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Rapid range expansion of boreal forest predators onto the tundra may disrupt local ecological processes, notably through competition with ecologically similar species. Red foxes (Vulpes vulpes) have expanded their range northwards throughout the Canadian Arctic, inducing competition with endemic Arctic foxes (V. lagopus). We studied competition between Arctic and red foxes, with a focus on interference competition, and winter movements of red foxes using satellite telemetry and den occupancy data from both species. We worked at Bylot Island (Nunavut) and Herschel Island (northern Yukon), two sites at the northern limit of the red fox's range. As expected, red fox home ranges were 56% larger on average than Arctic fox home ranges. However, red foxes did not exclude Arctic foxes regionally nor did they prevent them from breeding successfully in their vicinity. On Bylot Island, Arctic foxes did not spatially avoid red foxes more than their conspecifics, as evidenced by similar intra- and interspecific home-range overlaps. On Herschel Island, the red fox pair's home range extensively overlapped the home range of their Arctic fox neighbors. While red foxes tracked on Bylot Island survived several winters without expanding or leaving their home ranges, those on Herschel Island moved onto the sea ice and died. Overall, our results demonstrate low levels of interference competition between the two species in the High Canadian Arctic. When red fox density is low, as in our study areas where land protection prevents predator subsidization by anthropogenic food sources, Arctic and red foxes may be able to co-exist with limited antagonistic interactions. Our sample sizes were limited by the naturally low density of red foxes at their northernmost edge. Replication therefore is needed to fully understand winter space use and intraguild interactions in this species at its northern range limit. L'expansion rapide de l'aire de répartition des prédateurs de la forêt boréale vers la toundra risque de perturber plusieurs processus écologiques locaux, notamment par le biais d'une compétition accrue entre espèces écologiquement similaires. Le renard roux (Vulpes vulpes) a étendu son aire de répartition vers le nord à travers tout l'Arctique canadien, induisant une compétition avec une espèce endémique, le renard arctique (V. lagopus). Nous avons étudié la compétition entre ces deux espèces, principalement la compétition par interférence, ainsi que les déplacements hivernaux des renards roux, à deux sites situés à la limite nordique de l'aire de répartition du renard roux. Nous avons combiné des données de télémétrie satellitaire et d'occupation des tanières des deux espèces étudiées à l'île Bylot (Nunavut) et à l'île Herschel (nord du Yukon). En accord avec nos prédictions, les domaines vitaux des renards roux étaient en moyenne 56 % plus grands que ceux des renards arctiques. Cependant, les renards roux n'ont pas exclu les renards arctiques des régions utilisées et ne les ont pas empêchés de se reproduire avec succès. À l'île Bylot, un chevauchement similaire des domaines vitaux au sein et entre les espèces indiquait que les renards arctiques n'évitaient pas les renards roux plus que leurs propres congénères. À l'île Herschel, le domaine vital du couple de renards roux chevauchait largement celui des renards arctiques voisins. Alors que les renards roux de l'île Bylot ont survécu plusieurs hivers sans agrandir ou quitter leur domaine vital, ceux de l'île Herschel se sont dispersés sur la banquise et sont morts. Dans l'ensemble, nos résultats démontrent un faible niveau de compétition par interférence entre ces deux espèces dans l'Arctique canadien. Dans nos aires d'étude, la protection du territoire empêche l'apport de nourriture d'origine anthropique qui pourrait soutenir des prédateurs. Lorsque la densité de renards roux est faible, les renards arctiques et roux pourraient coexister sans fortes interactions antagonistes. Nos tailles déchantillons étaient limitées par la faible densité de renards roux à leur limite septentrionale. Il faudra donc répliquer cette étude pour bien comprendre l'utilisation de l'espace en hiver et les interactions intraguildes du renard roux au nord de sa limite de répartition.

Allelopathy has been suggested as a mechanism promoting the monoculture formation of some invasive exotic plants. Previous studies have shown that hydrophobic extracts of the roots and soil of exotic bitou bush (Chrysanthemoides monilifera spp. rotundata (DC.) T. Norl.) inhibited the seedling growth of five Australian native plants, including the dominant acacia (Acacia longifolia var. sophorae (Labill.) F. Muell.). Based on this finding, we compared the hydrophobic root and soil chemical profiles of bitou bush and acacia to determine whether bitou bush roots release allelopathic compounds that are novel to the invaded system. We detected three compounds that were exclusive to the bitou bush root and soil, and seven compounds that were common to the bitou bush and acacia roots but only present in the bitou bush soil. The compounds unique to the bitou bush invaded soil were all sesqui- and diterpenes. Several of these compounds were found to inhibit the seedling growth of a native sedge, Isolepis nodosa (Rott.) R. Br. Of particular interest are the sesquiterpenes: β-maaliene, α-isocomene, β-isocomene, δ-cadinene, 5-hydroxycalamenene and 5-methoxycalamenene which were found in high concentrations in the bitou bush root and soil extracts and exhibited phytotoxic activity. Therefore, we present evidence to suggest that bitou bush exudes low molecular weight volatile compounds into the soil which inhibit native plant seedling growth. The reduced establishment of native plants via allelopathy is likely to create space and contribute to the invasion of bitou bush on the eastern Australian coast.

Elucidating complex interactions between bacteria and fungi that determine microbial community structure, composition, and functions in soil, as well as regulate carbon (C) and nutrient fluxes, is crucial to understand biogeochemical cycles. Among the various interactions, competition for resources is the main factor determining the adaptation and niche differentiation between these two big microbial groups in soil. This is because C and energy limitations for microbial growth are a rule rather than an exception. Here, we review the C and energy demands of bacteria and fungi—the two major kingdoms in soil—the mechanisms of their competition for these and other resources, leading to niche differentiation, and the global change impacts on this competition. The normalized microbial utilization preference showed that bacteria are 1.4–5 times more efficient in the uptake of simple organic compounds as substrates, whereas fungi are 1.1–4.1 times more effective in utilizing complex compounds. Accordingly, bacteria strongly outcompete fungi for simple substrates, while fungi take advantage of complex compounds. Bacteria also compete with fungi for the products released during the degradation of complex substrates. Based on these specifics, we differentiated spatial, temporal, and chemical niches for these two groups in soil. The competition will increase under the main five global changes including elevated CO2, N deposition, soil acidification, global warming, and drought. Elevated CO2, N deposition, and warming increase bacterial dominance, whereas soil acidification and drought increase fungal competitiveness.

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.

Does competition influence patterns of coexistence between closely related taxa? Here we address this question by analyzing patterns of range overlap between related species of birds (‘sister pairs’) co‐occurring on a tropical elevational gradient. We explicitly contrast the behavioral dimension of interspecific competition (interference competition) with similarity in resource acquisition traits (exploitative competition). Specifically, we ask whether elevational range overlap in 118 sister pairs that live along the Manu Transect in southeastern Peru is predicted by proxies for competition (intraspecific territorial behavior) or niche divergence (beak divergence and divergence times, an estimate of evolutionary age). We find that close relatives that defend year‐round territories tend to live in non‐overlapping elevational distributions, while close relatives that do not defend territories tend to broadly overlap in elevational distribution. In contrast, neither beak divergence nor evolutionary age was associated with patterns of range limitation. We interpret these findings as evidence that behavioral interactions – particularly direct territorial aggression – can be important in setting elevational range limits and preventing coexistence of closely related species, though this depends upon the extent to which intraspecific territorial behavior can be extended to territorial interactions between species. Our results suggest that interference competition can be an important driver of species range limits in diverse assemblages, and thus highlight the importance of considering behavioral dimensions of the niche in macroecological studies.

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.

Most ecosystems have multiple predator species that not only compete for shared prey, but also pose direct threats to each other. These intraguild interactions are key drivers of carnivore community structure, with ecosystem‐wide cascading effects. Yet, behavioral mechanisms for coexistence of multiple carnivore species remain poorly understood. The challenges of studying large, free‐ranging carnivores have resulted in mainly coarse‐scale examination of behavioral strategies without information about all interacting competitors. We overcame some of these challenges by examining the concurrent fine‐scale movement decisions of almost all individuals of four large mammalian carnivore species in a closed terrestrial system. We found that the intensity of intraguild interactions did not follow a simple hierarchical allometric pattern, because spatial and behavioral tactics of subordinate species changed with threat and resource levels across seasons. Lions (Panthera leo) were generally unrestricted and anchored themselves in areas rich in not only their principal prey, but also, during periods of resource limitation (dry season), rich in the main prey for other carnivores. Because of this, the greatest cost (potential intraguild predation) for subordinate carnivores was spatially coupled with the highest potential benefit of resource acquisition (prey‐rich areas), especially in the dry season. Leopard (P. pardus) and cheetah (Acinonyx jubatus) overlapped with the home range of lions but minimized their risk using fine‐scaled avoidance behaviors and restricted resource acquisition tactics. The cost of intraguild competition was most apparent for cheetahs, especially during the wet season, as areas with energetically rewarding large prey (wildebeest) were avoided when they overlapped highly with the activity areas of lions. Contrary to expectation, the smallest species (African wild dog, Lycaon pictus) did not avoid only lions, but also used multiple tactics to minimize encountering all other competitors. Intraguild competition thus forced wild dogs into areas with the lowest resource availability year round. Coexistence of multiple carnivore species has typically been explained by dietary niche separation, but our multi‐scaled movement results suggest that differences in resource acquisition may instead be a consequence of avoiding intraguild competition. We generate a more realistic representation of hierarchical behavioral interactions that may ultimately drive spatially explicit trophic structures of multi‐predator communities.

The role of microbial secondary metabolites in the ecology of the organisms that produce them remains poorly understood. Variation in aflatoxin production by Aspergillus flavus is maintained by balancing selection, but the ecological function and impact on fungal fitness of this compound are unknown. We hypothesize that balancing selection for aflatoxin production in A. flavus is driven by interaction with insects. To test this, we competed naturally occurring aflatoxigenic and non-aflatoxigenic fungal isolates against Drosophila larvae on medium containing 0–1750 ppb aflatoxin, using quantitative PCR to quantify A. flavus DNA as a proxy for fungal fitness. The addition of aflatoxin across this range resulted in a 26-fold increase in fungal fitness. With no added toxin, aflatoxigenic isolates caused higher mortality of Drosophila larvae and had slightly higher fitness than non-aflatoxigenic isolates. Additionally, aflatoxin production increased an average of 1.5-fold in the presence of a single larva and nearly threefold when the fungus was mechanically damaged. We argue that the role of aflatoxin in protection from fungivory is inextricably linked to its role in interference competition. Our results, to our knowledge, provide the first clear evidence of a fitness advantage conferred to A. flavus by aflatoxin when interacting with insects.

Bacteria secrete antibiotics to inhibit their competitors, but the presence of competitors can determine whether these toxins are produced. Here, we study the role of the competitive and resource environment on antibiotic production in Streptomyces , bacteria renowned for their production of antibiotics. One of the most important ways that bacteria compete for resources and space is by producing antibiotics that inhibit competitors. Because antibiotic production is costly, the biosynthetic gene clusters coordinating their synthesis are under strict regulatory control and often require “elicitors” to induce expression, including cues from competing strains. Although these cues are common, they are not produced by all competitors, and so the phenotypes causing induction remain unknown. By studying interactions between 24 antibiotic-producing strains of streptomycetes, we show that strains commonly inhibit each other’s growth and that this occurs more frequently if strains are closely related. Next, we show that antibiotic production is more likely to be induced by cues from strains that are closely related or that share secondary metabolite biosynthetic gene clusters (BGCs). Unexpectedly, antibiotic production is less likely to be induced by competitors that inhibit the growth of a focal strain, indicating that cell damage is not a general cue for induction. In addition to induction, antibiotic production often decreases in the presence of a competitor, although this response was not associated with genetic relatedness or overlap in BGCs. Finally, we show that resource limitation increases the chance that antibiotic production declines during competition. Our results reveal the importance of social cues and resource availability in the dynamics of interference competition in streptomycetes. IMPORTANCE Bacteria secrete antibiotics to inhibit their competitors, but the presence of competitors can determine whether these toxins are produced. Here, we study the role of the competitive and resource environment on antibiotic production in Streptomyces , bacteria renowned for their production of antibiotics. We show that Streptomyces cells are more likely to produce antibiotics when grown with competitors that are closely related or that share biosynthetic pathways for secondary metabolites, but not when they are threatened by competitor’s toxins, in contrast to predictions of the competition sensing hypothesis. Streptomyces cells also often reduce their output of antibiotics when grown with competitors, especially under nutrient limitation. Our findings highlight that interactions between the social and resource environments strongly regulate antibiotic production in these medicinally important bacteria.

Biological invasions are a contemporary global threat because invasive species can have substantial negative economic and ecological impacts. Invasive species can outcompete native species through two main mechanisms: interference competition (direct, negative interactions like aggression) and/or exploitative competition (indirect, negative interactions resulting from species using the same, limited resources like food). The invasive Italian wall lizard (Podarcis siculus) was introduced into Lisbon, Portugal, 20 years ago, and is believed to be locally displacing the native green Iberian wall lizard (Podarcis virescens). We experimentally tested for competition between these two lizard species by establishing heterospecific (one pair of each species) and conspecific (two pairs of the same species; control) treatments in enclosures containing a high- and a low-quality refuge. Lizards were fed from food dishes every other day. We tested if species showed interference (aggressive behaviour, stealing food and shelter exclusion) or exploitative competition (tolerance between species but differences in food consumption efficiency). We found evidence for exploitative competition: the invasive species arrived first at food stations, consumed more food and gained more weight than the native species. We suggest that exploitative competition may, in part, explain the observed displacement of P. virescens from contact areas with the invasive P. siculus. Deciphering the competitive mechanisms between invasive and native species is vital for understanding the invasion process.