 892 stream biofilm samples, collected monthly for 36‐months from six streams. The streams were located a maximum of 118 km apart and drained three different catchment types (forest, urban and rural land uses). We identified repeatable seasonal patterns among bacterial taxa, allowing their separation into three ecological groupings, those following linear, bloom/trough and repeated, seasonal trends. Various physicochemical parameters (light, water and air temperature, pH, dissolved oxygen, nutrients) were linked to temporal community changes. Our models indicate that bloom events and seasonal episodes modify biofilm bacterial populations, suggesting that distinct microbial taxa thrive during these events including non‐cyanobacterial community members. These models could aid in determining how temporal environmental changes affect community assembly and guide the selection of appropriate statistical models to capture future community responses to environmental change.

Tropical forest loss can drive the extinction of forest‐dependent species. Yet, non‐forest species can proliferate in deforested landscapes, thus enabling community‐level attributes (e.g. total abundance and richness) to be maintained in the remaining forest patches. Such compensatory dynamics have been, however, poorly investigated regarding the phylogenetic dimension of species diversity. Here, we assessed whether compensatory dynamics can stabilize the phylogenetic richness, divergence and structure of bird communities in response to forest loss in two regions in the Brazilian Atlantic forest, each under with different levels of land use intensification. We surveyed birds in 40 forest sites, and assessed the response of five phylogenetic metrics to forest cover measured in local (600‐m radius) landscapes. We separately assessed the entire community, forest‐dependent and non‐forest‐dependent species and used information‐theoretic criteria to assess the effect of forest cover on each response variable. In particular, we evaluated the plausibility of four models: a null model (no effect of forest cover), a linear model, a power law model (nonlinear effect) and an analysis of covariance model (to assess whether the effect of forest cover differed between regions). Forest cover varied from 7% to 98%, and was positively related to the phylogenetic richness of forest‐dependent species, but negatively related to the phylogenetic richness and divergence of non‐forest birds, particularly in the more disturbed region. As consequence, the phylogenetic richness and divergence of the entire community were weakly related to forest cover. Forest birds were less phylogenetically clustered in sites surrounded by lower forest cover, but the phylogenetic structure of non‐forest birds was independent of forest cover. Synthesis and applications. The phylogenetic impoverishment of forest‐dependent birds is offset by the phylogenetic enrichment and divergence of non‐forest‐dependent birds in severely tropical deforested landscapes. These compensatory dynamics suggest that both bird groups are important for safeguarding bird evolutionary diversity in human‐modified landscapes. Although deforested landscapes are reservoirs of bird phylogenetic diversity, suggesting that ecosystem functioning may be maintained in these sites, preventing further deforestation is urgently needed to preserve forest birds and their key ecological roles in the ecosystem.

The relationship between biodiversity and ecosystem functions (BEFs) has attracted great interest. Studies on BEF have so far focused on the average trend of ecosystem function as species diversity increases. A tantalizing but rarely addressed question is why large variations in ecosystem functions are often observed across systems with similar species diversity, likely obscuring observed BEFs. Here we use a multi-trophic food web model in combination with empirical data to examine the relationships between species richness and the variation in ecosystem functions (VEFs) including biomass, metabolism, decomposition, and primary and secondary production. We then probe the mechanisms underlying these relationships, focusing on the role of trophic interactions. While our results reinforce the previously documented positive BEF relationships, we found that ecosystem functions exhibit significant variation within each level of species richness and the magnitude of this variation displays a hump-shaped relationship with species richness. Our analyses demonstrate that VEFs is reduced when consumer diversity increases through elevated nonlinearity in trophic interactions, and/or when the diversity of basal species such as producers and decomposers decreases. This explanation is supported by a 34-year empirical food web time series from the Gulf of Riga ecosystem. Our work suggests that biodiversity loss may not only result in ecosystem function decline, but also reduce the predictability of functions by generating greater function variability among ecosystems. It thus helps to reconcile the debate on the generality of positive BEF relationships and to disentangle the drivers of ecosystem stability. The role of trophic interactions and the variation in their strengths mediated by functional responses in shaping ecosystem function variation warrants further investigations and better incorporation into biodiversity-ecosystem functioning research.

Ecosystem coupling: A unifying framework to understand the functioning and recovery of ecosystems

Biotic indicators have been widely used to monitor wetland health. However, few studies have explicitly evaluated if plant diversity could serve as a useful community-level indicator of wetland stability, especially when wetlands are confronted with anthropogenic perturbations. Based on three-year record of wetland plant species abundance in Napahai plateau wetland, Shangri-la under the influence of varying anthropogenic perturbation types, our study tests the impact of such perturbations on plant richness and the relationship between ecosystem temporal stability and plant richness, and further assesses the effectiveness of using plant diversity indicator to probe ecosystem temporal stability of Napahai plateau wetland and the potential mechanisms. The results showed that anthropogenic perturbations could have contributed significantly to realistic variation in plant diversity, and further demonstrated that ecosystem temporal stability was positively related to realistic variation in plant diversity. In particular, communities with high levels of diversity might have better capacity to dampen perturbation impacts than communities with low levels of diversity, and statistical averaging could have played an important role in causing greater stability in more diverse communities. Also, asynchrony might have a stabilizing effect on community stability, and diversity could have stabilized communities through both species asynchrony and population stability propagation. Therefore, our results suggest that plant diversity could be used as a useful indicator of the stability conditions of plateau wetland ecosystems confronted with anthropogenic perturbations, and the preservation of plant communities at sufficient abundance and diversity is necessary for maintaining healthy plateau wetlands and for sustaining their essential ecosystem functions and services.