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1. Mechanistic links between biodiversity effects on ecosystem functioning and stability in a multi‐site grassland experiment

   https://doi.org/10.1111/1365-2745.13725  

   Yan, Ying ; Connolly, John ; Liang, Maowei ; Jiang, Lin ; Wang, Shaopeng ( July 2021 , Journal of Ecology)

   Although the positive effects of biodiversity on ecosystem functioning and stability have been extensively documented in the literature, previous studies have mostly explored the mechanisms of functioning and stability independently. It is unclear how biodiversity effects on functioning may covary with those on stability.

   Here we developed an integrated framework to explore links between mechanisms underlying biodiversity effects on functioning and those on stability. Specifically, biodiversity effects on ecosystem functioning were partitioned into complementarity effects (CE) and selection effects (SE), and those on stability were partitioned into species asynchrony and species stability. We investigated howCEandSEwere linked to species asynchrony and stability and how their links might be mediated by species evenness, using a multi‐site grassland experiment.

   Our mixed‐effects models showed that a higher community productivity was mainly due toCEand a higher community stability was mainly due to species asynchrony. Moreover,CEwas positively related to species asynchrony, thus leading to a positive association between ecosystem productivity and stability.

   We used a structural equation model to illustrate how species evenness might mediate links between the various mechanisms. Communities with a higher evenness exhibited a higherCEand species asynchrony, but a lowerSEand species stability. These evenness‐mediated associations enhanced the positive relationship betweenCEand species asynchrony, but blurred that betweenSEand species asynchrony.

   Synthesis. Our findings demonstrate mechanistic links between biodiversity effects on ecosystem functioning and stability. By doing so, our study contributes a novel framework for understanding ecological mechanisms of the functioning–stability relationship, which has important implications for developing management plans focused on strengthening synergies between ecosystem functioning and stability over the long term.

    

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2. Foundation species promote community stability by increasing diversity in a giant kelp forest

   https://doi.org/10.1002/ecy.2987  

   Lamy, Thomas ; Koenigs, Craig ; Holbrook, Sally J. ; Miller, Robert J. ; Stier, Adrian C. ; Reed, Daniel C. ( February 2020 , Ecology)

   Foundation species structure communities, promote biodiversity, and stabilize ecosystem processes by creating locally stable environmental conditions. Despite their critical importance, the role of foundation species in stabilizing natural communities has seldom been quantified. In theory, the stability of a foundation species should promote community stability by enhancing species richness, altering the population fluctuations of individual species, or both. Here we tested the hypothesis that the stability of a marine foundation species, the giant kelpMacrocystis pyrifera, increased the stability of the aggregate biomass of a phylogenetically diverse assemblage of understory algae and sessile invertebrates that compete for space beneath the giant kelp canopy. To achieve this goal, we analyzed an 18‐yr time series of the biomass of giant kelp and its associated benthic community collected from 32 plots distributed among nine shallow reefs in the Santa Barbara Channel, USA. We showed that the stability of understory algae and sessile invertebrates was positively and indirectly related to the stability of giant kelp, which primarily resulted from giant kelp's direct positive association with species richness. The stability of all community types was positively related to species richness via increased species stability and species asynchrony. The stabilizing effects of richness were three to four times stronger when algae and invertebrates were considered separately rather than in combination. Our finding that diversity–stability relationships were stronger in communities consisting of species with similar resource requirements suggests that competition for shared resources rather than differential responses to environmental conditions played a more important role in stabilizing the community. Increasing threats to structure‐forming foundation species worldwide necessitates a detailed understanding of how they influence their associated community. This study is among the first to show that dampened temporal fluctuations in the biomass of a foundation species is an important determinant of the stability of the complex communities it supports.

    

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3. A new variance ratio metric to detect the timescale of compensatory dynamics

   https://doi.org/10.1002/ecs2.3114  

   Zhao, Lei ; Wang, Shaopeng ; Hallett, Lauren M. ; Rypel, Andrew L. ; Sheppard, Lawrence W. ; Castorani, Max C. N. ; Shoemaker, Lauren G. ; Cottingham, Kathryn L. ; Suding, Katharine ; Reuman, Daniel C. ( May 2020 , Ecosphere)

   Understanding the mechanisms governing ecological stability—why a property such as primary productivity is stable in some communities and variable in others—has long been a focus of ecology. Compensatory dynamics, in which anti‐synchronous fluctuations between populations buffer against fluctuations at the community level, are a key theoretical mechanism of stability. Classically, compensatory dynamics have been quantified using a variance ratio approach that compares the ratio between community variance and aggregate population variance, such that a lower ratio indicates compensation and a higher ratio indicates synchrony among species fluctuations. However, population dynamics may be influenced by different drivers that operate on different timescales, and evidence from aquatic systems indicates that communities can be compensatory on some timescales and synchronous on others. The variance ratio and related metrics cannot reflect this timescale specificity, yet have remained popular, especially in terrestrial systems. Here, we develop a timescale‐specific variance ratio approach that formally decomposes the classical variance ratio according to the timescales of distinct contributions. The approach is implemented in a new R package, called tsvr, that accompanies this paper. We apply our approach to a long‐term, multisite grassland community dataset. Our approach demonstrates that the degree of compensation vs. synchrony in community dynamics can vary by timescale. Across sites, population variability was typically greater over longer compared to shorter timescales. At some sites, minimal timescale specificity in compensatory dynamics translated this pattern of population variability into a similar pattern of greater community variability on longer compared to shorter timescales. But at other sites, differentially stronger compensatory dynamics at longer compared to shorter timescales produced lower‐than‐expected community variability on longer timescales. Within every site, there were plots that exhibited shifts in the strength of compensation between timescales. Our results highlight that compensatory vs. synchronous dynamics are intrinsically timescale‐dependent concepts, and our timescale‐specific variance ratio provides a metric to quantify timescale specificity and relate it back to the classic variance ratio.

    

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4. Plant traits modulate grassland stability during drought and post‐drought periods

   https://doi.org/10.1111/1365-2435.14409  

   Luo, Wentao ; Shi, Yuan ; Wilkins, Kate ; Song, Lin ; Te, Niwu ; Chen, Jiaqi ; Zhang, Hongxiang ; Yu, Qiang ; Wang, Zhengwen ; Han, Xingguo ; et al ( July 2023 , Functional Ecology)

   Grasslands are subject to climate change, such as severe drought, and an important aspect of their functioning is temporal stability in response to extreme climate events. Previous research has explored the impacts of extreme drought and post‐drought periods on grassland stability, yet the mechanistic pathways behind these changes have rarely been studied.

   Here, we implemented an experiment with 4 years of drought and 3 years of recovery to assess the effects of drought and post‐drought on the temporal stability of above‐ground net primary productivity (ANPP) and its underlying mechanisms. To do so, we measured community‐weighted mean (CWM) of six plant growth and nine seed traits, functional diversity, population stability and species asynchrony across two cold, semiarid grasslands in northern China. We also performed piecewise structural equation models (SEMs) to assess the relationships between ANPP stability and its underlying mechanisms and how drought and post‐drought periods alter the relative contribution of these mechanisms to ANPP stability.

   We found that temporal stability of ANPP was not reduced during drought due to grasses maintaining productivity, which compensated for increased variation of forb productivity. Moreover, ANPP recovered rapidly after drought, and both grasses and forbs contributed to community stability during the post‐drought period. Overall, ANPP stability decreased during the combined drought and post‐drought periods because of rapid changes in ANPP from drought to post‐drought. SEMs revealed that the temporal stability of ANPP during drought and post‐drought periods was modulated by functional diversity and community‐weighted mean traits directly and indirectly by altering species asynchrony and population stability. Specifically, the temporal stability of ANPP was positively correlated with functional divergence of plant communities. CWMs of seed traits (e.g. seed width and thickness), rather than plant growth traits (e.g. specific leaf area and leaf nutrient content), stabilized grassland ANPP. Productivity of plant communities with large and thick seeds was less sensitive to precipitation changes over time.

   These results emphasize the importance of considering both the functional trait distribution among species and seed traits of dominant species since their combined effects can stabilize ecosystem functions under global climate change scenarios.

   Read the freePlain Language Summaryfor this article on the Journal blog.

    

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5. Belowground community turnover accelerates the decomposition of standing dead wood

   https://doi.org/10.1002/ecy.3484  

   Bradford, Mark A. ; Maynard, Daniel S. ; Crowther, Thomas W. ; Frankson, Paul T. ; Mohan, Jacqueline E. ; Steinrueck, Corinna ; Veen, G. F. ; King, Joshua R. ; Warren, II, Robert J. ( October 2021 , Ecology)

   Standing dead trees (snags) decompose more slowly than downed dead wood and provide critical habitat for many species. The rate at which snags fall therefore influences forest carbon dynamics and biodiversity. Fall rates correlate strongly with mean annual temperature, presumably because warmer climates facilitate faster wood decomposition and hence degradation of the structural stability of standing wood. These faster decomposition rates coincide with turnover from fungal‐dominated wood decomposer communities in cooler forests to codomination by fungi and termites in warmer regions. A key question for projecting forest dynamics is therefore whether temperature effects on wood decomposition arise primarily because warmer conditions facilitate faster decomposer metabolism, or are also influenced indirectly by belowground community turnover (e.g., termites exert additional influence beyond fungal‐plus‐bacterial mediated decomposition). To test between these possibilities, we simulate standing dead trees with untreated wooden posts and follow them in the field across 5 yr at 12 sites, before measuring buried, soil–air interface and aerial post sections to quantify wood decomposition and organism activities. High termite activities at the warmer sites are associated with rates of postfall that are three times higher than at the cooler sites. Termites primarily consume buried wood, with decomposition rates greatest where termite activities are highest. However, where higher microbial and termite activities co‐occur, they appear to compensate for one another first, and then to slow decomposition rates at their highest activities, suggestive of interference competition. If the range of microbial and termite codomination of wood decomposer communities expands under climate warming, our data suggest that expansion will accelerate snag fall with consequent effects on forest carbon cycling and biodiversity in forests previously dominated by microbial decomposers.

    

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