Biotic Interactions Research Articles

Population Dynamics of the Exotic Flatworm Obama nungara in an Invaded Garden.

Population dynamics and the way abundance fluctuates over time may be key determinants of the invasion success of an introduced species. Fine-scale temporal monitoring of invasive species is rarely carried out due to the difficulties in collecting data regularly and over a long period. Thanks to the collaboration of an amateur naturalist, a unique dataset on the abundance of the invasive land flatworm Obama nungara was obtained during a 4-year survey of a French private garden, where up to 1585 O. nungara were recorded in 1 month. Daily monitoring data revealed high population size fluctuations that may be explained by meteorological factors as well as intra- and inter-specific interactions. Bayesian modeling confirmed that O. nungara's abundance fluctuates depending on temperature, humidity, and precipitation. Population growth seems to be favored by mild winters and precipitation while it is disadvantaged by drought. These exogenous factors affect both directly this species, which is sensitive to desiccation, and indirectly since they are known to affect the populations of its prey (earthworms and terrestrial gastropods). We also suggested the important resilience of O. nungara population in this site, which was able to recover from a drastic demographic bottleneck due to a severe drought, as well to systematic removal by the owner of the site. These findings highlight the potentially high invasiveness of O. nungara and raise concerns about the major threat these invasive flatworms pose to the populations of their prey.

Microbial Regulation of Interspecific Interaction and Metabolism in Anammox Process to Achieve Coadaptation to Artificial Sweeteners

Artificial sweeteners (ASs) were frequently detectable in wastewater, which pose high risks to human health and ecological security. The feasibility of anaerobic ammonium oxidation (anammox) process for treatment of ASs-containing wastewater was evaluated in this study. The 86-d continuous flow experiment results showed that 0-30μgL-1 cyclamate and acesulfame did not significantly affect the nitrogen removal efficiency (NRE) of anammox processes, which were 94.5 ± 3.0% and 96.6 ± 2.5%, respectively. Simultaneously, specific anammox activity (SAA) was inhibited by 15μgL-1 ASs. Fortunately, anammox consortia adapted to the ASs stress by secreting extracellular polymeric substance (EPS). The relative abundances of Candidatus Kuenenia slightly decreased by 0.2% and 2.3% under stress of two ASs, and the microbial diversity increased. In addition, the anammox consortia regulated metabolites expression by cell energy allocation. The dominant metabolic pathways were amino acid metabolism, lipid metabolism and nucleotide metabolism. Particularly, the abundances of 5-hydroxylysinonorleucine and L-hypoglycin A significantly increased with ASs concentrations, which were crucial for bacterial proliferation. The co-metabolism between different bacteria might contribute to the biodegradation of ASs. This work demonstrates the feasibility of anammox process to treat the ASs-containing wastewater and reveals the regulation and adaptation mechanism of anammox microbiota, which further drives the implementation and development of anammox process.

Boosting Rice Resilience: Role of Biogenic Nanosilica in Reducing Arsenic Toxicity and Defending against Herbivore.

The use of nanoparticles is a promising ecofriendly strategy for mitigating both abiotic and biotic stresses. However, the physiological and defense response mechanisms of plants exposed to multiple stresses remain largely unexplored. Herein, we examined how foliar application of biogenic nanosilica (BNS) impacts rice plant growth, molecular defenses, and metabolic responses when subjected to arsenic (As) toxicity and infested by the insect Chilo suppressalis. We show that BNS significantly increased shoot and root silicon accumulation but reduced the shoot As content by 34.7% under herbivory. Additionally, BNS reduced C. suppressalis larval weight gain by 34.5 and 12.3% without and with As stress, respectively. Importantly, BNS enhanced antioxidant enzyme activity under As stress, herbivore attack, and combined pressures, surpassing the effects of traditional silicate fertilizers. BNS ultimately increased rice shoot biomass by 8.2-23.4% under the respective stress conditions compared to the control treatment. Moreover, while As stress alone diminished the plant's resistance to herbivores, BNS application countered this effect by increasing detoxifying compound (e.g., glutathione) production and antioxidant enzyme activity. This study highlights the impact of biotic and abiotic stress interactions on BNS-enhanced plant resilience mechanisms in rice plants, reallocating resources to counter heavy metal toxicity and herbivore damage in agroecosystems.

Calibrated Ecosystem Models Cannot Predict the Consequences of Conservation Management Decisions.

Ecosystem models are often used to predict the consequences of management interventions in applied ecology and conservation. These models are often high-dimensional and nonlinear, yet limited data are available to calibrate or validate them. Consequently, their utility as decision-support tools is unclear. In this paper, we calibrate ecosystem models to time series data from 110 different experimental microcosm ecosystems, each containing three to five interacting species. Then, we assess their ability to predict the consequences of management interventions. Our results show that for each time series dataset, multiple divergent parameter sets offer equivalent, good fits. However, these models have poor predictive accuracy when forecasting future dynamics or when predicting how the ecosystem will respond to management intervention. Closer inspection reveals that the models fail because calibration cannot determine the nature of the interspecific interactions. Our findings question whether ecosystem models can support applied ecological decision-making when calibrated against real-world datasets.

Temporal changes in taxon abundances are positively correlated but poorly predicted at the global scale

Linking changes in taxon abundance to biotic and abiotic drivers over space and time is critical for understanding biodiversity responses to global change. Furthermore, deciphering temporal trends in relationships among taxa, including correlated abundance changes (e.g. synchrony), can facilitate predictions of future shifts. However, what drives these correlated changes over large scales are complex and understudied, impeding our ability to predict shifts in ecological communities. We used two global datasets containing abundance time‐series (BioTIME) and biotic interactions (GloBI) to quantify correlations among yearly changes in the abundance of pairs of geographically proximal taxa (genus pairs). We used a hierarchical linear model and cross‐validation to test the overall magnitude, direction and predictive accuracy of correlated abundance changes among genera at the global scale. We then tested how correlated abundance changes are influenced by latitude, biotic interactions, disturbance and time‐series length while accounting for differences among studies and taxonomic categories. We found that abundance changes between genus pairs are, on average, positively correlated over time, suggesting synchrony at the global scale. Furthermore, we found that abundance changes are more positively correlated with longer time‐series, with known biotic interactions and in disturbed habitats. However, the magnitude of these ecological drivers alone are relatively weak, with model predictive accuracy increasing approximately two‐fold with the inclusion of study identity and taxonomic category. This suggests that while patterns in abundance correlations are shaped by ecological drivers at the global scale, these drivers have limited utility in forecasting changes in abundances among unknown taxa or in the context of future global change. Our study indicates that including taxonomy and known ecological drivers can improve predictions of biodiversity loss over large spatial and temporal scales, but also that idiosyncrasies of different studies continue to weaken our ability to make global predictions.

Novel approach to studying marine fauna: using long-life remote underwater video cameras to assess occurrence and behaviour of threatened and data-deficient elasmobranch species in southern Mozambique

Understanding the behaviour and ecological role of elasmobranchs is essential for their conservation, particularly in regions harbouring threatened and data-deficient species like the Inhambane coastline in southern Mozambique, southwestern Indian Ocean. This study employed long-life remote underwater video cameras (LL-RUV) to observe elasmobranch occurrence and behaviour at a rocky reef near Praia do Tofo known for frequent elasmobranch sightings. Between 2021 and 2024, 524 hours of LL-RUV data were collected, revealing the presence of 14 threatened and data-deficient elasmobranch species. Reef manta rays (Mobula alfredi), small eye stingrays (Megatrygon microps), and oceanic manta rays (Mobula birostris) were identified as the primary elasmobranch users of the studied cleaning stations (n = 81, n = 72 and n = 61 respectively), engaging in mutualistic interactions with cleaner fish and spending significant amounts of time at the studied reef. In contrast, spotted eagle rays (Aetobatus narinari) and blacktip sharks (Carcharhinus limbatus) were solely observed cruising over the reef without engaging in cleaning interactions (n = 40 and n = 27 respectively). In addition, this study provides evidence of intra- and inter-specific interactions between reef and oceanic manta rays, small eye stingrays and bowmouth guitarfish (Rhina ancylostoma) and co-occurrences of both manta ray species and smalleye stingrays with “hitchhiker” species including cobia (Rachycentron canadum) and remoras (Echeneis spp.). The use of LL-RUV cameras represents a significant advancement in marine research. These cameras enable continuous, non-intrusive, long-term monitoring of marine environments, capturing natural behaviours, while minimising disturbances caused by divers. As a result, more accurate observations of elasmobranch behaviour and cleaning station dynamics can be recorded, which might be missed during short-term surveys. This research highlights the potential of LL-RUV cameras as powerful tools for advancing our understanding of elasmobranch occurrence and behaviour and underscores their value in informing targeted and effective conservation strategies. Beyond elasmobranch research, LL-RUVs hold tremendous potential for studying a wide range of marine species and habitats, offering a versatile tool for ecological monitoring and conservation efforts across diverse marine ecosystems.

The Temporal Order of Mixed Viral Infections Matters: Common Events That Are Neglected in Plant Viral Diseases.

Mixed infections of plant viruses are common in crops and represent a critical biotic factor with substantial epidemiological implications for plant viral diseases. Compared to single-virus infections, mixed infections arise from simultaneous or sequential infections, which can inevitably affect the ecology and evolution of the diseases. These infections can either exacerbate or ameliorate symptom severity, including virus-virus interactions within the same host that may influence a range of viral traits associated with disease emergence. This underscores the need for a more comprehensive understanding of how the order of virus arrival to the host can impact plant disease dynamics. From this perspective, we reviewed the current evidence regarding the impact of mixed infections within the framework of simultaneous and sequential infections in plants, considering the mode of viral transmission. We also examined how the temporal order of mixed infections could affect the dynamics of viral populations and present a case study of two aphid-transmitted viruses infecting melon plants, suggesting that the order of virus arrival significantly affects viral load and disease outcomes. Finally, we anticipate future research that reconciles molecular epidemiology and evolutionary ecology, underlining the importance of biotic interactions in shaping viral epidemiology and plant disease dynamics in agroecosystems.

Beyond predation: Fish-coral interactions can tip the scales of coral disease.

Coral reefs are critical ecosystems, fostering biodiversity and sustaining the livelihoods of millions globally. Nonetheless, they confront escalating threats, with infectious diseases emerging as primary catalysts for extensive damage, surpassing the impacts of other human-induced stressors. Disease transmission via biotic factors, particularly during fish predation, is a crucial yet often overlooked pathway. While their feeding can spread infectious diseases through spores, it also controls the growth of macroalgae, a major competitor for space on the reef. Given this dual effect, the precise impact of fish on coral disease remains ambiguous and requires additional investigation. In this study, we addressed this gap for the first time by employing a mathematical model. Our analyses unveil intricate interactions between fish predation and coral health, revealing potential benefits and drawbacks for coral reef ecosystems. Coral survival hinges on a delicate balance of fish predation, with extremes (both low and high) offering some protection against disease outbreaks compared to moderate predation, which can cause sudden die-offs. More specifically, as fish predation intensifies, the ecosystem undergoes a tipping point, transitioning from a disease-dominated state to a healthier one. Moreover, the interplay between transmission rate and virulence in coral populations is significantly shaped by fish predation rates. Specifically, the threshold ratio of transmission to virulence, signalling a regime shift from a healthy to a disease-dominated state, exhibits a linear increase with fish predation rate. Overall, our findings emphasize the importance of considering biotic interactions in coral disease ecology and offer insights essential for effective reef conservation strategies.

Discarded sequencing reads uncover natural variation in pest resistance in Thlaspi arvense.

Understanding the genomic basis of natural variation in plant pest resistance is an important goal in plant science, but it usually requires large and labor-intensive phenotyping experiments. Here, we explored the possibility that non-target reads from plant DNA sequencing can serve as phenotyping proxies for addressing such questions. We used data from a whole-genome and -epigenome sequencing study of 207 natural lines of field pennycress (Thlaspi arvense) that were grown in a common environment and spontaneously colonized by aphids, mildew, and other microbes. We found that the numbers of non-target reads assigned to the pest species differed between populations, had significant SNP-based heritability, and were associated with climate of origin and baseline glucosinolate contents. Specifically, pennycress lines from cold and thermally fluctuating habitats, presumably less favorable to aphids, showed higher aphid DNA load, i.e., decreased aphid resistance. Genome-wide association analyses identified genetic variants at known defense genes but also novel genomic regions associated with variation in aphid and mildew DNA load. Moreover, we found several differentially methylated regions associated with pathogen loads, in particular differential methylation at transposons and hypomethylation in the promoter of a gene involved in stomatal closure, likely induced by pathogens. Our study provides first insights into the defense mechanisms of Thlaspi arvense, a rising crop and model species, and demonstrates that non-target whole-genome sequencing reads, usually discarded, can be leveraged to estimate intensities of plant biotic interactions. With rapidly increasing numbers of large sequencing datasets worldwide, this approach should have broad application in fundamental and applied research.

Integrating habitat suitability, disturbance, and biotic interactions into the ecological restoration of the saguaro (Carnegiea gigantea) in drylands of the southwest of the United States and northern Mexico

This study proposes a combined approach encompassing habitat suitability, biotic interactions, and disturbance to identify high‐value restoration areas (HVRA) for the saguaro (Carnegiea gigantea, Cactaceae)—that is, areas with high habitat suitability for the saguaro and species that favor its establishment, growth, and dispersal (hereafter associated species), which were damaged by wildfires. We used species distribution modeling to produce habitat suitability maps for the saguaro and associated species (four nurse‐plants and 63 animals). We used Hot Spot Spatial Analysis to estimate hotspots of habitat suitability for the saguaro (HSS), nurse species (HNS), and associated animal species (HAS), and Moderate Resolution Imaging Spectroradiometer to identify burned (disturbed) areas. Finally, we estimated the overlay across habitat suitability hotspots and burned areas to identify HVRA. Overall, HSS, HNS, and HAS were mostly distributed across the northeast part of the Sonoran Desert. Results also indicated a strong overlay among HSS, HAS, and HNS. For the first time, this study provides distributional maps using biotic and bioclimatic variables for the giant saguaro cactus. Beyond saguaro conservation, our study can assist conservationists and managers in planning and implementing post‐fire regeneration strategies (e.g. monitoring the spread of exotic invasive grasses across burned areas). HVRA can also aid managers in preserving undisturbed priority areas, managing burned landscapes, prioritizing restoration activities, and evaluating post‐fire vegetation responses.

Low Mortality Rates Among Tropical Ferns

Tropical ferns are underrepresented in demographic studies, despite their ecological importance in forest ecosystems. This study investigates the mortality rates of terrestrial ferns along an elevational gradient (500–4000 m a.s.l.) in Ecuador, focusing on relationships with environmental variables, community characteristics, and plant size. Over two years (2009–2011), 3213 individuals representing 88 species were monitored in 22 permanent plots across eight elevations. Mortality rates, calculated as the percentage of individuals lost annually, averaged 0.87%, with a hump-shaped trend along the gradient and a significant negative relationship with temperature. Mortality rates were positively correlated with species richness and fern density, suggesting competition may influence community structure. Larger individuals exhibited higher mortality rates, likely due to greater resource demands and exposure to environmental stressors. These findings emphasize the interplay of abiotic factors, such as elevation and temperature, and biotic interactions, including competition and herbivory, in shaping fern population dynamics. The low mortality rates observed reflect population stability, potentially linked to unique life history traits, such as extended generation times. This study provides critical insights into the demographic strategies of tropical ferns and underscores the need for long-term research to better understand their responses to environmental and biotic pressures.

The distribution of distances to the edge of species coexistence

In Lotka–Volterra community models, given a set of biotic interactions, recent approaches have analysed the probability of finding a set of species intrinsic growth rates (representing intraspecific demographic features) that will allow coexistence. Several metrics have been used to quantify the fragility of coexistence in the face of variations in those intrinsic growth rates (representing environmental perturbations), thus probing a notion of ‘distance' to the edge of coexistence of the community. Here, for any set of interacting species, we derive an analytical expression for the whole distribution of distances to the edge of their coexistence. Remarkably, this distribution is entirely driven by (at most) two characteristic distances that can be directly computed from the matrix of species interactions. We illustrate on data from experimental plant communities that our results offer new ways to study the contextual role of species in maintaining coexistence, and allow us to quantify the extent to which intraspecific features and biotic interactions combine favorably (making coexistence more robust than expected), or unfavourably (making coexistence less robust than expected). Our work synthesizes different study of coexistence and proposes new, easily calculable metrics to enrich research on community persistence in the face of environmental disturbances.

Terroir and rootstock effects on leaf shape in California Central Valley vineyards

Societal Impact StatementThe innumerable effects of terroir—including climate, soil, microbial environment, biotic interactions, and cultivation practice—collectively alter plant performance and production. A more direct agricultural intervention is grafting, in which genetically distinct shoot and root genotypes are surgically combined to create a chimera that alters shoot performance at a distance. Selection of location and rootstock are intentional decisions in viticulture to positively alter production outcomes. Here, we show that terroir and rootstock alter the shapes of grapevine leaves in commercial vineyards throughout the California Central Valley, documenting the profound effects of these agricultural interventions that alter plant morphology.Summary Embedded in a single leaf shape are the latent signatures of genetic, developmental, and environmental effects. In viticulture, choice of location and rootstock are important decisions that affect the performance and production of the shoot. We hypothesize that these effects influence plant morphology, as reflected in leaf shape. We sample 1879 leaves arising from scion and rootstock combinations from commercial vineyards in the Central Valley of California. Our design tests 20 pairwise contrasts between Cabernet Sauvignon and Chardonnay scions from San Joaquin, Merced, and Madera counties from vines grafted to Teleki 5C, 1103 Paulsen, and Freedom rootstocks. We quantify clear differences between Cabernet Sauvignon and Chardonnay leaves. However, we also detect a separate, statistically independent source of shape variance that affects both Cabernet Sauvignon and Chardonnay leaves similarly. We find that this other shape difference is associated with differences in rootstock and location. The shape difference that arises from rootstock and location affects the basal part of the leaf near the petiole, known as the petiolar sinus, and affects its closure. This shape effect is independent from previously described shape differences that arise from genetic, developmental, or size effects.

Trophic Structure and Isotopic Niche of Invaded Benthic Communities on Tropical Rocky Shores.

When a species is introduced in a new location, it is common for it to establish itself when it finds favorable conditions in the receptor community with regard to interspecific interactions with native species. The azooxanthellate corals Tubastraea coccinea and Tubastraea tagusensis are invasive species introduced in the Caribbean Sea, the Gulf of Mexico, and the Brazilian Southwest Atlantic. They are successful competitors for space, have multiple reproductive modes, and have high larval dispersion and recruitment, but studies on food and trophic relationships of the genus Tubastraea are still scarce. In the present study, we used isotopic values of δ13C and δ15N to investigate trophic relationships in rocky shore communities invaded by T. tagusensis and T. coccinea corals under different oceanographic and anthropogenic contexts. Using metrics derived from the isotopic values, we show that invaded communities have a lower degree of trophic diversity, with species characterized by similar trophic ecologies while abiotic factors seem to contribute to the biotic resistance of communities exposed to invasion events. Tubastraea spp. occupy a niche space similar to that occupied by the native community of suspension feeders, sharing resources already consumed by the receptor community, which makes invading corals successful competitors for food.

Abundance-mediated species interactions.

Species interactions shape biodiversity patterns, community assemblage, and the dynamics of wildlife populations. Ecological theory posits that the strength of interspecific interactions is fundamentally underpinned by the population sizes of the involved species. Nonetheless, prevalent approaches for modeling species interactions predominantly center around occupancy states. Here, we use simulations to illuminate the inadequacies of modeling species interactions solely as a function of occupancy, as is common practice in ecology. We demonstrate erroneous inference into species interactions due to error in parameter estimates when considering species occupancy alone. To address this critical issue, we propose, develop, and demonstrate an abundance-mediated interaction framework designed explicitly for modeling species interactions involving two or more species from detection/non-detection data. We present Markov chain Monte Carlo (MCMC) samplers tailored for diverse ecological scenarios, including intraguild predation, disease- or predator-mediated competition, and trophic cascades. Illustrating the practical implications of our approach, we compare inference from modeling the interactions in a three-species network involving coyotes (Canis latrans), fishers (Pekania pennanti), and American marten (Martes americana) in North America as a function of occupancy states and as a function of abundance. When modeling interactions as a function of abundance rather than occupancy, we uncover previously unidentified interactions. Our study emphasizes that accounting for abundance-mediated interactions rather than simple co-occurrence patterns can fundamentally alter our comprehension of system dynamics. Through an empirical case study and comprehensive simulations, we demonstrate the importance of accounting for abundance when modeling species interactions, and we present a statistical framework equipped with MCMC samplers to achieve this paradigm shift in ecological research.

A snapshot in time: composition of native primary fauna of gall wasps in Spanish contact zones with chestnut trees infested by Dryocosmus kuriphilus.

One of the most prominent problems related to biological invasions is the variation of local species composition, which often leads to ex novo interspecific interactions. Here, we explored and analysed the native species composition of gall inducers and their associated parasitoids and inquilines in Spanish areas invaded by Dryocosmus kuriphilus Yasumatsu 1951 (Hymenoptera: Cynipidae), an invasive pest of chestnut trees. After a quantitative description of these species' assemblages, we analysed through bipartite networks the level of the trophic specialisation of parasitoids and inquilines when considering either the host taxonomic identity, the host plant species or the host gall morphological type. We sampled galls of D. kuriphilus and native species of Cynipidae in different Spanish areas, including those where the exotic parasitoid Torymus sinensis Kamijo 1982 (Hymenoptera: Torymidae) had been released for D. kuriphilus biological control. The results indicate that the native parasitoids recruited by D. kuriphilus come almost exclusively from native communities on Quercus galls, except for one species from Rosa. Galls of D. kuriphilus had the second most diverse species composition; despite this species assemblage arose ex novo in less than a decade. The bipartite networks resulted more specialised when considering host plant taxa than when gall types and the host taxa were accounted. In such trophic webs, there were few parasitoid/inquiline specialist and many generalist species, which agrees with the rapid recruitment by D. kuriphilus. Higher parasitoid species richness in D. kuriphilus galls is likely due to their being a largely unexploited available resource for the native natural enemies of cynipid wasps.

BASS - Biodiversity Assessments at Small Scales

Much of the work developed on biodiversity dynamics due to climate change focuses on large scales. Yet, we know that small scale is critical to fully understand biodiversity change, particularly for plants and small or less mobile organisms which might seek refuge in sites that keep specific microclimatic and biotic conditions dampening the effects of large-scale changes. The project BASS - Biodiversity Assessment at Small Scales - aims to explore the intricate relationships between small-scale environmental variations in space and time and biodiversity patterns. Central to our study is researching how microclimatic conditions, such as potential solar radiation, influence species occurrence, abundance, community composition and biotic interactions within a Mediterranean context. Our objectives include gaining a deeper understanding of the effects of localised environmental conditions and their change in time on biodiversity, providing critical data for an under-researched Mediterranean Biodiversity Hotspot region, and examining the dynamics of small-sized species, particularly plants and invertebrates. We have established a network of 16 fixed sampling points across the Lisbon University field station - Herdade da Ribeira Abaixo (HRA), Grândola (South Portugal): eight with high and eight with low potential solar radiation. Each of these plots will serve as a 'mesocosm' for detailed ecological studies in the next decades. This framework will support a variety of research projects each focusing on different taxa and questions, including Masters' theses, PhD dissertations and independent studies, thereby fostering a collaborative research environment. By integrating previously collected data during the last three decades with new findings, we aim to offer valuable insights into the processes underlying ecosystem functioning and change at small spatial scales. This project not only addresses fundamental ecological questions, but also contributes to sustainable landscape management and biodiversity conservation efforts.

European Native Oyster Reef Ecosystems Are Universally Collapsed

ABSTRACTOyster reefs are often referred to as the temperate functional equivalent of coral reefs. Yet evidence for this analogy was lacking for the European native species Ostrea edulis. Historical data provide a unique opportunity to develop a robust definition for this ecosystem type, confirm that O. edulis are large‐scale biogenic reef builders, and assess its current conservation status. Today, O. edulis occur as scattered individuals or, rarely, as dense clumps over a few m2. Yet historically, O. edulis reef ecosystems persisted at large scales (several km2), with individual reefs within the ecosystems present at the scale of several hectares. Using the IUCN Red List of Ecosystems Framework, we conclude the European native oyster reef ecosystem type is collapsed under three of five criteria (A: reduction in geographic distribution, B: restricted geographic range, and D: disruption of biotic processes and interactions). Criterion C (environmental degradation) was data deficient, and Criterion E (quantitative risk analysis) was not completed as the ecosystem was already deemed collapsed. Our assessment has important implications for conservation policy and action, highlighting that the habitat definitions on which conservation policies are currently based reflect a highly shifted baseline, and that the scale of current restoration efforts falls far short of what is necessary for ecosystem recovery.

Antagonistic biotic interactions mitigate the positive effects of warming on wood decomposition.

Global change drivers such as habitat fragmentation, species invasion, and climate warming can act synergistically upon native systems; however, global change drivers can be neutralized if they induce antagonistic interactions in ecological communities. Deadwood comprises a considerable portion of forest carbon, and it functions as refuge, nesting habitat and nutrient source for plant, animal and microbial communities. We predicted that thermophilic termites would increase wood decomposition with experimental warming and in forest edge habitat. Alternately, given that predatory ants also are thermophilic, they might limit termite-mediated decomposition regardless of warming. In addition, we predicted that a non-native, putative termite-specialist ant species would decrease termite activity, and consequently decomposition, when replacing native ants. We tested these hypotheses using experimental warming plots (~ 2.5°C above ambient) where termites, and their ant predators, have full access and vary in abundance at microscales. We found that termite activity was the strongest control on decomposition of field wood assays, with mass loss increasing 20% with each doubling of termite activity. However, both native and non-native ant abundance increased with experimental warming and, in turn, appeared to equally limit termite activity and, consequently, reduced wood decomposition rates. As a result, experimental warming had little net effect on the decomposition rates-likely because, although termite activity increased somewhat in warmed plots, ant abundances increased more than five times as much. Our results suggest that, in temperate southern U.S. forests, the negative top-down effects of predatory ants on termites outweighed the potential positive influences of warming on termite-driven wood decomposition rates.

How does co‐occurrence of Daphnia species affect their gut microbiome?

Species co‐occurrence can lead to competitive interactions that influence fitness. Competition is typically assumed to be modulated by species niche, especially food‐acquisition related traits. The influence of interspecific interactions on host microbiome communities has rarely been considered, and yet may provide an alternative mechanism regarding the effect of host species co‐occurrence on their fitness. Here, we investigated whether the composition of the gut microbial community differs between two Daphnia species (D. magna and D. pulex), and whether the gut microbiome of one species depends on the presence of the other. We hypothesized the stronger filter‐feeder D. magna to have a larger effect on the gut microbiome of the weaker filter‐feeder D. pulex than vice versa. To this purpose, three D. magna and three D. pulex genotypes were first made axenic and then grown in monocultures or in co‐cultures in natural environmental bacterioplankton‐enriched water, before assessing the community composition of the gut microbiomes and bacterioplankton. We found that the composition of the gut microbiome of the two Daphnia species did not significantly differ overall. However, subtle differences (i.e. the relative abundance of certain bacteria) between mono‐ and co‐cultures were found at the Daphnia genotype level. For most genotype combinations (six out of nine), the microbiome of D. pulex changed more (i.e. distance in microbiome composition was more sensitive to culture type in D. pulex than in D. magna) when grown in co‐cultures with D. magna than in monocultures. This provides limited support for our hypothesis that the stronger filter‐feeder has a larger effect on the gut microbiome of the weaker one than vice versa, and that this effect is possibly mediated via the bacterioplankton community.