Direct interactions among conspecific and heterospecific animals are often mediated by aggressive behavior. We analyze the ecology and evolution of resourc-related heterospecific aggression (HA) by reviewing and meta-analysing 126 studies, contrasting HA with conspecfic aggression (CA), and discussing terminological confusions and conceptual models. HA occurred in 78% of tests (n = 459), suggesting a high prevalence and potential effect on niche use and community structure. The benefits of both CA and HA are linked to resource defensibility and abundance, yet HA can change independently of CA. Ecological inferences about HA are often weak because they assume that interference always results from resource competition, and evolutionary inferences made by comparing HA to CA are also weak because they usually ignore history. We believe that comparisons between situations where a focal species is allopatric from and sympatric with a heterospecfic competitor provide better opportunities to test hypotheses about HA. In general, according to our data set, aggression was higher with increased resource overlap as expected, both because CA was greater than HA, and HA was greater within compared to between genera. Progress in understanding HA requires distinguishing traits (aggressive behavior) from interactions (agonism, interference), as well as from the ecological and evolutionary causer (competition, ancestry) and consequences (dominance, territoriality, exclusion) of those interactions.

Behavioral interference between species, such as territorial aggression, courtship, and mating, is widespread in animals. While aggressive and reproductive forms of interspecific interference have generally been studied separately, their many parallels and connections warrant a unified conceptual approach. Substantial evidence exists that aggressive and reproductive interference have pervasive effects on species coexistence, range limits, and evolutionary processes, including divergent and convergent forms of character displacement. Alien species invasions and climate change-induced range shifts result in novel interspecific interactions, heightening the importance of predicting the consequences of species interactions, and behavioral interference is a fundamental but neglected part of the equation. Here, we outline priorities for further theoretical and empirical research on the ecological and evolutionary consequences of behavioral interference. Interspecific Aggression and Reproductive InterferenceFew subjects in animal behavior have attracted more attention than aggression and sex, yet research tends to stop at species boundaries even when the behaviors themselves do not. Aggressive and sexual interactions between species are surprisingly common and share many parallels in their causes and ecological and evolutionary effects [1][2][3][4][5][6]. Both types of behavioral interference (Box 1) have been hypothesized to: (i) arise as a byproduct of intraspecific interactions (Box 2); (ii) cause local extinction as well as temporal and spatial habitat partitioning; (iii) prevent species from coexisting that otherwise would be expected to coexist; (iv) enable coexistence between species that otherwise would not be expected to coexist; (v) promote or prevent species range shifts and the spread of invasive species; (vi) cause sympatric species to diverge or converge through character displacement processes; (vii) cause populations within a species to diverge from each other due to character displacement in areas of sympatry; and (viii) contribute to reproductive isolation and speciation ( Figure 1).Despite their connections, aggressive interference and reproductive interference (see Glossary) have largely been studied by different researchers in relation to different theoretical frameworks [2,4,7] and in different study systems [3], even though many closely related species interfere with each other in both ways (see Table S1 in [8]). We do not believe that these two categories of interspecific interactions should be synonymized, because this would obscure important differences between them. Instead, we propose that their similarities and interrelationships merit a common conceptual framework, which we introduce here ( Figure 1). TrendsAggressive and reproductive forms of behavioral interference between species are widespread in animals and share many parallels in their underlying causes and their ecological and evolutionary effects.Behavioral interference can determine whether species coexist and, thus, affects speci...

Competition has always been a cornerstone of evolutionary biology, and aggression is the predominant form of direct competition in animals, but the evolutionary effects of aggression between species are curiously understudied. Only in the past few years, existing theoretical frameworks have been extended to include interspecific aggression, and significant empirical advances have been made. After arguing that agonistic character displacement (ACD) theory provides the most suitable theoretical framework, we review new empirical evidence for ACD and the results of mathematical models of the process. We consider how ACD can be distinguished empirically from ecological and reproductive character displacement and the additional challenges posed by developmental plasticity. We also provide the first taxonomically broad review of theoretical and empirical work on the effects of interspecific aggression on species coexistence and range limits. We conclude by highlighting promising directions for future research on the evolutionary effects of interspecific aggression.

Humans have modified planet Earth extensively, with impacts ranging from reduced habitat availability to warming temperatures. Here we provide an overview of how humans have modified the nutritional physiology and ecology of wild organisms, and how nutrition is vital to successful conservation practices.

Many morphological, behavioral, physiological, and life-history traits covary across the biological scales of individuals, populations, and species. However, the processes that cause traits to covary also change over these scales, challenging our ability to use patterns of trait covariance to infer process. Trait relationships are also widely assumed to have generic functional relationships with similar evolutionary potentials, and even though many different trait relationships are now identified, there is little appreciation that these may influence trait covariation and evolution in unique ways. We use a trait-performance-fitness framework to classify and organize trait relationships into three general classes, address which ones more likely generate trait covariation among individuals in a population, and review how selection shapes phenotypic covariation. We generate predictions about how trait covariance changes within and among populations as a result of trait relationships and in response to selection and consider how these can be tested with comparative data. Careful comparisons of covariation patterns can narrow the set of hypothesized processes that cause trait covariation when the form of the trait relationship and how it responds to selection yield clear predictions about patterns of trait covariation. We discuss the opportunities and limitations of comparative approaches to evaluate hypotheses about the evolutionary causes and consequences of trait covariation and highlight the importance of evaluating patterns within populations replicated in the same and in different selective environments. Explicit hypotheses about trait relationships are key to generating effective predictions about phenotype and its evolution using covariance data.

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.

24Urbanization is modifying previously pristine natural habitats and creating "new" ecosystems for 25 wildlife. As a result, some animals now use habitat fragments or have colonized urban areas. 26Such animals are exposed to novel stimuli that they have not been exposed to in their 27 evolutionary history. Some species have adapted to the challenges they face -a phenomenon 28 known as synurbanization -while others have not. Here we present a review of the sublethal 29 consequences of life in the city for wild vertebrates, and demonstrate that urban animals face an 30 almost completely different set of physiological and behavioural challenges compared to their 31 rural counterparts. We focus on the negative fitness-related impacts of urbanization, but also 32 identify instances where there are benefits to wildlife. The effects of urbanization appear to be 33 both species-and context-dependent, suggesting that although the field of urban ecology is far 34 from nascent, we are still just beginning to understand how the intricacies of biodiversity on our 35 planet are affected by our presence. 36 37

Agonistic behavior between heterospecifics, in which individuals of one species attack another, may cause a subordinate species to shift resource or habitat use. Subsequent evolutionary responses to selection may mimic shifts expected under ecological character displacement, but with no role played by exploitative competition. Alternatively, aggressive behavior can evolve when fitness is improved by excluding members of a coexisting species from a defendable resource through interference. We tested whether heterospecific agonistic behavior has evolved in brook stickleback (Culaea inconstans) by comparing replicate allopatric populations to those sympatric with ninespine stickleback (Pungitius pungitius). We also tested for heritable variation in heterospecific aggressive behavior by rearing family groups in a common environment. Allopatric populations of brook stickleback were more aggressive than ninespine stickleback, suggesting that pre-existing aggression in brook stickleback contributed to niche shifts by ninespine stickleback. In addition, sympatric adult brook stickleback were more aggressive toward ninespine stickleback than brook stickleback from allopatric populations. Overt heterospecific aggressive behaviors were heritable, and aggression in juvenile brook stickleback increased with age in sympatric but not in allopatric populations reared in a common environment. Brook stickleback have evolved increased aggression when they coexist with ninespine stickleback. These stickleback communities have been structured by both evolved and pre-existing variation in heterospecific aggressive behavior in brook stickleback.