Stability Of Ecosystem Functions Research Articles

Ecosystem stability of temperate grasslands in response to variability of hydrological conditions

AbstractThe relationship between biodiversity and the stability of ecosystem functioning over time has been widely studied. The current global context has refloated this topic for biodiversity's role in buffering the effects of different disturbances. In general, the results of these studies show that ecosystem functioning is more stable over time in more diverse systems. However, these results are derived from empirical research on small‐scale studies, where species and disturbances conditions are manipulated. In this work, we used climate and floristic information data obtained from surveys over an extended period on Flooding Pampa grasslands (Argentina) with a remotely sensed indicator of the stability of net primary productivity at a regional scale over a broad temporal range to evaluate the relationship between species diversity and the stability of ecosystem functioning under different water conditions. We found a close correlation between Normalized Difference Vegetation Index responses of natural grasslands and climate variability in the study area. Besides, grasslands with higher species richness and diversity showed greater stability in ecosystem functioning at different water conditions. The results obtained could be relevant in natural resource management for the close relationship between diversity–stability in a local and regional productive context characterized by a simplified landscape of space and time.

Food web structure and energy flux dynamics, but not taxonomic richness, influence microbial ecosystem functions in a Sphagnum-dominated peatland

Soil microbial communities are vital for multiple ecosystem processes and services. In particular, soil microbial food webs are key determinants of soil biodiversity, functioning and stability. Unclear, however, is how structural features of food webs, such as species richness and turnover, biomass and energy transfer across trophic levels, influence the provisioning and stability of ecosystem functioning. Here, we explore the relationships between different facets of microbial food web structure (e.g. species richness, connectance, biomass and energy fluxes across trophic levels) and ecosystem functions (i.e. decomposition and microbial enzyme activity) across different habitats and depths in a peatland. We show that no aspect of taxonomic richness directly explained variation in ecosystem functions. Instead, we find that trophic interactions between basal species and primary consumers, and especially increasing connectance, biomass and energy flux transiting from decomposers and phototrophs to algivores, bacterivores and fungivores, enhance ecosystem functions in the peatland. These findings demonstrate that focusing on taxonomic diversity without explicit inclusion of food web structure and energy flows therein gives an incomplete and uninformative comprehension of relationships between biodiversity and ecosystem functioning, at least in peatlands. Our findings further suggest that the inclusion of soil microbial food webs in large-scale biogeochemical models is of fundamental importance to provide the necessary guidance for managing and mitigating the effects of environmental change.

Diversity, food web structure and the temporal stability of total plant and animal biomasses

Food‐web complexity and species richness are predicted to have tremendous effects on ecosystem functioning stability. Yet, our understanding of the relation between diversity and the stability of ecosystem functioning is still mainly limited to single trophic level communities and highly simplified food webs. To start filling this knowledge gap, we model allometric food webs and use structural equation modelling (SEM) to investigate the relations between diversity, food web structure and the temporal variability of total plant and animal biomasses and their components, i.e. synchrony and mean population variability. We find that stability responds differently depending on the metric used. When looking at total biomass variability, higher total biomasses and biomass stored at higher trophic level have the strongest stabilising effects, while species richness has lower impact than previously found. We confirm that synchrony among species is important for the stability of the total plant biomass. However, synchrony only weakly explains variations in the stability of total animal biomass among food webs. Species richness and food web variables often have opposite impacts on synchrony and mean population variability, leading to more ambiguous results for the plant community as synchrony matters only for plant stability. Our approach thus provides new insight on the complexity of the stability of ecosystem functioning in complex food webs.

Biotic Interactions as Mediators of Context-Dependent Biodiversity-Ecosystem Functioning Relationships

Biodiversity drives the maintenance and stability of ecosystem functioning as well as many of nature’s benefits to people, yet people cause substantial biodiversity change. Despite broad consensus about a positive relationship between biodiversity and ecosystem functioning (BEF), the underlying mechanisms and their context-dependencies are not well understood. This proposal, submitted to the European Research Council (ERC), aims at filling this knowledge gap by providing a novel conceptual framework for integrating biotic interactions across guilds of organisms, i.e. plants and mycorrhizal fungi, to explain the ecosystem consequences of biodiversity change. The overarching hypothesis is that EF increases when more tree species associate with functionally dissimilar mycorrhizal fungi. Taking a whole-ecosystem perspective, we propose to explore the role of tree-mycorrhiza interactions in driving BEF across environmental contexts and how this relates to nutrient dynamics. Given the significant role that mycorrhizae play in soil nutrient and water uptake, BEF relationships will be investigated under normal and drought conditions. Resulting ecosystem consequences will be explored by studying main energy channels and ecosystem multifunctionality using food web energy fluxes and by assessing carbon storage. Synthesising drivers of biotic interactions will allow us to understand context-dependent BEF relationships. This interdisciplinary and integrative project spans the whole gradient from local-scale process assessments to global relationships by building on unique experimental infrastructures like the MyDiv Experiment, iDiv Ecotron and the global network TreeDivNet, to link ecological mechanisms to reforestation initiatives. This innovative combination of basic scientific research with real-world interventions links trait-based community ecology, global change research and ecosystem ecology, pioneering a new generation of BEF research and represents a significant step towards implementing BEF theory for human needs.

Effects of Nutrient Levels and Rice Cultivation on Taxonomic and Functional Diversity of Bacterial Communities in Flooded Soils of the Hanon Maar Crater, Korea

Agricultural land use may deteriorate soil bacterial diversity and function in an agroecosystem. This study aimed to explore the impact of agricultural disturbance on the taxonomic and functional diversity of soil bacteria using a high-throughput sequencing method. We examined the bacterial community diversity in five types of flooded soils in the Hanon Maar Crater from two types of canals characterized by different nutrient levels and three field types with a different rice cultivation history. Proteobacteria (43.2%), Chloroflexi (19.8%), Acidobacteria (15.8%), Actinobacteria (5.1%), and Nitrospirae (5.0%) were the dominant phyla (>5%). The relative abundance of Actinobacteria was 7.1 times greater in the abandoned fields than in the polluted canal. Alpha diversity indices of taxonomic diversity showed strong negative correlations with C, N, and NH4+ levels. The 1.7-fold greater number of operational taxonomic units (OTUs) in abandoned fields than in paddy fields may be caused by factors other than nutrients. Functional analysis revealed that 11 putative functions, including cellulolysis and ligninolysis, were significantly affected by soil management. Functional diversity indices showed negative correlations with electrical conductivity (EC) and NH4+. Nitrogen input had a greater effect on bacterial taxonomic diversity than on functional diversity. Available P was positively correlated with the diversity indices. Taken together, these results suggest that keeping land fallow for more than 5 years and monitoring of C, N, and P levels are practical approaches for restoring taxonomic diversity but not functional diversity of soil bacteria. Our study demonstrated a decoupled response of taxonomic and functional diversity to rice cultivation, highlighting the necessity of further studies on the impact of decoupling on the stability of ecosystem functioning.

Functional diversity and groups of crustacean zooplankton in the southern Yellow Sea

Functional trait and functional diversity indices reflect the variations of community structure and indicate their responses to environmental stress. In this study, based on four functional traits, including body length, feeding type, trophic group, and reproductive mode, the functional diversity and functional groups of crustacean zooplankton from the southern Yellow Sea (SYS) were explored over four seasons of 2019. A total of 53 species were identified and categorized into six functional groups. Copepods with ambush-feeding and omnivore–carnivore diet (Group Ⅱ) were dominant in spring (55.6%), while omnivore–herbivore copepods (Group Ⅰ) were the most abundant group in the other three seasons (>54.7%). The comparable distributions of functional diversity indices in different seasons were most likely due to hydrological variations. The Changjiang River Diluted Water promoted the coexistence of multiple traits carried by different functional groups (high functional richness (FRic) and functional dispersion (FDis)), but the stability of ecosystem function in this water mass was vulnerable to the loss of individual species (low functional evenness (FEve)) in summer. In winter, as a result of the Yellow Sea Warm Current, warm-water taxa increased FRic and FEve, suggesting that the community could buffer environmental fluctuations more effectively. Moreover, distribution of FRic values indicates the possible range and influence intensity of the Yellow Sea Cold Water Mass.

Nutrient-induced shifts of dominant species reduce ecosystem stability via increases in species synchrony and population variability.

The mechanisms underlying nutrient-induced diversity-stability relationships have been examined extensively. However, the effects of nutrient-induced shifts of dominant species on ecosystem stability have rarely been evaluated. We compiled a dataset from a long-term nitrogen (N) and phosphorus (P) enrichment experiment conducted in an alpine grassland on the Tibetan Plateau to test the effects of nutrient-induced shifts of dominant species on stability. Our results show that N enrichment increased synchrony among the dominant species, which contributed to a significant increase in synchrony of the whole community. Meanwhile, N-induced shifts in dominant species composition significantly increased population variability. Increases in species synchrony and population variability resulted in a decline in ecosystem stability. Our study has important implications for progress in understanding the role of plant functional compensation in the stability of ecosystem functions, which is critical for better understanding the mechanisms driving both community assembly and ecosystem functions.

The relative importance of pollinator abundance and species richness for the temporal variance of pollination services.

The relationship between biodiversity and the stability of ecosystem function is a fundamental question in community ecology, and hundreds of experiments have shown a positive relationship between species richness and the stability of ecosystem function. However, these experiments have rarely accounted for common ecological patterns, most notably skewed species abundance distributions and non-random extinction risks, making it difficult to know whether experimental results can be scaled up to larger, less manipulated systems. In contrast with the prolific body of experimental research, few studies have examined how species richness affects the stability of ecosystem services at more realistic, landscape scales. The paucity of these studies is due in part to a lack of analytical methods that are suitable for the correlative structure of ecological data. A recently developed method, based on the Price equationfrom evolutionary biology, helps resolve this knowledge gap by partitioning the effect of biodiversity into three components: richness, composition, and abundance. Here, we build on previous work and present the first derivation of the Price equationsuitable for analyzing temporal variance of ecosystem services. We applied our new derivation to understand the temporal variance of crop pollination services in two study systems (watermelon and blueberry) in the mid-Atlantic United States. In both systems, but especially in the watermelon system, the stronger driver of temporal variance of ecosystem services was fluctuations in the abundance of common bee species, which were present at nearly all sites regardless of species richness. In contrast, temporal variance of ecosystem services was less affected by differences in species richness, because lost and gained species were rare. Thus, the findings from our more realistic landscapes differ qualitatively from the findings of biodiversity-stability experiments.

Extremophiles: photosynthetic systems in a high-altitude saline basin (Altiplano, Chile)

Studies of different hypersaline systems have revealed various types of limitation. We evaluated the phototrophic microbial assemblages over a whole seasonal cycle (wet vs dry) in the Salar de Alconcha, a high-altitude (4250 m altitude) saline basin. Phototrophic microbial communities were obtained from contrasting ecotypes, and examined for the effects of proximity and salinity variations. We also analyzed pigment profiles pointing to photosynthetic activity. While taxonomic diversity was limited to three algal groups (chlorophytes, diatoms, and cyanobacteria) ecological preferences were highly variable. Physical limitations when the photosynthetic system turn drier (maintaining viability and stability) appear to be the most successful adaptation (constrained assemblages) to the extreme condition in the Altiplano. This suggests that phototrophic microorganisms rarely achieve optimal growth, and could only do so when rain events reduce salinity (e.g. austral summer). However, environmental condition over the salt crust (total salt concentration: 119.74 g l−1) was an important driver to algal biomass. Overall, dominated by Dunaliella salina (≈18,000 cell ml−1) turning the water into a red–orange colored system (β-carotene); aplanospore cysts were observed only during the driest season (austral winter). Our results suggest specific restrictive environments (e.g. environmental dissimilarity in the physical landscape) for phototrophic microbial colonization in high-altitude saline systems quite dependent upon water availability (system on the edge). The present study is a contribution for a better understanding of both the ecology of extreme environments and polyextremophiles communities (phototrophs) that inhabit them. Active salars are considered to be useful analogs of ancient photosynthetic systems, currently very pressured by groundwater extraction. Thus, altering the volume of water through the basin would have negative consequences on the structure and dynamics of local communities, and also in the stability of ecosystem functions.

An improved model to predict the effects of changing biodiversity levels on ecosystem function

SummaryThe development of models of the relationship between biodiversity and ecosystem function (BEF) has advanced rapidly over the last 20 years, incorporating insights gained through extensive experimental work. We proposeGeneralisedDiversity‐Interactions models that include many of the features of existing models and have several novel features.GeneralisedDiversity‐Interactions models characterise the contribution of two species to ecosystem function as being proportional to the product of their relative abundances raised to the power of a coefficient θ.A value of θ < 1 corresponds to a stronger than expected contribution of species' pairs to ecosystem functioning, particularly at low relative abundance of species.Varying the value of θ has profound consequences for community‐level properties ofBEFrelationships, including: (i) saturation properties of theBEFrelationship; (ii) the stability of ecosystem function across communities; (iii) the likelihood of transgressive overyielding.For low values of θ, loss of species can have a much greater impact on ecosystem functioning than loss of community evenness.GeneralisedDiversity‐Interactions models serve to unify the modelling ofBEFrelationships as they include several other current models as special cases.GeneralisedDiversity‐Interactions models were applied to seven data sets and three functions: total biomass (five grassland experiments), community respiration (one bacterial experiment) and nitrate leaching (one earthworm experiment). They described all the nonrandom structure in the data in six experiments, and most of it in the seventh experiment and so fit as well or better than competingBEFmodels for these data. They were significantly better than Diversity‐Interactions models in five experiments.Synthesis. We show thatGeneralizedDiversity‐Interactions models quantitatively integrate several methods that separately address effects of species richness, evenness and composition on ecosystem function. They describe empirical data at least as well as alternative models and improve the ability to quantitatively test among several theoretical and practical hypotheses about the effects of biodiversity levels on ecosystem function. They improve our understanding of important aspects of the relationship between biodiversity (evenness and richness) and ecosystem function (BEF), which include saturation, effects of species loss, the stability of ecosystem function and the incidence of transgressive overyielding.

Inconsistent impacts of decomposer diversity on the stability of aboveground and belowground ecosystem functions

The intensive discussion on the importance of biodiversity for the stability of essential processes in ecosystems has prompted a multitude of studies since the middle of the last century. Nevertheless, research has been extremely biased by focusing on the producer level, while studies on the impacts of decomposer diversity on the stability of ecosystem functions are lacking. Here, we investigate the impacts of decomposer diversity on the stability (reliability) of three important aboveground and belowground ecosystem functions: primary productivity (shoot and root biomass), litter decomposition, and herbivore infestation. For this, we analyzed the results of three laboratory experiments manipulating decomposer diversity (1–3 species) in comparison to decomposer-free treatments in terms of variability of the measured variables. Decomposer diversity often significantly but inconsistently affected the stability of all aboveground and belowground ecosystem functions investigated in the present study. While primary productivity was mainly destabilized, litter decomposition and aphid infestation were essentially stabilized by increasing decomposer diversity. However, impacts of decomposer diversity varied between plant community and fertility treatments. There was no general effect of the presence of decomposers on stability and no trend toward weaker effects in fertilized communities and legume communities. This indicates that impacts of decomposers are based on more than effects on nutrient availability. Although inconsistent impacts complicate the estimation of consequences of belowground diversity loss, underpinning mechanisms of the observed patterns are discussed. Impacts of decomposer diversity on the stability of essential ecosystem functions differed between plant communities of varying composition and fertility, implicating that human-induced changes of biodiversity and land-use management might have unpredictable effects on the processes mankind relies on. This study therefore points to the necessity of also considering soil feedback mechanisms in order to gain a comprehensive and holistic understanding of the impacts of current global change phenomena on the stability of essential ecosystem functions.

Distribution and seasonal fluctuations in the aquatic biodiversity of the southern Altiplano

We compared the distribution and seasonal fluctuations in the aquatic biota in relation to chemical and physical water variables in the Altiplano watersheds of the Ascotán, Carcote and Huasco salars; Chungará and Cotacotani lakes; Isluga and Lauca Rivers and the Parinacota wetland. We sampled during the austral autumn–winter of 2006 and in the spring–summer of 2006–2007, using three sampling stations for each system. We used canonical correspondence analysis to establish relations between frequency of taxa and environmental variables. We demonstrate that the structure and composition of the aquatic biota in humid areas of the Altiplano is determined by physical and chemical variables of the water. The most relevant one is total nitrogen, which is also the limiting nutrient for phytoplankton production in tropical systems. Benthos and zooplankton showed significant associations with the set of environmental variables (Monte Carlo test, p<0.05); however, the association was not significant for phytoplankton. Lake Chungará showed the greatest variation in composition and abundance of zooplankton between autumn-winter and spring-summer, while in the Huasco salar the physical and chemical characteristics were related to the composition and abundance of the benthonic fauna. Thus, changes in the water volume of these systems would have repercussions in chemical and physical variables, altering the species assemblage and possibly the efficiency and stability of ecosystem functions.

The role of conservation in expanding biodiversity research

It has been suggested that current reductions in global biodiversity may impair the functioning of ecosystems. This biodiversity‐ecosystem function (BD‐EF) hypothesis represents a new avenue of ecological research originating from conservation concerns. However, the subsequent evolution of BD‐EF research has reflected academic concerns more than conservation priorities. I suggest three questions for BD‐EF research, which would benefit both ecological theory and conservation. (1) Is biodiversity the main driver of ecosystem function? Several experiments show that biodiversity loss is a minor link between habitat change and ecosystem function. (2) How will extinction patterns change BD‐EF relationships? Biased extinctions may have additional impacts on ecosystem function, which can be deduced by comparison with random‐loss models. (3) Will conserving regional biodiversity conserve local ecosystem function? The answer to this question may differ between saturated and unsaturated communities, and may depend on whether the magnitude or stability of ecosystem function is measured.

Diversity-dependent production can decrease the stability of ecosystem functioning.

There is concern that species loss may adversely affect ecosystem functioning and stability. But although there is evidence that biodiversity loss can lead to reductions in biomass production, there is no direct evidence that biodiversity loss affects ecosystem resistance (ability to withstand perturbation) or resilience (recovery from perturbation). Yet theory, laboratory experiments and indirect experimental evidence strongly suggest that diversity and stability are related. Here we report results from a field experiment with factorially crossed perturbation and diversity manipulations. We simulated drought perturbation on constructed grassland ecosystems containing 1, 2, 4, 8 or 32 plant species. Under unperturbed conditions, the species-poor systems achieved lower biomass production than the species-rich systems. However, the species-poor systems were more resistant to perturbation than the species-rich systems. The species-poor systems also showed a larger initial resilience following perturbation, although the original relationship between diversity and productivity was fully restored after 1year. Our results confirm that biodiversity increases biomass production, but they also point to the fact that such diversity--production associations may lead to an inverse relationship between biodiversity and the stability of ecosystem functioning.

Species richness and parasitism in a fragmented landscape: experiments and field studies with insects on Vicia sepium.

Effects of habitat fragmentation on species diversity and herbivore-parasitoid interactions were analyzed using the insect community of seed feeders and their parasitoids in the pods of the bush vetch (Vicia sepium L.). Field studies were carried out on 18 old meadows differing in area and isolation. The area of these meadows was found to be the major determinant of species diversity and population abundance of endophagous insects. Effects of isolation were further analyzed experimentally using 16 small plots with potted vetch plants isolated by 100-500 m from vetch populations on large old meadows. The results showed that colonization success greatly decreased with increasing isolation. In both cases, insect species were not equally affected. Parasitoids suffered more from habitat loss and isolation than their phytophagous hosts. Minimum area requirements, calculated from logistic regressions, were higher for parasitoids than for herbivores. In addition, percent parasitism of the herbivores significantly decreased with area loss and increasing isolation of Vicia sepium plots, supporting the trophic-level hypothesis of island biogeography. Species with high rates of absence on meadows and isolated plant plots were not only characterized by their high trophic level, but also by low abundance and high spatial population variability. Thus conservation of large and less isolated habitat remnants enhances species diversity and parasitism of potential pest insects, i.e., the stability of ecosystem functions.