Overlapping niches between two co‐occurring invasive fish: the topmouth gudgeon Pseudorasbora parva and the common bleak Alburnus alburnus

Abstract

Invasive fish species impact aquatic ecosystems and modify native communities, often leading to a decline in local species. These ecological impacts include the transmission of pathogens, predation, competition as well as hybridization. Two invasive fish species, the common bleak Alburnus alburnus and the topmouth gudgeon Pseudorabora parva, have both been recently found co-occurring in several regions of southern Europe, such as the Italian Arno River. Nonetheless, the trophic relationships among invasive fish species, especially cyprinids, remain poorly understood, and no studies have reported the trophic interaction between these two species. This study compared length-weight relationship and used stomach content and stable isotope analysis of two co-occurring populations in the Arno River to characterize the growth and overlap of potential trophic niches. It also found similar allometric growth in both species, a wider generalist trophic niche for P. parva and a more specialized niche for A. alburnus. A considerable niche overlap was found, suggesting that feeding competition can occur if resources were to be limited. Moreover, the niche of P. parva was more likely to overlap with that of A. alburnus than vice versa, suggesting that P. parva can be considered as a potential over competitor. Nonetheless, the authors found in the overlapping populations no evidence of realized competition, probably avoided through a combination of fine-scale mechanisms. They also highlighted that these two invasive species can co-exist and share resources, at least in an open ecosystem like a river, thus potentially doubling up their trophic impact on local communities.

Metal accumulation in relation to size and body condition in an all-alien species community

“…One of the examined species for which significant relationships were identified (P. clarkii), owing to its high impacts and costs (Haubrock et al 2021d;Kourantidou et al 2021), is listed among the worst invasive species in Europe (Nentwig et al 2018) and in the Union list of invasive species of concern attached to the EU Regulation 1143/2014 on invasive alien species (the list of invasive species for which management actions are mandatory). With almost no native fish species left in the Arno River (Balzani et al 2020;Haubrock et al 2021a), our finding that predatory fish species were the only ones with significant relationships, suggesting that feeding habitats are likely among the primary drivers of metal accumulation, is key to future restoration initiatives. Indeed, despite the poor environmental quality status of the Arno River, several ecosystem services, which include supporting services related to aquatic biodiversity in the river and its main tributaries, seem to be of great importance to nearby communities (Pacetti et al 2020), reinforcing the need for restoration actions that require an adequate understanding of the underlying ecological mechanisms.…”

Seasonal variability in the diet of juvenile European catfish, Silurus glanis, in the Arno River (Italy) in Florence

“…The reasons for this could be (i) seasonally varying occurrences of prey (Salfina and Burger 1985), (ii) dietary shifts in accordance with physiological requirements (Uys 1989), or (iii) shifts in competition with other co-occurring species. Similarly, interactions and especially niche overlap between the almost analogous cyprinid species P. parva and A. alburnus in the Arno River (Balzani et al 2020) were not limiting despite the significant overlap, and this led to competition. While these potential reasons should be the aim of future studies, the variability in this predatory feeding behavior despite being limited to immature individuals is important.…”

Expanding the invasion toolbox: including stable isotope analysis in risk assessment

“…Stable isotope analysis has been proven to be a useful tool in the field of invasion ecology (Vander Zanden et al 1999). It is often used to assess the impacts of introduced species on other taxa in term of predation (Haubrock et al 2019a;Gaiotto et al 2020;Oe et al 2020) and competition with native (Balzani et al 2016) and other alien species (Balzani et al 2020;Haubrock et al 2020a). Moreover, it can be used to reveal the role of new alien prey in the diet of resident predators (Juarez-Sanchez et al 2019;Stellati et al 2019), compare trophic levels between introduced and native populations of invasive species (Balzani et al 2021), as well as to disentangle trophic relationships among alien species in invaded communities (Haubrock et al 2019a;Bissattini et al 2021).…”