Species coexistence is shaped by a range of biotic and abiotic factors. Beyond predation, parasitism, and competition, one species may interfere with another's reproduction to induce sexual exclusion from a habitat. Here, we test for reproductive interference from inter-species mating between sympatric nematodes Caenorhabditis macrosperma and C. nouraguensis. Higher intrinsic population growth of C. nouraguensis arises from greater reproductive output by both sexes, predicting it to be superior in resource competition. Mate discrimination between species is incomplete, however, with inter-species mating errors reducing lifespan and reproductive fitness of female C. nouraguensis only. These asymmetric costs arise within hours, due to ectopic migration of C. macrosperma's giant sperm cells. We modelled the population dynamic impacts of reproductive interference, then confirmed rapid sexual exclusion in mixed-species communities with multi-generation experiments. These findings demonstrate the profound ecological implications of reproductive interference for demographic parameters and species coexistence through a cell-mediated mechanism of inter-species harm.

A document by Tyson Wepprich. Click on the document to view its contents.

It remains challenging to understand why natural food webs are remarkably stable despite pronounced variability in environmental factors and population densities. We analysed the dynamics in the structure and stability of the pelagic food web of Lake Constance using seven years of high-frequency observations of biomasses and production, leading to 59 seasonally resolved quantitative food web descriptions. We analysed the dynamics in asymptotic food web stability using maximum loop weight, which revealed mechanisms governing stability. Maximum loop weight showed a recurrent seasonal pattern while indicating consistently high stability despite pronounced dynamics in biomasses and fluxes. This arose from rewiring of the food web structure along seasons, which counteracted destabilization by enhanced productivity. The rewiring originated from energetic constraints within loops and how loops were embedded into food web structure. The stabilizing dynamics originated from the counter-acting effect between high metabolic activity and competitiveness/susceptibility to predation within a diverse grazer community.

With many species interacting in nature, determining which describe community dynamics is nontrivial. By applying a new Bayesian-sparse modelling approach to an extensive field survey, we assessed the importance of interactions from con- and hetero-specific plants, pollinators, and insect herbivores on plant performance. We compared the inclusion of the interaction effects as aggregate "generic" terms versus specific terms. We found that a continuum of positive to negative interactions, containing mostly generic but a few strong specific interactions, was sufficient to describe variation in plant performance. While interactions with herbivores and conspecifics varied from weakly negative to weakly positive, heterospecific plants mainly promoted competition and pollinators facilitated plants. The consistency of these empirical findings over three years suggests that a broad resolution, including the generic effects of guilds and a few specific groups rather than all pairwise and high-order interactions, can accurately describe species variation in plant performance across natural communities.

Climate change can influence populations of monogamous species by affecting pair-bond dynamics. This study examined the impact of climate on widowhood and divorce, and the subsequent effects on individual vital rates and life-history outcomes over 54 years in a snow petrel (Pagodroma nivea) population. We found that environmental conditions can affect pair-bond dynamics both directly and indirectly. Divorce was adaptive, occurring more frequently after breeding failure and leading to improved breeding success. Divorce probabilities also increased under severe climatic conditions, regardless of prior breeding success, supporting the ”Habitat-mediated” mechanisms. Generally, pair-bond disruptions reduced subsequent vital rates and lifetime outcomes. Climate forecasts from an Atmosphere-Ocean General Circulation Model projected increased male widowhood rates due to decreased sea ice negatively affecting female survival, despite considerable uncertainty. These findings highlight the importance of environmentally induced changes in demographic and pair-bond disruption rates as crucial factors shaping demographic responses to climate change.

A major challenge in ecology is to understand how different species interact to determine ecosystem function, particularly in communities with large numbers of co-occurring species. We use a trait-based model of microbial litter decomposition to quantify how different taxa impact ecosystem function. Further, we build a novel framework that highlights the interplay between taxon traits and environmental conditions, focusing on their combined influence on community interactions and ecosystem function. Our results suggest that the impact of a taxon is driven by its resource acquisition traits and the community functional capacity, but that physiological stress amplifies the impact of both positive and negative interactions. Further, net positive impacts on ecosystem function can arise even as microbes have negative pairwise interactions with other taxa. As communities shift in response to global climate change, our findings reveal the potential to predict the biogeochemical functioning of communities from taxon traits and interactions.

Warming climate impacts aquatic ectotherms both directly, by altering individual vital rates, and indirectly through environmental feedbacks and declines in body size, a phenomenon known as the temperature-size rule (TSR). However, understanding the relative importance of these effects in shaping community responses to environmental change remains limited. We employ a tri-trophic food chain model with size- and temperature-dependent vital rates and species interaction strengths to explore the role of direct kinetic effects of temperature and TSR on community structure along resource productivity and temperature gradients. We find that community structure, including the propensity of sudden shifts, is primarily driven by the direct kinetic effects of temperature on vital rates and thermal mismatches between the consumer and predator species, overshadowing the indirect effects through the TSR. Overall, our study enhances the understanding of the complex interplay between temperature, species traits and community dynamics in aquatic ecosystems.

In tropical forests, trees strategically balance growth patterns to optimize fitness amid multiple environmental stressors. Wind poses the primary risk to a tree’s mechanical stability, prompting developments such as thicker trunks to withstand the bending forces. Therefore, a trade-off in resource allocation exists between diameter growth and vertical growth to compete for light. We explore this trade-off by measuring the relative wind mortality risk for 96 trees in a tropical forest in Panama and testing how it varies with tree size, species and wind exposure. Surprisingly, local wind exposure and tree size had minimal impact on wind mortality risk; instead, species wood density emerged as the crucial factor. Low wood density species exhibited a significantly greater wind mortality risk, suggesting a prioritization of competition for light over biomechanical stability. Our study highlights the pivotal role of wind safety in shaping the life-history strategy of trees and structuring diverse tropical forests.

Accurately representing the relationships between nitrogen supply and photosynthesis is crucial for reliably predicting carbon-nitrogen cycle coupling in Earth System Models (ESMs). Most ESMs assume positive correlations among soil nitrogen supply, leaf nitrogen content, and photosynthetic capacity. However, leaf photosynthetic nitrogen demand may influence the leaf nitrogen response to soil nitrogen supply, thus responses to nitrogen supply are expected to be largest in environments where demand is greatest. Using a nutrient addition experiment replicated at 26 sites spanning four continents, we demonstrated that climate variables were stronger predictors of leaf nitrogen content than soil nutrient supply. Leaf nitrogen increased more strongly with soil nitrogen supply in regions with highest theoretical leaf nitrogen demand, increasing more in colder and drier environments than warmer and wetter ones. Thus, leaf nitrogen responses to nitrogen supply are primarily influenced by climatic gradients in photosynthetic nitrogen demand, an insight that will improve ESM predictions.

Plant-microbe associations are ubiquitous, but parsing the contributions of dispersal, host filtering, competition, and the environment on microbial community composition is challenging. Floral nectar-inhabiting microbes offer a tractable system to disentangle community assembly processes. We inoculated a synthetic community of yeasts and bacteria into nectars of 31 phylogenetically diverse plant species while excluding pollinators. We monitored weather conditions and, after 24 hours, collected and cultured communities. We found a strong signature of plant species on resulting microbial abundance and community composition, in part explained by plant phylogeny and nectar peroxide content, but not measured floral morphological traits. Higher maximum and minimum temperatures increased microbial growth overall and favored certain microbes over others. Our work supports the roles of plant identity and abiotic conditions in assembly and growth of plant-associated microbial communities and finds evidence for diversity-productivity relationships within plant-associated microbiomes.

Quantifying trade-offs within populations is important in life-history theory. However, most studies focusing on life-history trade-offs focus on two traits and assume trade-offs to be static. Our work provides a framework for understanding covariation among multiple traits and how population density influences the traits. Using detailed individual-based data for Soay sheep, we find density strongly shapes life-history trade-offs and distribution of lifetime reproductive success (LRS). At low density, a trade-off between juvenile survival and growth structures life-history variation whereas at equilibrium density (K), trade-off between reproduction and juvenile survival is the major structuring axes. Contrary to Lomnicki’s prediction, we find the distribution of LRS is highly constrained at K, with mothers of adult sizes contributing the most to reproduction. Our results offer insights into how high density limits diversity of individual life-histories, advance an understanding of dynamic nature of trade-offs and have implications for evolution via density-dependent selection.

Understanding microbial adaptation is crucial for predicting how soil carbon dynamics and global biogeochemical cycles will respond to climate change. This study employs the DEMENT model of microbial decomposition, along with empirical mutation and dispersal rates, to explore the roles of mutation and dispersal in adaptation of soil microbial populations to shifts in litter chemistry, changes that are anticipated with climate-driven vegetation dynamics. Following a change in litter chemistry, mutation generally allows for a higher rate of litter decomposition than dispersal, especially when dispersal predominantly introduces genotypes already present in the population. These findings challenge the common idea that mutation rates are too low to affect ecosystem processes on ecological timescales. These results demonstrate that evolutionary processes, such as mutation, can help maintain ecosystem functioning as the climate changes.

Pollinators are unquestionably declining, however, current knowledge on the rate of decline is biased in two aspects which are fragmented (West-dominated) geographic scope and narrow (bee-dominated) taxonomic focus of studies. This bias has resulted in an unfortunate imbalance, whereby the most biologically diverse regions are less furnished with diversified data, and diverse pollinator groups are out of scope. We suggest evaluation of four major drivers of this bias – (i) concept generalization, (ii) data accessibility, (iii) scattered environmental regulations, and (iv) shifted infrastructure and funding resources. We argue that the complex interplay between these drivers has created a bias in knowledge that needs addressing. Using search engines in different languages and closer cooperation between developed and developing countries may help to overcome geographic bias in pollinator studies. The direction of research toward pollinator diversity and involvement of scientists in environmental policies can help to reach knowledge balance on the topic.

Most eco-evolutionary research focuses on ecological effects of single-species evolution. We therefore know little of eco-evolutionary dynamics when multiple species evolve simultaneously. We quantified evolution-mediated ecological effects in communities equivalent in genetic diversity and starting biomass, but different in selection background (heatwave exposure) of one or all four zooplankton species (three Daphnia and one Scapholeberis species). We observed transient eco-evolutionary effects that differed depending on which species in the community had evolved. Evolution did not always lead to higher abundances of the evolved species. Indirect effects on species abundances caused by evolution of another species could be as strong as direct effects mediated by its own evolution. The cumulative effect of evolution in multiple species was antagonistic for community composition and grazing pressure but additive for community-wide biomass. Our results imply that focusing on single species’ evolutionary effects on ecology may lead to unreliable predictions when multiple species evolve simultaneously.

The Kenya Long-term Exclosure Experiment (KLEE) was established in 1995 in a semi-arid savanna rangeland on the Laikipia Plateau to examine the separate and combined effects of livestock, wildlife, and megaherbivores (elephants and giraffes) on their shared environment and on each other. The long-term nature of this experiment also allowed us to measure these effects and related questions of stability and resilience in the context of multiple drought-rainy cycles. Here we outline some of the lessons learned over the last 29 years. In particular, we summarize three ways that KLEE exemplifies the value of long-term studies: 1) identifying experimental effects that take a many years to express themselves, 2) quantifying the effects of different years, especially multiple droughts, and 3) capturing time periods long enough to see the signature of systemic, anthropogenic change in the broader landscape. Across all aspects of a long-term study such as this one, there is a need to incorporate both consistency and flexibility to ensure deeper understanding.

Changing CO2 concentrations have and will continue to affect plant growth with consequences for ecosystem functioning. The adaptive capacity of C3 photosynthesis to changes in atmospheric CO2 concentrations is, however, insufficiently investigated so far. Here we focused on the phylogenetic dynamics of maximum carboxylation rate (Vcmax) and maximum electron transport rate (Jmax) – two key determinants of photosynthetic efficiency in C3 plants – and their relation to deep-time dynamics in species diversification, speciation and atmospheric CO2 concentrations during the last 120 million years. We observed very strong positive relationships between photosynthetic efficiency and species diversification as well as speciation rates. Vcmax as well as species speciation and diversification furthermore increased during periods of low prehistoric CO2 concentrations. From our results we conclude strong links between photosynthetic efficiency and evolutionary dynamics in C3 plants. We furthermore conclude, that increasing future CO2 concentrations might rather hinder than facilitate evolutionary dynamics in C3 plants.

The rhizosphere influence on the soil microbiome and function of crop wild progenitors remains virtually unknown, despite its relevance to develop microbiome-oriented tools in sustainable agriculture. Here, we quantified the rhizosphere influence -- a comparison between rhizosphere and bulk soil samples -- on bacterial, fungal, protists and invertebrates communities and on soil multifunctionality across nine crop wild progenitors in their sites of origin. Overall, rhizosphere influence was higher on abundant taxa across the four microbial groups, and had a positive influence on increased rhizosphere carbon storage and nutrient contents compared to bulk soils. The rhizosphere influence on abundant soil microbiomes were more important for soil multifunctionaility than rare taxa and envirommental conditions. Our results are a starting point to uncover the roles of both abundant and rare soil taxa in enhancing multifunctionality in agroecosystems.

Shelter-building insects are important ecosystem engineers, playing critical roles in structuring arthropod communities. Nonetheless, the influence of leaf shelters and arthropods on plant-associated microbiota remains largely unexplored. Arthropods that visit or inhabit plants can contribute to the leaf microbial community, resulting in significant changes in plant-microbe interactions. By artificially constructing leaf shelters, we provide evidence that shelter-building insects influence not only the arthropod community structure but also impact the phyllosphere microbiota. Leaf shelters exhibited higher abundance and richness of arthropods, leading to changes in the associated arthropod community composition. These shelters also altered the composition and community structure of phyllosphere microbiota, promoting greater richness and diversity of bacteria at the phyllosphere. In leaf shelters, microbial diversity increased with the richness and diversity of herbivores. These findings demonstrate the critical role of leaf shelters in structuring arthropod communities by facilitating colonization and influencing microbial communities through altered microhabitats and community interactions.