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Global biodiversity is undergoing a grand reshuffling with species across taxa and biomes shifting their ranges in response to climate change. Research on the ecological impacts of range‐shifting species has prioritized linking the traits of the range‐shifting species themselves to impacts, with studies giving more limited attention to the characteristics of the recipient community and its prey composition. Understanding how community composition and structure can alter the impact of novel species via prey preferences is important for predicting and managing ecological changes. We used the range‐shifting predatory whelk Mexacanthina lugubris as a case study to investigate how prey composition might influence prey preferences and overall range shift impacts on prey species. Specifically, we hypothesized that Mexacanthina lugubris' consumptive effects on a single prey species would be modified by the presence (or abundance) of a second prey species. We tested this hypothesis via a field experiment in southern California, where we caged whelks at a gradient of densities and observed their predation on mussels, barnacles living on bare rock, and barnacles living on mussels over 8 weeks. We found that Mexacanthina lugubris consumed barnacles on bare rock preferentially before consuming barnacles on mussels and mussels themselves. Our findings demonstrate that the presence of mussels (which act as both habitat and prey) can mitigate the overall impact of the range‐shifting predator by altering accessibility of barnacle prey. This context‐dependent attenuation of predator impacts highlights a form of apparent facilitation among prey and underscores the importance of considering recipient community traits when assessing or managing the ecological consequences of range‐shifting species.

In addition to their direct trophic effects, some consumers have a positive indirect effect on their resource, due to niche construction. A predator can facilitate its prey resource acquisition, through prey transport, or through modifications of nutrient cycling. Alternatively, a predator may defend its prey against other predators, or actively manage it, as in agriculture, which is found in numerous taxa such as humans, ants, beetles, fishes and microbes.Here, we investigate the ecological consequences of considering such positive effects in a simple two-resource–one-consumer module, in which the consumer has a positive effect on one of the resources.We consider several scenarios, in which the positive effect on the resource is either not costly, that is resulting from a by-product of the consumer phenotype such as nutrient cycling, or costly. The cost either decreases the exploitation of the cultivated resource or the opportunity to forage the alternative resource. We investigate how the intensity of niche construction impacts species coexistence, the distribution of biomass among the three species and the stability of the community.We show that by modifying the trophic interactions in the module, niche construction alters the apparent competition between the resources, thereby impacting their coexistence.When niche construction has little or no cost to the consumer, it leads to higher consumer and cultivated resource densities, while decreasing the alternative resource density. Alternatively, when niche construction has higher costs, the alternative resource can increase in density, niche construction thereby leading to the emergence of facilitative interactions among resource species

The importance of density-mediated indirect effects (e.g., keystone predators) in marine communities has been widely recognized. Behaviorally mediated indirect interactions (BMIIs) may be equally important in marine systems, but have received relatively little attention. BMIIs occur when a change in an \"initiator\" species causes a behavioral shift in a \"transmitter\" species that, in turn, affects a \"receiver\" species. BMIIs between initiator and receiver species can be described by the ecological relationships between initiator and transmitter, and between transmitter and receiver (i.e., predator and prey, competitors, or no relationship), and the nature of the indirect effect on the receiver (i.e., positive or negative). We review published examples of BMIIs in marine communities, showing that BMIIs may create, enhance, ameliorate, or even reverse the sign of the direct interactions between species. Models that only include direct interactions or density-mediated indirect ones cannot predict some of these effects. BMIIs are likely to be ubiquitous in marine communities and have important implications for both understanding community dynamics and managing these systems. A thorough understanding of BMIIs is particularly important for conservation and management, as humans may play the role of an initiator, transmitter, or receiver of these effects in a variety of marine communities.

Indirect interactions occur when the effect of one species on another is mediated by a third species. These interactions occur in most multi-species assemblages and are diverse in their mechanistic pathways. The interest in indirect interactions has increased exponentially over the past three decades, in recognition of their importance in determining plant community dynamics and promoting species coexistence. Here, we review the literature on indirect interactions among plants published since 1990, using a novel synthetic framework that accounts for and classifies intervening species and mechanisms within trophic networks. The objectives of this review are: (1) to identify the geographical regions and ecosystem types where indirect interactions have been examined; (2) to summarize the information on the number of trophic levels examined in studies of indirect interactions; (3) to test whether the frequency of indirect interactions varies across environmental gradients; and (4) to identify the experimental approaches most commonly used in studies of indirect interactions. Studies examining indirect interactions in plants have been conducted primarily in the Northern Hemisphere, with a focus on grasslands and forests. The majority of studies (67%) examined two trophic levels. Indirect facilitation and apparent competition are the interactions that have been most frequently examined, with the latter being reported more frequently in relatively productive environments. Other indirect interactions reported include associational resistance, exploitative competition or facilitation, shared defenses, and trophic cascades. Generally, field experiments tested indirect interactions based on single target species. While the majority of studies on indirect interactions dealt with basic ecology issues, several studies have dealt with such interactions in the context of biological invasions (18%) and rangeland management (12%). This review allowed us identifying a number of research needs, including the study of non-feeding interactions and that for more realistic complex designs, explicitly testing indirect interactions across different trophic levels, in geographical regions that have been under-examined to date, and in stressful ecosystems.

Indirect biotic interactions play a crucial role in structuring ecological communities, but many of these interactions have not been explored. Algal competition and corallivory are two major stressors contributing to the decline of coral reefs. Here, we provide the first evidence of algal‐induced corallivory and synergistic effects between the two stressors on corals. When corals (Montastraea faveolata) were placed in contact with algae (Halimeda opuntia) together with corallivorous fireworms (Hermodice carunculata) in aquaria, corals suffered high tissue mortality. This mortality was reduced in the presence of algae only, and no mortality occurred in the presence of fireworms only or when excluding both algae and fireworms. These findings were supported by field observations showing a predominance of fireworms inside algae contacting live corals, and by an in situ experiment demonstrating higher coral mortality in contact with algae left undisturbed than with algae from which all mobile epifauna were periodically removed. Among the main contributing mechanisms, we suggest that algal contact produces decaying coral tissue that attracts the corallivore and enhances its aggregation behavior. Our study demonstrates an indirect effect pathway by which algae can impact corals, which shares similarities with the classic models of apparent competition and habitat facilitation.

Individuals with autism often show a fragmented way of perceiving their environment, suggesting a disorder of information integration, possibly due to disrupted communication between brain areas. We investigated thirteen individuals with high-functioning autism (HFA) and thirteen healthy controls using the metastable motion quartet, a stimulus consisting of two dots alternately presented at four locations of a hypothetical square, thereby inducing an apparent motion percept. This percept is vertical or horizontal, the latter requiring binding of motion signals across cerebral hemispheres. Decreasing the horizontal distance between dots could facilitate horizontal percepts. We found evidence for altered horizontal binding in HFA: Individuals with HFA needed stronger facilitation to experience horizontal motion. These data are interpreted in light of reduced cross-hemispheric communication.

Plant cover plays a major role in shaping the nature of recruitment microsites through direct (resource mediated) and indirect (consumer mediated) interactions. Understorey plants may differentially affect seedling establishment, thus contributing to regeneration-niche separation among canopy tree species. We examined patterns of early tree seedling survival resulting from interactive effects of understorey bamboo (Chusquea culeou) and resident consumers in a mixed temperate Patagonian forest, Argentina. Newly germinated seedlings of Nothofagus dombeyi and Austrocedrus chilensis were planted in bamboo thickets and non-bamboo patches, with or without small-vertebrate exclosures. We found species-specific patterns of seedling survival in relation to bamboo cover. Nothofagus survival was generally low but increased under bamboo, irrespective of cage treatment. Desiccation stress accounted for most Nothofagus mortality in open, non-bamboo areas. In contrast, Austrocedrus survival was highest in non-bamboo microsites, as most seedlings beneath bamboo were killed by small vertebrates through direct consumption or non-trophic physical damage. There was little evidence for a negative impact of bamboo on tree seedling survival attributable to resource competition. The balance of simultaneous positive and negative interactions implied that bamboo presence facilitated Nothofagus early establishment but inhibited Austrocedrus recruitment via apparent competition. These results illustrate the potential for dominant understorey plants to promote microsite segregation during early stages of recruitment between tree seedlings having different susceptibilities to water stress and herbivory. We recognise, however, that patterns of bamboo-seedling interactions may be conditional on moisture levels and consumer activity during establishment. Hence, both biotic and abiotic heterogeneity in understorey environments should be incorporated into conceptual models of regeneration dynamics and tree coexistence in forest communities.

Many studies demonstrated the importance of facilitative effect by nurse plant on seedling establishment. Few studies evaluated the negative effects of consumers on plant establishment under nurse plants by dealing with them during multiple demographic processes. We investigated the balance between the facilitative effect and negative effects of consumers during multiple demographic processes in Malawi in southeastern Africa. We chose Ficus natalensis as a nurse plant and compared it with three other microsites in tropical woodlands: Brachystegia floribunda (a dominant woodland species), Uapaca kirkiana (a woodland species), and a treeless site. We quantified the seed rain, postdispersal seed predation, germination, and seedling survival of Syzygium guineense ssp. afromontanum (a common forest species). Within each microsite, we quantified the overall probability of recruitment. We also measured seedling abundance of S. guineense ssp. afromontanum. We found that Ficus natalensis exerted both positive and negative impacts on the establishment of S. guineense ssp. afromontanum. Ficus natalensis facilitated seed deposition, seed germination, and seedling survival. On the other hand, seed removal at postdispersal stage was highest under F. natalensis. Interestingly, B. floribunda also had positive effects on germination and seedling survival, but not on seed deposition. When we excluded the seed arrival stage from our estimation of the recruitment probability, the highest value was found under B. floribunda, not under F. natalensis. When we included the seed arrival stage, however, the order of recruitment probability between F. natalensis and B. floribunda was reversed. The probability was one order of magnitude higher under F. natalensis than under B. floribunda. Our estimation of the probability which included the seed arrival stage was consistent with natural patterns of S. guineense ssp. afromontanum establishment. Despite the presence of opposite effects, the net effects of F. natalensis on S. guineense ssp. afromontanum recruitment in tropical woodlands can be positive.

Invasive plants exhibit both direct and indirect negative effects on recruitment of natives following invasion. We examined indirect effects of the invader Bromus tectorum (cheatgrass) on seed fates of two native grass species, Elymus elymoides and Pseudoroegneria spicata, by removing B. tectorum and by adding inoculum of the shared seed pathogen Pyrenophora semeniperda in factorial experiments at xeric and mesic field sites. We also included a supplemental watering treatment to increase emergence and also the potential for pathogen escape. We recorded emergence and survival of native seedlings and also determined the fate of unemerged seeds. At the xeric site, Pyrenophora-caused mortality was high (34 %), and effects of other pathogens and failed emergence of germinants were smaller. Cheatgrass removal negatively affected both emergence (35 vs. 25 %) and spring survival (69 vs. 42 %). Pyrenophora-caused seed mortality increased with inoculum augmentation for both species (22 vs. 47 % overall), but emergence was negatively impacted only for P. spicata (20 vs. 34 %). At the mesic site, Pyrenophora-caused mortality was low (6 %). Cheatgrass removal doubled emergence (26 vs. 14 %). Seed mortality increased significantly with inoculum augmentation for P. spicata (12 vs. 5 %) but not E. elymoides, while emergence was not significantly affected in either species. A large fraction of seeds produced germinants that failed to emerge (37 %), while another large fraction (35 %) was killed by other pathogens. We conclude that facilitation by cheatgrass at the xeric site but interference at the mesic site was probably mediated through litter effects that could be ameliorative or suppressive. Apparent competition between cheatgrass and native grasses could occur through Pyrenophora, especially in a xeric environment, but effects were weak or absent at emergence. This was probably because Pyrenophora attacks the same slow-germinating fraction that is subject to pre-emergence mortality from other causes, including attack by other pathogens such as Fusarium.

1. Facilitation of recruitment by 'nurse' plants can play a major role in harsh environments. Yet the extent to which consumer-mediated apparent competition from habitat-forming plants may counteract facilitative interactions remains largely unexplored. 2. We examined whether seedling predation by tenebrionid beetles seeking refuge under nurse shrubs may prevent tree recruitment facilitation in a Patagonian steppe-woodland ecotone. Newly emerged seedlings of Austrocedrus chilensis were planted in shrub canopy, off-shrub shelter and bare soil microsites, and monitored for causes of early mortality and for overall survival under ambient and elevated beetle densities. 3. Most seedlings in open microsites died from abiotic stress, whereas shrub cover and artificial shelters decreased desiccation mortality. Herbivory was the main cause of mortality in shrub microsites. Beetle addition increased predation beneath shrubs and in off-shrub shelters, indicating that apparent competition 'spilled over' from shrubs with high insect densities. 4. Litter removal from shrubs prevented seedling predation suggesting that nurse plants altered recruitment by providing food as well as shelter to insects. Herbivory rates did not depend on seedling patch density but decreased with seedling age, with 1-week old plants being most vulnerable to beetle predation. 5. Synthesis. Apparent competition from nurse plants can strongly reduce recruitment facilitation in stressful environments, although weak herbivore density dependence and seedling growth into ontogenetic refuges may limit the strength of apparent competition. An explicit consideration of negative, as well as positive, herbivore-mediated indirect effects from habitat-forming plants would broaden the understanding of community dynamics along stress gradients.