Niche dimensionality provides a general theoretical explanation for biodiversity-more niches, defined by more limiting factors, allow for more ways that species can coexist. Because plant species ...compete for the same set of limiting resources, theory predicts that addition of a limiting resource eliminates potential trade-offs, reducing the number of species that can coexist. Multiple nutrient limitation of plant production is common and therefore fertilization may reduce diversity by reducing the number or dimensionality of belowground limiting factors. At the same time, nutrient addition, by increasing biomass, should ultimately shift competition from belowground nutrients towards a one-dimensional competitive trade-off for light. Here we show that plant species diversity decreased when a greater number of limiting nutrients were added across 45 grassland sites from a multi-continent experimental network. The number of added nutrients predicted diversity loss, even after controlling for effects of plant biomass, and even where biomass production was not nutrient-limited. We found that elevated resource supply reduced niche dimensionality and diversity and increased both productivity and compositional turnover. Our results point to the importance of understanding dimensionality in ecological systems that are undergoing diversity loss in response to multiple global change factors.
Summary
Under the mentor effect, compatible heterospecific pollen transfer induces self‐pollen germination in otherwise self‐incompatible plants. The mentor effect could be considered a novel mode of ...reproductive interference if it negatively impacts fitness. Yet to date, this phenomenon has predominately been investigated under experimental conditions rather than in situ. We address this gap in natural populations of the self‐incompatible native dandelion, Taraxacum ceratophorum, where selfing only occurs in association with hybridization from exotic Taraxacum officinale.
We tested whether self‐fertilization rate increases in the hybrid zone, as predicted due to the mentor effect. Using results from these investigations, we created an exponential growth model to estimate the potential demographic impacts of the mentor effect on T. ceratophorum population growth.
Our results demonstrate that the strength of the mentor effect in Taraxacum depends on the prevalence of pollinator‐mediated outcross pollen deposition rather than self‐pollination. Demographic models suggest that reduced outcrossing in T. ceratophorum under exotic invasion could negatively impact population growth through inbreeding depression.
We demonstrate the mentor effect is rare in natural populations of T. ceratophorum due to masking by early life cycle inbreeding depression, prevalent outcrossing, and ovule usurpation by heterospecific pollen.
Ecosystems are exposed to multiple stressors which can compromise functioning and service delivery. These stressors often co‐occur and interact in different ways which are not yet fully understood. ...Here, we applied a population model representing a freshwater amphipod feeding on leaf litter in forested streams. We simulated impacts of hypothetical stressors, individually and in pairwise combinations that target the individuals' feeding, maintenance, growth and reproduction. Impacts were quantified by examining responses at three levels of biological organisation: individual‐level body sizes and cumulative reproduction, population‐level abundance and biomass and ecosystem‐level leaf litter decomposition. Interactive effects of multiple stressors at the individual level were mostly antagonistic, that is, less negative than expected. Most population‐ and ecosystem‐level responses to multiple stressors were stronger than expected from an additive model, that is, synergistic. Our results suggest that across levels of biological organisation responses to multiple stressors are rarely only additive. We suggest methods for efficiently quantifying impacts of multiple stressors at different levels of biological organisation.
Abstract
Herbivores shape plant invasions through impacts on demography and dispersal, yet only demographic mechanisms are well understood. Although herbivores negatively impact demography by ...definition, they can affect dispersal either negatively (e.g., seed consumption), or positively (e.g., caching). Exploring the nuances of how herbivores influence spatial spread will improve the forecasting of plant movement on the landscape. Here, we aim to understand how herbivores impact how fast plant populations spread through varying impacts on plant demography and dispersal. We strive to determine whether, and under what conditions, we see net positive effects of herbivores, in order to find scenarios where herbivores can help to promote spread. We draw on classic invasion theory to develop a stage‐structured integrodifference equation model that incorporates herbivore impacts on plant demography and dispersal. We simulate seven herbivore “syndromes” (combinations of demographic and/or dispersal effects) drawn from the literature to understand how increasing herbivore pressure alters plant spreading speed. We find that herbivores with solely negative effects on plant demography or dispersal always slow plant spreading speed, and that the speed slows monotonically as herbivore pressure increases. However, we also find that plant spreading speed can be hump shaped with respect to herbivore pressure: plants spread faster in the presence of herbivores (for low herbivore pressure) and then slower (for high herbivore pressure). This result is robust, occurring across all syndromes in which herbivores have a positive effect on plant dispersal, and is a sign that the positive effects of herbivores on dispersal can outweigh their negative effects on demography. For all syndromes we find that sufficiently high herbivore pressure results in population collapse. Thus, our findings show that herbivores can speed up or slow down plant spread. These insights allow for a greater understanding of how to slow invasions, facilitate native species recolonization, and shape range shifts with global change.
Women are underrepresented in science, technology, engineering, and mathematics (STEM) disciplines. Evidence suggests the microclimate of the classroom is an important factor influencing female ...course grades and interest, which encourages retention of women in STEM fields. Here, we test whether the gender composition of small (8-9 person) learning groups impacts course performance, sense of social belonging, and intragroup peer evaluations of intellectual contributions. Across two undergraduate active learning courses in introductory biology, we manipulated the classroom microclimate by varying the gender ratios of learning groups, ranging from 0% female to 100% female. We found that as the percent of women in groups increased, so did overall course performance for all students, regardless of gender. Additionally, women assigned higher peer- evaluations in groups with more women than groups with less women. Our work demonstrates an added benefit of the retention of women in STEM: increased performance for all, and positive peer perceptions for women.
Build up big-team science Coles, Nicholas A; Hamlin, J Kiley; Sullivan, Lauren L ...
Nature (London),
01/2022, Volume:
601, Issue:
7894
Journal Article
Peer reviewed
Human infants are perhaps the most powerful learning machines on the planet - and understanding how that learning occurs could inform artificial intelligence, public policy, education and more. In a ...proof-of-concept study, the ManyBabies Consortium used word of mouth, social media and e-mail lists to amass a team of 69 labs to test whether infants across several world regions prefer 'baby talk': the high-pitched, sing-song speech that adults in many cultures use with babies. In addition to the ManyBabies Consortium, the authors have collectively been involved in creating the Psychological Science Accelerator (involving some 1,200 researchers)5, the Disturbance and Resources Across Global Grasslands network (DRAGNet; around 100 researchers; https://dragnetglobal.weebly.com) and the ManyPrimates project (comprising about 150 researchers6; see 'Examples of big-team science'). The price tag gets much bigger when factoring in labour for project management, which included acquiring more than 150 ethics-approval documents, translating study materials into 23 languages and developing research tools to track progress and validate data from labs all over the world (see go.nature.com/3jcsutx).
Stochasticity is a core component of ecology, as it underlies key processes that structure and create variability in nature. Despite its fundamental importance in ecological systems, the concept is ...often treated as synonymous with unpredictability in community ecology, and studies tend to focus on single forms of stochasticity rather than taking a more holistic view. This has led to multiple narratives for how stochasticity mediates community dynamics. Here, we present a framework that describes how different forms of stochasticity (notably demographic and environmental stochasticity) combine to provide underlying and predictable structure in diverse communities. This framework builds on the deep ecological understanding of stochastic processes acting at individual and population levels and in modules of a few interacting species. We support our framework with a mathematical model that we use to synthesize key literature, demonstrating that stochasticity is more than simple uncertainty. Rather, stochasticity has profound and predictable effects on community dynamics that are critical for understanding how diversity is maintained. We propose next steps that ecologists might use to explore the role of stochasticity for structuring communities in theoretical and empirical systems, and thereby enhance our understanding of community dynamics
Cross-ecosystem material flows, in the form of inorganic nutrients, detritus and organisms, spatially connect ecosystems and impact food web dynamics. To date research on material flows has focused ...on the impact of the quantity of these flows and largely ignored their elemental composition, or quality. However, the ratios of elements like carbon, nitrogen and phosphorus can influence the impact material flows have on food web interactions through stoichiometric mismatches between resources and consumers. The type and movement of materials likely vary in their ability to change stoichiometric constraints within the recipient ecosystem and materials may undergo changes in their own stoichiometry during transport. In this literature review we evaluate the importance of cross-ecosystem material flows within the framework of ecological stoichiometry. We explore how movement in space and time impacts the stoichiometry of material flow, as these transformations are essential to consider when assessing the ability of these flows to impact food web productivity and ecosystem functioning. Our review suggests that stoichiometry of cross-ecosystem material flows are highly dynamic and undergo changes during transport across the landscape or from human influence. These material flows can impact recipient organisms if they change stoichiometry of the abiotic medium, or provide resources that have a different stoichiometry to in situ resources. They might also alter consumer excretion rates, in turn altering the availability of nutrients in the recipient ecosystem. These alterations in stoichiometric constraints of recipient organisms can have cascading trophic effects and shape food web dynamics. We highlight significant gaps in the literature and suggest new avenues for research that explore how cross-ecosystem material flows impact recipient ecosystems when considering differences in stoichiometric quality, their movement through the landscape and across ecosystem boundaries, and the nutritional constraints of the recipient organisms.
Dispersal is a key process in community assembly but is often considered separately from downstream assembly processes (e.g., competition, herbivory). However, dispersal varies by species and can ...interact with other assembly processes through establishment as species enter communities. Here, we sought to distinguish the role of dispersal in community assembly and its interaction with two biotic assembly processes: competition and herbivory. We used a tallgrass prairie restoration experiment that manipulated the competitive and herbivore environments while allowing for natural dispersal and establishment from a diverse regional species pool into areas of low diversity. Dispersal, competition, and herbivory all influenced local communities. By tracking the spread of four target species across the plots, we found interspecific and intraspecific differences in establishment patterns, with herbivores influencing the number of individuals present and the distances species moved. At the community level, only dispersal and competition significantly influenced alpha diversity, but all three processes additively influenced community composition. There was also evidence of herbivore–competition and herbivore–colonization trade‐offs in our experiment. Some species that could tolerate herbivory were less likely to establish in competitive environments, while others that could tolerate herbivory were more likely to disperse greater distances. More work is needed to understand the contexts under which dispersal variation affects community assembly and its synergy with other processes.
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