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

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.

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.

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.

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.

Taxonomic diversity effects on forest productivity and response to climate extremes range from positive to negative, suggesting a key role for complex interactions among neighbouring trees. To elucidate how neutral interactions, hierarchical competition and resource partitioning between neighbours shape tree growth and climate response in a highly diverse Amazonian forest, we combined 30 years of tree censuses with measurements of water and carbon related traits. We modelled individual tree growth response to climate and neighbourhood to disentangle the relative effect of neighbourhood densities, trait hierarchies and dissimilarities. While neighbourhood densities consistently decreased tree growth, trait dissimilarity increased it, and both influenced climate response. Greater water conservatism provided a competitive advantage to focal trees in normal years, but water spender neighbours reduced this effect in dry years. By highlighting the importance of density and trait-mediated neighbourhood interactions, our study offers a way towards improving predictions of forest response to climate change.

Recent international agreements have strengthened and expanded commitments to protect and restore native habitats. Nevertheless, biodiversity conservation is hindered because how such commitments should be implemented has been strongly debated. By bringing together researchers on both sides of the habitat fragmentation debate, we identify three incontrovertible principles for area-based biodiversity conservation. Such principles are related to habitat geographic coverage, amount, and connectivity. They emerge from our fundamental agreement that, while large areas of nature are important and must be protected, conservation or restoration of multiple small habitat patches is also critical for global conservation, particularly in regions with high land use. We contend that the many area-based conservation initiatives expected in the coming decades should follow the principles we propose. Considering the importance of biodiversity for maintenance of ecosystem services, we suggest that this would bring unequivocal societal benefits.

Understanding how diversity is maintained in plant communities requires that we first understand the mechanisms of competition for limiting resources. In ecology, there is an underappreciated, but fundamental distinction between systems in which the depletion of limiting resources reduces the growth rates of competitors versus systems in which resource depletion reduces the time available for competitors to grow, a mechanism we call “competition for time.” Importantly, modern community ecology, and our framing of the coexistence problem are built on the implicit assumption that competition reduces the growth rate. However, recent theoretical work suggests competition for time may be the predominant competitive mechanism in a broad array of natural communities, a significant advance given coexistence follows naturally when species compete for time. In this study we first introduce competition for time conceptually using a simple model of interacting species. Then, we perform an experiment in a Mediterranean annual grassland to determine whether competition for time is an important competitive mechanism in a field system. Indeed, we find that species respond to increased competition through reductions in their lifespan rather than their rate of growth. In total, our study suggests competition for time may be overlooked as a mechanism of biodiversity maintenance.

Most plant thermal tolerance studies focus on single critical thresholds, which limit the capacity to generalise across studies and predict heat stress under natural conditions. In animals and microbes, thermal tolerance landscapes describe the more realistic, cumulative effects of temperature. We tested this in plants by measuring the decline in leaf photosynthetic efficiency (FV/FM) following a combination of temperatures and exposure times, then modelled these physiological indices alongside recorded environmental temperatures. We demonstrate that a general relationship between stressful temperatures and exposure durations can be effectively employed to quantify and compare heat tolerance within and across plant species and over time. Importantly, we show how FV/FM curves translate to plants under natural conditions, suggesting that environmental temperatures often impair photosynthetic function. Our findings provide more robust descriptors of heat tolerance in plants and suggest that heat tolerance in disparate groups of organisms can be studied with a single predictive framework.

Invasions are commonly found to benefit from disturbance events. However, the importance of the relative timing and order of the invasion and disturbance for invader success remains uncertain. Here, we experimentally test this by invading a five-species bacterial community on eight separate occasions -- four before a disturbance and four after. Invader success and impact on community composition was greatest when the invasion immediately followed the disturbance. However, the subsequent invasions had negligible success or impact. Pre-disturbance, invader success and impact was greatest when the invader was added just before the disturbance. Importantly however, the first three pre-disturbance invasion events had significantly greater success than the last three post-disturbance invasions. Moreover, these findings were consistent across a range of propagule pressures. Overall, we demonstrate that timing is highly important for both the success and impact on community composition of an invader, with both being on average greater pre-disturbance.

Anthropogenic habitat modification is especially detrimental to social species. Apart from direct fitness effects, it can destroy group structure and affect social interactions crucial for reproduction and survival. Here, we assessed the impact of habitat modification on the fitness and life history traits of a cooperative breeder, the Arabian babbler (Argya squamiceps). We collected spatial, reproductive, and social data on 572 individuals belonging to 21 social groups over six years and combined it with remote sensing to characterize group territories. Groups in modified habitats bred more and had greater productivity during dry years. Males living in modified habitats dispersed and acquired dominance at a younger age, showing a faster pace of life. However, group performance and total fitness were higher in natural habitats during average years. Habitat modification indirectly affected fitness by altering social structure, whereby younger males who lacked experience became dominant, leading to reduced nesting success.