Predicting the competitive interactions and trophic niche consequences of a globally invasive fish with threatened native species

Abstract

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Novel trophic subsidies from recreational angling transform the trophic ecology of freshwater fishes

“…While the lack of treatment replication limits some of the inferences on the generality of the patterns and processes detected, the two allopatric treatments and the sympatric treatment had strong temporal replication by running between 2016 and 2019 in subsidy absence. In this period, the isotopic niches of both fish species were strongly associated with the putative macroinvertebrate prey, with differences in the fish isotopic niches between allopatry and sympatry resulting from processes including intraspecific and interspecific competition (Dominguez Almela et al, 2021). The addition of the subsidy to the allopatric treatments in 2020 then resulted in substantial isotopic niche shifts towards enriched δ 13 C values in both fishes, with the isotopic niches in the non‐subsidised sympatric treatment remaining relatively similar to previous years.…”

“…Correspondingly, over the 15‐week treatment period in 2020, approximately 2 kg of pellets per week were released by hand into each allopatric pond, with the pellets fed into discrete areas of the ponds to replicate angling activities. In contrast, the adjacent sympatric pond did not receive any angler bait subsidy in 2020, with the trophic niche positions and sizes of the species determined according to natural prey availability and interactions between the two sympatric fish species (Figure S1B; Dominguez Almela et al, 2021).…”

“…These samples, along with samples of the pellets that were fed as the subsidy, were dried to constant mass at 60°C and analysed at the Cornell University Stable Isotope Laboratory as previously described. As there were some differences in the macroinvertebrate SI data between the three ponds in 2020 (Table S3), and in the 2017–2019 data (Dominguez Almela et al, 2021), then the SI data were also converted to δ 13 C corr and TP.…”

“…The ponds were located in southern England and were used between 2016 and 2019 to investigate the trophic interactions of the two species with only natural prey resources present (cf. Dominguez Almela et al, 2021). In short, three ponds (approximately 400 m 2 , maximum depths of 1.2 m) were used that, prior to fish stocking in January 2016, were fishless.…”

First record of non-native Xiphophorus maculatus (Günther, 1866) (Cyprinodontiformes, Poeciliidae) in the state of Maranhão, northeastern Brazil

“…According to the limiting similarity hypothesis, when functionally similar native and invasive species coexist, there is a likelihood of biotic resistance of native fish assemblages where they are not under stress and the habitat is pristine (MacArthur and Levins 1967). However, this may vary depending on the niche plasticity of both the native and invasive species, as well as localized patterns of resource availability which may allow the invader to occupy a previously unexploited niche or broadening its trophic niche under competition (Dominguez et al 2021). In Maranhão there are five native poeciliid species: Poecilia (Micropoecilia) branneri Eigennman, 1894, Poecilia (Micropoecilia) sarrafae Bragança & Costa, 2011, Poecilia (Pamphorichtys) hollandi (Henn, 1916, Poecilia (Pamphorichthys) araguaiensis (Costa, 1991), and Poecilia (Poecilia) vivipara Bloch & Schneider, 1801 (Figueiredo 1997;Bragança and Costa 2011;Ramos et al 2014;Melo et al 2016;Piorski et al 2017;Brito et al 2019Brito et al , 2020Guimarães et al 2020aGuimarães et al , 2020bGuimarães et al , 2021Oliveira et al 2020), as well as diverse yet functionally similar small fish assemblages (Oliveira et al 2020).…”