Differences in composition of macroinvertebrate communities with invasive and native Gammarus spp. (Crustacea: Amphipoda)

Abstract

SUMMARY 1. Assessing the effects on communities of invasive species is often confounded by environmental factors. In Irish rivers, the introduced amphipod Gammarus pulex replaces the native G. duebeni celticus in lowland stretches. The two amphipods are associated with different macroinvertebrate communities, which may in part be the result of natural longitudinal physicochemical change. However, this hinders assessment of any direct community impacts of the invasive as compared with the native species. Here, we report on a fortuitous circumstance that allowed us to uncouple the community effects of Gammarus species from environmental differences. 2. The lowland stretch of the River Lissan is dissected by a weir, which has slowed the upstream invasion by G. pulex. We took physicochemical measurements and macroinvertebrate samples from three contiguous 150 m reaches of this stretch with G. pulex only, mixed Gammarus and G. d. celticus only communities. 3. We found no biologically significant differences in physicochemistry among the three reaches. Overall invertebrate densities did not differ among reaches. However, G. pulex numerically dominated its reach, whilst G. d. celticus abundance was relatively low in its reach. The G. pulex reach had significantly higher overall biomass because of high invader abundance. In addition, both diversity and species richness of macroinvertebrate communities were lower in the G. pulex than the G. d. celticus reach, with the mixed Gammarus reach intermediate. 4. Ordination indicated distinctly different associations of invertebrate community samples and taxa that were best explained by the distributions of the Gammarus species. Again, the mixed Gammarus species samples were intermediate. 5. This study indicates that the invasive G. pulex has a greater impact on macroinvertebrate community composition than the native G. d. celticus, probably through biotic interactions such as predation.

Environmental and morphological factors influencing predatory behaviour by invasive non-indigenous gammaridean species

“…Such species displacements by invasive gammaridean species have been recorded on several occasions all over the world (Pinkster et al 1977;Dick et al 1993Dick et al , 1995Dick 1996;Dick andPlatvoet 1996, 2000;Dermott et al 1998;Jazdzewski andKonopacka 2000, 2002;Jazdzewski et al , 2004Jazdzewski et al , 2005; MacNeil and Prenter 2000; Van der Velde et al 2000Van Overdijk et al 2003;Kelly et al 2003;MacNeil et al 2004;Kelly and Dick 2005;Meyer et al 2005;Grabowski et al 2006Grabowski et al , 2007Felten et al 2008a).…”

“…Gammaridean amphipods are considered to be detritivores (phyto-detritophages, detritophages), omnivores (phyto-zoophages, zoophytophages) or predators (zoophages) (Monakov 2003). During invasions, increased predation on other macroinvertebrates and fish by gammaridean species is sometimes recorded, for instance in the case of the invasion of the North American gammaridean Gammarus tigrinus in continental Europe (Schmitz 1960) and the invasion of Gammarus pulex in Ireland (Kelly et al 2003(Kelly et al , 2006.…”

Roles of parasites in animal invasions

“…In invasion scenarios, the facilitation of the invasion process through parasites might lead to a species replacement, with the new resident having profoundly different impacts on the wider community compared with the native. For example, freshwater community structure is radically altered when the invasive amphipod G. pulex replaces the native G. d. celticus [56]. Many studies, however, have used two-host, one-parasite systems to suggest, by extrapolation, that parasites structure biological communities or assemblages [46,57].…”

A species invasion mediated through habitat structure, intraguild predation, and parasitism

“…However, replacement of G. duebeni subsp. celticus by the more abundant, aggressive, and predatory G. pulex is likely to drastically alter community structure at various trophic levels (Savage 2000;Kelly et al 2003).…”

“…Although these species are from the same biogeographic region, G. pulex is considered invasive due to the previous isolation of G. duebeni subsp. celticus and the rapid impacts of the invader following anthropogenic introduction (Kelly et al 2003). While G. duebeni subsp.…”