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Abstract Darwin's theory of natural selection provides two seemingly contradictory hypotheses for explaining the success of biological invasions: (1) the pre‐adaptation hypothesis posits that introduced species that are closely related to native species will be more likely to succeed due to shared advantageous characteristics; (2) the limiting similarity hypothesis posits that invaders that are more similar to resident species will be less likely to succeed due to competitive exclusion. Previous studies assessing this conundrum show mixed results, possibly stemming from inconsistent study spatial scales and failure to integrate both functional and phylogenetic information. Here, we address these limitations using a 33‐year grassland successional survey at Cedar Creek Ecosystem Science Reserve (USA). We incorporate functional dissimilarities, phylogenetic distances, environmental covariates, and species origin data for 303 vascular plant taxa (256 native, 47 introduced), collected from 2700 plots. In contrast with other studies, we test both hypotheses at two fine spatial scales—neighborhood (0.5 m²) and site (~40 m²)—to better capture competition and environmental filtering, respectively. Findings related to Darwin's naturalization conundrum depended on spatial scale and dissimilarity metric. Our results agreed with the pre‐adaptation hypothesis at site scale (40 m²)—a much finer resolution than typically used to test the pre‐adaptation hypothesis—highlighting the role of environmental filtering. At the neighborhood scale (0.5 m²), support for the limiting similarity hypothesis emerged when using functional dissimilarity, while phylogenetic distance aligned with the pre‐adaptation hypothesis, demonstrating that different dissimilarity metrics can yield contrasting conclusions. In addition, native and introduced species showed different abundance patterns in relation to functional ranked dissimilarities, with introduced species reaching higher cover when they were taller than co‐occurring species, had higher leaf dry matter content (LDMC) and lower seed mass. Introduced species also reached high cover with higher soil N concentrations and a shorter time after colonization, relative to native species. Our results suggest that inconsistent findings related to Darwin's naturalization conundrum may arise from an overreliance on single dissimilarity metrics and the use of spatial scales failing to capture underlying ecological processes. This highlights the need for more nuanced methodologies when testing the pre‐adaptation and limiting similarity hypotheses. 

Abstract In our changing world, understanding plant community responses to global change drivers is critical for predicting future ecosystem composition and function. Plant functional traits promise to be a key predictive tool for many ecosystems, including grasslands; however, their use requires both complete plant community and functional trait data. Yet, representation of these data in global databases is sparse, particularly beyond a handful of most used traits and common species. Here we present the CoRRE Trait Data, spanning 17 traits (9 categorical, 8 continuous) anticipated to predict species’ responses to global change for 4,079 vascular plant species across 173 plant families present in 390 grassland experiments from around the world. The dataset contains complete categorical trait records for all 4,079 plant species obtained from a comprehensive literature search, as well as nearly complete coverage (99.97%) of imputed continuous trait values for a subset of 2,927 plant species. These data will shed light on mechanisms underlying population, community, and ecosystem responses to global change in grasslands worldwide. 

Abstract Temperature and biodiversity changes occur in concert, but their joint effects on ecological stability of natural food webs are unknown. Here, we assess these relationships in 19 planktonic food webs. We estimate stability as structural stability (using the volume contraction rate) and temporal stability (using the temporal variation of species abundances). Warmer temperatures were associated with lower structural and temporal stability, while biodiversity had no consistent effects on either stability property. While species richness was associated with lower structural stability and higher temporal stability, Simpson diversity was associated with higher temporal stability. The responses of structural stability were linked to disproportionate contributions from two trophic groups (predators and consumers), while the responses of temporal stability were linked both to synchrony of all species within the food web and distinctive contributions from three trophic groups (predators, consumers, and producers). Our results suggest that, in natural ecosystems, warmer temperatures can erode ecosystem stability, while biodiversity changes may not have consistent effects. 

The inclusion of community voices in research is important. Over the years, research training programs have continued to emphasize that engagement with communities at the focus of research can promote thoughtful, sensitive designs ( Rivera et al., 2004 ). In this paper, we discuss a method for youth participation in the research process. In an attempt to move beyond “staged and superficial” participation in gathering youth perspectives, we advocate for including co-researchers in the development and modification of fundamental aspects of the research process, from data analysis to the development of additional research questions and collection methods ( Guishard & Tuck, 2013 ). In the course of a study designed to enroll middle school students in participatory co-design sessions ( Cahill, 2007 ) to aid in the development of educational technologies, it became apparent that our youth participants, as co-researchers, could also aid in the development, analysis, and coding of anonymized interview transcripts; development of themes; and creation of models for behaviors found in the transcripts ( Docan-Morgan, 2010 ; Luchtenberg et al., 2020 ). Thus, this paper presents a practical example of a co-research process that includes youth participants, with an emphasis on training in qualitative coding and the fundamentals of research design. 

Abstract The measurement of uncharacterized pools of biological molecules through techniques such as metabarcoding, metagenomics, metatranscriptomics, metabolomics, and metaproteomics produces large, multivariate datasets. Analyses of these datasets have successfully been borrowed from community ecology to characterize the molecular diversity of samples ( ɑ -diversity) and to assess how these profiles change in response to experimental treatments or across gradients ( β -diversity). However, sample preparation and data collection methods generate biases and noise which confound molecular diversity estimates and require special attention. Here, we examine how technical biases and noise that are introduced into multivariate molecular data affect the estimation of the components of diversity (i.e., total number of different molecular species, or entities; total number of molecules; and the abundance distribution of molecular entities). We then explore under which conditions these biases affect the measurement of ɑ - and β -diversity and highlight how novel methods commonly used in community ecology can be adopted to improve the interpretation and integration of multivariate molecular data. 

Global change drivers, such as anthropogenic nutrient inputs, are increasing globally. Nutrient deposition simultaneously alters plant biodiversity, species composition and ecosystem processes like aboveground biomass production. These changes are underpinned by species extinction, colonisation and shifting relative abundance. Here, we use the Price equation to quantify and link the contributions of species that are lost, gained or that persist to change in aboveground biomass in 59 experimental grassland sites. Under ambient (control) conditions, compositional and biomass turnover was high, and losses (i.e. local extinctions) were balanced by gains (i.e. colonisation). Under fertilisation, the decline in species richness resulted from increased species loss and decreases in species gained. Biomass increase under fertilisation resulted mostly from species that persist and to a lesser extent from species gained. Drivers of ecological change can interact relatively independently with diversity, composition and ecosystem processes and functions such as aboveground biomass due to the individual contributions of species lost, gained or persisting. 

Abstract Human impacts have led to dramatic biodiversity change which can be highly scale‐dependent across space and time. A primary means to manage these changes is via passive (here, the removal of disturbance) or active (management interventions) ecological restoration. The recovery of biodiversity, following the removal of disturbance, is often incomplete relative to some kind of reference target. The magnitude of recovery of ecological systems following disturbance depends on the landscape matrix and many contingent factors. Inferences about recovery after disturbance and biodiversity change depend on the temporal and spatial scales at which biodiversity is measured.We measured the recovery of biodiversity and species composition over 33 years in 17 temperate grasslands abandoned after agriculture at different points in time, collectively forming a chronosequence since abandonment from 1 to 80 years. We compare these abandoned sites with known agricultural land‐use histories to never‐disturbed sites as relative benchmarks. We specifically measured aspects of diversity at the local plot‐scale (α‐scale, 0.5 m²) and site‐scale (γ‐scale, 10 m²), as well as the within‐site heterogeneity (β‐diversity) and among‐site variation in species composition (turnover and nestedness).At our α‐scale, sites recovering after agricultural abandonment only had 70% of the plant species richness (and ~30% of the evenness), compared to never‐ploughed sites. Within‐site β‐diversity recovered following agricultural abandonment to around 90% after 80 years. This effect, however, was not enough to lead to recovery at our γ‐scale. Richness in recovering sites was ~65% of that in remnant never‐ploughed sites. The presence of species characteristic of the never‐disturbed sites increased in the recovering sites through time. Forb and legume cover declines in years since abandonment, relative to graminoid cover across sites.Synthesis.We found that, during the 80 years after agricultural abandonment, old fields did not recover to the level of biodiversity in remnant never‐ploughed sites at any scale. β‐diversity recovered more than α‐scale or γ‐scale. Plant species composition recovered, but not completely, over time, and some species groups increased their cover more than others. Patterns of ecological recovery in degraded ecosystems across space and long time‐scales can inform targeted active restoration interventions and perhaps, lead to better outcomes. 

Abstract Diversity and nitrogen addition have positive relationships with plant productivity, yet climate‐induced changes in water availability threaten to upend these established relationships. Using long‐term data from three experiments in a mesic grassland (ranging from 17 to 34 yr of data), we tested how the effects of species richness and nitrogen addition on community‐level plant productivity changed as a function of annual fluctuations in water availability using growing season precipitation and the Standardized Precipitation‐Evapotranspiration Index (SPEI). While results varied across experiments, our findings demonstrate that water availability can magnify the positive effects of both biodiversity and nitrogen addition on productivity. These results suggest that productivity responses to anthropogenic species diversity loss and increasing nitrogen deposition could depend on precipitation regimes, highlighting the importance of testing interactions between multiple global change drivers. 

Feedbacks are an essential feature of resilient socio-economic systems, yet the feedbacks between biodiversity, ecosystem services and human wellbeing are not fully accounted for in global policy efforts that consider future scenarios for human activities and their consequences for nature. Failure to integrate feedbacks in our knowledge frameworks exacerbates uncertainty in future projections and potentially prevents us from realizing the full benefits of actions we can take to enhance sustainability. We identify six scientific research challenges that, if addressed, could allow future policy, conservation and monitoring efforts to quantitatively account for ecosystem and societal consequences of biodiversity change. Placing feedbacks prominently in our frameworks would lead to (i) coordinated observation of biodiversity change, ecosystem functions and human actions, (ii) joint experiment and observation programmes, (iii) more effective use of emerging technologies in biodiversity science and policy, and (iv) a more inclusive and integrated global community of biodiversity observers. To meet these challenges, we outline a five-point action plan for collaboration and connection among scientists and policymakers that emphasizes diversity, inclusion and open access. Efforts to protect biodiversity require the best possible scientific understanding of human activities, biodiversity trends, ecosystem functions and—critically—the feedbacks among them.