Biotic complexity, encompassing both competitive interactions within trophic levels and consumptive interactions among trophic levels, plays a fundamental role in maintaining ecosystem stability. While theory and experiments have established that plant diversity enhances ecosystem stability, the role of consumers in the diversity−stability relationships remains elusive. In a decade-long grassland biodiversity experiment, we investigated how heterotrophic consumers (e.g., insects and fungi) interact with plant diversity to affect the temporal stability of plant community biomass. Plant diversity loss reduces community stability due to increased synchronization among species but enhances the population-level stability of the remaining plant species. Reducing trophic complexity via pesticide treatments does not directly affect either community- or population-level stability but further amplifies plant species synchronization. Our findings demonstrate that loss of arthropod or fungal consumers can destabilize plant communities by exacerbating synchronization, underscoring the crucial role of trophic complexity in maintaining ecological stability.

Climate change is increasing extreme heating events and the potential for disease outbreaks. Whether hosts can adapt to infection with rising temperatures is important for forecasting species persistence. We tested whether warming -- at different host life-stages -- affects the ecological and evolutionary dynamics of resistance in Caenhorabditis elegans infected by a wild bacterial pathogen. We competed genotypes across 10 passages and tracked the spread of resistance in the population. Infection and prolonged warming strongly selected for the resistant genotype. Warming during host development induced plastic defenses against infection, reducing the selective pressure for costly genetic-based resistance. Resistance was lost under ambient temperatures and periodic warming. Selection for resistance was likely weakened at ambient temperatures by the dilution effect, whereby resistant genotype reduced pathogen transmission. Evolutionary dynamics of resistance depend on the balance among pathogen virulence, costs of genetic-based resistance, the dilution effect, and plastic defenses induced by temperature stress.

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.

Freezing tolerance plays a pivotal role in shaping the distribution and diversification of organisms. We investigated the dynamics of adaptation to climate and potential trade-offs between stem freezing tolerance and growth rate in 48 Quercus species. Species from colder regions exhibited higher freezing tolerance, lower growth rates and higher winter-acclimation potential than species from warmer climates. Despite an evolutionary lag, freezing tolerance in oaks is closely aligned with its optimal state. Deciduous species showed marked variability in freezing tolerance across their broad climatic range while evergreen species, confined to warm climates, displayed low freezing tolerance. Annual growth rates were constrained in all deciduous species but those that evolved in warm latitudes lost freezing tolerance precluding a trade-off between freezing tolerance and growth. We provide evidence that capacity to adapt to a wide range of thermal environments was critical to adaptive radiation and current dominance of the North American oaks.

Dispersal is a fundamental process driving many ecological patterns. During transfer, species often make large-scale displacements resulting in significant energetic losses with implications for fitness and survival, however generalising these losses across different taxonomic groups is challenging. We developed a bioenergetic dispersal model based on fundamental processes derived from species traits. By balancing energy storage and energy loss during active dispersal, our mechanistic model can quantify energetic expenditures depending on landscape configuration and the species in focus. Moreover, it can be used to predict the maximum dispersal capacity of animals, which we compare with recorded maximum dispersal distances (n = 1571). Due to its foundation in bioenergetics it can easily be integrated into various ecological models, such as food-web and meta-community models. Furthermore, as dispersal is integral to ecological research, the quantification of dispersal capacities provides valuable insight into landscape connectivity, species persistence, and distribution patterns with implications for conservation research.

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.

Understanding the drivers of spatially and temporally correlated (synchronous) fluctuations in abundance is a fundamental challenge in ecology and conservation. Synchronous fluctuations in different demographic rates can potentially drive or dampen abundance synchrony, but demographic synchrony is generally poorly understood. Using long-term count and demographic data for breeding land-birds at sites across Europe, we show that the strength and scale of synchrony are greatest in productivity, followed by adult survival rates and then counts. However, count fluctuations are more synchronous with survival than with productivity. Despite migratory and resident species having similar periodicities of count synchrony, synchrony in both demographic rates was more common over long-timescales in resident species and short-timescales in migrant species. These findings suggest local impacts of synchronous fluctuations in adult survival rates on count synchrony, potentially dampening effects of large-scale synchrony in productivity, and that the environmental drivers of synchrony may differ between residents and migrants.

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.