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Interactions with competitors and predators can generate strong selection and favour the evolution of novel strategies for mitigating fitness costs. Adaptations to mitigate competition and predation risk often involve evolution of traits which directly reduce costs. Simultaneously, the evolution of behaviours that co‐opt the functional traits of non‐interacting, third‐party species have also been observed but remain poorly studied (e.g. anointing behaviour, tri‐trophic interactions). Here we investigate if the novel behavioural co‐option of conifer resin in a cavity‐nesting bird can ameliorate interactions with nest predators and nest site competitors. Red‐breasted nuthatches (Sitta canadensis) collect resin from live trees and apply it around the entrances of their nest cavities in dead trees. Using paired nest boxes, we mimicked the nuthatch behaviour by apply resin around the hole of one and not the paired box in two field experiments to test a priori hypotheses about the evolution and adaptive value of this behaviour. The first experiment baited the paired boxes with food to attract mammalian predators (e.g. red squirrels Tamiasciurus hudsonicus). The second experiment left boxes available for breeding by cavity‐nesting birds that compete with nuthatches for nest sites (e.g. house wrens Troglodytes aedon). We also used ancestral trait reconstruction to test whether resin use is a non‐adaptive derivation of mud‐plastering behaviour observed in numerous congeners. Experimental nest boxes with resin applied to the entrance were less likely to have bait removed and less likely to have nests built or initiated than paired nest boxes without resin. Ancestral trait reconstruction suggested that resin use was more likely (>77%) to have evolved in ancestors that did not exhibit mud‐plastering behaviour. Our results do not support a major role of phylogenetic inertia and provide experimental evidence that application of conifer resin to nest cavities ameliorates interference competition from other cavity‐nesting species and reduces nest predation risk. Overall, our results showcase the ecological function of behavioural co‐option and its important consequences for fitness in nature. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

The processing of organic matter is a central ecosystem function in freshwater ecosystems that allows the integration of terrestrial plant material into aquatic heterotrophic food webs. From an energetic perspective, many temperate aquatic systems fundamentally depend on such allochthonous inputs. Current research established that this central ecosystem function may be linked to population density of few yet dominant invertebrate detritivores, showing a negative density‐dependent relationship. Here, we extended the current knowledge and experimentally assessed the processing of leaf litter by freshwater amphipods, using broad density gradients, interspecific competition, and laboratory and field experiments. We used two species of dominant amphipods, namely the native Gammarus fossarum and the non‐native Gammarus roeselii, varying their density by two orders of magnitude, both in single‐species and two‐species treatments. Results from 252 mesocosms in the lab and 97 mesocosms in a natural stream show that per capita leaf litter processing rates are strongly negatively dependant on population density in monocultures. Interspecific competition in two‐species treatments corroborated the negative density‐dependent ecosystem function and highlighted the functional redundancy of the two detritivore species. We identified a flattening in the processing rates at previously unreported but well‐defined breakpoints. These breakpoints may reflect minimal metabolic requirements at which survival takes precedence over any other process, such as interference competition. The breakpoints were consistent across both species, indicating that they must process leaf litter equalling one fifth to one fourth of their dry body weight per day as a minimal nutritional threshold. Our results suggest the need for integrating nonlinear density‐dependencies and breakpoint population densities in key ecosystem functions in aquatic ecosystem modelling alongside classical biodiversity–ecosystem functioning relationships. Depending on the population density the corresponding ecosystem functioning could differ significantly. This corroborates the need to better understand biodiversity–abundance relationships when protecting aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Pear psyllid (Cacopsylla pyri) is a persistent pest to the pear industry; with an estimated cost of £5 million per annum in the UK alone. This phloem feeding insect is resistant to a large proportion of approved pesticides, necessitating the use of alternative control strategies. Many pear growers practice integrated pest management (IPM) of pear psyllid, focusing on maximizing natural enemy populations, whilst minimizing the use of agrochemical sprays. The anthocorid Anthocoris nemoralis and the European earwig Forficula auricularia are particularly effective at controlling pear psyllid populations during the summer months. Despite the effectiveness of both natural enemies, there is a lack of understanding on whether both species should be promoted together or separately, due to the risk of intraguild predation (IGP) or interference competition. Furthermore, abiotic factors including temperature may influence both behaviors, altering activity level and niche overlap. Although IGP and interference competition have been documented between multiple species of natural enemies neither have been studied between these two specific predators. Using microcosm experiments, olfactometer assays and survival analyses this study demonstrated whether A. nemoralis and F. auricularia can be used in synchrony to control pear psyllid. Results indicated that IGP is present; F. auricularia will consume A. nemoralis when predators are not spatially separate and in absence of psyllid prey. There was no evidence for interference competition, although both predators consumed more prey at higher temperatures. This confirms that pear growers can encourage both predators for the control of pear psyllid without losing predation efficacy. [ABSTRACT FROM AUTHOR]

Free ranging-dogs are being recognized as a potential threat for native wildlife around the globe. They interact with native wildlife at multiple levels, ranging from predation, competition, acting as a reservoir for diseases and hybridization with the native carnivores. We have recorded cases that focus on interactions of dogs with wildlife in and around Ranthambhore Tiger Reserve (RTR). Between 2017–2020, we collected data on free-ranging dogs interacting with native wildlife of RTR. We classified the interactions into two categories: resource acquisition and predation. Based on our results we propose that dogs in rural settings around wildlife reserves can cause more resource competition for the existing carnivore scavenging guild resulting in reduced biomass consumption for the native scavengers. When present in large numbers, they can have a negative interaction with native wildlife through predation and harassment. To understand how dogs can pose threats to the native wildlife, there is a need for an extensive study on the ecology of dogs around wildlife reserves, pertaining to their feeding ecology and their raging behaviour. [ABSTRACT FROM AUTHOR]

The relationships between body size and density of salmonids in natural streams have been well studied, and density‐dependent growth (somatic growth) is interpreted as the principal mechanism responsible for the relationship. Moreover, the body size–density relationship is known to vary over ontogeny. However, the relationship has been studied mostly by experimental procedures (e.g. stocking fish into streams), and knowledge about the relationship in natural populations (e.g. no human‐induced input of fish) is still inadequate. In this study, we compared the relationships between body size and density of young‐of‐the‐year (YOY) masu salmon, Oncorhynchus masou, between different ontogenetic stages, that is, fry (spring) and juveniles (autumn). We used the monitoring data of YOY body sizes and densities across three study sites collected from Horokashubuto stream in Hokkaido, northern Japan, from 2014 to 2022. In the juvenile stage, YOY body size correlated negatively with increasing density. This pattern is typical of the density dependence of salmonid growth demonstrated in many previous studies. In the fry stage, however, YOY body size correlated positively with increasing density. This study suggested that the patterns of density dependence vary as functions of the ontogenetic stages of salmonids. [ABSTRACT FROM AUTHOR]

Competition between native and alien species is often described as a main driver of biodiversity loss. Nevertheless, there is limited evidence of animal declines and extinctions actually determined by competition. The Aeolian lizard, Podarcis raffonei, is critically endangered because it suffered dramatic declines and extinctions throughout its range. Competition and hybridization with invasive Italian lizards, Podarcis siculus, have been proposed as a driver of the shrinkage of Aeolian lizards, still the mechanisms underlying their decline remain poorly resolved. We used observations of behavioral encounters, combined with morphological data and robust species identification based on genomics, to test whether agonistic interactions with the invasive Italian lizard can explain the competitive exclusion and rapid decline of the native Aeolian lizard while accounting for hybridization. Invasive lizards were larger, with larger heads, and showed higher bite tendency against neutral items. In agonistic encounters between males, Aeolian lizards received more attacks and escaped more frequently than invasive males. The performance of Aeolian males was particularly poor in interspecific encounters. Genomic data verified that tested individuals were all pure P. raffonei or P. siculus, with a single hybrid individual detected. The strong competitive advantage of invasive males can allow them monopolizing territories, potentially hampering the reproduction of both native males and females, thus resulting in a mechanism of sterilizing interference. Reproductive interference competition mediated by spatial exclusion might be an unappreciated process determining rapid decline in endemic species. Safeguarding areas devoid of invasive species should be the priority strategy to avoid the extinction of the Aeolian lizards.

Theorists have identified several mechanisms through which species that compete exploitatively for resources could coexist. By contrast, under the current theory, interference competitors could coexist only in rare circumstances. Yet, some types of interference competition, such as interspecific territoriality, are common. This mismatch between theory and nature inspired us to model interference competition in an eco-evolutionary framework. We based the model on the life cycle of territorial birds and ran simulations to examine whether natural selection could rescue a superior interference competitor from extinction without driving a superior exploitative competitor extinct. We found that coexistence between interference competitors can occur over a wide range of ecologically plausible scenarios, and up to the highest levels of resource overlap. An important caveat is that coexistence requires the species to co-evolve. Reductions in population size and levels of genetic variation could destabilise coexistence between interference competitors, and thereby increase extinction rates over current estimates.

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Behavioural interactions between alien invasive fishes and native fishes is considered one of the drivers of native fish decline. However, there are few experimental studies on their behavioural interactions at the individual level. In this study, we investigated the behavioural interactions between the threatened native killifish Valencia letourneuxi, and the alien invasive Eastern mosquitofish Gambusia holbrooki, thought to induce the killifish's rapid population decline. The aim was to assess aggressive behaviours, disruption in activity, stress levels, boldness, forging efficiency and shelter use by the native fish in the presence of the mosquitofish. Interspecies interactions were assessed in a three-tiered experimental setup, i.e. in an empty arena, in the presence of an artificial cover, and during feeding, using two opponents at each trial. The behaviours recorded and assessed were nips, following, approach, moving/immobile, top/bottom, erratic movement, cover use, feeding and latency to exit. The results showed that the mosquitofish was bolder, followed the native species, spent significantly less time under the cover and consumed food, as opposed to no following by the native species, significantly higher cover use and time immobile, as avoidance behaviours, and zero feeding in the presence of the mosquitofish. More significantly, the native species received direct aggression by the mosquitofish, as opposed to no aggression at all exhibited by it. Future research needs, as well as the conservation implications of our findings are briefly discussed. [ABSTRACT FROM AUTHOR]

Male–male combat occurs in many snake species and is often thought to result from competition for mates. We argue a more thorough assessment of the contexts in which combat occurs is warranted for snakes. We made field video observations of Agkistrodon conanti in central Florida, A. piscivorus in eastern North Carolina, and A. contortrix in eastern Kentucky. These observations were made in frequently used foraging sites; near drying ephemeral ponds in Florida and North Carolina and in a forested area with abundant emerging cicadas in Kentucky. In all three populations, males engaged in ritualized combat. In four instances, a variety of lines of evidence including season, local food resource abundance, local female abundance, and postcombat behaviors all indicated that access to food resources, rather than mating opportunities, was the catalyst for agonistic behavior. Behaviorally, food-induced combat appears nearly identical to mating-induced combat. Simplistic assumptions about the environmental contexts that induce combat may lead researchers to make inaccurate conclusions concerning the duration of the breeding season and the frequency of intraspecific competition for food in snake species. We outline a rigorous set of criteria that should be used to determine the context of male–male combat bouts. Videos showing the examples of combat discussed are available at http://www.momo-p.com/showdetail-e.php?movieid=momo231230ac01a, http://www.momo-p.com/showdetail-e.php?movieid=momo231230ac02a, http://www.momo-p.com/showdetail-e.php?movieid=momo231228ap01a, and http://www.momo-p.com/showdetail-e.php?movieid=momo231230ap01a. [ABSTRACT FROM AUTHOR]

Interference competition between native and invasive species can be an important driver of the local extirpation of native species; however, extinctions resulting from competition are rare. This study investigates competitive interactions between an invasive and an imperiled species to assess whether competition is an important mechanism behind this species replacement. Freshwater crayfish are one of the most imperiled taxonomic groups in North America, and nonnative crayfish pose a major threat to native crayfishes. Many crayfish have limited distributions, so merely moving crayfish between adjacent drainages can cause species replacements that threaten native species. Here, we examine competitive interactions between the imperiled Black Creek crayfish (BCC; Procambarus pictus), which is endemic to the lower St. Johns River drainage, Florida, and the white tubercled crayfish (WTC; P. spiculifer), an introduced species from a neighboring drainage. We found that WTC grew more rapidly than BCC in common conditions, and when WTC was larger, this species won aggressive interactions and was dominant in shelter competition with the imperiled species. However, when the species were size matched, BCC was more competitive than WTC. These results highlight the importance of size and growth rate for determining the outcome of interference competition. WTC is replacing BCC throughout a substantial portion of its limited range, and our results suggest that size-mediated competition between these species may be an important mechanism for this species replacement. [ABSTRACT FROM AUTHOR]

AbstractInterspecific territoriality has complex ecological and evolutionary consequences. Species that interact aggressively often exhibit spatial or temporal shifts in activity that reduce the frequency of costly encounters. We analyzed data collected over a 13-year period on 50 populations of rubyspot damselflies (Hetaerina spp.) to examine how rates of interspecific fighting covary with fine-scale habitat partitioning and to test for agonistic character displacement in microhabitat preferences. In most sympatric species, interspecific fights occur less frequently than expected based on the species’ relative densities. Incorporating measurements of spatial segregation and species discrimination into the calculation of expected frequencies accounted for most of the reduction in interspecific fighting (subtle differences in microhabitat preferences could account for the rest). In 23 of 25 sympatric population pairs, we found multivariate differences between species in territory microhabitat (perch height, stream width, current speed, and canopy cover). As predicted by the agonistic character displacement hypothesis, sympatric species that respond more aggressively to each other in direct encounters differ more in microhabitat use and have higher levels of spatial segregation. Previous work established that species with the lowest levels of interspecific fighting have diverged in territory signals and competitor recognition through agonistic character displacement. In the other species pairs, interspecific aggression appears to be maintained as an adaptive response to reproductive interference, but interspecific fighting is still costly. We now have robust evidence that evolved shifts in microhabitat preferences also reduce the frequency of interspecific fighting.

Understanding the competition and coexistence of flagship carnivores is key to creating strategies for their conservation in the face of global carnivore declines. Although studies exploring the dynamics and competition between tigers (Panthera tigris) and leopards (P. pardus) span decades, there is a lack of understanding regarding the factors that influence their coexistence mechanisms on a broad scale, as well as the drivers determining their exploitative and interference competition. We gathered a comprehensive list of research papers among which 36 papers explored the interspecific interactions between tigers and leopards and tested the influence of biotic and abiotic factors on the coexistence mechanisms along three dimensions using multiple response variables regression models; we also tested the influence of ecological drivers determining the exploitative or interference competition between tigers and leopards. Elevation and ungulate density were the most important predictors in regulating the coexistence mechanisms. Tigers and leopards exhibited more positive relations/higher overlaps as elevation increased in the spatial niche. In addition, they showed a higher dietary overlap in the prey‐rich regions. We determined that interference competition between tigers and leopards was less frequently observed in habitats with dense tree cover and homogeneous vegetation structures. Meanwhile, studies with multiple metrics would promote the detection of interference competition. Our study provides new insight into the competitive interactions and coexistence mechanisms of tigers and leopards on a broad scale. Policy‐makers and managers should pay more attention to the factors of elevation, prey abundance, and habitat structures for the conservation of tigers and leopards. [ABSTRACT FROM AUTHOR]

Context: Invasive species can threaten native species through exploitative and interference competition if they occupy similar ecological niches. The invasive plague skink (Lampropholis delicata) has been accidently introduced to New Zealand, Lord Howe Island, and the Hawaiian Islands. Resource usage overlaps between plague skinks and several New Zealand skinks, suggesting the potential for exploitative and interference competition. However, no competitive mechanism or population impact has been identified. In 2014–15, plague skinks colonised Bream Head Scenic Reserve, Northland, New Zealand, where they overlap in occupancy and habitat with the 'Nationally Critical' kakerakau skink (Oligosoma kakerakau). Aims: We investigated intra- and interspecific interference competition between kakerakau and plague skinks in the wild. Methods: We recorded naturally occurring encounters and quantified aggression at a short-lived resource (sun-basking sites). Key results: Behavioural interactions were observed in 72% of all encounters with similar proportions of encounters resulting in agonistic interactions between intraspecific kakerakau skink encounters and interspecific kakerakau-plague encounters. Although kakerakau skinks and plague skinks reacted equally aggressively in an interspecific interaction, kakerakau skinks behaved significantly more aggressively in an interaction with a plague skink than with a conspecific. Juvenile kakerakau skinks were more likely than adults to exhibit submissive behaviours such as fleeing during interspecific interactions. Conclusions: This is the first evidence of interference competition occurring between plague skinks and a native skink. Our study suggests that kakerakau skinks, particularly juveniles, may experience competitive exclusion at important resources. Implications: Our findings indicate that plague skinks may pose a threat to native skink populations when habitat use overlaps. Biological invasions are a major cause of biodiversity loss. However, the behavioural interactions occurring between native and invasive species are often unknown. We report aggression in the wild between the invasive plague skink and a native New Zealand skink. Our study demonstrates that plague skinks may pose a threat to native skinks. [ABSTRACT FROM AUTHOR]

Interactions between different species of predators are not uncommon, yet they are generally understudied in North America. Across their range, gray wolves (Canis lupus) and wolverines (Gulo gulo) occupy similar habitats and dietary niches. However, due to the elusiveness and relatively low density of these two species, interactions between them are not well documented. Here, we describe three instances of a single wolf pack killing a wolverine in the span of 13 months. None of the wolverines killed by wolves were consumed, suggesting that food was not the primary motivation behind the killings. Alternatively, defense of a food resource, territoriality, interspecific competitive killing, or some combination of those behaviors appear to be the cause of these actions. Documentation of these occurrences improves our understanding of wolf and wolverine ecology, interspecific predator interactions, and potential future changes to this aspect of community ecology. [ABSTRACT FROM AUTHOR]

Intraspecific interactions between mesocarnivores are not commonly observed and consequentially not well understood, particularly for species inhabiting wilderness regions. Using a remote camera, we captured interactions between a Canada lynx (Lynx canadensis) and wolverine (Gulo gulo) scavenging on the remains of a bison (Bison bison). Over a 23‐min period representing nine photographic sequences (1–3 photographs per sequence), we observed (1) a wolverine approach the remains that were being fed on by a lynx, (2) the two animals feeding on the remains at the same time for about 19 min, (3) the wolverine chasing the lynx off of the carcass and, thereafter, (4) the wolverine excluding the lynx from the carcass. Our observation is of potential scientific value because it sheds light on behavioral interactions between these two species, particularly at a rich food source. Intraguild interactions between these species appear to include tolerance toward one another, as well as interference competition, with the wolverine being the dominant species. Our observation highlights the new information on interactions between mesocarnivores that are becoming illuminated with the use of remote cameras, revealing that these interactions may be more complex than once thought. [ABSTRACT FROM AUTHOR]

Costly interactions between species that arise as a by-product of ancestral similarities in communication signals are expected to persist only under specific evolutionary circumstances. Territorial aggression between species, for instance, is widely assumed to persist only when extrinsic barriers prevent niche divergence or selection in sympatry is too weak to overcome gene flow from allopatry. However, recent theoretical and comparative studies have challenged this view. Here we present a large-scale, phylogenetic analysis of the distribution and determinants of interspecific territoriality. We find that interspecific territoriality is widespread in birds and strongly associated with hybridization and resource overlap during the breeding season. Contrary to the view that territoriality only persists between species that rarely breed in the same areas or where niche divergence is constrained by habitat structure, we find that interspecific territoriality is positively associated with breeding habitat overlap and unrelated to habitat structure. Furthermore, our results provide compelling evidence that ancestral similarities in territorial signals are maintained and reinforced by selection when interspecific territoriality is adaptive. The territorial signals linked to interspecific territoriality in birds depend on the evolutionary age of interacting species, plumage at shallow (within-family) timescales, and song at deeper (between-family) timescales. Evidently, territorial interactions between species have persisted and shaped phenotypic diversity on a macroevolutionary timescale.

Interspecific competition from introduced and naturally colonizing species has potential to affect resident populations, but demographic consequences for vertebrates have rarely been tested. We tested hypotheses of interspecific and intraspecific competition for density, body mass, and fertility of adult female Roe Deer (Capreolus capreolus) across a heterogeneous forest landscape occupied by two introduced deer species: Mediterranean Fallow Deer (Dama dama); and subtropical Reeve's Muntjac (Muntiacus reevesi). Species-specific deer densities in buffers around culling locations of 492 adult female Roe Deer, sampled over seven years, were extracted from spatially explicit models calibrated through annual nocturnal distance sampling. Roe Deer fertility and body mass were related to species-specific deer densities and extent of arable lands using piecewise structural equation models. Reeve's Muntjac density was lower at higher Fallow Deer densities, suggesting interspecific avoidance via interference competition, but greater when buffers included more arable land. Roe Deer body mass was marginally greater when buffers included more arable land and was independent of deer densities. However, Roe Deer fertility was unrelated to female body mass, suggesting that fertility benefits exceeded an asymptotic threshold of body condition in this low-density population. However, Roe Deer fertility was slightly greater rather than reduced in areas with greater local Roe Deer density, suggesting negligible intraspecific competition. In contrast, Roe Deer was less fertile in areas with greater Reeve's Muntjac densities; thus, interspecific exceeded intraspecific competition in this assemblage. In contrast, we found no support for any effects of Fallow Deer density on Roe Deer density, body mass, or fertility. Complex networks of interspecific competition operating in this deer assemblage include: interspecific interference from Fallow Deer exceeded habitat effects for Reeve's Muntjac; and interspecific competition from introduced, smaller sedentary Reeve's Muntjac reduced fertility, unlike intraspecific, or potential competition with larger, more mobile, Fallow Deer for native Roe Deer. Mechanisms driving Roe Deer fertility may include interspecific behavioral interference or stress–resource depletion is considered less likely because Roe Deer fertility was independent of body mass. Findings emphasize the importance of ensuring appropriate management strategies for controlling invasive species. [ABSTRACT FROM AUTHOR]

Interference competition has the potential to alter avian assemblages at long‐lasting arid zone waterholes, particularly in a warming world, as more potentially aggressive species frequent these sites to drink. We used camera traps and observational surveys to investigate interference competition between terrestrial avian species at six long‐lasting waterholes across three sampling seasons (two summers and one winter) within the MacDonnell Ranges Bioregion in central Australia. The proportion of individuals drinking for each of four dietary classes (granivores, nectarivores, omnivores, and insectivores) was modelled in relation to their abundance in the immediate waterhole habitat, which informed the potential for competition in each season. We then used the temporal overlap estimators to quantify the degree of competition between species at waterholes with species grouped into families (Meliphagidae, Ptilonorhynchidae, Estrildidae, and Rhipiduridae). We found the proportion of individuals drinking at waterholes was greatest during hot and dry periods, suggesting the potential for interference competition is greatest during these times. This was particularly the case for nectarivores where, in hot and dry conditions, the proportion of drinking individuals increased significantly as their abundance also increased in the waterhole habitat. We predicted that subordinate species would alter their activity periods to avoid competitive interactions with meliphagids (honeyeaters), however, we found there was a high degree of temporal overlap between all families sampled across all seasons. These results suggest subordinate species are unlikely to be excluded from long‐lasting waterholes by potentially aggressive species, such as honeyeaters. However, some species may face trade‐offs between foraging and accessing waterholes to stay hydrated as they shift their activity to avoid the hottest parts of the day during the summer months. Under global warming, extended hot and dry periods will likely create conditions where balancing energy and hydration requirements becomes increasingly difficult and results in the loss of body condition. [ABSTRACT FROM AUTHOR]

Abstract Intraspecific interactions between mesocarnivores are not commonly observed and consequentially not well understood, particularly for species inhabiting wilderness regions. Using a remote camera, we captured interactions between a Canada lynx (Lynx canadensis) and wolverine (Gulo gulo) scavenging on the remains of a bison (Bison bison). Over a 23‐min period representing nine photographic sequences (1–3 photographs per sequence), we observed (1) a wolverine approach the remains that were being fed on by a lynx, (2) the two animals feeding on the remains at the same time for about 19 min, (3) the wolverine chasing the lynx off of the carcass and, thereafter, (4) the wolverine excluding the lynx from the carcass. Our observation is of potential scientific value because it sheds light on behavioral interactions between these two species, particularly at a rich food source. Intraguild interactions between these species appear to include tolerance toward one another, as well as interference competition, with the wolverine being the dominant species. Our observation highlights the new information on interactions between mesocarnivores that are becoming illuminated with the use of remote cameras, revealing that these interactions may be more complex than once thought.

Interference competition, a category of interspecific competition, is a critical aspect of understanding the dynamics of carnivore communities, as it can result in a decline in the health and reduced opportunity for resource acquisition of one or both competing species. Heavy snowfall environments during winter are expected to exacerbate interference competition due to decreased food resources and limited foraging opportunities caused by snow cover. However, knowledge on interference competition in such environments is limited. Using camera traps with baits, we evaluated the interference competition among three sympatric medium-sized carnivores, red foxes, raccoon dogs, and Japanese martens, within a heavy snowfall region of northeastern Japan. As in previous studies, we hypothesized that body weight would serve as a determining factor for superiority in winter snow environments. Diel activity patterns using the visitation time to baits did not reveal any clear differences. Nevertheless, the daytime occurrence frequency of Japanese martens during the snowfall season was higher than that of the other two species, indicating inferiority to the other species. The analysis of time intervals between species visiting baits revealed no clear superiority among the target species. These findings suggest that the interspecific relationships among medium-sized carnivores in winter snowy environments are complex and not easily determined. [ABSTRACT FROM AUTHOR]

Competition for limited nest sites among secondary cavity-nesting bird species is intense and may result in loss of nests, physical conflict, injury, and occasionally death. The Prothonotary Warbler ( Protonotaria citrea ) is a secondary cavity-nesting species that has experienced a 38% population decline over the past five decades. In the northern portion of their range, Prothonotary Warblers are sympatric with two cavity-nesting species known for their nest usurpation behaviors: the House Wren ( Troglodytes aedon ) and Tree Swallow ( Tachycineta bicolor ). From 2017–2023 we monitored Prothonotary Warbler nests. House Wrens destroyed and usurped 38% of Prothonotary Warbler nests, which represented the greatest cause of nest failure, while Tree Swallows usurped only 1.5% of Prothonotary Warbler nests. We also documented two instances of adult Prothonotary Warblers likely killed by Tree Swallows. Interference competition from House Wrens is likely a significant factor limiting Prothonotary Warbler reproductive success where it is sympatric with these nest competitors.

Many interspecifically territorial species interfere with each other reproductively, and in some cases, aggression towards heterospecifics may be an adaptive response to interspecific mate competition. This hypothesis was recently formalised in an agonistic character displacement (ACD) model which predicts that species should evolve to defend territories against heterospecific rivals above a threshold level of reproductive interference. To test this prediction, we parameterised the model with field estimates of reproductive interference for 32 sympatric damselfly populations and ran evolutionary simulations. Asymmetries in reproductive interference made the outcome inherently unpredictable in some cases, but 80% of the model's stable outcomes matched levels of heterospecific aggression in the field, significantly exceeding chance expectations. In addition to bolstering the evidence for ACD, this paper introduces a new, predictive approach to testing character displacement theory that, if applied to other systems, could help in resolving long-standing questions about the importance of character displacement processes in nature.

Simple Summary: Exploitative competition and interference competition differ in the way access to resources is modulated by a competitor. Exploitative competition implies resource depletion and usually produces spatial segregation, while interference competition is independent from resource availability and can result in temporal niche partitioning. Here, we inferred the presence of these two patterns of competition on a two-salamander system in Northern Italy. We found evidence supporting interference competition and temporal niche partitioning. Exploitative competition and interference competition differ in the way access to resources is modulated by a competitor. Exploitative competition implies resource depletion and usually produces spatial segregation, while interference competition is independent from resource availability and can result in temporal niche partitioning. Our aim is to infer the presence of spatial or temporal niche partitioning on a two-species system of terrestrial salamanders in Northern Italy: Speleomantes strinatii and Salamandrina perspicillata. We conducted 3 repeated surveys on 26 plots in spring 2018, on a sampling site where both species are present. We modelled count data with N-mixture models accounting for directional interactions on both abundance and detection process. In this way we were able to disentangle the effect of competitive interaction on the spatial scale, i.e., local abundance, and from the temporal scale, i.e., surface activity. We found strong evidence supporting the presence of temporal niche partitioning, consistent with interference competition. At the same time, no evidence of spatial segregation has been observed. [ABSTRACT FROM AUTHOR]

Aims: Understanding how historical and ecological (species interactions) factors affect species and shape community structure is a fundamental goal in ecology. However, these two components are difficult to disentangle and are often confounded. We address the influence of these factors in governing the structure of bird assemblages. Location: Southeastern Australia. Taxon: The Meliphagoidea superfamily. Methods: By adopting a semi‐experimental approach (i.e. high vs low interference competition), we examine the influence of a genus (Manorina) of honeyeater species that is well known for its hyper‐aggressiveness and strong competitive capacity on the phylogenetic and functional structure of local assemblages across three different habitats (eucalypt woodlands, mallee and cleared habitat). We applied a model that explicitly incorporates the effects of neutral colonization and local extinction in shaping community structure and estimated the contributions of niche‐based and neutral processes to community assembly using the STEPCAM technique. Results: Communities with the presence of Manorina species were characterized by faster rates of colonization and local extinction and exhibited a higher degree of phylogenetic clustering than communities without these despotic species, which suggests that this model not only mirrors habitat preferences, but also unintendedly accounts for the effect of biotic interactions. Stochastic processes had a lower contribution in the presence of Manorina species, whereas the role of filtering tended to be higher. We observed habitat differences in terms of functional (but not phylogenetic) structure, with more functionally clustered assemblages in the cleared habitat. Main Conclusions: Although recent studies have suggested that neutral‐species processes are sufficient to explain local assemblage phylogenetic structure, our capacity to isolate them from contemporary ecological processes is still limited. This study also reinforces the idea that biotic interactions can also lead to patterns of underdispersion and thus, assumptions behind null model approaches for community assembly should be carefully considered in each case. [ABSTRACT FROM AUTHOR]

Simple Summary: Organisms compete for resources, such as food and space, and competition can occur in two ways: exploitative competition or interference competition. In exploitative competition, organisms consume the same limited resources, directly reducing the availability of those resources for other individuals, while in the case of interference competition, organisms actively prevent others from accessing resources, independently of resource availability. We tested for the presence and type of foraging competition in two species of forest-dwelling salamanders in Italy: Speleomantes strinatii and Salamandrina perspicillata. Our results suggested the presence of an interference/interaction occurring between the two species and affecting the foraging activity of the smaller one (Salamandrina perspicillata). This competitive interaction is size mediated and configured as interference competition rather than exploitative competition. Exploitative competition and interference competition differ in the way they affect re-source availability for competitors: in the former, organisms reduce resource availability for the competitors; in the latter, one organism actively prevents the competitor from accessing resources, independently of their availability. Our aim is to test for the presence of foraging competition in two forest-dwelling salamanders in Italy: Speleomantes strinatii and Salamandrina perspicillata. We also aim at testing for size-mediated competition. We obtained stomach contents from 191 sampled individuals by means of stomach flushing at 8 sampling sites where both species occur. We focused our analysis on the core prey taxa shared by both species: Collembola and Acarina. We found that the foraging activity of S. perspicillata is positively affected by body size and negatively affected by potential competitor's activity on the forest floor during the sampling, which also significantly weakened the positive relationship with body size. These results suggest the presence of an interference/interaction occurring between the two species and affecting the foraging activity of S. perspicillata. This competitive interaction is size mediated and configured as interference competition rather than exploitative competition. [ABSTRACT FROM AUTHOR]

Unravelling how biodiversity is maintained despite species competition for shared resources has been a central question in community ecology, and is gaining relevance amidst the current biodiversity crisis. Yet, we have still a poor understanding of the mechanisms that regulate species coexistence and shape the structure of assemblages in highly competitive environments such as carrion pulsed resources. Here, we study how large vertebrates coexist in scavenger assemblages by adapting their diel activity at large ungulate carcasses in NW Spain. We used camera traps to record vertebrate scavengers consuming 34 carcasses of livestock and hunted wild ungulates, which allowed us to assess also differences regarding carcass origin. To evaluate temporal resource partition among species, we estimated the overlap of diel activity patterns and the mean times of each scavenger at carcasses. We recorded 16 species of scavengers, 7 mammals and 9 birds, and found similar richness at both types of carcasses. Birds and mammals showed contrasting diel activity patterns, with birds using carcasses during daytime (mean= 11:38 h) and mammals mostly at night (23:09 h). The unimodal activity patterns of scavengers showed asynchronous peaks among species. Subordinate species modified their activity patterns at carcasses used by apex species to reduce temporal overlap. Also, diel activity patterns of vultures closely followed those of corvids, suggesting facilitation processes in which corvids would enhance carcass detection by vultures. Two mammal species (12.5%) increased nocturnality at carcasses of hunted ungulates, which could be a response to human disturbance. Our results suggest that both temporal segregation and coupling mediate the coexistence of large vertebrates at carcasses. These mechanisms might lead to richer scavenger assemblages and thereby more efficient ones in driving critical ecosystem functions related to carrion consumption, such as energy and nutrient recycling and biodiversity maintenance.

Rising temperatures can enhance foraging activity and accelerate the encounter rate of different predators, which may increase their interference competition strengths. However, limited information is available on such effects of temperature, and on the consequences for their predation rates. We used a functional response approach to experimentally quantify the interspecific interference competition strength of two species of ladybirds, Harmonia axyridis and Propylea japonica (Coleoptera: Coccinellidae), toward their prey Myzus persicae (Hemiptera: Aphididae) at 23 and 33 °C, respectively. The results indicated that high temperature could cause P. japonica to be more active and interfere with H. axyridis more often, and strengthened the interference competition between these two predators. The functional response of H. axyridis was changed from type II in single H. axyridis treatment to type III in paired predator assays at 23 and 33 °C. Moreover, single H. axyridis consumed more aphids than H. axyridis in heterospecific predator trials at aphid densities below 50 and 35 at 23 and 33 °C treatments, respectively. For P. japonica, type II functional responses were detected in all assays. Additionally, when competing with H. axyridis, the predation rate of P. japonica at 23 °C was almost unchanged compared to that of single P. japonica, but fewer aphids were eaten compared with single P. japonica across all aphid densities at 33 °C. Thus, with interference competition, two predator species respond differently to temperature changes in terms of foraging efficiency, which may further affect the population adaptability and control efficiency of these two focal species. [ABSTRACT FROM AUTHOR]

Being the first to discover a resource can provide a competitive advantage (priority effect), even for an animal that is inferior in aggressive contests. Nicrophorus spp. (burying beetles) are known for caching a small vertebrate carcass as provision for their young, reducing volatile cues available to rivals by burying the carcass (vertical movement) and by altering the microbial community. A decomposing carcass, however, can leave cues (residues of decay) on soil and leaf litter that a burying beetle has less opportunity to neutralize. I investigated whether horizontal movement of the carcass by burying beetles, separating the carcass from soil at the site of death, might reduce competition from congeners. When fresh carcasses were placed in the field on top of soil with residues of decay, akin to no horizontal displacement, carcasses were discovered within 24 h by free-flying competitors more frequently (58.2%) than when the carcass was placed 1 m from treated soil (8.3%). In a second experiment, carcasses were more likely to be discovered by burying beetles when a chemical attractant (methyl thiocyanate) was placed near a carcass (0.03 and 0.25 m) than when it was placed more distant (1 and 5 m) or for controls (no attractant). The results suggest that horizontal displacement of a carcass after discovery serves not only to locate a suitable spot for burial but also to reduce information available to rivals searching for the resource. [ABSTRACT FROM AUTHOR]

Arboreal birds in the Sahel are highly selective in their tree choice. Most migrant, but also resident, birds are found in a few tree species and within those species often only in trees with abundant leaves and flowers. For this reason alone, preferred trees were expected to teem with birds. This was not the case. Most bird species were present in trees as singletons, even half of the Senegal Eremomela Eremomela pusilla – the most social species of all – were recorded as solitary birds. The probability that two different bird species were in the same tree was also very small, 2.8% on average. Mixed-group foraging flocks of arboreal birds, as so often reported for tropical forests, did not occur in the Sahel. Perhaps birds forage singly because they have no need to fear the raptors that are common in the forests further south. Some species, such as European Pied Flycatcher Ficedula hypoleuca and Common Redstart Phoenicurus phoenicurus, defend winter territories, but for other species individual home ranges show overlap. In the humid forests further south, and among resident species in the Sahel, few agonistic interactions were seen, but migratory birds were often agonistic with congeners and even more frequently with birds of other species. Larger bird species usually won agonistic interactions, but Western Olivaceous Warblers Iduna opaca chased off birds twice their own body size. Subalpine Warbler Curruca iberiae + subalpina + cantillans and other Curruca species, with the exception of Lesser Whitethroat Curruca curruca, were also intolerant. Western Bonelli's Warblers Phylloscopus bonelli, and during migration also Willow Warblers Phylloscopus trochilus, were most often on the receiving end of agonistic interactions. Far fewer agonistic interactions were recorded in the more humid regions to the south of the Sahel. This disparity may hinge on the higher intra- and interspecific encounter rate in the Sahel, where a greater fraction of trees are occupied by birds, than in the humid forests. [ABSTRACT FROM AUTHOR]

Community structure depends jointly on species' responses to, and effects on, environmental factors. Many such factors, including detritus, are studied in ecosystem ecology. Detritus in terrestrial ecosystems is dominated by plant litter (nonliving organic material), which, in addition to its role in material cycling, can act as a niche factor modulating interactions among plants. Litter thus links traditional community and ecosystem processes, which are often studied separately. We explore this connection using population dynamics models of two plant species and a litter pool. We first find conditions determining the outcome of interactions between these species, highlighting the role that litter plays and the role of broader ecosystem parameters, such as decomposition rate. Species trade-offs in tolerance to direct competition and litter-based interference competition allow for coexistence, provided the litter-tolerant species produces more litter at the population level; otherwise, priority effects may result. When species coexist, litter-mediated interactions between plants disrupt the traditional relationship between biomass accumulation and decomposition. Increasing decomposition rate may have no effect on standing litter density and, in some cases, may even increase litter load. These results illustrate how ecosystem variables can influence community outcomes that then feed back to influence the ecosystem. [ABSTRACT FROM AUTHOR]

The epibiotic relationship was studied between the rotifer Brachionus rubens and five cladocerans (Daphnia carinata, Moina micrura, Simocephalus vetulus, Diaphanosoma sarsi, and Ceriodaphnia cornuta) present in lentic waters of four water bodies in the Jammu region of India. The association was assessed to be facultative in nature. This epizoic lifestyle of B. rubens is predicted to be a defence against predatory rotifers because the co-occurrence of B. rubens and its predator Asplanchna was observed during periods of infestation. The epibiotic rotifer seemed to have several adverse effects on its cladoceran hosts, including reduced locomotion. Epibiosis was observed particularly during the period with low dissolved oxygen levels. The findings of this study imply that the occurrence of epibiosis is related to high organic contents in the water body. This type of epibiotic association is reported for the first time from water bodies in this region of India. [ABSTRACT FROM AUTHOR]

Abstract Background Winter numbers of the northwest European population of Bewick’s Swans (Cygnus columbianus bewickii) declined recently by c. 40%. During the same period, numbers of two sympatric and ecologically-similar congeners, the Mute Swan (Cygnus olor) and Whooper Swan (Cygnus cygnus) showed increases or stability. It has been suggested that these opposing population trends could have a causal relationship, as Mute and Whooper Swans are larger and competitively dominant to Bewick’s Swans in foraging situations. If so, effects of competition of Mute and Whooper Swans on Bewick’s Swans should be detectable as measurable impacts on behaviour and energetics. Methods Here, we studied the diurnal behaviour and energetics of 1083 focal adults and first-winter juveniles (“cygnets”) of the three swan species on their winter grounds in eastern England. We analysed video recordings to derive time-activity budgets and these, together with estimates of energy gain and expenditure, were analysed to determine whether individual Bewick’s Swans altered the time spent on key behaviours when sharing feeding habitat with other swan species, and any consequences for their energy expenditure and net energy gain. Results All three swan species spent a small proportion of their total time (0.011) on aggressive interactions, and these were predominantly intraspecific (≥ 0.714). Mixed-effects models indicated that sharing feeding habitat with higher densities of Mute and Whooper Swans increased the likelihood of engaging in aggression for cygnet Bewick’s Swans, but not for adults. Higher levels of interspecific competition decreased the time spent by Bewick’s Swan cygnets on foraging, whilst adults showed the opposite pattern. When among low densities of conspecifics (

Abstract Many mangrove crab species drag freshly fallen leaf litter into their burrows and store it there for some time prior to consumption. Potential explanations for this behavior include (a) avoidance of competition for a scarce resource, (b) prevention of removal of a scarce resource upon tidal outwelling, or (c) processing of an initially unpalatable food source, be it physically through leaching, through the activity of the sediment microbiota, or driven by the activity of the crab itself. To test the latter, we study the effect of burying mangrove leaf litter on two relevant physicochemical litter characteristics and on its digestibility to crabs in a laboratory experiment, using artificial substratum with low microbial activity. Freshly fallen leaves of two common mangrove species, Bruguiera gymnorhiza and Ceriops tagal, were left for two weeks either inside burrows used by Neosamartium asiaticum (Sesarmidae), or on top of the substratum, before they were offered to the crabs as food. Leaf toughness and total phenolic content differed significantly between mangrove species. Upon two weeks of decay, phenolic content of both leaf litter species and toughness of B. gymnorhiza​ changed significantly. However, neither litter characteristcs nor assimilation efficiency differed between treatments. We conclude that storing mangrove leaf litter in crab burrows in a microbe‐poor environment does not affect litter digestibility. Hence, crabs themselves do not contribute to litter processing during storage inside the burrow. If it is litter processing, rather than the avoidance of competition or litter removal by tides, that renders the storage of litter inside the burrow advantageous, it will be microbial activity that drives this process. Further studies should explicitly focus on processing through the activity of the sediment microbiota.

Honey bees (Apis mellifera L.) are important agricultural pollinators, and there is increasing demand for forage habitat for managed colonies. However, there is also evidence that pasturing honey bee colonies within natural landscapes may negatively affect wild bees through resource competition.To assess resource competition between managed honey bees and wild bees, we conducted repeated, short‐term deployments of honey bee colonies within Florida forests coinciding with seasonal wildflower bloom, and compared wild bee foraging with and without honey bee colonies present over multiple seasons.We recorded over 2000 bee visits including 196 pairwise bee–plant interactions. Deploying honey bee colonies was associated with a reduction in wild bee foraging rates, and honey bee and wild bee foraging rates were significantly, negatively correlated. Honey bees disproportionately visited resources with high floral density. Honey bee foraging preferences differed significantly from genera with small‐bodied (Lasioglossum, Perdita, Augochlorella), and/or specialist species (Perdita, Andrena), as well as with Megachile, but overlapped with genera including larger‐bodied (Bombus, Habropoda, Osmia, Xylocopa) and/or generalist species (Bombus, Xylocopa, Agapostemon). Deploying honey bee colonies did not significantly affect plant–pollinator network metrics.These results illustrate that short‐term honey bee colony deployment can negatively affect wild bee foraging and that competition may be greater for certain genera, particularly larger‐bodied bees or those with generalist diets though less for smaller‐bodied and/or specialist bees. Our short‐term, low‐density deployment treatments may have precluded significant effects on network metrics and likely underestimate the effects of typical higher density and longer‐term honey bee deployment. [ABSTRACT FROM AUTHOR]

Resource competition theory predicts coexistence and exclusion patterns based on species' R *s, the minimum resource values required for a species to persist. A central assumption of the theory is that all species have equal access to resources. However, many systems are characterized by preemption exploitation, where some species deplete resources before their competitors can access them (e.g., asymmetric light competition, contest competition among animals). We hypothesized that coexistence under preemption requires an R *-preemption trade-off—that is, the species with the priority access should have a higher R * (lower "efficiency"). Thus, we developed an extension of resource competition theory to investigate partial and total preemption (in the latter, the preemptor is unaffected by species with lower preemption rank). We found that an R *-preemption trade-off is a necessary condition for coexistence in all models. Moreover, under total preemption, the trade-off alone is sufficient for coexistence. In contrast, under partial preemption, more conditions are needed, which restricts the parameter space of coexistence. Finally, we discuss the implications of our finding for seemingly distinct trade-offs, which we view as special cases of the R *-preemption trade-off. These trade-offs include the digger-grazer trade-off, the competition-colonization trade-off, and trade-offs related to light competition between trees and understories. [ABSTRACT FROM AUTHOR]

Abstract Interference competition occurs when two species have similar resource requirements and one species is dominant and can suppress or exclude the subordinate species. Wolves (Canis lupus) and coyotes (C. latrans) are sympatric across much of their range in North America where white‐tailed deer (Odocoileus virginianus) can be an important prey species. We assessed the extent of niche overlap between wolves and coyotes using activity, diet, and space use as evidence for interference competition during three periods related to the availability of white‐tailed deer fawns in the Upper Great Lakes region of the USA. We assessed activity overlap (Δ) with data from accelerometers onboard global positioning system (GPS) collars worn by wolves (n = 11) and coyotes (n = 13). We analyzed wolf and coyote scat to estimate dietary breadth (B) and food niche overlap (α). We used resource utilization functions (RUFs) with canid GPS location data, white‐tailed deer RUFs, ruffed grouse (Bonasa umbellus) and snowshoe hare (Lepus americanus) densities, and landscape covariates to compare population‐level space use. Wolves and coyotes exhibited considerable overlap in activity (Δ = 0.86–0.92), diet (B = 3.1–4.9; α = 0.76–1.0), and space use of active and inactive RUFs across time periods. Coyotes relied less on deer as prey compared to wolves and consumed greater amounts of smaller prey items. Coyotes exhibited greater population‐level variation in space use compared to wolves. Additionally, while active and inactive, coyotes exhibited greater selection of some land covers as compared to wolves. Our findings lend support for interference competition between wolves and coyotes with significant overlap across resource attributes examined. The mechanisms through which wolves and coyotes coexist appear to be driven largely by how coyotes, a generalist species, exploit narrow differences in resource availability and display greater population‐level plasticity in resource use.

Predators compete aggressively for resources, establishing trophic hierarchies that influence ecosystem structure. Competitive interactions are particularly important in invaded ecosystems where introduced predators can suppress native prey species. We investigated whether niche partitioning exists within a guild of invasive mammalian predators and determined the consequences for native species. Over 4405 camera‐trap days, we assessed interactions among three invasive predators: two apex predators (feral cats Felis catus and ferrets Mustela furo) and a mesopredator (stoats Mustela erminea), in relation to their primary prey (lagomorphs, rodents and birds) and habitat use. Further, we tested for mesopredator release by selectively removing cats and ferrets in a pulse perturbation experiment. We found compelling evidence of niche partitioning; spatiotemporal activity of apex predators maximized access to abundant invasive prey, with ferrets targeting lagomorphs and cats targeting rodents. Mesopredators adjusted their behavior to reduce the risk of interference competition, thereby restricting access to abundant prey but increasing predation pressure on diurnal native birds. Stoats were only recorded at the treatment site after both larger predators were removed, becoming the most frequently detected predator at 6 months post‐perturbation. We suggest there is spatial and resource partitioning within the invasive predator guild, but that this is incomplete, and avoidance is achieved by temporal partitioning within overlapping areas. Niche partitioning among invasive predators facilitates coexistence, but simultaneously intensifies predation pressure on vulnerable native species. [ABSTRACT FROM AUTHOR]

Antagonism among bacteria is widespread and plays an important role in structuring communities. Inhibitory compounds can confer competitive advantage, but energetic trade-offs can result in non-transitive (i.e. 'rock-paper-scissors') interactions, ultimately allowing co-existence and community stability. Competition in sedimentary habitats is especially keen given high densities and attachment to inorganic particles. Because measuring trade-offs between bacterial species is challenging, much of our understanding of competitive interactions is based on theoretical modelling and simplified in vitro experiments. Our objectives were to determine (1) if interference competition occurs in microcosms mimicking in situ conditions; (2) whether the presence of sediment influences antagonistic interactions; and (3) if more complex assemblages alleviate or synergize interactions. Four sedimentary isolates, including antibiotic-producing, resistant and susceptible strains were incubated in porewater microcosms in 1-, 2- and 3-species combinations, both with and without natural sediments. Microcosms were sampled over 72 h to generate growth curves using quantitative PCR. Multiple growth attributes (growth rate, maximum density, lag time) were used to assess effects of treatment (species combinations) and environment (sediment vs porewater alone). Antimicrobial producers were more effective at inhibiting target species in microcosms that included sediment, in agreement with theory. We observed growth inhibition by antimicrobial-producing bacteria in both 2- and 3-species microcosms. However, the expected protection of sensitive bacterial strains by resistant strains was observed in only one (of four) 3-species combinations, thus the 'rock-paper-scissors' prediction was not fully supported. These results reinforce the notion that interspecies interactions are context-dependent, reliant on environmental conditions and the species involved. [ABSTRACT FROM AUTHOR]

Competition between apex predators can alter the strength of top‐down forcing, yet we know little about the behavioral mechanisms that drive competition in multipredator ecosystems. Interactions between predators can be synergistic (facilitative) or antagonistic (inhibitive), both of which are widespread in nature, vary in strength between species and across space and time, and affect predation patterns and predator–prey dynamics. Recent research has suggested that gray wolf (Canis lupus) kill rates decrease where they are sympatric with brown bears (Ursus arctos), however, the mechanisms behind this pattern remain unknown. We used data from two long‐term research projects in Scandinavia (Europe) and Yellowstone National Park (North America) to test the role of interference and exploitation competition from bears on wolf predatory behavior, where altered wolf handling and search time of prey in the presence of bears are indicative of interference and exploitation competition, respectively. Our results suggest the mechanisms driving competition between bears and wolves were dependent on the season and study system. During spring in Scandinavia, interference competition was the primary mechanism driving decreased kill rates for wolves sympatric with bears; handling time increased, but search time did not. In summer, however, when both bear and wolf predation focused on neonate moose, the behavioral mechanism switched to exploitation competition; search time increased, but handling time did not. Alternartively, interference competition did affect wolf predation dynamics in Yellowstone during summer, where wolves prey more evenly on neonate and adult ungulates. Here, bear presence at a carcass increased the amount of time wolves spent at carcasses of all sizes and wolf handling time for small prey, but decreased handling time for the largest prey. Wolves facilitate scavenging opportunities for bears, however, bears alter wolf predatory behavior via multiple pathways and are primarily antagonistic to wolves. Our study helps to clarify the behavioral mechanisms driving competition between apex predators, illustrating how interspecific interactions can manifest into population‐level predation patterns. [ABSTRACT FROM AUTHOR]

Unravelling how biodiversity is maintained despite species competition for shared resources has been a central question in community ecology, and is gaining relevance amidst the current biodiversity crisis. Yet, we have still a poor understanding of the mechanisms that regulate species coexistence and shape the structure of assemblages in highly competitive environments such as carrion pulsed resources. Here, we study how large vertebrates coexist in scavenger assemblages by adapting their diel activity at large ungulate carcasses in NW Spain. We used camera traps to record vertebrate scavengers consuming 34 carcasses of livestock and hunted wild ungulates, which allowed us to assess also differences regarding carcass origin. To evaluate temporal resource partition among species, we estimated the overlap of diel activity patterns and the mean times of each scavenger at carcasses. We recorded 16 species of scavengers, 7 mammals and 9 birds, and found similar richness at both types of carcasses. Birds and mammals showed contrasting diel activity patterns, with birds using carcasses during daytime (mean= 11:38 h) and mammals mostly at night (23:09 h). The unimodal activity patterns of scavengers showed asynchronous peaks among species. Subordinate species modified their activity patterns at carcasses used by apex species to reduce temporal overlap. Also, diel activity patterns of vultures closely followed those of corvids, suggesting facilitation processes in which corvids would enhance carcass detection by vultures. Two mammal species (12.5%) increased nocturnality at carcasses of hunted ungulates, which could be a response to human disturbance. Our results suggest that both temporal segregation and coupling mediate the coexistence of large vertebrates at carcasses. These mechanisms might lead to richer scavenger assemblages and thereby more efficient ones in driving critical ecosystem functions related to carrion consumption, such as energy and nutrient recycling and biodiversity maintenance. [ABSTRACT FROM AUTHOR]

Organisms compete for food in many ways, but it is often difficult to know why they use certain competition strategies over others. Bats compete for food either through aggression coupled with food-claiming signals or by actively interfering with a competitor’s sensory processing during prey pursuit (i.e., jamming). It is not known why these different behaviors are exhibited. I studied food competition between Mexican free-tailed bats (Tadarida brasiliensis) at foraging sites in Arizona and New Mexico using passive acoustic recording, insect sampling and 3-D infrared videography with or without supplemental lighting that concentrated prey. Bat activity was quantified by the number of recorded echolocation calls, while feeding behavior was indicated by feeding buzzes. Two competitive behaviors were observed—song, which was produced by bats chasing conspecifics, and sinFM calls, which jam echolocation of competitors pursuing prey. Song production was most common when few bats were present and feeding at low rates. In contrast, jamming signals were most common with many bats present and feeding at high rates. Supplemental lighting increased the numbers of bats, feeding buzzes and sinFM calls, but not song. These results indicate that bats employ different strategies—singing and chasing competitors at low bat densities but jamming competitors at high bat densities. Food claiming signals (song) may only be effective with few competitors present, whereas jamming can be effective with many bats at a foraging site. Multiple competition strategies appear to have evolved in bats that are used under different densities of competitors.

Interspecific territoriality may play an important role in structuring ecological communities, but the causes of this widespread form of interference competition remain poorly understood. Here, we investigate the phenotypic, ecological and phylogenetic correlates of interspecific territoriality in wood warblers (Parulidae). Interspecifically territorial species have more recent common ancestors and are more similar phenotypically, and are more likely to hybridise, than sympatric, non-interspecifically territorial species. After phylogenetic corrections, however, similarity in plumage and territorial song are the only significant predictors of interspecific territoriality besides syntopy (fine-scale geographic overlap). Our results do not support the long-standing hypothesis that interspecific territoriality occurs only under circumstances in which niche divergence is restricted, which combined with the high incidence of interspecific territoriality in wood warblers (39% of species), suggests that this interspecific interaction is more stable, ecologically and evolutionarily, than commonly assumed.

Abstract Plant litter can alter ecosystems and promote plant invasions by altering resource availability, depositing phytotoxins, and transmitting microorganisms to living plants. Transmission of microorganisms from invasive plant litter to live plants may gain importance as invasive plants, which often escape pathogens upon introduction to a new range, acquire new pathogens over time. It is unclear, however, if invasive plant litter affects native plant communities by promoting disease. Microstegium vimineum is an invasive grass that suppresses native populations, in part through litter production, and has acquired new fungal leaf spot diseases since its introduction to the United States. In a greenhouse experiment, we evaluated how M. vimineum litter and its pathogens mediated competition with the native grass Elymus virginicus. M. vimineum litter promoted disease on E. virginicus and suppressed establishment and biomass of both species. Litter had stronger negative effects on E. virginicus than M. vimineum, increasing the relative biomass of M. vimineum. Live plant competition reduced biomass of both species and live M. vimineum increased disease incidence on E. virginicus. Altogether, invasive grass litter suppressed both species, ultimately favoring the invasive species in competition, and increased disease incidence on the native species.

Invasive species cause substantial changes to the biodiversity of freshwater systems. The African Nile tilapia (Oreochromis niloticus) is now widely distributed in tropical freshwaters globally. Despite indications that feral populations can influence native species through competitive effects, direct evidence of competition between Nile tilapia and native species is rare. Moreover, it is not clear if environmental variables such as temperature and oxygen concentration modulate competition. Here, interactions between Nile tilapia and the native Mayan cichlid (Mayaheros urophthalmus) were studied in experimental mesocosms in south-eastern Mexico. We found that Nile tilapia was the more active and aggressive of the two species, and their movement was only weakly influenced by temperature and oxygen concentration. By contrast, movement of the Mayan cichlid was strongly predicted by the movement and aggression of Nile tilapia, and the Mayan cichlid showed a steep decline in behaviours with increased water temperature and reduced oxygen. Our results suggest that broad environmental tolerance of the intrinsically aggressive Nile tilapia provides it with an advantage over native species. Collectively these traits may help to exacerbate its invasive success as those environmental conditions become more commonplace in a changing world. [ABSTRACT FROM AUTHOR]