The role of aggression in range expansion and biological invasions

Abstract

Traits that aid in the invasion process should exhibit a gradient across the expansion range in response to changing selection pressures. Aggression has been repeatedly associated with invasion success in many taxa, as it may help invaders to wrestle the resources from other species which enhances their success in a novel environment. However, aggression primarily allows individuals to overcome conspecific rivals, providing advantages in competition over resources. Agonistic prowess could therefore increase fitness at both ends of the expansion gradient. Here we review the role of aggression in range expansion of invasive species, and its potential role as a driver of range expansion. We analyze how these different mechanisms could affect trait variation in expanding and invasive populations. Specifically, we look at how aggression could help dilate the edges of a population through niche competition, as well as lead to exclusion from the center (i.e. areas of high population density) by the conspe-cifics. Both of these processes will result in a characteristic spatial distribution of phenotypes related to aggression that could provide insights into the ecological pressures and dynamics of expanding populations, potentially providing clues to their success as niche competitors and invasive species.

Differences in aggressive behaviour along the expanding range of an invasive crayfish: an important component of invasion dynamics

“…Under such conditions, less successful competitors could end up being squeezed out by more successful conspecifics and pushed to the population fringe (Hamilton 1971;Schradin and Lamprecht 2002). Range expansion would be driven from the core outwards through endogenous, centrifugal pressure of intraspecific competition building up as the density of the founding population increases (range expansion by exclusion from population centre), rather than by highly aggressive competitors that comprise the population at rapidly expanding invasion fronts (range expansion by dilation of population edges; Hudina et al 2014). Expanding range and corresponding decrease in competitive pressure at the front will also potentially allow individuals to acquire more resources.…”

“…This is consistent with the classic concept of a dominant role of population density as an endogenous driver of dispersal, population growth, and the trade-offs and evolution of traits during range expansion (Bowler and Benton 2005;Burton et al 2010). A shift in balance between the rate of population growth (and the An important component of invasion dynamics resulting centrifugal pressure from competition stemming from population density) and counteracting pressures from other populations/niche competitors could, therefore, be a key event in invasion dynamics of introduced species and also one of the determinants of a lag between establishment and expansion of introduced species (Hudina et al 2014). Differential expression of traits along the expanding range also means that sampling and evaluation of trait's contribution to range expansion, as well as associated assessments of invasion risk, should take into account both this bias and potentially less pronounced expression of a beneficial trait in individuals at the invasion front.…”

“…Therefore, in addition to being good dispersers, highly competitive individuals could also have an advantage in situations where high levels of aggressive motivation are needed to secure scarce resources (Grafen 1987). In such case, rather than dilating population edges, aggression would drive range expansion through exclusion from population centres (Hudina et al 2014). Given that a greater competitive ability and aggressive motivation could increase fitness at both ends of the expansion gradient, it is not immediately obvious which of these opposing tendencies, edge dilation or exclusion from centre, will have a prevailing effect on the distribution of aggressive phenotypes along the range expansion gradient.…”

Phenotypic variability of rusty crayfish (Faxonius rusticus) at the leading edge of its riverine invasion

“…First, the range expansion of rusty crayfish might be driven by the exclusion of subdominant individuals from high-density population centres, therefore leading to the widespread presence of competitively inferior crayfish at the invasion leading edge (Hudina, Hock, & Zganec, 2014). First, the range expansion of rusty crayfish might be driven by the exclusion of subdominant individuals from high-density population centres, therefore leading to the widespread presence of competitively inferior crayfish at the invasion leading edge (Hudina, Hock, & Zganec, 2014).…”

The effect of density on aggression between a highly invasive and native fish

“…The underlying commonality that unites these interactions is some form of aggression (Grether et al, ). Invasive species are frequently observed to display more inter‐specific aggression than native species, which is often considered to be a key factor in their success in spreading to and becoming established in novel systems (Holway & Suarez, ; Hudina, Hock, & Zganec, ; Pintor, Sih, & Bauer, ). The ultimate outcome of aggressive interactions may be the displacement of a native species as their access to food, shelter and reproductive partners becomes increasingly limited (Amarasekare, ).…”