Prey utilisation and trophic overlap between the non native mosquitofish and a native fish in two Mediterranean rivers

Abstract

Non native freshwater fish species have been long implicated in the decline of native Mediterranean ichthyofauna, through hybridization, disease transmission, competition for food and habitat, predation and/or ecosystem alteration; our knowledge, however, on the underlying mechanisms of these ecological impacts remains very limited. To explore the potential for trophic competition between the widespread Eastern mosquitofish Gambusia holbrooki and its co-occurring native toothcarp Valencia letourneuxi we compared resource use, feeding strategies, trophic selectivities and diet niche overlap. For this purpose, we studied two populations of the two species from a freshwater and a brackish habitat respectively, characterized by different food resource availabilities. In both habitats, the mosquitofish consumed a greater diversity of invertebrates and preyed on terrestrial invertebrates more frequently than the native toothcarp. Furthermore, in the less diverse and less rich brackish habitat, the non native relied heavily on plant material to balance a decrease in animal prey consumption and modified its individual feeding strategy, whereas these adaptive changes were not apparent in the native species. Their diet overlapped, indicating trophic competition, but this overlap was affected by resource availability variation; in the freshwater habitat, there was limited overlap in their diet, whereas in the brackish habitat, their diets and prey selectivities converged and there was high overlap in resource use, indicative of intense interspecific trophic competition. Overall, it appears that the underlying mechanism of the putative negative impacts of the mosquitofish on the declining Corfu toothcarp is mainly trophic competition, regulated by resource variability, though there is also evidence of larvae predation by the mosquitofish.

Risk screening of non‐native, translocated and traded aquarium freshwater fishes in Greece using Fish Invasiveness Screening Kit

“…More recently, Kalogianni et al . () demonstrated that G. holbrooki can exert trophic competition and larvae predation on native zournas Valencia letourneuxi (Sauvage). Although potential impacts in Greece are not proven (being either descriptive or speculative) for C. carpio , C. auratus (Leonardos et al .…”

“…; Kalogianni et al . ), but the lack of evidence does not necessarily imply the absence of an adverse impact. This is particularly evident in the case of the underestimated impact of non‐native disease agents on native freshwater fishes, where available data are largely based on a few farmed species (Athanassopoulou & Ragias ; Athanassopoulou et al .…”

“…aquaria and mesocosms) experimental and quantitative assessments are generally lacking for Greece, similar to the rest of Europe (Gozlan et al 2010;Ribeiro & Leunda 2012). Adverse impacts of nonindigenous or translocated species on native fishes in Greece have been documented only in a few cases (see Economidis et al 2000;Paschos et al 2004;Perdikaris et al 2012;Kalogianni et al 2014), but the lack of evidence does not necessarily imply the absence of an adverse impact. This is particularly evident in the case of the underestimated impact of non-native disease agents on native freshwater fishes, where available data are largely based on a few farmed species (Athanassopoulou & Ragias 1998;Athanassopoulou et al 2004;Xylouri et al 2007).…”

Impacts of the alien mosquitofish on the abundance and condition of two Mediterranean native fish

“…However, there are few studies assessing the presumed negative impacts of the mosquitofish on the two Greek Valencia species or the mechanisms underlying them. In a recent comparative dietary study, evidence has been presented that the underlying mechanism of the putative negative impacts of the mosquitofish on the declining Corfu Valencia is mainly trophic competition, regulated by resource variability, though there is also evidence of larvae predation by the mosquitofish (Kalogianni et al, 2014). More experimental as well as in situ studies are, however, required in order to determine the effects of the mosquitofish/native species' agonistic interactions and/ or trophic competition on the abundance, condition and reproduction of native fishes.…”

Alien freshwater fish species in the Balkans—Vectors and pathways of introduction

“…Invasive species are often superior competitors in relation to the evolutionary isolated native species populations (Mills, Rader, & Belk, 2004;Townsend, 1996), and they have broader environmental tolerances, being thus able to thrive in degraded habitats (Courtenay & Meffe, 1989;Kennard et al, 2005). Their negative impacts on native species include predation, trophic competition, behavioural interference, hybridization, spread of novel parasites and diseases, alteration of food webs and modification of biochemical cycles (Arthington & Lloyd, 1989;Mills et al, 2004;Keller & Brown, 2008;Kalogianni, Giakoumi, Andriopoulou, & Chatzinikolaou, 2014; for reviews, see Leunda, 2010;Cucherousset & Olden, 2011). However, the invasion process contains a series of stages, from introduction, survival and reproduction to dispersal, with species having to overcome barriers to reach the next step, with differing invasion success (Blackburn et al, 2011).…”