Current velocity shapes co‐existence patterns among invasive Dikerogammarus species

Abstract

Summary Facilitative interactions among co‐evolved representatives of the endemic Ponto‐Caspian fauna are regarded as a major factor of their invasion success. Nevertheless, the most renowned examples represent interactions between different trophic levels or functional groups, while ecologically similar species can be expected to show competition‐based niche partitioning. Here, we test for differences in the realized niche of three invasive Dikerogammarus species (Crustacea: Gammaridae) in their co‐occurring range. We sampled multiple habitats within sites distributed along the River Danube to test whether some environmental variables could reveal spatial niche differentiation among the three species of Dikerogammarus, and if so, to test a predictive model outside the zone of co‐occurrence. Spatial niche differentiation was present among the species, primarily determined by current velocity (and associated substrate preference), likely reflecting a stress tolerance–competitive ability trade‐off. Suspended matter concentration was also relevant, suggesting food resources (through filter feeding) might represent another important niche axis, somewhat loosening the terms of co‐existence between D. haemobaphes and the other two species. Environmental variables could effectively explain the absence of D. bispinosus in the Lower Danube, implying that the co‐existence of the three species is possible only along a sufficiently wide current velocity gradient, and the observed turnovers are the result of niche expansion in the absence of the stronger competitor. Hence, differences in invasion success may be attributed to a stress tolerance–competitive ability trade‐off. Our results suggest the advantage of D. villosus is attributable to its competitive dominance, allowing it to monopolize lentic and/or structured habitats, which represents a fortunate pre‐adaptation to anthropogenic alterations of aquatic ecosystems. The presence of D. villosus does not greatly affect the expansion of D. haemobaphes; however, the exclusion of D. bispinosus from lentic habitats by D. villosus probably strongly limits its potential to spread by active dispersal.

Abiotic factors affecting habitat selection by two invasive gammarids Dikerogammarus villosus and Pontogammarus robustoides

“…Perhaps the adaptations of P. robustoides to commonly occupied sandy areas (Wawrzyniak-Wydrowska & Gruszka, 2005;_ Zytkowicz et al, 2008), which are poorly sheltered and exposed to wave actions, allowed it to counteract the water flow in our experiment. In a field study, D. villosus was found to be the least rheotolerant compared to D. haemobaphes and D. bispinosus and the most associated with structured habitats offering protection against flow (Borza et al, 2017). Our experiment confirmed its ability to locate and utilize lentic microhabitats which can help it thrive in flowing waters.…”

“…5A), which may limit their distribution to lentic areas or structured habitats _ Zytkowicz et al, 2008;Grabowski et al, 2009;Borza et al, 2017). Avoidance of fast flowing waters distinguishes invasive amphipods from those staying within their native ranges (Devin & Beisel, 2007).…”

“…We expected that gammarids originating from brackish water habitats (Rozengurt, 1971) would exhibit preferences for increased ionic content in water (Piscart et al, 2005), preventing them from entering small, more freshwater affluents of large rivers (Grabowski et al, 2009). We also assumed that both species would select lentic sites (Devin & Beisel, 2007;Borza et al, 2017), but that P. robustoides, as a more common inhabitant of stagnant waters (Ja_ zd_ zewski et al, 2002) would be relatively less adapted to flow. Finally, we expected that P. robustoides would be better adapted to counteract negative aspects of life in very shallow locations (WawrzyniakWydrowska & Gruszka, 2005;_ Zytkowicz et al, 2008), such as extreme temperatures.…”

How to coexist with the ‘killer shrimp’ Dikerogammarus villosus? Lessons from other invasive Ponto‐Caspian peracarids

“…All target species were present in almost the entire section of the Danube studied, except for D. bispinosus (Table ; Borza et al, ). Dikerogammarus villosus proved to be the most widespread and – on average – most abundant species during the survey, followed by C. ischnus and O. obesus , which in turn reached a maximum density even higher than D. villosus (Table ).…”

“…The effect of substrate types was further analysed in a univariate context using generalized linear models (GLMs) on count data for C. ischnus , J. sarsi , and O. obesus ( T. trichiatus was excluded from this analysis owing to its rarity in the material, and Dikerogammarus species were excluded because factors other than substrate type have a strong influence on their habitat preferences; Borza et al, ). The negative binomial family with log‐link function was used ( glm.nb function in the mass package; Venables & Ripley, ), as it provided a better fit than Poisson and quasi‐Poisson models based on the distribution of the deviance residuals (Zuur, Ieno, Walker, Saveliev, & Smith, ).…”