Importance Of Biotic Interactions Research Articles

The importance of biotic interactions in distribution models of wild bees depends on the type of ecological relations, spatial scale and range

The importance of biotic interactions in distribution models of wild bees depends on the type of ecological relations, spatial scale and range

Climate or diet? The importance of biotic interactions in determining species range size

AbstractAimSpecies geographical range sizes play a crucial role in determining species vulnerability to extinction. Although several mechanisms affect range sizes, the number of biotic interactions and species climatic tolerance are often thought to play discernible roles, defining two dimensions of the Hutchinsonian niche. Yet, the relative importance of the trophic and the climatic niche for determining species range sizes is largely unknown.LocationCentral and northern Europe.Time periodPresent.Major taxa studiedGall‐inducing sawflies and their parasitoids.MethodsWe use data documenting the spatial distributions and biotic interactions of 96 herbivore species, and their 125 parasitoids, across Europe and analyse the relationship between species range size and the climatic and trophic dimensions of the niche. We then compare the observed relationships with null expectations based on species occupancy to understand whether the relationships observed are an inevitable consequence of species range size or if they contain information about the importance of each dimension of the niche on species range size.ResultsWe find that both niche dimensions are positively correlated with species range size, with larger ranges being associated with wider climatic tolerances and larger numbers of interactions. However, diet breadth appears to more strongly limit species range size. Species with larger ranges have more interactions locally and they are also able to interact with a larger diversity of species across sites (i.e. higher β‐diversity), resulting in a larger number of interactions at continental scales.Main conclusionsWe show for the first time how different aspects of species diet niches are related to their range size. Our study offers new insight into the importance of biotic interactions in determining species spatial distributions, which is critical for improving understanding and predictions of species vulnerability to extinction under the current rates of global environmental change.

Not only climate: The importance of biotic interactions in shaping species distributions at macro scales.

Abiotic factors are usually considered key drivers of species distribution at macro scales, while biotic interactions are mostly used at local scales. A few studies have explored the role of biotic interactions at macro scales, but all considered a limited number of species and obligate interactions. We examine the role of biotic interactions in large-scale SDMs by testing two main hypotheses: (1) biotic factors in SDMs can have an important role at continental scale; (2) the inclusion of biotic factors in large-scale SDMs is important also for generalist species. We used a maximum entropy algorithm to model the distribution of 177 bat species in Africa calibrating two SDMs for each species: one considering only abiotic variables (noBIO-SDMs) and the other (BIO-SDMs) including also biotic variables (trophic resource richness). We focused the interpretation of our results on variable importance and response curves. For each species, we also compared the potential distribution measuring the percentage of change between the two models in each pixel of the study area. All models gave AUC >0.7, with values on average higher in BIO-SDMs compared to noBIO-SDMs. Trophic resources showed an importance overall higher level than all abiotic predictors in most of the species (~68%), including generalist species. Response curves were highly interpretable in all models, confirming the ecological reliability of our models. Model comparison between the two models showed a change in potential distribution for more than 80% of the species, particularly in tropical forests and shrublands. Our results highlight the importance of considering biotic interactions in SDMs at macro scales. We demonstrated that a generic biotic proxy can be important for modeling species distribution when species-specific data are not available, but we envision that a multi-scale analysis combined with a better knowledge of the species might provide a better understanding of the role of biotic interactions.

Animal functional traits: Towards a trait‐based ecology for whole ecosystems

Abstract Functional traits and associated trait‐based concepts have driven rapid innovation in ecology over recent years, with most progress based on insights from plants. However, plants are almost entirely restricted to a single trophic level, and an over‐reliance on plant traits therefore neglects the complexity and importance of biotic interactions across trophic levels. The need to expand the focus of trait‐based ecology to account for trophic complexity has led to an upsurge in attention on animal functional traits and the emergence of new concepts relevant to community ecology, macroecology and ecosystem science. Recent progress in the compilation of global trait datasets for some animal taxa has opened up new possibilities for testing ecological theory. In this Special Focus, we explore how trait‐based ecology can expand the scope of investigation from single to multiple trophic levels, how insights from these investigations can be used to upscale understanding from local communities to biogeographical patterns and how this can ultimately help to predict the impacts of global change on ecosystem functions. To address these key questions, we showcase studies on diverse animal taxa ranging in size from springtails to crocodiles and spanning multiple trophic levels from primary consumers to apex predators. This collection of studies shows how precise measurements of morphological or physiological traits can increase mechanistic understanding of community assembly across trophic levels, particularly of the mechanisms underpinning large‐scale biodiversity patterns. Furthermore, a clearer picture is emerging of systematic animal responses to environmental change that shape the trait composition of ecological communities and affect ecosystem functioning. The articles in this volume highlight the need to move trait‐based ecology beyond the limits of taxonomic boundaries. The integration of trait data and concepts across trophic levels opens up new possibilities for identifying general ecological mechanisms that shape patterns and processes operating at different scales. The identification of key functional traits and their interplay across trophic levels can underpin the development of a trait‐based ecology for whole ecosystems, which could eventually enable predictions of the ecosystem‐level consequences of biodiversity loss. Read the free Plain Language Summary for this article on the Journal blog.

Comparative impacts of long‐term trends in snowmelt and species interactions on plant population dynamics

Abstract Climate change can impact plant fitness and population persistence directly through changing abiotic conditions and indirectly through its effects on species interactions. Pollination and seed predation are important biotic interactions that can impact plant fitness, but their impact on population growth rates relative to the role of direct climatic effects is unknown. We combined 13 years of experiments on pollen limitation of seed set and pre‐dispersal seed predation in Ipomopsis aggregata, a subalpine wildflower, with a long‐term demographic study that has documented declining population growth with earlier spring snowmelt date. We determined how pollen limitation and seed predation changed with snowmelt date over 21 years and incorporated those effects into an integral projection model to assess relative impacts of biotic factors on population growth. Both pollen limitation and the difference in stigma pollen load between pollen‐supplemented and control plants declined over years. Neither pollen limitation nor seed predation changed detectably with snowmelt date, suggesting an absence of indirect effects of that specific abiotic factor on these indices of biotic interactions. The projected biotic impacts of pollen limitation and seed predation on population growth rate were small compared to factors associated with snowmelt date. Providing full pollination would delay the projected date when earlier snowmelt will cause populations to fall below replacement by only 14 years. Synthesis. Full pollination and elimination of seed predation would not compensate for the strong detrimental effects of early snowmelt on population growth rate, which in I. aggregata appears driven largely by abiotic environmental factors. The reduction over two decades in pollen limitation also suggests that natural selection on floral traits may weaken with continued climate change. These results highlight the value of studying both abiotic factors and biotic interactions to understand how climate change will influence plant populations.

First report of Avicennia germinans (Acanthaceae) as a larval host of Junonia litoralis (Nymphalidae) causing higher foliar damage in seedlings than trees

AbstractHerbivory is considered an important biotic interaction in mangroves. Nevertheless, detailed information on specific plant–herbivore interactions that might have considerable influence in ecological and evolutionary processes is still very poor and fragmented. Herbivory damage was quantified during December 2015 in seedlings and trees in monospecific stands of Avicennia germinans in Laguna Madre of Tamaulipas, Mexico. The use of this mangrove species as a larval host is well documented; however, this is the first report for Junonia litoralis. These lepidopteran larvae consumed, on average, 10.2% of the leaf area; but herbivory was higher on seedlings (mean 15%) than on trees (mean 2.3%). These values are comparable to estimations of 10% mean herbivory damage in other field studies. This indicates that herbivores cause greater damage in seedlings than in trees. Herbivore activity by J. litoralis only occurred in A. germinans and did not affect associated herbs or shrubs of other species. The close interaction between J. litoralis and A. germinans may have profound implications for ecological and evolutionary processes of mangroves and enables a better understanding of ecosystem function and its conservation. Further studies are needed to investigate such interactions and their implications including long‐term monitoring of interstitial salinity and leaf chemistry at different stages of growth and maturity of the host species.

Using molecular and stable isotope markers to identify the main predators of Nephrops norvegicus in Mediterranean deep-water ecosystems

To obtain a better understanding of the functioning of ecosystems and how they respond to disturbance, it is necessary to identify the relevant biotic interactions and specific trophic roles. Predation is one of the most important biotic interactions that can also define the spatial patterns of other species. Many predators are considered key species for the functioning and maintenance of ecosystems, as they play an important ecological role that can influence the dynamics at lower trophic levels. The Norway lobster Nephrops norvegicus is one of the most valued European fishing stocks. However, its value and capture have declined over the last decade. In the Atlantic Ocean, Atlantic cod Gadus morhua is the main predator of N. norvegicus. However, this species is not present in the Mediterranean Sea, and little is known about which species might prey on N. norvegicus in this area. Here, we combine 2 methodologies—genetic identification of stomach contents and stable isotope analyses—to identify, for the first time, the main predators of N. norvegicus in the Mediterranean Sea. Moreover, we have created the Predation Index, which determines the most influential predator affecting N. norvegicus population dynamics. Our results reveal that the major predators are the cephalopods Sepietta spp. and Abralia veranyi, which probably affect the early stages of N. norvegicus, followed by the elasmobranch Scyliorhinus canicula and the bony fishes Merluccius merluccius, Trigla lyra, and Conger conger. To evaluate possible fluctuations in the N. norvegicus population, we consider the assessment of these predator populations crucial.

Bioregions are predominantly climatic for fishes of northern lakes

AbstractAimRecurrent species assemblages integrate important biotic interactions and joint responses to environmental and spatial filters that enable local coexistence. Here, we applied a bipartite (site–species) network approach to develop a natural typology of lakes sharing distinct fish faunas and provide a detailed, hierarchical view of their bioregions. We then compared the roles of key biogeographical factors to evaluate alternative hypotheses about how fish communities are assembled from the regional species pool.LocationOntario, Canada and the Upper Midwest, USA.Time period1957–2017.Major taxa studiedFreshwater fishes.MethodsBipartite modularity analysis was performed on 90 taxa from 10,016 inland lakes in the Southwestern Hudson Bay, Mississippi River and St. Lawrence River drainages, uncovering bioregionalization of North American fishes at a large, subcontinental scale. We then used a latent variable approach, pairing non‐metric partial least‐squares structural equation modelling with multiple logistic regression, to show differences in the biogeographical templates of each type of community. Indicators of contemporary and historical connectivity, climate and habitat constructs were estimated using a geographical information system.ResultsFish assemblages reflected broad, overlapping patterns of postglacial colonization, climate and geological setting, but community differentiation was most linked to temperature, precipitation and, for certain groups, lake area and water quality. Bioregions were also marked by non‐native species, showing broad‐scale impacts of introductions to the Great Lakes and surrounding basins.Main conclusionsThe dominant effects of climate across broad spatial gradients indicate differing sensitivities of fish communities to rapidly accelerating climate change and opportunities for targeted conservation strategies. By assessing biological variation at the level of recurrent assemblages, we accounted for the non‐stationarity of macroecological processes structuring different sets of species on the landscape and offer novel inference on the assembly of inland fish communities.

Inferring predator\u2013prey interaction in the subterranean environment: a case study from Dinaric caves

Predator–prey interactions are among the most important biotic interactions shaping ecological communities and driving the evolution of defensive traits. These interactions and their effects on species received little attention in extreme and remote environments, where possibilities for direct observations and experimental manipulation of the animals are limited. In this paper, we study such type of environment, namely caves of the Dinarides (Europe), combining spatial and phylogenetic methods. We focused on several species of Niphargus amphipods living in phreatic lakes, as some of them use the dorsal spines as putative morphological defensive traits. We predicted that these spines represent a defense strategy against the olm (Proteus anguinus), a top predator species in the subterranean waters. We tested for spatial overlap of the olm and Niphargus species and showed that spined species live in closer proximity to and co-occur more frequently with the olm than non-spined species. Modeling of the evolution of the spines onto Niphargus phylogeny implies coevolution of this trait in the presence of olm. We conclude that these spines likely evolved as defensive traits in a predator–prey arms race. Combining multiple analyses, we provide an example for a methodological framework to assess predator–prey interactions when in-situ or laboratory observations are not possible.

Temporal fluctuations in zooplankton size, abundance, and taxonomic composition since 1995 in the North Western Mediterranean Sea

AbstractIn the Gulf of Lions, small pelagic fish have shown reduced body size and body condition after 2007 that would result from changes in zooplankton community. We therefore examined zooplankton density, body size, and taxonomic composition at the closest long-term monitoring station (1995–2019): the coastal Point-B. To cover a broader spectrum of zooplankton community, samples obtained from two nets, the WP2 (200 µm mesh size) and the Regent (690 µm), were analysed with the imaging Zooscan method. One important result was the high stability through time of the zooplankton community. No long-term monotonous trends in density, size, and taxonomic composition were detected. Interannual variations in zooplankton size and density were not significantly correlated to any environmental variable, suggesting the possible importance of biotic interactions. Still, an increase in temperature was followed by a sharp decrease of zooplankton density in 2015, after which only gelatinous groups recovered. No change in the zooplankton community was detected around 2007 to support bottom-up control on small pelagic fish. Whether this derives from different local processes between the Gulf of Lions and the Ligurian Sea cannot be excluded, highlighting the need for simultaneous monitoring of different ecosystem compartments to fully understand the impact of climate change.

Mixing tree species associated with arbuscular or ectotrophic mycorrhizae reveals dual mycorrhization and interactive effects on the fungal partners.

Recent studies found that the majority of shrub and tree species are associated with both arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungi. However, our knowledge on how different mycorrhizal types interact with each other is still limited. We asked whether the combination of hosts with a preferred association with either AM or EM fungi increases the host tree roots’ mycorrhization rate and affects AM and EM fungal richness and community composition.We established a tree diversity experiment, where five tree species of each of the two mycorrhiza types were planted in monocultures, two‐species and four‐species mixtures. We applied morphological assessment to estimate mycorrhization rates and next‐generation molecular sequencing to quantify mycobiont richness.Both the morphological and molecular assessment revealed dual‐mycorrhizal colonization in 79% and 100% of the samples, respectively. OTU community composition strongly differed between AM and EM trees. While host tree species richness did not affect mycorrhization rates, we observed significant effects of mixing AM‐ and EM‐associated hosts in AM mycorrhization rate. Glomeromycota richness was larger in monotypic AM tree combinations than in AM‐EM mixtures, pointing to a dilution or suppression effect of AM by EM trees. We found a strong match between morphological quantification of AM mycorrhization rate and Glomeromycota richness. Synthesis. We provide evidence that the combination of hosts differing in their preferred mycorrhiza association affects the host's fungal community composition, thus revealing important biotic interactions among trees and their associated fungi.

Biotic and abiotic determinants of finescale dace distribution at the southern edge of their range

AbstractAimThe factors that set range limits for animal populations can inform management plans aimed at maintaining regional biodiversity. We examine abiotic and biotic drivers of the distribution of finescale dace (Chrosomus neogaeus) in two Great Plains basins to identify limiting factors for a threatened freshwater fish population at the edge of their range.LocationGreat Plains, Nebraska, South Dakota and Wyoming, USA.MethodsWe investigated abiotic and biotic factors influencing the contemporary distribution of finescale dace in the Belle Fourche and Niobrara River basins with Random Forests classification models using fish surveys from multiple agencies spanning 2008–2019 and GIS‐derived environmental data.ResultsIn both basins, finescale dace occurrence exhibited a nonlinear response to mean August water temperature. Abiotic covariates, including streamflow, water temperature and channel slope, were important limiting factors in the final model fit with Belle Fourche River basin surveys (n = 131). In contrast, a biotic covariate, native minnow richness, was the most important predictor of finescale dace occurrence in the Niobrara River basin model (n = 27). In the Niobrara River, native minnow richness was lower at sites with non‐native northern pike (Esox lucius).Main conclusionsBasin‐specific analyses revealed context dependencies for species–environment relationships, which can inform targeted restoration actions. Similar relationships between water temperature and finescale dace occurrence across both basins suggest summer thermal habitat as a regional limiting factor. The importance of biotic interactions in the Niobrara River highlights an emergent threat from invasive predators to a distinct assemblage of native prairie fishes.

Spatiotemporal Patterns in Diversity and Assembly Process of Marine Protist Communities of the Changjiang (Yangtze River) Plume and Its Adjacent Waters.

Marine protists are highly heterogeneous and play key roles in the structure and functioning of marine ecosystems. However, little is known on the underlying biogeographic processes and seasonal diversity patterns that shape their community assembly in a regional scale in marginal sea. In this study, we conducted high-throughput sequencing of 18S rRNA gene to survey the protist community compositions (PCCs) of the Changjiang (Yangtze River) plume, an intensely human-affected coastal area, to the adjacent continental shelf waters over three seasons. Furthermore, the different impacts of environmental and spatial factors on marine PCCs were examined. The results revealed significant dissimilarities of PCC’s diversity among seasons and habitats, with more obvious seasonal variations in the Changjiang plume. Procrustes analysis showed better consistency of the community-environment relationship in shelf area, further supported by stronger correlation coefficients computed in the Mantel tests. This might be explained by seasonal dynamics of Changjiang Diluted Waters (i.e., the mixing of the Changjiang runoff with inshore water of the East China Sea) that changed the environmental conditions of coastal area dramatically, resulting in lower importance of spatial factors (dispersal limitation) on PCCs compared with environmental filters, including physicochemical properties (e.g., water temperature, salinity, dissolved oxygen, and nutrients), as well as biotic factors (e.g., Chl a and food abundance). This was further explained by higher immigration rate and fitness to neutral model, which suggested a predominant role of neutral process in shaping the PCCs in coastal area. Different richness, diversity, and taxonomic compositions but comparable biogeographic patterns were observed among abundant and rare sub-communities. In general, the abundant sub-communities exhibited higher dispersal ability which tend to respond to environmental selection during dispersal, whereas the rare sub-communities appeared to be present only in few samples due to dispersal limitation. Co-occurrence network further indicated the importance of biotic interactions in community assembly and potential roles of rare taxa in maintaining the community structure. Overall, this study suggests the dynamic in the biogeographic patterns of PCCs of the Changjiang plume to the adjacent waters in the ECS responding with the changing environmental conditions and geographical factors.

Vertical niche definition of test‐bearing protists (Rhizaria) into the twilight zone revealed by in situ imaging

AbstractThe Rhizaria is a super‐group of amoeboid protists with ubiquitous distributions, from the euphotic zone to the twilight zone and beyond. While rhizarians have been recently described as important contributors to both biogenic silica and carbon fluxes, we lack the most basic information about their ecological habitats and preferences. Here, using in situ imaging (Underwater Vision Profiler 5), we characterize the vertical ecological niches of different test‐bearing pelagic rhizarian taxa in the southernCalifornia Current Ecosystem. We define three vertical layers between 0 and 500 m occupied, respectively, by (1) surface dwelling and mostly symbiont‐bearing rhizarians (Acantharia and Collodaria), (2) flux‐feeding phaeodarians in the lower epipelagic (100–200 m), and (3) Foraminifera and Phaeodaria populations adjacent to the oxygen minimum zone. We then use Generalized Additive Models to analyze the response of each rhizarian category to a suite of environmental variables. The models explain between 9% and 93% of the total variance observed for the different groups. While temperature and the depth of the deep chlorophyll maximum appear as the main abiotic factors influencing populations in the upper 200 m, dissolved silicon concentration is related to the abundance of mesopelagic phaeodarians, though it explains only a portion of the variance. The importance of biotic interactions (e.g., prey availability, predation, parasitism, symbiosis) is still to be considered, in order to fully incorporate the dynamics of test‐bearing pelagic rhizarians in ecological and biogeochemical models.

Plant-soil feedback effects altered by aboveground herbivory explain plant species abundance in the landscape.

Relatively little is known about how plant-soil feedbacks (PSFs) may affect plant growth in field conditions where factors such as herbivory may be important. Using a potted experiment in a grassland, we measured PSFs with and without aboveground insect herbivory for 20 plant species. We then compared PSF values to plant landscape abundance. Aboveground herbivory had a large negative effect on PSF values. For 15 of 20 species, PSFs were more negative with herbivory than without. This occurred because plant biomass on "home" soils was smaller with herbivory than without. PSF values with herbivory were correlated with plant landscape abundance, whereas PSF values without herbivory were not. Shoot nitrogen concentrations suggested that plants create soils that increase nitrogen uptake, but that greater shoot nitrogen values increase herbivory and that the net effect of positive PSF and greater aboveground herbivory is less aboveground biomass. Results provided clear evidence that PSFs alone have limited power in explaining species abundances and that herbivory has stronger effects on plant biomass and growth on the landscape. Our results provide a potential explanation for observed differences between greenhouse and field PSF experiments and suggest that PSF experiments need to consider important biotic interactions, like aboveground herbivory, particularly when the goal of PSF research is to understand plant growth in field conditions.

Local Adaptation to Biotic Interactions: A Meta-analysis across Latitudes.

Adaptation to local conditions can increase species' geographic distributions and rates of diversification, but which components of the environment commonly drive local adaptation-particularly the importance of biotic interactions-is unclear. Biotic interactions should drive local adaptation when they impose consistent divergent selection; if this is common, we expect transplant experiments to detect more frequent and stronger local adaptation when biotic interactions are left intact. We tested this hypothesis using a meta-analysis of transplant experiments from >125 studies (mostly of plants). Overall, local adaptation was common, and biotic interactions affected fitness. Nevertheless, local adaptation was neither more common nor stronger when biotic interactions were left intact, either between experimental treatments within studies (control vs. biotic interactions experimentally manipulated) or between studies that used natural versus biotically altered transplant environments. However, the effect of ameliorating negative interactions varied with latitude, suggesting that interactions may promote local adaptation more often in tropical than in temperate ecosystems, although few tropical studies were available to test this. Our results suggest that biotic interactions often fail to drive local adaptation even though they strongly affect fitness, perhaps because temperate biotic environments are unpredictable at the spatiotemporal scales required for local adaptation.

Diatom red tide significantly drive the changes of microbiome in mariculture ecosystem

Some diatom species cause red tides under eutrophic conditions, but little is known about their impact on the ecological structure of coastal systems. In this study, the effects of diatom red tides on the bacterial and eukaryotic communities in aquaculture systems were analyzed using high-throughput sequencing. The correlation between these communities and environmental factors was also analyzed. Principal coordinate analysis (PCoA) and non-metric multidimensional scaling (NMDS) showed that there were significant differences in the microbiome in red tide ponds and normal ponds (p < .05). The dominant bacterial taxa in red tide and normal ponds were Proteobacteria, Actinobacteria, Cyanobacteria, Bacteroidetes, Verrucomicrobia and Planctomycetes. There were significant differences in the abundance of bacteria genera, such as Planctomyces, Marivita, Synechococcus and Marinobacterium, in red tide ponds and normal ponds (p < .05). Functional predictions showed that red tides affect carbon, nitrogen, sulfur and phosphorus metabolism in ponds. There were significant differences in the dominant eukaryotic genera in red tide ponds and normal ponds (p < .05). Red tide ponds were dominated by Skeletonema, Thalassiosira, and Cyclotella, while Ostreococcus, Hemiselmis, Glycine, and Cryothecomonas were dominant in normal ponds. Canonical correlation analysis (CCA) indicated that pH, DO salinity, nitrate, nitrite, ammonium and phosphate were significantly correlated with microbiomes in red tide and normal ponds. OTU (operational taxonomic unit) network analysis results showed that the dominant OTUs of Thalassiosira and Skeletonema were negatively correlated with most of the dominant OTUs of Proteobacteria, Actinobacteria, Bacteroidetes and Cyanobacteria. The importance of biotic interactions when investigating the link between the microbiome and red tide species has also been highlighted. This study revealed the important influence of a diatom red tides on bacterial and eukaryotic communities, and provided new insights into the impact of diatom red tides on mariculture ecosystems.

Positive co‐occurrence between feeding‐associative savannah fishes depends on species and habitat

Abstract Understanding the relative importance of abiotic factors and biotic interactions in determining species co‐occurrence is a fundamental goal in ecology. Most studies of ecology of freshwater fishes have focused on negative biotic interactions (competition and predation), and much less is known about more positive interactions. The goal of this study was to quantify the relative importance of habitat features and biotic interactions (positive and negative) on co‐occurrence of three pairs of feeding‐associative Leporinus (L.) fishes in rivers of central Brazil (L. friderici–L. octomaculatus, L. striatus–L. octomaculatus, L. friderici–L. striatus). We sampled 146 sites on two rivers of central Brazil and used two‐species occupancy models to examine the relative importance of habitat features and commensalistic feeding association for determining co‐occurrence of the three species pairs. Using an information–theoretic framework, we compared weight‐of‐evidence for models containing effects of habitat covariates only, biotic interactions only, and their combination. Model evidence supported the hypothesis that feeding activity of L. friderici facilitates occurrence of L. octomaculatus and that the interaction is mediated by habitat covariates. In contrast, most evidence suggested that occurrence of L. striatus is independent of L. friderici, and is instead determined entirely by habitat features. Evidence for facilitation of L. octomaculatus by L. striatus was mixed—there is evidence supporting the habitat‐only hypothesis as well as habitat‐mediated facilitation. Our results suggest that positive interactions can affect co‐occurrence among freshwater fishes, at least for species that interact strongly. More facultative interactions, such as those between L. friderici and L. striatus, may be less important, at least in certain abiotic contexts. This study indicates that biotic interactions between species of freshwater fish can be evident beyond the microhabitat scale to positively influence species co‐occurrence and adds to evidence from other groups of freshwater organisms indicating the importance of biotic interactions in facilitating species co‐occurrence.

Crop competition in winter wheat has a higher potential than farming practices to regulate weeds

AbstractManagement of biotic interactions has been recognized as a potential substitute for costly agrochemical inputs. Competition is one of the most important biotic interactions known to regulate populations and govern species assemblages. However, although theoretical and empirical work has been produced on competition, in situ experimental evidence is much scantier, mainly because of the difficulty of manipulating competition in the field. Arable weeds offer an outstanding opportunity to meet this challenge, because of the relative ease of in situ experimental manipulation and because of the urgent need to find sustainable weed management strategies. Here, we assess the importance of crop competition and two main conventional farming practices (N fertilizer and weed control) on weed species richness, abundance, and biomass. We set up an experiment with a design with two factors, presence/absence of crops and presence/absence of N fertilizer and weed control, in working farm fields with winter cereals as the target crop. We found that the crop competition reduced weed biomass production by almost 65%, as a result of the crop's competitive advantage from its greater ability to take up N, while the effect on weed species richness was less important. Our results also show that the effect of crop competition on the weed assemblage was much stronger than the effect of N fertilizer and weed control. The decrease in weed abundance and biomass mainly resulted from a strong effect of the crop on the dominant species, while the abundance of intermediate species tended to be much less affected, a result consistent with studies in grasslands where the removal of the dominant species provides a competitive release for subordinate ones. Our results further give experimental support for crop competition as a way to reduce costly agricultural inputs for weed control. Conducting experiments with farmers in their field is a valuable approach to generate knowledge for the future delivery of sustainable management.

Biotic interactions in species distribution modelling: 10 questions to guide interpretation and avoid false conclusions

AbstractAimRecent studies increasingly use statistical methods to infer biotic interactions from co‐occurrence information at a large spatial scale. However, disentangling biotic interactions from other factors that can affect co‐occurrence patterns at the macroscale is a major challenge.ApproachWe present a set of questions that analysts and reviewers should ask to avoid erroneously attributing species association patterns to biotic interactions. Our questions relate to the appropriateness of data and models, the causality behind a correlative signal, and the problems associated with static data from dynamic systems. We summarize caveats reported by macroecological studies of biotic interactions and examine whether conclusions on the presence of biotic interactions are supported by the modelling approaches used.FindingsIrrespective of the method used, studies that set out to test for biotic interactions find statistical associations in species’ co‐occurrences. Yet, when compared with our list of questions, few purported interpretations of such associations as biotic interactions hold up to scrutiny. This does not dismiss the presence or importance of biotic interactions, but it highlights the risk of too lenient interpretation of the data. Combining model results with information from experiments and functional traits that are relevant for the biotic interaction of interest might strengthen conclusions.Main conclusionsMoving from species‐ to community‐level models, including biotic interactions among species, is of great importance for process‐based understanding and forecasting ecological responses. We hope that our questions will help to improve these models and facilitate the interpretation of their results. In essence, we conclude that ecologists have to recognize that a species association pattern in joint species distribution models will be driven not only by real biotic interactions, but also by shared habitat preferences, common migration history, phylogenetic history and shared response to missing environmental drivers, which specifically need to be discussed and, if possible, integrated into models.