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.

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.

While multiple reasons make long-term demographic studies disproportionally valuable, much of their importance comes from the ability to detect and quantify rare events. We argue here that rare events can be critical for understanding important ecological and evolutionary processes. We highlight the additive or interactive nature of anthropogenic rare events with environmental rare events that may cause outsized changes in vital rates and therefore in population dynamics. Rare events may also generate complex responses in populations due to interactions between demographic processes and evolutionary responses. Complex, non-linear dynamics of populations may include threshold, extreme responses such as long transients, tipping points, regime shifts and collapse. When occurring locally, rare events may also exacerbate spatial heterogeneity with consequences for demographic processes. In sum, these effects represent substantial challenges for prediction, especially when considering the increase in the frequency of rare extreme events, and emphasise the need for long-term studies. Our perspective attempts to integrate the occurrence of rare events in variable environments and the consequences for the overall fitness, growth rates, and the spatial-temporal dynamics of populations.

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.

Climate change is implicated as a leading cause of insect declines. One way that insects respond to the warming climate is by advancing phenology and increasing voltinism (adding generations). However, if earlier phenology changes cue-response relationships, then late season generations might lack time or resources to complete development before winter and insects attempt doomed “lost generations”. Using 27 years of monitoring of 30 butterfly species, we find the opposite, as added generations increase population growth rates of multivoltine butterflies. We find lost generations are rare and occur at cooler sites in years with cold winters or early frosts. Overall, long-term population trends are positively correlated with increasing voltinism over time, suggesting additional generations as one mechanism by which species adapt to the changing climate. Long-term monitoring programs can test mechanistic hypotheses about biotic responses to warming while simultaneously tracking if population consequences match the predicted outcomes.

The endophytic fungi of certain grasses and other herbaceous plants have long been known to provide plants with anti-herbivore defense compounds, but there is little information about whether the endophytes of trees also engage in such mutualisms. We investigated the influence of the endophytic fungus Cladosporium cladosporioides on the chemical defenses of black poplar (Populus nigra) trees and the consequences for feeding preference and fitness of herbivorous insects and insect community assembly. Endophyte colonization increased both constitutive- and induced poplar defenses. Generalist Lymantria dispar larvae preferred and performed better on uninfected over endophyte-infected poplar leaves, most likely due to higher concentrations of salicinoids in endophytic leaves and the endophyte-produced alkaloid stachydrine. Under field conditions, the endophytic fungus also shapes insect community assembly in young black poplar trees. Our results show that endophytic fungi can play a major role both in defending trees against herbivorous insects and in structuring insect communities.

A document by Ismaël Lajaaiti. Click on the document to view its contents.

Trophic change has induced substantial changes in biomass and composition of aquatic communities. Based on phytoplankton data from Lake Constance we demonstrate that community function is closely connected to community composition and responds strongly to trophic change. Community mean traits phosphate affinity and light affinity are tightly linked to trophic state during eutrophication and re-oligotrophication, suggesting reversibility of community function. Phosphate and light affinity are anti-correlated. This anti-correlation is weak in the species pool distinguished in the dataset, but strong when weighting the traits by the species biovolumes or when comparing community mean traits from different trophic states. The emergence of this tradeoff between phosphate and light affinity indicates competitive advantage of species with traits near the tradeoff line. The correlation between community mean maximum growth rate and trophic state turned out to be spurious and resulted from the development of Dinophyceae spp. which have an alternative mode of nutrition.

Global change drivers alter multiple components of community composition, with cascading impacts on ecosystem stability. However, few studies have examined the complex interplay between global change drivers, synchrony, and diversity, especially over long-term successional dynamics. We analyzed a 22-year time series of grassland community data from Cedar Creek, USA, to examine the joint effects of pulse soil disturbance and press nitrogen addition on community synchrony, diversity, and stability during transient and post-transient periods of succession. Using multiple regression and structural equation modeling, we found that global change drivers decreased both synchrony and stability, thereby decoupling classic theoretical relationships, such as the portfolio effect. While the effect of soil disturbance weakened through time, nitrogen addition induced unexpected dynamics with maintained long-term impacts on composition, synchrony, and stability. Our findings underscore the need for long-term data and a comprehensive approach when managing ecosystems under ongoing global environmental changes.

Early life experiences have a disproportionate impact on individuals’ fitness, but most research has focused on the effects of single experiences, or stressors, often under controlled conditions. Protecting natural populations that must contend with co-occurring stressors requires a better understanding of how multiple early-life stressors affect the health and ecology of natural systems. However, the complexity of such research has limited its advancement. To address this challenge, human studies adopted cumulative risk models that predict adult health risk based on early adversity exposure. We propose a novel framework on how to adapt such models to assess the health and ecology of natural populations. In this framework we detail how and when to develop various types of cumulative early adversity (CEA) indices for wild populations. We then use a case study to demonstrate that such indices can predict pup survival and adult longevity in a wild population of yellow-bellied marmots (Marmota flaviventer). Our results highlight that CEA indices yield unique insights and improve model fit. With this framework we hope to spur further investigations on the impact of cumulative adversity in natural systems, which is critical to inform conservation and management in the Anthropocene.

Community assembly provides the foundation for applications in biodiversity conservation, climate change, invasion ecology, restoration ecology, and synthetic ecology. Predicting and prioritizing community assembly outcomes remains challenging. We address this challenge via a mechanism-free LOVE (Learning Outcomes Via Experiments) approach suitable for cases where little data or knowledge exist: we carry out actions (randomly-sampled combinations of species additions), measure abundance outcomes, and then train a model to predict arbitrary outcomes of actions, or prioritize actions that would yield the most desirable outcomes. When trained on <100 randomly-selected actions, LOVE predicts outcomes with 2-5% error across datasets, and prioritizes actions for maximizing richness, maximizing abundance, or minimizing abundances of unwanted species, with 94-99% true positive rate and 12-83% true negative rate across tasks. LOVE complements existing approaches for community ecology by providing a foundation for additional mechanism-first study, and may help address numerous ecological applications.

Plant-soil feedback (PSF), the reciprocal interaction between plants and their soil environment, is a fundamental ecological process that influences coexistence and functional structure in plant communities. Current theory establishes that PSF may enhance diversity or lead to exclusion depending on whether soil conditioning disproportionately benefits heterospecific or conspecific individuals. However, a more complete picture of the impact of PSF requires understanding how PSF synergizes with competition. To that end, here we propose an integrated mathematical model combining trait-based competition and soil-explicit PSF. Contrary to the current paradigm, we find that soil conditioning that disproportionately favors conspecific individuals can promote coexistence. Additionally, we show that priority effects are common when soil-conditioning species differ in their edaphic preferences. These effects can allow species with large differences in competitive ability to coexist under certain soil conditions. Our results provide testable predictions tying community-level functional patterns in plant communities to PSF and competition.

In socially monogamous species, sexual selection not only depends on initial mate choice but also mate switching. To date, studies lack assessment of differences between passive (widowhood) and active (divorce) mate switching, longer-term fitness consequences, and how age masks reproductive costs and benefits of divorce. We investigated causes and long-term consequences of divorce and their age-dependence using longitudinal data on Seychelles warblers (Acrocephalus sechellensis), and experimentally test for short-term effects of mate-switching. Young and old males, but not females, divorced most frequently. Divorce propensity declined with pair bond duration and reproductive success in both sexes, but mate switching did not result in short-term costs. Divorcees did not gain short- or long-term fitness benefits compared to non-divorcees. In fact, female early-life divorcees that lost their breeding position had lower survival than females that never divorced. Divorce is likely a strategy to escape poor-quality partnerships, but not all divorcees benefit from divorcing.

Long-term studies are subject to stochastic forces as well as deterministic, ecological differences. We illustrate this by means of Polya’s urn scheme and two examples based on our long-term study of the behavioral ecology of the acorn woodpecker (Melanerpes formicivorus). In both cases, the years during which the study was conducted had a large, apparently stochastic influence on population dynamics. Despite such variability, long-term studies offer several notable benefits, including the opportunity to gain a more nuanced understanding of a particular system and the ability to incorporate technological and theoretical advances. Ultimately, it is with long-term data that we can hope to disentangle and understand the stochastic and deterministic factors that drive ecological systems.

Environmental change is becoming synchronous across sites with frequent emergence of extremes in recent years, with alarming potential impacts on species’ synchronous abundance over large scales. With 23 years of breeding bird survey data across North America, we found that some birds are becoming synchronously rare across sites, while others are becoming synchronously common. We evaluated the relative importance of two co-occurring mechanisms (environment-driven and dispersal-driven) to explain such spatial synchrony in extreme low or high abundance (i.e., tail-dependent synchrony). We found that spatial synchrony in temperature extremes (i.e., tail-dependence in climate) was the major driver for birds’ tail-dependent spatial synchrony up to 250 Km. In addition, temperature extremes and dispersal trait both favored synergistically some species making them synchronously common across sites. In a rapidly changing environment, these findings highlight the importance of considering synchronized climatic extremes to assess species’ tail-dependent spatial synchrony across large scale.

Understanding how species adjust to seasonality is fundamental in ecology, especially with rapidly increasing global air temperatures. Bioacoustic monitoring offers promise for tracking shifts in seasonal timing of vocal species, as recent automated sound recorders enable large-scale and long-term data collection. Yet, analyzing vast datasets necessitates automation and innovative detection methods. Here, we introduce BioSoundNet, a deep learning model designed for bird vocalization detection. Trained on field data and open-access databases, BioSoundNet achieved AUC scores of 0.88-0.93 and average precisions of 0.87-0.97 across five datasets spanning various ecosystems, and effectively captured the temporal patterns of avian acoustic activity at different time scales. Our findings underline the importance of evaluating models in ecological contexts and to address the potential consequences of missing detections. Operating efficiently on standard computers, BioSoundNet is a robust tool for automated bird vocalization detection, providing a valuable resource for ecological phenology studies and acoustic dataset analysis.

Aquatic ectotherms often attain smaller body sizes at higher temperatures. By analysing ~15,000 coastal-reef fish surveys across a 15oC spatial sea surface temperature (SST) gradient, we found that the mean length of fish length in communities decreases by ~5% for each 1oC temperature increase across space. This equated to a 50% decrease in mean length from 14 to 29oC mean annual SST. We found that trophic guild composition shifts from domination by herbivores and planktivores in the tropics, to invertivores and piscivores in cooler waters. By investigating the contribution of trophic composition to community-level mean length, we show ~25% of temperature-related changes could be attributed to trophic composition at the warmest sites, but <1% at colder temperatures. Our findings suggest that small changes in temperature will lead to large changes in fish community body sizes, driven both by community trophic composition in warm waters and mean sizes within trophic guilds.

Human activities have altered the species composition of assemblages through introductions and extinctions, but it remains unclear how those changes can affect the different facets of biodiversity. Here we assessed the impact of changes in species composition on taxonomic, functional, and phylogenetic diversity across 281 bird assemblages worldwide. To provide a more nuanced understanding of functional diversity, we distinguished morphological from life-history traits. We showed that shifts in species composition could trigger a global decline in avian biodiversity due to the high number of potential extinctions. Moreover, these extinctions were not random but unique in terms of function and phylogeny at the regional level. Our findings demonstrated that non-native species cannot compensate for these losses, as they are both morphologically and phylogenetically close to the native fauna. In the context of the ongoing biodiversity crisis, such alterations in the functional and phylogenetic structure of bird assemblages could heighten ecosystem vulnerability.