Diversity-biomass Relationships Research Articles

Reverse diversity–biomass patterns in grasslands are constrained by climates and stoichiometry along an elevational gradient

Diversity and biomass play an important role in grassland ecosystem functions. However, diversity and biomass are variable because of their high sensitivity to environmental change in natural ecosystems. How plant diversity, biomass, and driving factors (climates, soils, and plants) in grasslands vary with environmental change remains unclear. We conducted intensive fieldwork (≈1000 km transect) on plant diversity, biomass, and associated drivers (i.e., climates, soils, and plants) to identify the patterns of diversity and biomass along an elevational gradient (50–4000 m) in grasslands of southwest China. Grassland biomass decreased significantly, but grassland diversity increased with increasing elevation. Consequently, a significant reverse pattern between biomass and diversity was detected along an elevational gradient. We also observed that the reverse pattern was primarily driven by the shifts in climates (i.e., temperature and precipitation), leaf stoichiometric traits (i.e., leaf N:P ratio), and soil properties (i.e., soil N content) along the elevational gradient. Our results contradicted previous studies on the positive diversity-biomass relationships, suggesting that previous studies might weaken the effects of climatic factors and plant stoichiometry under environmental change. These findings revealed that the reverse pattern between diversity and biomass in grasslands was shaped by the combined effects (climates, plants, soils) in grasslands, thus providing new insights into the debates and predictions on the diversity and biomass in grasslands under climate change.

Nitrogen Addition and Heterotroph Exclusion Affected Plant Species Diversity-Biomass Relationship by Affecting Plant Functional Traits.

(1) Background: Heterotrophs can affect plant biomass and alter species diversity-productivity relationships. However, these studies were conducted in systems with a low nitrogen (N) availability, and it is unclear how heterotroph removal affects the relationship between plant species diversity and productivity in different N habitats. (2) Methods: Three typical understory herbaceous plants were selected to assemble the plant species diversity (three plant species richness levels (1, 2, and 3) and seven plant species compositions), and the control, insecticide, fungicide, and all removal treatments were performed at each plant species diversity level in systems with or without N addition treatments. (3) Results: In systems without N addition, the insecticide treatment increased the plant aboveground biomass, total biomass, and leaf area, while the fungicide treatment reduced the plant belowground biomass, root length, and root tip number; the presence of Bidens pilosa increased the plant aboveground biomass. Similarly, the presence of Bletilla striata increased the plant belowground biomass and root diameter under each heterotroph removal treatment. In systems with N addition, all removal treatments reduced the plant belowground biomass and increased the plant leaf area; the presence of B. pilosa significantly increased the plant aboveground biomass, total biomass, and root length under each heterotroph removal treatment. The presence of B. striata significantly increased the plant belowground biomass and leaf area under insecticide and fungicide treatments. (4) Conclusions: Heterotroph removal alters the plant species diversity-biomass relationship by affecting the plant functional traits in systems with different N availabilities. The impact of biodiversity at different trophic levels on ecosystem functioning should be considered under the background of global change.

Functional diversity buffers biomass production across variable rainfall conditions through different processes above‐ versus below‐ground

Abstract Understanding precipitation controls on functional diversity is important in predicting how change in rainfall patterns will alter plant productivity in the future. Trait‐based approaches can provide predictive knowledge about how certain species will behave and interact with the community. However, how functional diversity relates to above‐ and below‐ground biomass production in variable rainfall conditions remains unclear. Here, we tested the role of mass ratio and niche complementarity hypotheses in shaping above‐ and below‐ground biomass–functional diversity relationships in seasonal drought. We implemented a fully crossed experiment that manipulated drought timing (fall dry, spring dry, consistent dry and ambient rainfall) and community composition (grass‐dominated, forb‐dominated and mixed grass–forb) in a California annual grassland. Plant communities with mixed functional groups showed higher above‐ and below‐ground biomass than either the grass‐ or forb‐dominant communities. We found divergent functional diversity–biomass relationships for above‐ and below‐ground biomass. Above‐ground biomass decreased with community weighted means (CWMs) of specific leaf area (SLA) and height, supporting the mass ratio hypothesis, which posits that dominant species with specific traits drive biomass production of the community. Below‐ground biomass showed no evidence of either mass ratio hypothesis or niche complementarity. While biomass was largely unaffected by the timing of drought in one season, we found community‐wide functional trait shifts in response to rainfall treatments. Above‐ground traits shifted to higher SLA in consistent dry compared to ambient. Below‐ground traits shifted to longer, finer and denser roots in fall and consistent dry, and shorter and coarser roots in spring dry. Functional diversity buffered biomass production by enabling shifts in above‐ and below‐ground functional traits across variable rainfall conditions. Read the free Plain Language Summary for this article on the Journal blog.

Scale‐dependent diversity–biomass relationships can be driven by tree mycorrhizal association and soil fertility

AbstractDiversity–biomass relationships (DBRs) often vary with spatial scale in terrestrial ecosystems, but the mechanisms driving these scale‐dependent patterns remain unclear, especially for highly heterogeneous forest ecosystems. This study explores how mutualistic associations between trees and different mycorrhizal fungi, i.e., arbuscular mycorrhizal (AM) vs. ectomycorrhizal (EM) association, modulate scale‐dependent DBRs. We hypothesized that in soil‐heterogeneous forests with a mixture of AM and EM tree species, (i) AM and EM tree species would respond in contrasting ways (i.e., positively vs. negatively, respectively) to increasing soil fertility, (ii) AM tree dominance would contribute to higher tree diversity and EM tree dominance to greater standing biomass, and that as a result (iii) mycorrhizal associations would exert an overall negative effect on DBRs across spatial scales. To empirically test these hypotheses, we collected detailed tree distribution and soil information (e.g., nitrogen, phosphorus, organic matter, pH) from seven temperate and subtropical AM–EM mixed forest megaplots (16–50 ha). Using a spatial codispersion null model and structural equation modeling, we identified the relationships among AM or EM tree dominance, soil fertility, tree species diversity, and biomass and, thus, DBRs across 0.01‐ to 1‐ha scales. We found the first evidence overall supporting the three aforementioned hypotheses in these AM–EM mixed forests: (i) In most forests, with increasing soil fertility, tree communities changed from EM‐dominated to AM‐dominated; (ii) increasing AM tree dominance had an overall positive effect on tree diversity and a negative effect on biomass, even after controlling for soil fertility and number of trees. Together, (iii) the changes in mycorrhizal dominance along soil fertility gradients weakened the positive DBR observed at 0.01‐ to 0.04‐ha scales in nearly all forests and drove negative DBRs at 0.25‐ to 1‐ha scales in four out of seven forests. Hence, this study highlights a soil‐related mycorrhizal dominance mechanism that could partly explain why, in many natural forests, biodiversity–ecosystem functioning (BEF) relationships shift from positive to negative with increasing spatial scale.

The interactive effects of soil fertility and tree mycorrhizal association explain spatial variation of diversity–biomass relationships in a subtropical forest

Abstract Observed biodiversity–ecosystem function (BEF) relationships are highly variable, particularly in natural forests. However, our understanding of the factors that generate these often contradictory patterns, especially the role of different mycorrhizal associations, is still limited. By relating tree species richness and above‐ground biomass (AGB) in a fully mapped 24‐ha subtropical forest dynamics plot, we evaluated the impacts of soil fertility and tree mycorrhizal type in mediating BEF relationships at multiple spatial scales. Our results demonstrate a highly positive total richness effect on AGB for arbuscular mycorrhizal (AM) trees but a negative effect on AGB for ectomycorrhizal (EcM) trees, and their relationships were highly spatial scale dependent. However, the observed BEF relationships turned into positive at small spatial scales (i.e. 10 and 20 m) after controlling for other confounding factors (i.e. topography, soil fertility and AM proportion). In addition, we found significant interactions between soil fertility and species richness on AGB. Specifically, the positive effect of total species richness on AGB for major mycorrhizal types gradually weakened with increasing soil fertility, while the positive effect of EcM species richness on AM AGB gradually enhanced at small spatial scales, suggesting the observed diversity effects can be largely attributed to resource niche complementarity and the role of EcM fungi. Synthesis. We conclude that the variable BEF relationships among forest communities could be explained by spatial variation in abiotic environments and community mycorrhizal composition because different types of symbionts perform different nutrient uptake strategies and ability in protection from antagonists. Our findings provide novel insights into the understanding of the variation in the shape of BEF relationships in natural forests, which is critical for forest management, conservation and restoration in a changing world.

Diversity of benthic diatoms in the Baltic Sea: alpha and beta diversity, environmental drivers, and diversity-biomass relationships

Benthic diatoms are crucial for the functioning of ecosystems, but their diversity patterns along large gradients are poorly studied. By using 3 self-collected data sets along large environmental gradients in the Baltic Sea, represented over spatial scales of 60, 1300, and 2300 km, I investigated whether different aspects of diversity follow general patterns or are context- and region-specific. General diversity patterns along different gradients would likely indicate high resilience of benthic diatoms against differences and changes in the environment, whereas context-dependent patterns would possibly suggest that environmental change is likely to modify diatom communities and that region-specific differences should be considered when designing ecosystem management. I investigated the effect of environmental conditions on taxonomic and functional diatom diversity with distance-based redundancy analyses, variability of taxonomic diversity with species accumulation curves, taxonomic and functional aspects of spatial beta diversity with pairwise Bray-Curtis dissimilarity indices and Mantel tests, and diversity-biomass relationships with generalized linear models. The effect of environment on diatom communities was context-dependent, and different factors controlled communities along different gradients. Diversity varied along gradients and correlated with salinity in a U-shaped way. Beta diversity followed a general pattern of high taxonomic but low functional beta diversity along all gradients. Relationships between diatom diversity and ecosystem biomass were weak along all gradients. These results suggest that although the regional diversity of diatoms seems resilient, environmental change is likely to modify the local diversity of diatom communities. Finding out how these changes will affect ecosystem functioning requires further investigation.

Drivers of aboveground biomass shift with forest stratum in temperate forest of North China

A better understanding of the underlying ecological mechanisms of diversity-biomass relationships in forest layers (i.e., overstory and understory) is critical to understand the importance of vertical stratification to the functioning of forest ecosystems. However, it is not clear how multiple abiotic (i.e., climate and geography) and biological (i.e., biodiversity, functional characteristics, and stand structural complexity) factors simultaneously determine the aboveground biomass (AGB) of each individual forest stratum. We used data on 156,270 trees from 1986 plots in North China to explore the relationships among biological diversity, plant functional traits, stand structure, climate and topography on variation in AGB of each stratum. The results showed that different biological factors determined the AGB of overstory and understory, and thus indicating different underlying ecological mechanisms in temperate forests. The effects of forest biodiversity on AGB were only significant in understory stratum. In the overstory of the forest, forests with high tree-size dimension inequality and high dominant tree height had larger AGB, hence mass ratio effect and stand structure complexity were the main ecological mechanisms for high biomass. In understory, diversity and overstory attributes were the main factors affecting biomass. Tree height and AGB of the overstory reduced the AGB of the understory layer. In consequence overstory attributes and niche complementation were the main ecological mechanisms in the understory. The overstory exerted influence on the understory through resource quantity and resource heterogeneity. Our findings have important implications for carbon management, enhancement of forest functions and sustainable forest management in temperate forests.

Species co‐occurrence shapes spatial variability in plant diversity–biomass relationships in natural rangelands under different grazing intensities

AbstractGrazing can alter plant species interactions in natural rangelands, which in turn might influence the productivity of the ecosystem but we do not fully understand how spatial variability in plant diversity‐biomass relationships are modulated by grazing intensity. Here, we hypothesized that plant species co‐occurrence in rangelands is mainly driven by niche segregation due to grazing and heterogeneity in local resources, and that grazing, therefore, modulates diversity–biomass relationships. We tested our hypothesis across 35 rangeland sites in Iran, using a species co‐occurrence index to assess plant spatial aggregation within each site. At each site, we measured aboveground biomass, plant diversity, topography, soil nutrients, and three levels of grazing intensity. High spatial segregation of plant communities (low species co‐occurrence) was found at heavily grazed sites, whereas greater spatial aggregation (high species co‐occurrence) was found on low and moderate grazed sites, showing varied associational patterns of species with grazing intensity. Soil nutrients increased with grazing intensity and spatial segregation of plant communities was greater at sites with high soil nutrient concentrations, indicating that grazing intensity influences the spatial heterogeneity of plant communities via nutrients deposited in urine and feces. Declining plant biomass with grazing intensity was related to a strong decline in graminoid species diversity, which suggests that the diversity‐biomass relationship is influenced by selective grazing of palatable species. The relationships between species co‐occurrence and biomass or plant diversity suggest non‐random patterns in species co‐occurrences with grazing intensity, which could be the result of competition driven by high livestock grazing intensity. We, therefore, suggest that rangeland stocking rates should be managed properly to maintain rangeland production while promoting plant diversity.

Soil microbial diversity\u2013biomass relationships are driven by soil carbon content across global biomes

The relationship between biodiversity and biomass has been a long standing debate in ecology. Soil biodiversity and biomass are essential drivers of ecosystem functions. However, unlike plant communities, little is known about how the diversity and biomass of soil microbial communities are interlinked across globally distributed biomes, and how variations in this relationship influence ecosystem function. To fill this knowledge gap, we conducted a field survey across global biomes, with contrasting vegetation and climate types. We show that soil carbon (C) content is associated to the microbial diversity–biomass relationship and ratio in soils across global biomes. This ratio provides an integrative index to identify those locations on Earth wherein diversity is much higher compared with biomass and vice versa. The soil microbial diversity-to-biomass ratio peaks in arid environments with low C content, and is very low in C-rich cold environments. Our study further advances that the reductions in soil C content associated with land use intensification and climate change could cause dramatic shifts in the microbial diversity-biomass ratio, with potential consequences for broad soil processes.

Testing the diversity–biomass relationship in riverine fish communities

AbstractAimWe examined the diversity–biomass relationship in stream fish communities and quantified direct and indirect effects of abiotic variables on this relationship.LocationFrance.Time period1992–2012.Major taxa studiedStream fishes.MethodsWe analysed the relationship between biodiversity (species richness and functional diversity) and fish community biomass at 1,357 stream sites distributed throughout France. We used piecewise path analysis to quantify effects of abiotic and biodiversity variables on biomass and assess relative contributions of native and non‐native species on the diversity–biomass relationship.ResultsBiodiversity showed a direct positive relationship with biomass after controlling for sampling effort, and direct effects of biodiversity variables on community biomass exceeded those of climate and physical habitat variables. Our analysis indicates that positive effects of species richness on biomass exceeded those of functional diversity. Indirect effects of abiotic variables mediated by biodiversity metrics indicated that biomass increased in warmer, lowland habitats. Human impact had no effect on native biodiversity but had a positive effect on non‐native biodiversity.Main conclusionsWe provide evidence that direct effects of biodiversity on community biomass outweigh those of abiotic variables in riverine fish communities, but resource partitioning alone is unlikely to drive the effects of biodiversity on biomass in this system. Quantification of the relative roles of anthropogenic impacts, biodiversity and environmental context in the regulation of ecosystem functioning will be necessary to understand the potential consequences of ongoing global change.

Temporal stability of aboveground biomass is governed by species asynchrony in temperate forests.

Understanding the effects of plant species diversity and trait composition on aboveground biomass is a central focus of ecology and has important implications for biodiversity conservation. However, the simultaneous direct and indirect effects of soil nutrients, species asynchrony, functional trait diversity, and trait composition for explaining the community temporal stability of aboveground biomass remain underrepresented in natural forests. Here, we hypothesized that species asynchrony relative to soil nutrients, functional trait diversity, and trait composition plays a central role in stabilizing the community temporal stability of natural forests. We tested this hypothesis using a structural equation model based on 10-year continuous monitoring data (i.e., three-time repeated forest inventories) in both second-growth and old-growth temperate forests in northeast China. Our results showed that the community temporal stability of aboveground biomass was driven by a strong direct positive effect of species asynchrony in both second-growth and old-growth temperate forests, whereas functional trait diversity and composition (i.e. community-weighted mean of leaf nitrogen content) were of additional importance in an old-growth forest only. Functional trait diversity decreased community-weighted mean of leaf nitrogen content in an old-growth forest, whereas this relationship was non-significant in a second-growth forest. Soil nutrients had non-significant effects on the community temporal stability of both second-growth and old-growth forests. Species asynchrony was the direct determinant of the community temporal stability of aboveground biomass in temperate forests. The direct effect of species asynchrony increased with forest succession, implying that temporal niche differentiation and facilitation increase over time. This study suggests that managing forests with mixtures of both early and late successional species or shade intolerant and tolerant species, not only species diversity, is important for maintaining forest stability in a changing environment. We argue that the species asynchrony effect is crucial to understand the underlying ecological mechanisms for a diversity-biomass relationship in natural forests.

Tree mycorrhizal associations mediate soil fertility effects on forest community structure in a temperate forest.

Soil fertility influences plant community structure, yet few studies have focused on how this influence is affected by the type of mycorrhizal association formed by tree species within local communities. We examined the relationship of aboveground biomass (AGB) and diversity of adult trees with soil fertility (nitrogen, phosphorus, organic matter, etc.) in the context of different spatial distributions of arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) trees in a temperate forest in Northeast China. Diversity showed a positive trend along the soil fertility gradient driven mostly by a positive relationship between AM tree abundance and soil fertility. By contrast, the AGB showed a negative trend along the soil fertility gradient driven mostly by a negative relationship between EM tree AGB and soil fertility. Furthermore, the opposite trend in the AGB and tree species diversity along the soil fertility gradient led to an overall negative diversity-biomass relationship at the 50-m scale but not the 20-m scale. These results suggest that tree mycorrhizal associations play a critical role in driving forest community structure along soil fertility gradients and highlight the importance of tree mycorrhizal associations in influencing how the diversity-ecosystem function (e.g. biomass) relationships change with soil fertility.

Multiple abiotic and biotic drivers of aboveground biomass shift with forest stratum

Insights into the underlying ecological mechanisms for diversity-biomass relationships across forest strata (i.e., overstorey and understorey) are crucial to understand the importance of vertical stratification on ecosystem function in natural forests. Yet, it remains unclear how multiple abiotic (i.e., soil nutrients) and biotic (i.e., biodiversity, functional identity and stand structural complexity) factors simultaneously determine aboveground biomass in each individual forest stratum and whole-community. To address this knowledge gap, we disentangled the relative effects of soil nutrients (soil fertility hypothesis), taxonomic, functional trait and evolutionary diversity (niche complementarity hypothesis), stand structural complexity (niche differentiation hypothesis based on tree sizes), and community-weighted mean trait values (mass ratio hypothesis) on aboveground biomass across forest strata and whole-community. We used forest inventory, functional traits and environmental factors datasets from 125 subtropical forest plots in Eastern China. Multiple linear regression models were performed for the selection of best predictors within each biotic group, and structural equation modelling was used to evaluating how multiple abiotic and biotic drivers determine aboveground biomass. In the overstorey, aboveground biomass was positively related to the community-weighted mean of tree height (i.e., functional dominance) and stand density but was negatively related to functional evenness on nutrient-rich soils. In the understorey, aboveground biomass was positively related to phylogenetic species richness and stand-level tree mean diameter (i.e., a proxy for forest growth) but was negatively related to Shannon’s species diversity on nutrient-poor soils. Understorey aboveground biomass was also determined by overstorey stand structure and functional dominance through direct and indirect effects via understorey biotic drivers. These results suggest that functional dominance and stand structural complexity are the main biotic drivers of overstorey aboveground biomass. Whereas, functional dominance and stand structural complexity of overstorey, soil nutrients, and niche complementarity among understorey species with the conservative strategy determine understorey aboveground biomass. Whole-community aboveground biomass might be resulting from the superior role of overstorey functional dominance. This study highlights that the niche complementarity, mass ratio and soil nutrients effects are important for driving aboveground biomass, but in different ways across overstorey and understorey strata in natural subtropical forests. We argue that the relative effect of biodiversity loss on aboveground biomass depends critically on the functional and evolutionary identity of the lost species in the specific forest stratum. Better insights can be gained into forest management and biodiversity conservation by considering overstorey and understorey strata separately in complex natural forests.

Relationships between plant diversity and biomass production of alpine grasslands are dependent on the spatial scale and the dimension of biodiversity

There is no consensus about the relationship between plant species diversity and productivity in grasslands. Lack of consensus might be caused by different diversity metrics used and different spatial scales examined. In particular, the impacts of different biodiversity indices on the plant diversity–plant productivity relationship of alpine grasslands at different spatial scales of the Qinghai–Tibetan Plateau (QTP) require investigation. We investigated the relations of multi-dimensional diversity indices (species richness, Shannon–Wiener diversity, and Pielou evenness) with aboveground and belowground plant biomass in the alpine grasslands of the QTP by linear mixed model (LMM). We assessed the plant diversity and biomass of alpine meadow, alpine steppe, and alpine desert steppe from 5 sites across the vast landscape of the QTP by using 6 randomly placed plots in each site and 27 replicated quadrats in each plot. The species richness of the studied alpine grasslands ranged from 2 to 35, aboveground plant dry biomass ranged from 17 to 838 g m−2, and belowground plant dry biomass ranged from 398 to 3945 g m−2. The species richness and Shannon–Wiener indices were positively correlated with aboveground plant biomass and belowground plant biomass at the landscape scale, whereas the Pielou evenness index was negatively correlated with aboveground plant biomass and belowground plant biomass at the landscape scale. Less than 20% sites showed significant relationships between plant diversity indices and plant biomass at site scale. Plant biomass partitioning between the root and shoot was not correlated with the species richness, Shannon–Wiener and Pielou evenness indices at all scales. The plant diversity–biomass relationships of the alpine grassland ecosystems in the QTP depend on both the type (or dimension) of the biodiversity index and the spatial scale of sampling. Thus, the design and implementation of plant diversity conservation should consider different dimensions of plant diversity. It is not enough to increase species richness only in the process of grassland restoration and conservation, but also to reduce species evenness so as to promote productivity more fully, for example, in planting artificial grassland.

Diversity-biomass relationship across forest layers: implications for niche complementarity and selection effects.

Forest stratification plays a crucial role in light interception and plant photosynthetic activities. However, despite the increased number of studies on biodiversity-ecosystem function, we still lack information on how stratification in tropical forests modulates biodiversity effects. Moreover, there is less investigation and argument on the role of species and functional traits in forest layers. Here, we analysed from a perspective of forest layer (sub-canopy, canopy and emergent species layers), the relationship between diversity and aboveground biomass (AGB), focusing on functional diversity and dominance, and underlying mechanisms such as niche complementarity and selection. The sub-canopy layer had the highest species richness and diversity, while the emergent layer had the highest AGB. Species richness-AGB relationship was positive for each forest layer, but stronger for sub-canopy layer than for canopy and emergent layers. Total AGB was strongly correlated with functional diversity, leaf and wood traits of species in the sub-canopy and canopy layers. This suggests that sub-canopy and canopy species are major drivers of stand diversity-AGB relationship, and that resource filtering by canopy or emergent trees may not reduce the strength of diversity-AGB relationship in the sub-canopy layer. We argue that complementary resource use by sub-canopy species that supports niche complementarity, is a key mechanism driving AGB in natural forests. Selection effects are most evident in emergent species and niche complementarity effects for sub-canopy and canopy species, supporting arguments that AGB is affected by sub-canopy species' efficient use of limited resources despite competition from emergent species.

Diversity-productivity dependent resistance of an alpine plant community to different climate change scenarios

Here we report from a experiment imposing different warming scenarios [control with ambient temperature, constant level of moderate warming for 3 years, stepwise increase in warming for 3 years, and one season of high level warming (pulse) simulating an extreme summer event] on an alpine ecosystem to study the impact on species diversity–biomass relationship, and community resistance in terms of biomass production. Multiple linear mixed models indicate that experimental years had stronger influence on biomass than warming scenarios and species diversity. Species diversity and biomass had almost humpback relationships under different warming scenarios over different experimental years. There was generally a negative diversity–biomass relationship, implying that a positive diversity–biomass relationship was not the case. The application of different warming scenarios did not change this tendency. The change in community resistance to all warming scenarios was generally negatively correlated with increasing species diversity, the strength of the correlation varying both between treatments and between years within treatments. The strong effect of experimental years was consistent with the notion that niche complementarity effects increase over time, and hence, higher biomass productivity over experimental years. The strongest negative relationship was found in the first year of the pulse treatment, indicating that the community had weak resistance to an extreme event of one season of abnormally warm climate. Biomass production started recovering during the two subsequent years. Contrasting biomass-related resistance emerged in the different treatments, indicating that micro sites within the same plant community may differ in their resistance to different warming scenarios.

Further re‐analyses looking for effects of phylogenetic diversity on community biomass and stability

Species richness (SR) and phylogenetic diversity (PD) are highly correlated measures of plant diversity. Each, by itself, is significantly associated with plant community biomass in biodiversity experiments. As presented by Cadotte (2015) and as we present below, reasonable but alternative analyses that attempt to control for this correlation in different ways provide contradictory or inconclusive support for the hypothesis that PD is superior to SR as a predictor of community biomass. In Venail et al. (2015), we re-analysed data from 16 experimental manipulations of grassland SR to look at how SR and PD influence variation in plant community biomass through time. Using four types of analyses, we showed that, after statistically controlling for variation in SR, PD was not related to community biomass or to the temporal stability of biomass. We did, however, find that SR tends to increase the biomass production of plant communities after controlling for PD. In his comment, Cadotte expressed two concerns about our analyses. One is that we used non-random subsets of experiments, rather than the full data set, for some of our analyses (types 2, 3). We were clear in stating these analyses were based on non-random subsets that were specifically chosen to minimize the SR–PD correlation and avoid problems associated with multicollinearity. We acknowledge that our tests are conservative, a cost of which is that they sacrifice statistical power while, at the same time, minimizing the chance of drawing an incorrect conclusion. But we disagree with Cadotte’s suggestion that our use of non-random data subsets led to ‘biased’ conclusions, and demonstrate later in this response that his claim of bias is unsubstantiated. Cadotte’s second concern was that our analyses did not account for differences in biomass across studies. This is an important criticism to consider; we made a mistake by not controlling for variation in biomass. To address this issue, Cadotte used mixed models where study was included as a random effect, and ran analyses that standardized biomass among sites. Collectively, these led Cadotte to conclude ‘All analyses strongly support previous literature claims about the value of PD and I further show that: (i) PD provides a more powerful explanation of variation in biomass production than species richness; (ii) PD explains variation in biomass production after controlling for richness; and (iii) the use of data subsets inadvertently biased the conclusions’. We have two concerns with Cadotte’s re-analysis. First, Cadotte’s approach largely ignores the concerns we raised about multicollinearity. When two or more predictors

Herbaceous biomass–species diversity relationships in nutrient hotspots of a semi-arid African riparian ecosystem

The hump-back relationship between species diversity and productivity predicts highest species richness at intermediate levels of biomass, and low species numbers in least and most productive habitats. Sodic patches of semi-arid savannas are considered ‘nutrient hotspots’ by producing high-quality forage. The impact of biomass reduction (due to overgrazing) and accumulation (in the absence of herbivores) on herbaceous species richness and diversity is still unknown for these hotspots. We tested the relationship between biomass and herbaceous species richness/diversity in savanna sodic sites across varying biomass levels obtained through different herbivore exclosures. LOWESS and quadratic regression analyses revealed a unimodal species richness/ diversity–biomass relationship for biomass <2 500 kg ha−1. Species richness and diversity in the sodic zone peaked at 1 300 kg ha−1, followed by a steady decline. At biomass levels exceeding 2 500 kg ha−1, i.e. where herbivores have been excluded for 10 years, the decline in species richness and diversity stabilised. Despite many debates surrounding unimodal relationships and the intermediate disturbance hypothesis, this study confirmed a peak in species richness and diversity at intermediate biomass levels in a herbivory-adapted ecosystem. Herbivores drive ecosystem heterogeneity and enhance herbaceous species richness and diversity by keeping biomass at intermediate levels (i.e. <2 500 kg ha−1 for this sodic site).

Is the relationship between algal diversity and biomass in North American lakes consistent with biodiversity experiments?

Over the past few decades, a large body of research has examined how biodiversity loss influences the functioning of ecosystems, as well as the cascading impacts on the goods and services ecosystems provide to humanity. The relationship between biodiversity and ecosystem functions quantified in prior experiments suggests that initial losses of biodiversity have relatively small impacts on properties like community biomass production; however, beyond some threshold, increasing losses lead to accelerating declines in function. Some have questioned whether a saturating relationship between diversity and community biomass production is an artifact of overly simplified experiments that manipulate diversity in homogeneous conditions over short time‐scales in which niche differences may not be realized. Others have questioned whether even the modest effects of biodiversity observed in experiments would be discernible in natural systems where they could be over‐ridden by the stronger influence of abiotic factors.Here, we used a biogeographic dataset to assess how the taxonomic richness of aquatic primary producers relates to community biomass in unmanipulated lake ecosystems in the US, and then compared these findings to prior experiments. We used structural equation modeling to evaluate hypotheses about the effects of algal richness on community biomass while accounting for covariance with environmental parameters measured in the USEPA's National Lakes Assessment (NLA), which sampled 1157 freshwater lakes. These analyses converged on a single best‐fit model (χ2= 0.31, p = 0.58) wherein community algal biomass was a function of three explanatory variables – nitrogen, phosphorus, and algal richness. The quantitative magnitude of the algal diversity (x) – biomass (y) relationship in the NLA dataset is statistically greater than that documented in the average biodiversity experiment. It did, however, lie at approximately the 75th percentile of experimental relationships, indicating the diversity–biomass relationship in unmanipulated lakes is within the range that has been characterized experimentally.

Spatiotemporal segregation regulates species richness along biomass gradients in estuarine fish assemblages

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 342:217-226 (2007) - doi:10.3354/meps342217 Spatiotemporal segregation regulates species richness along biomass gradients in estuarine fish assemblages Atahualpa Sosa-Lopez1, David Mouillot2,* 1Centro EPOMEX, Universidad Autónoma de Campeche, Av. Agustín Melgar s/n, Campeche, CP 24030, Campeche, Mexico 2UMR CNRS-UM2 5119 Ecosystèmes Lagunaires, Université Montpellier 2, CC 093, 34095 Montpellier Cedex 5, France *Corresponding author. Email: mouillot@univ-montp2.fr ABSTRACT: The number of fish species in subtropical and tropical estuaries is much greater than in temperate regions and is greater in large estuaries than in small ones. Thus, large estuaries of the tropics are of primary interest for biodiversity conservation, and the processes underpinning the distribution of fish diversity in these ecosystems deserve attention. Factors controlling biodiversity patterns have been the focus of numerous recent investigations and include species interactions, speciation, environmental gradients and heterogeneity, with all of these operating differently at each observation scale. Today, the question is no longer whether particular biodiversity patterns occur, but why they occur and whether they are consistent across scales and organisms under study. In this study we combined the results of 2 classical ecological patterns, namely diversity–biomass relationships and species co-occurrences, into a common framework. Fish sampling was carried out in the coastal Terminos Lagoon (southern Gulf of Mexico) during 2 periods (1980–1981 and 1998–1999) using 408 tows. A total of 22834 individuals representing 106 fish species were collected. Our study revealed that both diversity–biomass relationships and species co-occurrences show inconsistent patterns across years, seasons and zones. However, taken together, our results show that C-score values, which measure spatiotemporal segregation among species, were closely related to the shape of observed richness–biomass relationships. When fish assemblages showed positive C-score values (species segregation), the relationship between species richness and fish biomass was either hump-shaped or non-significant. Conversely, negative C-score values (species aggregation) were associated with an increase in fish species richness along the total biomass gradient. Our results support the idea that species segregation due to competition or spatiotemporal partitioning can be an important determinant of biodiversity patterns in species-rich tropical fish assemblages, but only during some periods and for some spatial strata. KEY WORDS: Terminos Lagoon · Co-occurrence · C-score index · Randomization · Species segregation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 342. Online publication date: July 24, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.