Competitive interactions between co-occurring invaders: identifying asymmetries between two invasive crayfish species

Abstract

Ecosystems today increasingly suffer invasions by multiple invasive species. Complex interactions between invasive species can have different fitness implications for each invader, which can in turn determine the future progression of their invasions and result in differential impacts on native species and ecosystems. To this end, through pairwise and group scale experiments, we examined possible interaction outcomes, competition effects and their potential fitness implications for two widespread invasive species of crayfish that increasingly co-occur in freshwater ecosystems of Europe (Pacifastacus leniusulus and Orconectes limosus). In all trials, P. leniusculus demonstrated the potential to outcompete O. limosus in both staged encounters and direct resource competition, being more likely to win heterospecific agonistic encounters and to acquire shelters at a higher rate. Observed dyadic dominance was translated to a broader social context of groupscale experiments, in which dominance of P. leniusculus was further strengthened by size differential between species. O. limosus was not able to compensate for competitive pressure by the dominant P. leniusculus and suffered wet weight loss and more frequent injuries in the presence of P. leniusculus. While both species are detrimental to native ecosystems, the ability of P. leniusculus to withstand competition pressure from another successful invasive species underscores its potential to establish dominant populations. Our results highlight the importance of understanding interspecies competition in prioritizing potential management activities or control efforts in contact zones.

Changes in population characteristics and structure of the signal crayfish at the edge of its invasive range in a European river

“…As allometric growth of certain body parameters (claws in males, abdomen in females) is a determinant of sexual dimorphism and reflects the onset of sexual maturity (Harioglu and Holdich, 2001;Streissl and Ho¨dl, 2002), both sexes were divided into two size classes: size class 1, animals < 9 cm TL (potentially immature individuals); and size class 2, animals > 9 cm TL (mature individuals). Such classification was based upon the large size of the smallest caught mature female recorded during year cycle research at M1 (85 mm TL; Hudina et al, 2011) which was close to the upper range of signal crayfish size at maturity recorded in the literature (6-9 cm TL; Westman et al, 1999;SoutyGrosset et al, 2006). Finally, in order to take into account the potential allometric growth in adult (i.e., mature) males and females, measured claw and abdomen parameters were compared between the sites as relative proportion of each respective parameter to TL.…”

“…1), where the highest dispersal rates of signal crayfish in Europe have been recorded by previous studies (Hudina et al, 2009). Signal crayfish populations at the most upstream sites of this section have been established for over 5 years and have reached relatively high population densities and balanced sex structure (Hudina et al, 2011). Therefore, the most upstream examined site is considered to represent a source population in the examined river section.…”

Causes and Consequences of Behavioral Interference between Species

“…Species replacements can also be affected by how standing behavioral variation within the invading population is spatially structured [15,[50][51][52]. For example, male western bluebirds at the invasion front are more aggressive than those in the resident population [15].…”

“…Aggressive interference in conjunction with habitat changes appears to account for the cyclical replacement of mountain bluebirds (Sialia currucoides) by western bluebirds (Sialia mexicana) in the northwestern USA [15]. Likewise, aggressive and reproductive interference combined with climate change appear to be driving the replacement of pied flycatchers (Ficedula hypoleuca) by collared flycatchers (Ficedula albicollis) on the Swedish Island of Öland [16,48].Species replacements can also be affected by how standing behavioral variation within the invading population is spatially structured [15,[50][51][52]. For example, male western bluebirds at the invasion front are more aggressive than those in the resident population [15].…”

Characteristics and movement patterns of a recently established invasivePacifastacus leniusculuspopulation in the river Mura, Croatia

“…The increase in proportion of overall injuries observed in July and August might be associated with molting. Finally, as claws represent a valuable and frequently damaged tool in aggressive interactions between crayfish (Schroeder and Huber, 2001) and proportion of claw injuries is frequently used as an indirect measure of competition intensity (Söderbäck, 1991;Hudina et al, 2011), the observed increase in the proportion of claw injuries in October is assumed to be the result of intensified competition during mating season. In analyses of signal crayfish movement patterns, the recorded values of cumulative distance moved by crayfish were in line with data obtained from other studies of signal crayfish spatial behavior (Bubb et al, 2002(Bubb et al, , 2004(Bubb et al, , 2006a(Bubb et al, , 2006bLight, 2003), while mean daily movement was substantially higher than in other analyzed populations (Bubb et al, 2004(Bubb et al, , 2006a.…”