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.