Disentangling the influence of abiotic variables and a non‐native predator on freshwater community structure

Abstract

Cause‐and‐effect interpretations of the apparent impacts of biological invasions are confounded by the coincident occurrence of non‐native species and changes to abiotic factors. Native community structure and function can vary greatly in space and time, owing to abiotic variables that could potentially be affected by non‐native species. Here, we sought to determine the relative importance of abiotic variables and an invasive predatory fish, the Eurasian round goby (Neogobius melanostomus), on local macroinvertebrate assemblages and benthic algal production in the St. Lawrence River. We used structural equation modeling to evaluate the strength of interaction pathways between hypothesized biotic and abiotic factors driving trophic cascades. Our results indicate that biotic interactions with the round goby drive changes in the abundances of native grazers and non‐native dreissenid mussels in the St. Lawrence River. However, the directionality of these effects contradicts previous studies of round goby impacts that emphasized top‐down control. We found positive correlations between round goby density and prey (dreissenid and grazer) densities, suggesting complex interactions between round gobies and benthic communities, including strong bottom‐up forces. Together with previous studies, our results suggest that, although the interactions between round gobies and benthic communities remain strong, the direction of these interactions varies over space and time. Our results highlight the importance of disentangling the respective roles of biotic interactions and abiotic factors, in order to properly assess the impacts of non‐native species as well as the spatiotemporal variability of such impacts.

Assessing the ecological impacts of invasive species based on their functional responses and abundances

“…Ecological impact increases from bottom left to top right aquaticus communities. However, only moderate impact would be predicted on E. berilloni using the FR method; indeed the overall differences in numbers of prey eaten by N. melanostomus and C. gobio found here, whilst significant, do not match well with the known extremely high impact of the invader on native macroinvertebrate and fish communities (Barton et al 2005;Pagnucco and Ricciardi 2015). We show, however, that an improvement in impact prediction is attained when ecologically comparable abundances of the invader and native are taken into account in the Relative Impact Prediction (RIP) biplots, which capture both the per capita predator effects (i.e.…”

“…Overall, N. melanostomus consumed greater numbers of prey than did C. gobio, which is indicative of its impact on native communities (Barton et al 2005;Pagnucco and Ricciardi 2015) and may allow impact prediction prior to it invading a naïve native community (Dick et al 2013. Both predators consumed significantly more of the gammarid, E. berilloni, than the isopod, A. aquaticus, but the latter prey species was disproportionately affected by predation from N. melanostomus.…”

“…Alexander et al 2014a, b;Dick et al 2013Dick et al , 2017Paterson et al 2014;Laverty et al 2015;Xu et al 2016) have shown that the comparative FR methodology is rapid, efficient and effective at explaining and predicting the ecological damage caused by invasive species. However, in some cases the FR of invasive species is unremarkable when compared to those of native species, yet ecological damage is known to occur, as is the case with N. melanostomus and P. parva toward invaded communities (Barton et al 2005;Britton et al 2010;Gozlan et al 2010;Pagnucco and Ricciardi 2015). When the abundances as well as FRs of invasive and native species are included in the ''Relative Impact Potential'' assessment, the overall forecast of impact is better reconciled with known field impacts.…”

“…Abundances were estimated from surveys and the literature. We chose the high-impact invasive round goby, Neogobius melanostomus, a Ponto-Caspian fish which has invaded freshwaters in Europe (Manné et al 2013) and N. America (Jude et al 1992), leading to drastic declines in native aquatic invertebrates and fish (Barton et al 2005;Pagnucco and Ricciardi 2015). We first experimentally derived the functional responses of N. melanostomus and a native trophic analogue, the European bullhead Cottus gobio, towards two benthic macroinverebrates, the amphipod Echinogammarus berilloni and the isopod Asellus aquaticus.…”

Responses of a wetland ecosystem to the controlled introduction of invasive fish

“…As a result, the effects of invasive species can vary across ecological scales, between discrete ecosystems, or over time (Strayer et al, 2006;Ricciardi et al, 2013;Latzka et al, 2016). For instance within the Laurentian Great Lakes Basin, where >180 invasive species have established, the effects of nonnative round gobies on benthic invertebrates can vary from strongly positive to strongly negative depending on the relative importance of top-down versus bottom-up controls on community dynamics (Pagnucco & Ricciardi, 2015). It remains relatively uncommon, however, to quantify such variation, examine its underlying drivers, or incorporate it into predictions or management efforts (Thomsen et al, 2011;Hulme et al, 2013;Dick et al, 2014).…”