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Recent work has shown that animals frequently use social information from individuals of their own species as well as from other species; however, the ecological and evolutionary consequences of this social information use remain poorly understood. Additionally, information users may be selective in their social information use, deciding from whom and how to use information, but this has been overlooked in an interspecific context. In particular, the intentional decision to reject a behaviour observed via social information has received less attention, although recent work has indicated its presence in various taxa. Based on existing literature, we explore in which circumstances selective interspecific information use may lead to different ecological and coevolutionary outcomes between two species, such as explaining observed co‐occurrences of putative competitors. The initial ecological differences and the balance between the costs of competition and the benefits of social information use potentially determine whether selection may lead to trait divergence, convergence or coevolutionary arms race between two species. We propose that selective social information use, including adoption and rejection of behaviours, may have far‐reaching fitness consequences, potentially leading to community‐level eco‐evolutionary outcomes. We argue that these consequences of selective interspecific information use may be much more widespread than has thus far been considered. [ABSTRACT FROM AUTHOR]

Phylogenetic inertia often drives sister species to exhibit similar acoustic signals, compromising species recognition and increasing competition for acoustic space. Consequently, natural selection favours acoustic divergence in sympatry through behavioural plasticity or character displacement. Although well-documented in temperate regions, these phenomena have been less investigated in tropical communities, characterised by more complex interactions and saturated acoustic spaces. Here we examined acoustic divergence in the advertisement calls of two closely related neotropical treefrogs that share similar signals, habitat, and phenology, and that hybridise in nature. Our results revealed differences in call parameters between syntopy and allotopy, each species showing a specific response. While the smaller-sized species, Boana bischoffi, increased dominant frequency in syntopy, Boana prasina prolonged call duration, both increasing acoustic divergence between these sister species. In contrast, morphological and environmental factors had little influence on acoustic parameters, with only body size affecting dominant frequency in B. bischoffi. These findings suggest that vocal adjustment (acoustic plasticity) or character displacement (local adaptation) may enlarge acoustic divergence in advertisement calls, reinforcing reproductive isolation and reducing interspecific competition for acoustic space in sister taxa. [ABSTRACT FROM AUTHOR]

Populations are embedded in communities, but despite their potential to affect individual fitness, it is unknown whether and how species interactions evolve in communities. Evolutionary outcomes are likely more complex in natural communities because (a) the evolution of interactions may not be evenly distributed among all community members and (b) coevolution is conditional on the environmental conditions within which interactions are playing out.To test the evolution of interaction strengths in natural communities, we performed two common garden experiments in grassland communities in Northern California. In each garden, we transplanted individuals of four populations (one local, three foreign) of an annual invasive grass Bromus hordeaceus into natural communities, characterized the interaction neighbourhood around each focal individual, and quantified individual fitness. This method allowed us to fit multispecies competition models to fitness data, estimating interaction strengths between focal B. hordeaceus populations and each of seven species that were common in the interaction neighbourhoods, in each garden.We found that interaction strengths significantly differed among local and foreign source populations, but the direction and magnitude of evolution differed among common gardens and among neighbour species—in neither garden were interactions experienced more strongly by foreign populations compared to local populations. The fitness of local populations (relative to foreign populations) decreased when neighbours were removed, strongly enough in one garden to cause strong local maladaptation, and the local population did not perform the best in either garden.Synthesis. Together, our results demonstrate how species interactions evolve to determine fitness in ecological communities, providing a richer view of adaptation in natural systems. In our study, this richness included the unique challenges populations face in nature: uneven abundances and a diffuseness of species interactions, nonlinear density effects on fitness, and evidence of (mal)adaptation that is conditional on local conditions. We conclude by hypothesizing the causes and consequences of challenges to adaptation and how they help identify priority areas for the field. [ABSTRACT FROM AUTHOR]

Morphological variation in biological structures may be driven by genetic and environmental factors, such as inter- and intraspecific competition for resources. In seabirds, although the bill is also involved in vocalization, olfaction, sexual selection and defence, the main drivers of high morphological plasticity in bill size and shape appear to relate primarily to diet and thus to niche differentiation. Here, we combined geometric morphometrics and comparisons of linear measurements as a precise tool for measuring shape variation in anatomical features, to investigate the differences among species and populations (island groups) in bill shape of three planktivorous petrels (Antarctic prion Pachyptila desolata, blue petrel Halobaena caerulea and thin-billed prion Pachyptila belcheri). Fieldwork was carried out in South Georgia (54° 0′ S, 38° 3′ W), Falkland (51° 42′ S, 57° 51′ W), Diego Ramírez (56° 31′ S, 68° 44′ W) and Kerguelen (49° 20′ S, 69° 20′ E) Islands, from 2010 to 2021. Results show that the bills of Antarctic prions were more robust and shorter, appropriate for filtering large amounts of small prey. Blue petrels and thin-billed prions had narrower and longer bills, effective for catching and tearing large single prey. Also, Antarctic prions and blue petrels from Kerguelen had longer and narrower bills than conspecifics from other colonies, which could potentially be explained by geographic variation in diet. In conclusion, prey availability and diversity appear to be important factors influencing variation in bill morphology. This study highlights the utility of geometric morphometrics for investigating bill shape variation in seabirds. Nevertheless, further studies are needed to better understand selective pressures leading to morphological variation of biological structures. [ABSTRACT FROM AUTHOR]

Flower colour differs dramatically between populations for some plant species; yet, we know little about what drives this variation. Such polymorphisms can be influenced by plant–pollinator interactions, but whether they are also influenced by pollinator‐mediated plant–plant interactions is unknown.We test whether flower colour polymorphisms can arise through convergence (facilitation) or divergence (competition) of flower phenotypes resulting from plant–plant interactions mediated by the shared, and only, pollinator (orange‐breasted sunbird) of 10 Erica communities in South Africa.Sunbird visitation rates to the less‐preferred Erica species in communities increased with colour similarity to the most‐visited species, suggesting that polymorphisms can be maintained by selection for colour convergence within communities, which promotes shared signals through rewarding mimicry (i.e. facilitation).Colour similarity was lowest when risk of reproductive interference was greatest: that is, when reproductive morphology (stigma–anther distance) and flowering phenology was most similar, and when floral density differed greatly between species. This implies that polymorphisms can also be maintained by selection for colour divergence, since this promotes assortative pollinator foraging (i.e. competition).Different populations of a species may experience opposite selective pressures, depending on their community context. This is the first evidence that a geographic mosaic of plant–plant pollination interactions could maintain colour polymorphisms in congeneric species sharing a single pollinator. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

The coexistence of cladogenesis, i.e., the branching of lineages along an evolutionary tree as observed in the fossil record, and anagenesis, which is the progressive evolution within populations, lacks a clear explanation. In this study, we examine a simple model that simulates the evolutionary changes occurring within populations inhabiting the same environment in sympatry, and driven by ecological competition. Our model characterizes populations through a set of evolving morphological traits represented by mathematical points within a two-dimensional morphospace. Such points may reproduce or die due to overcrowding, implying competition in morphospace as suggested by the ecological phenomenon of character displacement. By focusing on the morphospace rather than physical space, the model effectively captures the simultaneous evolution of coexisting populations. Central to the model is the delicate balance between the range of competition and the range of reproduction within the morphospace. Interesting patterns emerge when the ratio between the competition to reproducetion ranges, referred to as CR ratio, changes from values slightly smaller to significantly larger than unity. When competition acts over short distances relative to the reproduction range (low CR), the phylogenetic tree takes on a nearly uniform appearance, gradually transforming into a more bush-like structure for slightly higher CR values. With further increases in CR, evolutionary lineages become more discernible, and the morphogenetic pattern shifts from a bush-like shape to a more tree-like arrangement and few branches for very large CRs. At specific time sections, the synthetic phylogenetic tree appears as an assembly of clusters of individuals within the morphospace. These clusters, interpretable as simulated models of species, exhibit distinct separation within the morphospace and are subject to dynamic inter-cluster repulsion. Notably, clusters tend to be resistant to change. They maintain relatively constant abundances while gradually shifting their positions within the morphospace—a phase that aligns with the concept of phyletic gradualism. However, this predictable pattern is occasionally upset by the abrupt divisions into multiple groups, interpreted as cladogenesis events. The intricacies of the splitting process are explored, revealing that in scenarios with large CR values, the splitting can emerge much more rapidly than phyletic changes. This accelerated process of splitting is initiated by one or few individuals at the fringes of a cluster, where competition is minimal. The newly generated cluster then undergoes deformation, swiftly followed by divergence and splitting (seen as branching in the synthetic phylogenetic tree), as if an inherent "repulsion" triggered the division between species. The simple rules implied in the interacting-particle model may provide insight into the coexistence of gradualism and cladogenesis along lineages, illustrating the capacity for rapid shifts during cladogenesis and the more gradual process of anagenesis. [ABSTRACT FROM AUTHOR]

Character displacement, or a shift in traits where species co-occur, is one of the most common ecological patterns to result from interactions between closely related species. Usually, character displacement is associated to divergence in traits, though, they might be convergent, especially when used for aggressive interference between species. In the context of animal communication, territorial calls are predicted to converge in order to increase context recognition and decrease the costs of ecological interference competition. However, such signals might also be adapted to characteristics of the shared environment. In this study, we used data from 15 groups of two parapatric tamarins, Saguinus midas and S. bicolor, to test for similarities in long calls among sympatric and allopatric groups. We hypothesized that calls would converge in sympatric areas, as it would be mutually beneficial if both species recognize territorial contexts, but that convergence would depend on forest type due to acoustic adaptation. As predicted, long calls converged in sympatry, with S. midas shifting its calls towards S. bicolor's acoustic pattern. However, this shift only occurred in primary forest. In sympatric areas, S. midas produced sounds with narrower bandwidths in primary than in secondary forest, consistent with optimization of sound propagation while both species produced longer calls in primary forests independently of geographic location (i.e. sympatry and allopatry). Our results suggest that both social and environmental pressures are important in shaping tamarin sounds. As their effects can interact, analyses, which assume that these ecological pressures act independently, are likely to miss important patterns. Significance statement: Territorial signals between closely related sympatric species are expected to be convergent to increase context recognition and decrease the costs of interference competition. However, such signals might also be adapted to characteristics of the shared environment, such as forest structure characteristics. We analysed vocalisations from two parapatric tamarins and found that, though their long calls asymmetrically converged in sympatry, only red-handed tamarins shifted towards pied tamarin call type, and this only occurred in primary forest. Our results suggest that both social and environmental pressures are important in shaping primate calls. Because their effects can interact, analyses which assume that these pressures act independently, are likely to miss important patterns. [ABSTRACT FROM AUTHOR]

Negative interactions between species can generate divergent selection that causes character displacement. However, other processes cause similar divergence. We use spatial and temporal replication across island populations of Anolis lizards to assess the importance of negative interactions in driving trait shifts. Previous work showed that the establishment of Anolis sagrei on islands drove resident Anolis carolinensis to perch higher and evolve larger toepads. To further test the interaction's causality and predictability, we resurveyed a subset of islands nine years later. Anolis sagrei had established on one island between surveys. We found that A. carolinensis on this island now perch higher and have larger toepads. However, toepad morphology change on this island was not distinct from shifts on six other islands whose Anolis community composition had not changed. Thus, the presence of A. sagrei only partly explains A. carolinensis trait variation across space and time. We also found that A. carolinensis on islands with previously established A. sagrei now perch higher than a decade ago, and that current A. carolinensis perch height is correlated with A. sagrei density. Our results suggest that character displacement likely interacts with other evolutionary processes in this system, and that temporal data are key to detecting such interactions. [ABSTRACT FROM AUTHOR]

Understanding how ecological processes affect phenotypic evolution has been and continues to be an important goal of ecology and evolutionary biology. Interspecific competition for resources can be a selective force driving phenotypic differentiation that reduces competition among sympatric species (character divergence), enabling closely-related species to coexist. However, although patterns of character divergence are well documented in both empirical and theoretical researches, how local adaptation to abiotic environment affects trait evolution in the face of interspecific competition is less known. Here, we investigate how patterns in morphological traits of 2 parapatric frog species, Feirana quadranus and F. taihangnica , vary among allopatric and sympatric regions using range-wide data derived from extensive field surveys. Feirana quadranus was overall larger than F. taihangnica in body size (i.e. snout–vent length [SVL]), and the difference between SVL of both species in sympatry was larger than that in allopatry. From allopatry to sympatry, the 2 species diverged in foot and hand traits, but converged in eye size and interorbital span, even when we controlled for the effects of geographic gradients. Sympatric divergence in SVL, hand and foot traits is likely acting as a case of evolutionary shift caused by interspecific competition. In contrast, sympatric convergence of eye-related traits may derive at least partly from adaptation to local environments. These results imply the relative roles of interspecific competition and local adaptation in shaping phenotypic diversification. Our findings illustrate how traits evolve in parapatric species pair due to sympatric divergent and convergent evolution. It thus provides insights into understanding underlying evolutionary processes of parapatric species, that is, competition and local adaptation. [ABSTRACT FROM AUTHOR]

Interspecific competition for shared resources should select for evolutionary divergence in resource use between competing species, termed character displacement. Many purported examples of character displacement exist, but few completely rule out alternative explanations. We reared genetically diverse populations of two species of bean beetles, Callosobruchus maculatus and Callosobruchus chinensis, in allopatry and sympatry on a mixture of adzuki beans and lentils, and assayed oviposition preference and other phenotypic traits after four, eight, and twelve generations of (co)evolution. C. maculatus specializes on adzuki beans; the generalist C. chinensis uses both beans. C. chinensis growing in allopatry emerged equally from both bean species. In sympatry, the two species competing strongly and coexisted via strong realized resource partitioning, with C. chinensis emerging almost exclusively from lentils and C. maculatus emerging almost exclusively from adzuki beans. However, oviposition preferences, larval survival traits, and larval development rates in both beetle species did not vary consistently between allopatric versus sympatric treatments. Rather, traits evolved in treatment‐independent fashion, with several traits exhibiting reversals in their evolutionary trajectories. For example, C. chinensis initially evolved a slower egg‐to‐adult development rate on adzuki beans in both allopatry and sympatry, then subsequently evolved back toward the faster ancestral development rate. Lack of character displacement is consistent with a previous similar experiment in bean beetles and may reflect lack of evolutionary trade‐offs in resource use. However, evolutionary reversals were unexpected and remain unexplained. Together with other empirical and theoretical work, our results illustrate the stringency of the conditions for character displacement. [ABSTRACT FROM AUTHOR]

In a recent modeling study ("Limiting Similarity? The Ecological Dynamics of Natural Selection among Resources and Consumers Caused by Both Apparent and Resource Competition") that appeared in the April 2019 issue of The American Naturalist , Mark A. McPeek argued that ecologically equivalent species may emerge via competition-induced trait convergence, in conflict with naive expectations based on the limiting similarity principle. Although the emphasis on the possibility of the convergence of competitors is very timely, here we show that the proposed mechanism will only lead to actual coexistence in the converged state for specially chosen fine-tuned parameter settings. It is therefore not a robust mechanism for the evolution of ecologically equivalent species. We conclude that invoking trait convergence as an explanation for the co-occurrence of seemingly fully equivalent species in nature would be premature. [ABSTRACT FROM AUTHOR]

Although root traits play a critical role in mediating plant-plant interactions and resource acquisition from the soil environment, research examining whether and how belowground competition can influence the evolution of root traits remains largely unexplored. Here we examine the possibility that root traits may evolve as a target of selection from interspecific competition using Ipomoea purpurea and I. hederacea , two closely related morning glory species that commonly co-occur in the United States, as a model system. We show that belowground competitive interactions between the two species can alter the pattern of selection on root traits in each species. Specifically, competition with I. purpurea changes the pattern of selection on root angle in I. hederacea , and competitive interactions with I. hederacea change the pattern of selection on root size in I. purpurea. However, we did not uncover evidence that intraspecific competition altered the pattern of selection on any root traits within I. hederacea. Overall, our results suggest that belowground competition between closely related species can influence the phenotypic evolution of root traits in natural populations. Our findings provide a microevolutionary perspective of how competitive belowground interactions may impact plant fitness, potentially leading to patterns of plant community structure. [ABSTRACT FROM AUTHOR]

Most studies on the processes driving evolutionary diversification highlight the importance of genetic drift in geographical isolation and natural selection across ecological gradients. Direct interactions among related species have received much less attention, but they can lead to character displacement, with recent research identifying patterns of displacement attributed to either ecological or reproductive processes. Together, these processes could explain complex, trait-specific patterns of diversification. Few studies, however, have examined the possible effects of these processes together or compared the divergence in multiple traits between interacting species among contact zones. Here, we show how traits of two Pogoniulus tinkerbird species vary among regions across sub-Saharan Africa. However, in addition to variation between regions consistent with divergence in refugial isolation, both song and morphology diverge between the species where they coexist. In West Africa, where the species are more similar in plumage, there is possible competitive or reproductive exclusion. In Central and East Africa, patterns of variation are consistent with agonistic character displacement. Molecular analyses support the hypothesis that differences in the age of interaction among regions can explain why species have evolved phenotypic differences and coexist in some regions but not others. Our findings suggest that competitive interactions between species and the time spent interacting, in addition to the time spent in refugial isolation, play important roles in explaining patterns of species diversification. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Interspecific competition (IC) is often seen as a main driver of evolutionary patterns and community structure. Bats might compete for key resources, and cases of exaggerated divergence of resource‐related characters or trait overdispersion in bat assemblages are often explained in terms of current or past interspecific competition. However, other pressures leading to patterns that mimic the outcome of competition cannot always be ruled out.We present the state of knowledge on IC among bats, providing a critical evaluation of the information available and identifying open questions and challenges.We reviewed 100 documents addressing potential or actual IC in bats and categorised them in terms of the resource for which bats compete (food, foraging habitat, roosts, water, and acoustic space). We also examined the ecomorphological and behavioural traits considered therein to highlight responses to IC or niche partitioning.We found that: although resources should be limiting in order for competition to occur, this is seldom tested; sympatry is sometimes taken as synonymous of syntopy (yet sympatric species that are not syntopic will never experience competition); comparisons between sympatry and allopatry are rare; and testing of objective criteria exploring the existence of niche partitioning or character displacement is not commonly adopted.While morphological examination of food remains in droppings has often led to coarse‐grained analysis that proved insufficient to establish the occurrence of food niche overlap or partitioning, new frontiers are being opened by state‐of‐the‐art molecular dietary analysis.A better understanding of IC in bats is paramount, since distributional changes leading to novel bat assemblages driven by climate change are already taking place, and the dramatic decline in insect availability, as well as the global loss or alteration of foraging habitat, may generate new competitive interactions or exacerbate existing interactions in the Anthropocene, and into the future. [ABSTRACT FROM AUTHOR]

When animal mating signals diverge between populations, reproductive isolation and speciation may occur. Variation in animals' responses to these signals may reveal whether differences in perception contribute to behavioural differences between populations. We tested whether signal divergence influences receiver responses to playback in the rufous-capped warbler, Basileuterus rufifrons , a Neotropical resident songbird with a contact zone between two divergent subspecies, B. r. delattrii and B. r. rufifrons , in southern Mexico. Studying nearby populations of birds living in allopatry and sympatry, we presented warblers with playback-simulated territorial male rivals of each subspecies. In sympatry, both delattrii and rufifrons responded more strongly to songs of their own subspecies than to songs of the other subspecies, whereas in allopatry, delattrii responded strongly to songs of both subspecies, suggesting possible reproductive character displacement. Our research demonstrates that sympatric delattrii and rufifrons discriminate between each other's songs, suggesting that song is a premating isolating barrier between these divergent subspecies. This study adds to the growing literature on receiver response to vocal signal divergence in closely related sympatric and allopatric animal populations. • Song can act as an isolating barrier between bird populations living in sympatry. • We tested responses of two rufous-capped warbler subspecies to each other's songs. • In sympatry, both subspecies discriminated between each other's songs. • In allopatry, birds did not discriminate between the two types of song. • Our results are evidence of reproductive character displacement in responses. [ABSTRACT FROM AUTHOR]

Biological diversity depends on the interplay between evolutionary diversification and ecological mechanisms allowing species to coexist. Current research increasingly integrates ecology and evolution over a range of timescales, but our common conceptual framework for understanding species coexistence requires better incorporation of evolutionary processes. Here, we focus on the idea of evolutionarily stable communities (ESCs), which are theoretical endpoints of evolution in a community context. We use ESCs as a unifying framework to highlight some important but under‐appreciated theoretical results, and we review empirical research relevant to these theoretical predictions. We explain how, in addition to generating diversity, evolution can also limit diversity by reducing the effectiveness of coexistence mechanisms. The coevolving traits of competing species may either diverge or converge, depending on whether the number of species in the community is low (undersaturated) or high (oversaturated) relative to the ESC. Competition in oversaturated communities can lead to extinction or neutrally coexisting, ecologically equivalent species. It is critical to consider trait evolution when investigating fundamental ecological questions like the strength of different coexistence mechanisms, the feasibility of ecologically equivalent species, and the interpretation of different patterns of trait dispersion. [ABSTRACT FROM AUTHOR]

Highlights • Evolutionary adaption is insufficient to yield a stable three-species system. • Direct predator competition renders a coexistence state accessible. • Critical slowing-down occurs near the predator extinction thresholds. • Spatial extent may reduce the systems stability. • Character displacements are observed due to competition and evolution. Abstract We perform individual-based Monte Carlo simulations in a community consisting of two predator species that compete for a single prey species, with the purpose of studying biodiversity stabilization in this simple model system. Predators are characterized with predation efficiency and death rates, to which evolutionary adaptation is introduced. Competition for limited prey abundance drives the populations' optimization with respect to predation efficiency and death rates. We study the influence of various ecological elements on the final state, finding that both indirect competition and evolutionary adaptation are insufficient to yield a stable ecosystem. However, (quasi-stable) three-species coexistence is observed when direct interaction between the two predator species is implemented. [ABSTRACT FROM AUTHOR]

Invasive species are a global threat to biodiversity. Cases where the invasion has been tracked since its beginning are rare, however, such that the first interactions between invasive and native species remain poorly understood. Communication behavior is an integral part of species identity and is subject to selection. Consequently, resource use and direct interference competition between native and invasive species may drive its evolution. Here, we tested the role of interactions between the recently introduced invasive lizard Anolis cristatellus and the native Anolis oculatus on variation in behavior and communication in Calibishie (Dominica). From May to June 2016, we filmed 122 adult males of both species displaying in banana farms under two contexts (allopatry and sympatry). We then recorded (i) the proportion of time spent displaying and (ii) the relative frequency of dewlap vs. push-up displays. To control for habitat variation, we measured and compared the habitat characteristics (canopy openness and habitat openness) of 228 males in allopatry and sympatry. While the habitat characteristics and total display-time did not differ between the contexts for the two species, the proportion of display-time spent dewlapping by A. cristatellus decreased in sympatry. The display of A. oculatus did not differ between the contexts, however. Shifts in microhabitat use, predation pressure, or interspecific interference are potential factors which might explain the behavioral changes in display observed in A. cristatellus. This study highlights the role of behavioral traits as a first response of an invasive species to recent competition with a closely related native species. [ABSTRACT FROM AUTHOR]

Ecologists and evolutionary biologists have long been interested in the role of interspecific competition in the diversification of clades. These studies often focus on a single taxonomic group, making the implicit assumption that important competitive interactions occur only between closely related taxa, despite abundant documentation of intense competition between species that are distantly related. Specifically, this assumption ignores convergence of distantly related competitors on limiting niche axes and thus may miss cryptic effects of distantly related competitors on the evolution of focal clades. For example, distantly related competitors may act as important drivers of niche conservatism within clades, a pattern commonly ascribed to evolutionary constraints or the abiotic environment. Here we propose an alternative model of how niche similarity evolves when the functional traits of interest are mediated by unrelated phenotypic traits, as is often the case for distantly related competitors. This model represents an important conceptual step towards a more accurate, taxonomically inclusive understanding of the role that competition plays in the micro- and macroevolution of interacting species. [ABSTRACT FROM AUTHOR]

Character displacement was originally defined simply as a pattern - divergence between two species in sympatry but not allopatry - and it was recognized that multiple processes might generate this pattern. However, over time, character displacement has come to be nearly synonymous with the process of adaptive divergence between species caused by selection stemming from resource-competitive interactions (and if not, then from reproductive interactions). This tight link between character displacement and resource competition has generated, and continues to generate, imprecision and confusion in the literature. Here, to address this problem, we suggest unlinking character displacement - the pattern - from any specific process (e.g. natural selection arising from species interactions). That is, character displacement should be documented as a pattern, agnostically with respect to process. Purposeful, direct investigation of what process generated character displacement then naturally follows. This has the benefit of acknowledging that there can be many different avenues to divergence in sympatry. [ABSTRACT FROM AUTHOR]

Evolution of sexual dimorphism in ecologically relevant traits, for example, via resource competition between the sexes, is traditionally envisioned to stall the progress of adaptive radiation. An alternative view is that evolution of ecological sexual dimorphism could in fact play an important positive role by facilitating sex-specific adaptation. How competition-driven disruptive selection, ecological sexual dimorphism, and speciation interact during real adaptive radiations is thus a critical and open empirical question. Here, we examine the relationships between these three processes in a clade of salamanders that has recently radiated into divergent niches associated with an aquatic life cycle. We find that morphological divergence between the sexes has occurred in a combination of head shape traits that are under disruptive natural selection within breeding ponds, while divergence among species means has occurred independently of this disruptive selection. Further, we find that adaptation to aquatic life is associated with increased sexual dimorphism across taxa, consistent with the hypothesis of clade-wide character displacement between the sexes. Our results suggest the evolution of ecological sexual dimorphism may play a key role in niche divergence among nascent species and demonstrate that ecological sexual dimorphism and ecological speciation can and do evolve concurrently in the early stages of adaptive radiation. [ABSTRACT FROM AUTHOR]

Partitioning of the niche space is a mechanism used to explain the coexistence of similar species. Ectotherms have variable body temperatures and their body temperatures influence performance and, ultimately, fitness. Therefore, many ectotherms use behavioral thermoregulation to avoid reduced capacities associated with body temperatures far from the optimal temperature for performance. Several authors have proposed that thermal niche partitioning in response to interspecific competition is a mechanism that allows the coexistence of similar species of ectotherms. We reviewed studies on thermal resource partitioning to evaluate the evidence for this hypothesis. In almost all studies, there was insufficient evidence to conclude unequivocally that thermal resource partitioning allowed species coexistence. Future studies should include sites where species are sympatric and sites where they are allopatric to rule out alternative mechanisms that cause differences in thermal traits between coexisting species. There is evidence of conservatism in the evolution of most thermal traits across a wide range of taxa, but thermal performance curves and preferred temperatures do respond to strong selection under laboratory conditions. Thus, there is potential for selection to act on thermal traits in response to interspecific competition. Nevertheless, more stringent tests of the thermal resource partitioning hypothesis are required before we can assess whether it is widespread in communities of ectotherms in nature. [ABSTRACT FROM AUTHOR]

The incorporation of ecological processes into models of trait evolution is important for understanding past drivers of evolutionary change. Species interactions have long been thought to be key drivers of trait evolution. However, models for comparative data that account for interactions between species are lacking. One of the challenges is that such models are intractable and difficult to express analytically. Here we present phylogenetic models of trait evolution that include interspecific competition among chosen species. Competition is modeled as a tendency of sympatric species to evolve toward difference from one another, producing trait overdispersion and high phylogenetic signal. Themodel predicts elevated trait variance across species and a slowdown in evolutionary rate both across the clade and within each branch. Themodel also predicts a reduction in correlation between otherwise correlated traits. We use an approximate Bayesian computation approach to estimate model parameters. We find reasonable power to detect competition in sufficiently large (201species) trees compared with Brownian trait evolution and with Ornstein- Uhlenbeck and early burst models. We apply the model to examine the evolution of bill morphology of Darwin's finches and find evidence that competition affects the evolution of bill length. [ABSTRACT FROM AUTHOR]

Ecologists are increasingly interested in predicting how intraspecific variation and changing trait values impact species interactions and community composition. For many traits, much of this variation is caused by phenotypic plasticity, and thus the impact of plasticity on species coexistence deserves robust quantification. Partly due to a lack of sound theoretical expectations, empirical studies make contradictory claims regarding plasticity effects on coexistence. Our critical review of this literature, framed in modern coexistence theory, reveals that plasticity affects species interactions in ways that could impact stabilizing niche differences and competitive asymmetries. However, almost no study integrates these measures to quantify the net effect of plasticity on species coexistence. To address this challenge, we outline novel empirical approaches grounded in modern theory. [ABSTRACT FROM AUTHOR]

The ability of individuals to distinguish conspecifics from similar-looking congeners has important evolutionary consequences, yet few studies have determined which specific visual characteristics are used for species recognition, and whether closely related species use the same characteristics. In particular, sympatry with similar-looking congeners may influence which traits are important in species recognition. We presented elegant trogons, Trogon elegans , and black-headed trogons, Trogon melanocephalus , with models that closely resembled conspecifics and models that differed in either the colour of the belly, the colour of the upperparts or the tail-barring pattern, while broadcasting species-specific songs. Elegant trogons showed significantly more aggression towards the conspecific and tail models, suggesting that belly and back colour, but not tail-barring pattern, are important for species recognition in this species. In contrast, the black-headed trogon approached all models very closely, except for the conspecific model. We interpret this counterintuitive behaviour as reluctance to approach an unknown conspecific, suggesting that all three plumage traits are important for species recognition in black-headed trogons. Because the elegant trogon is not sympatric with a similar-looking congener, we argue that they may lack the ability to discriminate fine-barring tail differences or overlook this trait. Sympatry with the similar-looking violaceous trogon may have influenced species recognition in black-headed trogons, favouring the use of all three plumage characteristics, including tail-banding patterns, which differ between these species. Alternatively, it is possible that incongruent stimuli are attended to differently, with elegant trogons focusing on the acoustic traits and black-headed trogons focusing on visual cues. Nevertheless, our study provides the first experimental evidence that specific plumage patches are used for species recognition and that closely related species may use different traits for species recognition. Our findings also suggest that the presence of a similar-looking congener can influence which traits are important in species recognition. [ABSTRACT FROM AUTHOR]

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 FROM AUTHOR]

Interspecific competition for resources is generally considered to be the selective force driving ecological character displacement, and displacement is assumed to reduce competition. Skeptics of the prevalence of character displacement often cite lack of evidence of competition. The present article uses a simple model to examine whether competition is needed for character displacement and whether displacement reduces competition. It treats systems with competing resources, and considers cases when only one consumer evolves. It quantifies competition using several different measures. The analysis shows that selection for divergence of consumers occurs regardless of the level of between-resource competition or whether the indirect interaction between the consumers is competition (-,-), mutualism (+,+), or contramensalism (+,-). Also, divergent evolution always decreases the equilibrium population size of the evolving consumer. Whether divergence of one consumer reduces or increases the impact of a subsequent perturbation of the other consumer depends on the parameters and the method chosen for measuring competition. Divergence in mutualistic interactions may reduce beneficial effects of subsequent increases in the other consumer's population. The evolutionary response is driven by an increase in the relative abundance of the resource the consumer catches more rapidly. Such an increase can occur under several types of interaction. [ABSTRACT FROM AUTHOR]

Interspecific competitive interactions typically result in niche differentiation to alleviate competition through mechanisms including character displacement. However, competition is not the sole constraint on resource partitioning, and its effects are mediated by factors including the environmental context in which species coexist., Colonial seabirds provide an excellent opportunity to investigate the importance of competition in shaping realized niche widths because their life histories lead to variation in intra- and interspecific competition across the annual cycle. Dense breeding aggregations result in intense competition for prey in surrounding waters, whereas non-breeding dispersal to larger geographical areas produces lower densities of competitors., Bayesian hierarchical models of the isotopic niche, closely aligned to the trophic niche, reveal the degree of segregation between species and functional groups during both time periods. Surprisingly, species explained far more of the variance in the isotopic niche during the non-breeding than the breeding period., Our results underline the key role of non-breeding dynamics in alleviating competition and promoting distinctions between species through the facilitation of resource partitioning. Such situations may be common in a diverse range of communities sustained by ephemeral but abundant food items., This highlights how consideration of the hierarchical grouping of competitive interactions alongside consideration of abiotic constraints across the complete annual cycle allows a full understanding of the role of competition in driving patterns of character displacement. [ABSTRACT FROM AUTHOR]