The evolutionary consequences of interspecific aggression

Abstract

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.

Causes and Consequences of Behavioral Interference between Species

“…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.…”

“…More information about how behavioral interference is mediated by frequency dependence, dominance asymmetries, and other mechanisms that reduce the fitness of one or both species will help us to predict the rate and order of local extinctions in response to land-use change. also expected to increase temporal or spatial habitat segregation between species, and the resulting reduction in interspecific exploitative competition could lead to stable coexistence between species that otherwise would be unable to coexist [7,25]. …”

Heterospecific aggression bias towards a rarer colour morph

“…Indeed, aggressive interactions between species are actually very common, and can be as intense as aggression within a species [22,23]. Nevertheless, the evolutionary consequences of heterospecific aggression have often been overlooked [22][23][24].…”

Interspecific aggression, not interspecific mating, drives character displacement in the wing coloration of male rubyspot damselflies ( Hetaerina )

“…Interference competition between species, which in animals usually takes the form of aggressive interactions, is also very common [8], yet agonistic character displacement (ACD), a process whereby natural selection acts on traits that mediate the occurrence or outcome of interspecific aggression, remains relatively understudied [9,10]. While RCD and ACD can result in the same geographical patterns, the processes are conceptually distinct, because interspecific interference competition need not be related to competition for mates [10], and the dynamics of trait evolution can proceed quite differently [9,10]. As such, studies of selection on traits that mediate interspecific social interactions should distinguish between these two processes when drawing conclusions about the evolutionary history of such traits.…”

“…Evolutionary biologists have focused primarily on the ways in which selection acts to reduce the occurrence of costly reproductive interactions between heterospecific males and females in the context of reproductive character displacement (RCD) and reinforcement [1 -7]. Interference competition between species, which in animals usually takes the form of aggressive interactions, is also very common [8], yet agonistic character displacement (ACD), a process whereby natural selection acts on traits that mediate the occurrence or outcome of interspecific aggression, remains relatively understudied [9,10]. While RCD and ACD can result in the same geographical patterns, the processes are conceptually distinct, because interspecific interference competition need not be related to competition for mates [10], and the dynamics of trait evolution can proceed quite differently [9,10].…”