Biofilms are considered a basal resource with high nutritional quality in stream food webs, as periphytic algae are abundant of polyunsaturated fatty acids (PUFAs). PUFAs are essential for growth and reproduction of consumers who cannot or have very limited capacity to biosynthesize. Yet, how the nutritional quality based on PUFA of basal food sources changes with light intensity remains unclear. We conducted a manipulative experiment in mesocosms to explore the response and mechanisms of nutritional quality to shading, simulating riparian restoration. We found a significant increase in PUFA% (including arachidonic acid, ARA) under shading conditions. The increased PUFA is caused by the algal community succession from Cyanobacteria and Chlorophyta to Bacillariophyta which is abundant of PUFA (especially eicosapentaenoic acid, EPA; docosahexaenoic acid, DHA). On the other hand, shading increased PUFA via upregulating enzymes such as Δ12 desaturase (FAD2, EC:1.14.19.6) and 3-ketoacyl-CoA synthase (KCS, EC:2.3.1.199) in the biosynthesis of unsaturated fatty acid elongation pathways. Our findings imply that riparian reforestation by decreasing light intensity increases the nutritional quality of basal resources in streams, which may enhance transfer of good quality carbon to consumers in higher trophic levels through bottom-up effects.

Alarm calls produced by basal prey have a well-known informative value. In multi-predator communities, mesopredators, when faced with top predators, may emit alarm calls that could inform basal prey about their lowered predation risk. To test this unexplored possibility, we conducted one field and one mesocosm experiment in which we simulated alarm and non-alarm calls from little owls (Athene noctua) as mesopredators and measured their effects on grasshoppers as prey of little owls but not of top predators. In the field experiment, we found that grasshopper species were significantly more abundant in patches where we simulated either the presence of scared little owls (alarm treatment) or no owls (control treatment) compared to patches where the presence of non-scared little owls (non-alarm treatment) was simulated. In the mesocosm experiment, locusts (Locusta migratoria) moved significantly more to exposed areas when we simulated the presence of scared little owls (alarm treatment) or of a granivorous bird (control treatment), while they moved to sheltered areas when we simulated the presence of non-scared owls (non-alarm treatment). These results show that prey could cue on predators\' calls to assess their predation risk and make decisions, revealing unprecedented potential ecological consequences of alarm calls in invertebrate communities.

Most deep-ocean life relies on organic carbon from the surface ocean. While settling primary production rapidly attenuates in the water column, pulses of organic material can be quickly transported to depth in the form of food falls. One example of fresh material that can reach great depths across the tropical Atlantic Ocean and Caribbean Sea is the pelagic macroalgae Sargassum. However, little is known about the deep-ocean organisms able to use this food source. Here, we encountered the isopod Bathyopsurus nybelini at depths 5002-6288 m in the Puerto Rico Trench and Mid-Cayman Spreading Center using the Deep Submergence Vehicle Alvin. In most of the 32 observations, the isopods carried fronds of Sargassum. Through an integrative suite of morphological, DNA sequencing, and microbiological approaches, we show that this species is adapted to feed on Sargassum by using a specialized swimming stroke, having serrated and grinding mouthparts, and containing a gut microbiome that provides a dietary contribution through the degradation of macroalgal polysaccharides and fixing nitrogen. The isopod\'s physiological, morphological, and ecological adaptations demonstrate that vertical deposition of Sargassum is a direct trophic link between the surface and deep ocean and that some deep-sea organisms are poised to use this material.

Controlled sediment flushing operations (CSFOs) allow to recover reservoirs storage loss while rebalancing the sediment flux interrupted by dams but, at the same time, may cause unacceptable ecological impact. In this study, we investigated the responses of the food web of an upland stream to a CSFO, focusing on the effects of fine sediment deposition detected in three different mesohabitats, i.e., a pool, a riffle, and a step-pool. The field campaign lasted two years and included repeated measurements of fine sediment deposits, and sampling of periphyton, benthic macroinvertebrates and fishes. A moderate and patchy deposition occurred due to the CSFO with short and medium-term ecological impact on the lower trophic levels of the food web, which may affect the whole ecosystem functioning. The monitoring of all available mesohabitats in the investigated stream allowed to detect variations in the ecological response to CSFO, providing a more adequate assessment of the impact. As expected, sedimentation was larger in the pool but, in contrast to our hypotheses, the impact was lower and the recovery was longer for the benthic organisms inhabiting the riffle. In the case of fishes, no lethal impact of both brown trout and bullhead was recorded in the short term but the occurrence of longer lasting effects could not be excluded. To date, this is one of the few studies dealing with a detailed integrative assessment of the downstream impact of sediment management from reservoir on both abiotic and biotic components of stream ecosystem.

The dinoflagellate Alexandrium pseudogonyaulax, a harmful algal bloom species, is currently appearing in increasing frequency and abundance across Northern European waters, displacing other Alexandrium species. This mixotrophic alga produces goniodomins (GDs) and bioactive extracellular substances (BECs) that may pose a threat to coastal ecosystems and other marine resources. This study demonstrated the adverse effects of A. pseudogonyaulax on four marine trophic levels, including microalgae (Rhodomonas salina), microzooplankton (Polykrikos kofoidii) and mesozooplankton (Acartia tonsa), as well as fish gill cells (RTgill-W1, Oncorhynchus mykiss), ultimately leading to enhanced mortality and cell lysis. Furthermore, cell-free supernatants collected from A. pseudogonyaulax cultures caused complete loss of metabolic activity in the RTgill-W1 cell line, indicating ichthyotoxic properties, while all tested GDs were much less toxic. In addition, cell-free supernatants of A. pseudogonyaulax led to cell lysis of R. salina, while all tested GDs were non-lytic. Finally, reduced egg hatching rates of A. tonsa eggs exposed to cell-free supernatants of A. pseudogonyaulax and impaired mobility of P. kofoidii and A. tonsa exposed to A. pseudogonyaulax were also observed. Altogether, bioassay results suggest that the toxicity of A. pseudogonyaulax is mainly driven by BECs and not by GDs, although further research into factors modulating the lytic activity of Alexandrium spp. are needed.

The production of allelochemicals by the toxigenic dinoflagellate Alexandrium catenella is one of the suggested mechanisms to facilitate its bloom formation and persistence by outcompeting other phototrophic protists and reducing grazing pressure. In Southern California, toxic events caused by A. catenella and paralytic shellfish toxins (PSTs) regularly impact coastal ecosystems; however, the trophic interactions and mechanisms promoting this species in a food web context are still not fully understood. In the present study, we combined a dynamical mathematical model with laboratory experiments to investigate potential toxic and allelochemical effects of an A. catenella strain isolated off the coast of Los Angeles, Southern California, on competitors and a common zooplankton consumer. Experiments were conducted using three toxigenic strains of A. catenella, comparing the new Californian isolate (Alex Cal) to two strains previously described from the North Sea, a lytic (Alex2) and non-lytic (Alex5) strain, testing for donor density-dependent effects on two phytoplankton species (Rhodomonas salina, Tetraselmis sp.) and on the rotifer Brachionus plicatilis. Bioassays revealed a steep decline in competitor and consumer populations with increasing Alex Cal concentrations, indicating an intermediate lytic activity compared to the North Sea strains (lytic Alex2 and non-lytic Alex5). The rotifer fed and grew well on the PST- toxic, but non-lytic Alex5 strain, while its survival significantly decreased with increasing concentrations of the two lytic strains Alex Cal and Alex 2, indicating that negative effects on the rotifer were mediated by allelochemicals rather than PST-toxins. Mixed culture experiments including both competitors and consumers demonstrated that the intensity of allelochemical effects not only depended on the A. catenella density but also on the target density. Negative effects on grazers were alleviated by co-occurring competitors with a lower sensitivity to allelochemicals, thus reducing harmful compounds and allowing grazing control on the dinoflagellate to come into effect again. Results from mixed culture experiments were supported by the mathematical approach used in this study which was calibrated with data from simple monoculture growth, pairwise competition and predator-prey experiments, demonstrating the applicability of this model approach to predict the outcome of more complex food web dynamics at the community level.

The date palm (Phoenix dactylifera L.) (Arecales: Arecaceae) is the most economically important crop in Oman with an annual production of >360,000 tons of fruit. The Dubas bug (Ommatissus lybicus de Bergevin) (Hemiptera: Tropiduchidae) is one of the major pests of date palms, causing up to a 50% reduction in fruit production. Across the course of 2 seasons, a variety of arthropod predators living in the date palm canopy were investigated for possible biological control of Dubas bugs, given the growing interest in nonchemical insect pest control in integrated pest management. We collected ~6,900 arthropod predators directly from date palm fronds from 60 Omani date palm plantations and tested them for Dubas bug predation using PCR-based molecular gut content analysis. We determined that ≥56 species of arthropod predators feed on the Dubas bug. We found that predatory mites, ants, and the entire predator community combined showed a positive correlation between predation detection frequency and increasing Dubas bug density. Additionally, there was a significant impact of season on gut content positives, with the spring season having a significantly higher percentage of predators testing positive for Dubas bug, suggesting this season could be the most successful time to target conservation biological control programs utilizing a diverse suite of predators.

Matsuda and Abrams (Theor Popul Biol 45(1):76-91, 1994) initiated the exploration of self-extinction in species through evolution, focusing on the advantageous position of mutants near the extinction boundary in a prey-predator system with evolving foraging traits. Previous models lacked theoretical investigation into the long-term effects of harvesting. In our model, we introduce constant-effort prey and predator harvesting, along with individual logistic growth of predators. The model reveals two distinct evolutionary outcomes: (i) Evolutionary suicide, marked by a saddle-node bifurcation, where prey extinction results from the invasion of a lower forager mutant; and (ii) Evolutionary reversal, characterized by a subcritical Hopf bifurcation, leading to cyclic prey evolution. Employing an innovative approach based on Gröbner basis computation, we identify various bifurcation manifolds, including fold, transcritical, cusp, Hopf, and Bogdanov-Takens bifurcations. These contrasting scenarios emerge from variations in harvesting parameters while keeping other factors constant, rendering the model an intriguing subject of study.

Changes in the existence of mangroves will have an impact on changes in food webs in their respective areas. The purpose of this study was to determine the food source of the macrozoobenthos community within the Lubuk Damar mangrove ecosystem. Stable isotopes, carbon and nitrogen were used to describe the food sources for macrozoobenthos in the mangrove ecosystem of the Lubuk Damar Ecosystem, Aceh Tamiang, Indonesia. The stable isotope analysis of 13C and 15N was carried out using Isotopic-Ratio Mass Spectrometry. Potential food sources at the study site based on stable isotope ratios ranged between -29.08‰ to -20.66‰ (δ13C) and 4.07‰ to 5.63‰ (δ15N); macrozoobenthos -25.00‰ to -14.76‰ (δ13C) and 5.59‰ to 7.73‰ (δ15N). The potential food sources tested at the study site consisted of seven sources, but not all food sources in the ecosystem were consumed by the invertebrate community. This study shows that mangrove leaf litter serves as a food source for some invertebrates, such as the bivalves, gastropods, polychaetes, sipunculans, brachiopods and crustaceans. The results of this study evidence that the examined mangrove ecosystem has a function as a provider of food sources in the surrounding waters, therefore its existence is very important supporting diversity of coastal waters.

For prey, movement synchrony represents a potent antipredator strategy. Prey, however, must balance the costs and benefits of using conspecifics to mediate risk. Thus, the emergent patterns of risk-driven sociality depend on variation in space and in the predators and prey themselves. We applied the concept of predator-prey habitat domain, the space in which animals acquire food resources, to test the conditions under which individuals synchronize their movements relative to predator and prey habitat domains. We tested the response of movement synchrony of prey to predator-prey domains in two populations of ungulates that vary in their gregariousness and predator community: (i) elk, which are preyed on by wolves; and (ii) caribou, which are preyed on by coyotes and black bears. Prey in both communities responded to cursorial predators by increasing synchrony during seasons of greater predation pressure. Elk moved more synchronously in the wolf habitat domain during winter and caribou moved more synchronously in the coyote habitat domains during spring. In the winter, caribou increased movement synchrony when coyote and caribou domains overlapped. By integrating habitat domains with movement ecology, we provide a compelling argument for social behaviours and collective movement as an antipredator response. This article is part of the theme issue \'The spatial-social interface: A theoretical and empirical integration\'.