Field data and worldwide literature review reveal that alien crayfish mitigate the predation impact of the American bullfrog on native amphibians

Abstract

Biological invasion studies have focused mostly on the competition and predation impact of invaders on native species; however, introduced species frequently interact with each other and, contrary to the ‘invasional meltdown theory’, such interactions may have non‐interactive effects on native fauna. Here, the effects of the interaction between American bullfrogs (Lithobates catesbeianus) and decapod crayfish on native amphibians have been investigated. Introduced American bullfrog populations were studied at two sites in central Italy (Rome, Latium), with their selection based on the presence or absence of the alien Procambarus clarkii. The pattern emerging from the fieldwork was then verified by a worldwide literature review on the trophic niche of the American bullfrog. Both field surveys and global diet analysis showed that the abundance of native amphibians in the American bullfrog diet was reduced when introduced crayfish occurred in both native and non‐native ranges. Thus, an alternative invasion model can be proposed in which the occurrence of one invader (P. clarkii) may reduce the negative effect of an alien predator (L. catesbeianus) on native species. The present findings suggest that the removal of invaders may not always be the best solution for protecting native prey, especially when alien species are interspersed with other introduced species. In such cases, multispecies operations, sequenced appropriately or undertaken simultaneously, would be preferable. Moreover, the identification of mechanisms facilitating the coexistence of native species with invaders can offer important management options.

Two centuries for an almost complete community turnover from native to non‐native species in a riverine ecosystem

“…(2008), after 50 years and Kiesecker & Blaustein (1997) after 70 years. A further step, consisting in the temporary reduction of the invaders' abundance, should be carefully considered to avoid the ecological release of nontarget species (Bissattini et al., 2018).…”

Shared Histories of Co-evolution May Affect Trophic Interactions in a Freshwater Community Dominated by Alien Species

“…The result is a community structure more packed at higher than at lower trophic levels (Figure 1). Therefore, we speculate that, in the Arno River community, a diminished predator pressure could be not caused by the presence of a keystone species (such as in Bissattini et al, 2018), but by the potential competition among predators and potentially occurring competition-avoidance mechanisms (Haubrock et al, 2018b).…”

“…However, such complex interactions among invasive species are not well understood (Parker et al, 1999;Huxel et al, 2002;Strayer, 2010) but, as described in the "invasional meltdown theory, " can enhance the chance of a species to successfully establish itself and increase or add further impacts on the recipient environment (Simberloff and Von Holle, 1999;Simberloff, 2006). Otherwise, these interactions can lower the impact of predatory invasive species on native species in certain cases (Soluk and Collins, 1988a,b;Soluk, 1993;Rosenheim, 1998;Bissattini et al, 2018). Despite the utmost importance of such studies on multiple invaded ecosystems for practical management and control efforts (Polis and Strong, 1996;Rosenheim, 1998), they are still scarce (but see Johnson et al, 2009;Gherardi et al, 2011;Haubrock et al, 2019a).…”

Trophic structure of a pond community dominated by an invasive alien species: Insights from stomach content and stable isotope analyses

“…However, most often, the combined effects of non‐native predators on native prey species are lower than the expected sum of individual effects owing to antagonistic interactions among IAS (Jackson, 2015; Wasserman et al, 2016; Bissattini & Vignoli, 2017; Jackson et al, 2017; Bissattini, Buono & Vignoli, 2018; Bissattini, Buono & Vignoli, 2019). Indeed, there are several cases in which non‐native prey represents an alternative food source for non‐native predators, decreasing the predation pressure on native resources (Karl & Best, 1982; Murphy & Bradfield, 1992; Liu et al, 2015; Bissattini, Buono & Vignoli, 2018; Liu et al, 2018; Bissattini, Buono & Vignoli, 2019). This suggests that invaders in different trophic positions may replace the ecological role of extinct taxa, mitigating the trophic downgrading (Cucherousset, Blanchet & Olden, 2012).…”