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The strategies that allow invasive alien species to perpetuate themselves in the long term are still poorly understood in invasion science. Considering top predators, a key issue is how they overcome the prey decline which they have caused during the invasion process. We investigate factors related to the persistence, impacts and long‐term success of the emerging peacock bass (Cichlidae: Cichla) invasion, a fish native to the Amazon biome that has been introduced globally.We analysed a robust temporal database that includes comparisons (1994–2002 vs. 2015–2017) on the diet of Cichla ocellaris, the abundance of this invader, its prey and competitors in a human‐modified ecosystem. In addition, we compare the frequency of cannibalism (presence or absence) between native versus non‐native populations, and between natural versus human‐modified ecosystems in the American continent. Four hypotheses were tested: (i) prey and competitor populations decrease through time as a result of predation impacts; (ii) cannibalism is size‐ and density‐dependent, and increases after native prey decline; (iii) cannibalism is more frequent in non‐native populations; and (iv) the abundance of invader decreases over time because of reduced resources and increased cannibalism.Our results revealed that the impacts of introducing this predator into communities are temporally cumulative and continue to evolve even after 70 years since its introduction. These impacts have led to dramatic reductions in prey availability, resulting in widespread cannibalism. Adult individuals preying on juveniles in areas with higher abundances of peacock bass indicated that cannibalism is size‐ and density‐dependent. Cannibalism was more frequent in non‐native populations and in human‐modified ecosystems. A complex feedback process (reproduce and cannibalise frequently) may be responsible for overcoming long‐term resource scarcity, and the cannibalism may not be a regulatory force strong enough to surpass the reproductive success of the population.Our findings at the local and continental scale converge to confirm the cannibalism as an adaptive invasiveness strategy that facilitates the invasion process and makes populations self‐sustainable in the long term, which may jeopardise the efficacy of management actions for these top predators introduced globally. [ABSTRACT FROM AUTHOR]

Feeding habits of herbivorous fishes play an important role in shaping the form and function of coastal marine ecosystems. Rabbitfishes (Siganidae) are important consumers of macroalgae on Indo‐West Pacific coral reefs. However, it is unclear how their diet varies among and within species at biogeographical scales, casting doubt on their precise functional roles across different regions. The present study assessed the inter‐ and intra‐specific diet variation of four rabbitfishes (Siganus trispilos, Siganus corallinus, Siganus virgatus and Siganus doliatus) factored by morphological relatedness among populations from Ningaloo Reef (western Australia), the Great Barrier Reef (GBR, eastern Australia) and the Yaeyama Islands (Okinawa Prefecture, Japan). Results showed that the region had a strong effect on diet, effectively reducing the expected effect of morphologic similitude. While intra‐specific differences were only significant when populations inhabited different regions; interspecific differences were not as predicted, with different morphotypes having similar diets when populations inhabited the same regions. Rabbitfishes consumed more corticated and filamentous macroalgae on the GBR, more foliose and membranous macroalgae at the Yaeyama Islands, and more leathery macroalgae at Ningaloo Reef. The findings indicate that rabbitfishes have high diet plasticity, and hence their functional role as mediators of competition between macroalgae and corals can change across biogeographic regions. Local context is therefore important when assessing the diet and functional role of herbivorous fishes. As climate change unfolds, shifts in the distribution, trophic behaviour and function of species are expected, making the study of trophic plasticity more important. [ABSTRACT FROM AUTHOR]

Feeding habits of herbivorous fishes play an important role in shaping the form and function of coastal marine ecosystems. Rabbitfishes (Siganidae) are important consumers of macroalgae on Indo‐West Pacific coral reefs. However, it is unclear how their diet varies among and within species at biogeographical scales, casting doubt on their precise functional roles across different regions. The present study assessed the inter‐ and intra‐specific diet variation of four rabbitfishes (Siganus trispilos, Siganus corallinus, Siganus virgatus and Siganus doliatus) factored by morphological relatedness among populations from Ningaloo Reef (western Australia), the Great Barrier Reef (GBR, eastern Australia) and the Yaeyama Islands (Okinawa Prefecture, Japan). Results showed that the region had a strong effect on diet, effectively reducing the expected effect of morphologic similitude. While intra‐specific differences were only significant when populations inhabited different regions; interspecific differences were not as predicted, with different morphotypes having similar diets when populations inhabited the same regions. Rabbitfishes consumed more corticated and filamentous macroalgae on the GBR, more foliose and membranous macroalgae at the Yaeyama Islands, and more leathery macroalgae at Ningaloo Reef. The findings indicate that rabbitfishes have high diet plasticity, and hence their functional role as mediators of competition between macroalgae and corals can change across biogeographic regions. Local context is therefore important when assessing the diet and functional role of herbivorous fishes. As climate change unfolds, shifts in the distribution, trophic behaviour and function of species are expected, making the study of trophic plasticity more important. [ABSTRACT FROM AUTHOR]

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Copyright of African Journal of Ecology is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Back‐to‐back marine heatwaves in 2016 and 2017 resulted in severe coral bleaching and mortality across the Great Barrier Reef (GBR). Encouragingly, some corals that survived these events exhibit increased bleaching resistance and may represent thermally tolerant populations that can better cope with ocean warming. Using the GBR as a natural laboratory, we investigated whether a history of minimal (Heron Island) or severe (Lizard Island) coral bleaching in 2016 and 2017 equates to stress tolerance in a successive heatwave (2020). We examined the genetic diversity, physiological performance, and trophic plasticity of juvenile (<10 cm) and adult (>25 cm) corals of two common genera (Pocillopora and Stylophora). Despite enduring greater cumulative heat stress (6.3°C week−1 vs. 5.6°C week−1), corals that experienced the third marine heatwave in 5 years (Lizard) exhibited twice as high survival and visual bleaching thresholds compared to corals that had not experienced significant bleaching in >10 years (Heron). Surprisingly, only one shared host–Symbiodiniaceae association was uncovered between locations (Stylophora pistillata–Cladocopium "C8 group") and there was no genetic overlap in Pocillopora–Cladocopium partnerships, suggesting turnover in species composition from recent marine heatwaves. Corals within the species complex Pocillopora that survived the 2016 and 2017 marine heatwaves at Lizard Island were the most resilient, exhibiting three times greater calcification rates than conspecifics at Heron Island. Further, surviving corals (Lizard) had distinct isotopic niches, lower host carbon, and greater host protein, while conspecifics that had not experienced recent bleaching (Heron) had two times greater symbiont carbon content, suggesting divergent trophic strategies that influenced survival (i.e., greater reliance on heterotrophy vs. symbiont autotrophy, respectively). Ultimately, while corals may experience less bleaching and survive repeated thermal stress events, species‐specific trade‐offs do occur, leaving open many questions related to the long‐term health and recovery of coral reef ecosystems in the face of intensifying marine heatwaves. [ABSTRACT FROM AUTHOR]

Coral communities can survive in stressful environments; however, the mechanisms corals employ to endure challenging conditions are poorly understood. This study assessed how the heterotrophy of three coral genera (Acropora spp., Porites spp. and Platygyra spp.) varies among sites in the Dampier Archipelago, Western Australia, exposed to different levels of turbidity. Stable isotope δ13C and δ15N analysis of coral host and endosymbionts were combined with modern Bayesian isotopic niche analysis to demonstrate that heterotrophy in all three coral genera increased in highly turbid environments. While all coral genera were found to be more heterotrophic in highly turbid waters, Porites spp. favoured heterotrophy across all levels of turbidity, whereas Platygyra spp. and Acropora spp. were less heterotrophic at sites with lower turbidity. Thus, some scleractinian corals can alter their feeding strategies in response to turbidity levels. As nearshore coral reefs experience increased and prolonged turbidity with intensifying climate change and anthropogenic development, the knowledge gained from this study will allow for improved environmental impact assessment and predictive modelling for future coral reef conservation. [ABSTRACT FROM AUTHOR]

The diet of widely distributed species is influenced by the availability of food resources, which can vary according to local conditions. Thus, heterogeneity in diet patterns can help understand population structure and illustrate biogeographic boundaries. In this study, published and unpublished datasets of regurgitated material and stable isotopes of carbon (δ13C) and nitrogen (δ15N) from whole blood of brown boobies (Sula leucogaster) in the southwestern Atlantic Ocean (27°51′S to 0°55′N) were used to assess dietary spatial patterns. The variations in prey composition and isotopic niche breadth were associated with colony location (coastal/oceanic), genetic population structure, and marine biogeographic zonings—Large Marine Ecosystems, Longhurst's Biogeochemical Provinces, and Spalding's Provinces and Ecoregions. Boobies from coastal and southern colonies showed higher diversity in their diet compared with boobies from oceanic and northern colonies, given the presence of demersal taxa associated with bottom trawling discards. The variation in prey composition from regurgitates and stable isotopes was well framed with genetic structure and biogeographic boundaries, although less fitting with Spalding's zoning. The brown booby showed trophic plasticity throughout the study area, suggesting that their diet is shaped by food resources available around the colonies, including those from fishery discards. These results demonstrate that highly mobile vertebrates are potentially useful samplers of the marine environment, able to indicate the diversity of prey organisms available in the foraging area through diet, and support biogeographic zonings. Furthermore, diet composition associated with population structure sheds light on local adaptation as a potential mechanism for promoting/disrupting gene flow in seabirds. [ABSTRACT FROM AUTHOR]

Many traits including trophic niche parameters are attributed to species. However, generalist species may vary in trophic niches with environments, making species‐based knowledge hard to extrapolate beyond local food webs. Here we tested trophic consistency in oribatid mite species (Acari), one of the most abundant arthropods that occupy all trophic levels in soil food webs. We used stable isotope analysis to compare trophic niches of 40 Oribatida species that co‐occur in litter (OL) and soil (0–5 cm, mainly OF/H, AH) of five forest types (native European beech, non‐native Douglas fir, range‐expanding Norway spruce, two beech–conifer mixed forests). Although stable isotope signatures of bulk material differed between litter and soil, 13C and 15 N values of Oribatida species were remarkably stable irrespective of soil depth. Furthermore, Oribatida were more enriched in 13C in European beech than in coniferous forests, but forest type little affected 15 N values of Oribatida across a range of site conditions. We conclude that Oribatida species occupy virtually identical trophic niches (δ13C and δ15N values) irrespective of the soil depth they colonize and that forest management including non‐native tree species little affects trophic position (δ15N values) of oribatid mites. Our findings suggest that the trophic position can be used as a trait in community analysis of Oribatida across forest ecosystems. Our results further indicate that trophic niches of generalist species can be highly consistent irrespective of environment. [ABSTRACT FROM AUTHOR]

Simple Summary: The population of the pipefish Syngnathus acus inhabiting Cíes Archipelago (NW Spain) was monitored in 2017–2018 for spatial and temporal changes in abundances, reproduction traits, trophic niche occupancy, and dietary regimes across reproduction states, through an isotopic (δ13C and δ15N) approach. The population consisted almost exclusively of large adults, whose abundances decreased significantly from mid-autumn after the breeding season. S. acus is a secondary consumer that prefers amphipods, but mature specimens were less selective than immature fish. The present study highlights the outstanding size of the fish and the exceptional occurrence of breeders on the studied area. The great pipefish Syngnathus acus is one of the most representative European syngnathids, being highly associated with seagrass and macroalgal beds. Surprisingly, the ecology of this large ovoviviparous marine fish has received scanty attention. The population inhabiting three sites on Cíes Archipelago (Atlantic Islands National Park, NW Spain) was monitored in 2017–2018 for spatial and temporal changes in abundances, reproduction traits, trophic niche occupancy, and dietary regimes across reproduction states, through an isotopic (δ13C and δ15N) approach. Abundances were highly variable across seasons and sites, decreasing significantly from mid-autumn. The population consisted almost exclusively of large adults that migrate by the end of the breeding season, which extended from mid-spring to summer. Operational sex ratios suggest that the species is sex-role reversed. S. acus is a secondary consumer (Trophic position = 3.36 ± 0.05), preferring amphipods but displaying annual and seasonal dietary plasticity. Mature fish were less selective than immatures (especially females), with a higher preference for amphipods (36–68%) in the former. The second most-preferred prey were carideans, copepods, or isopods, depending on the year and the reproduction state. Overall, the wider trophic niches in females and immature specimens compared to males and mature fish would indicate a higher variability in both the use of prey resources and/or their origin. The present study highlights the trophic plasticity and unique features of S. acus population in the Cíes Archipelago, especially regarding the outstanding size of the fish and the exceptional occurrence of breeders. [ABSTRACT FROM AUTHOR]

As the environment is getting warmer and species are redistributed, consumers can be forced to adjust their interactions with available prey, and this could have cascading effects within food webs. To better understand the capacity for foraging flexibility, our study aimed to determine the diet variability of an ectotherm omnivore inhabiting kelp forests, the sea urchin Echinus esculentus, along its entire latitudinal distribution in the northeast Atlantic. Using a combination of gut content and stable isotope analyses, we determined the diet and trophic position of sea urchins at sites in Portugal (42° N), France (49° N), southern Norway (63° N), and northern Norway (70° N), and related these results to the local abundance and distribution of putative food items. With mean estimated trophic levels ranging from 2.4 to 4.6, omnivory and diet varied substantially within and between sites but not across latitudes. Diet composition generally reflected prey availability within epiphyte or understorey assemblages, with local affinities demonstrating that the sea urchin adjusts its foraging to match the small-scale distribution of food items. A net "preference" for epiphytic food sources was found in northern Norway, where understorey food was limited compared to other regions. We conclude that diet change may occur in response to food source redistribution at multiple spatial scales (microhabitats, sites, regions). Across these scales, the way that key consumers alter their foraging in response to food availability can have important implication for food web dynamics and ecosystem functions along current and future environmental gradients. [ABSTRACT FROM AUTHOR]

The colonization of novel reservoirs tends to support opportunistic species that undergo mass proliferation after the reservoir is formed. It is common that in this process, a species will change its diet based on resource availability. This is the case in the Salto Caxias reservoir, Iguaçu River, where five Astyanax species presented changes in their diets after damming. The present study aimed to evaluate possible changes in the feeding activity and condition factor of five sympatric species of Astyanax in the Salto Caxias reservoir in different areas impacted by damming. Sampling was carried out before and after damming the Salto Caxias reservoir. The fish feeding activity and nutritional status were inferred by the mean stomach repletion index and the mean condition factor, respectively. Most of the studied species showed a general decrease in feeding activity and condition factor. Both studied regions, the upstream region and the dam region, presented changes in the analyzed factors. These observations suggest that regardless of diet changes, nutritional status is negatively impacted in altered environments. The nutritional deficit occurs (i) if the diet is altered due to adaptive limitations on the use of the available resources and (ii) if the diet remains unaltered due to the scarcity of the preferred feeding resource. Such decreases might lead to reductions in the population size due to limitations on growth and reproduction until the environment feeding resources can sustain those populations. [ABSTRACT FROM AUTHOR]

The invasion of non-native fishes is a leading cause of extinction and imperilment of native freshwater fishes. Evidence suggests that introduced species with generalist diets have the potential for greatest impacts through competition and predation even though populations are often comprised of specialist individuals. The northern pike (Esox lucius), a predatory fish, has been widely introduced outside its native range for recreational fishing purposes, especially in western North America, and it has been implicated in declines and extirpations of native fishes. We synthesized over 2900 individual northern pike diet records across 31 waterbodies from the native and introduced ranges in Alaska to quantify the extent of diet specialization and generalization relative to freshwater prey communities. To control for effects of ontogenetic diet shifts, we separately analyzed major size classes of northern pike and inferred and visualized trophic plasticity from prey-specific abundance indices and ordination. Diet generalization was common in northern pike among waterbodies and usually consisted of individuals consuming macroinvertebrates. However, when available, individual northern pike diets showed specialization on fishes, amphibians, small mammals, and dragonflies. The reliance on macroinvertebrate prey by northern pike from small, isolated lakes in the native and invasive ranges suggests that dietary plasticity facilitates persistence of these predators in the absence of preferred fish prey. Broadly, this synthesis supports the hypothesis that trophic plasticity and diet generalization widely occur among invasive and native populations of northern pike which is likely to enhance the probability of introduction success, exacerbate their environmental impacts, and complicate management of this potentially invasive freshwater predator. [ABSTRACT FROM AUTHOR]

Abiotic change can alter species interactions by modifying species' trophic roles, but this has not been well studied. Until now, bromeliad-dwelling tipulid larvae were thought to positively affect other macroinvertebrates via a facilitative processing chain. However, under drought, we found the opposite. We performed two microcosm experiments in which we factorially manipulated water level and predation by tipulids, and measured the effects on mosquito and chironomid larvae. The experiments differed in whether high water was contrasted with low or no water, allowing us to distinguish between the effects of desiccation stress (no water) and increased encounter rates due to compression of habitat or reductions in prey mobility (low and no water). We also included a caged tipulid treatment to measure any non-consumptive effects. As well as directly reducing prey survival, reductions in water level indirectly decreased chironomid and mosquito survival by altering the trophic role of tipulids. Our results suggest that increased encounter rates with prey led to tipulids becoming predatory under simulated drought, as tipulids consumed prey under both low and no water. When water level was high, tipulids exerted negative non-consumptive effects on prey survival. Because opportunistic predators are common throughout aquatic ecosystems, the effects of drought on the trophic roles of species may be widespread. Such restructuring of food webs should be considered when attempting to predict the ecological effects of environmental change. [ABSTRACT FROM AUTHOR]

Running waters are among the most threatened ecosystems globally, having altered hydrological regimes, homogenized habitat, and impaired water quality. These multiple stressors impact aquatic biodiversity and ecosystem function across space and time, although a clear mechanistic understanding is still lacking. Here, we examined the trophic response of macroinvertebrates among streams in a Swiss lowland catchment encompassing a gradient of land uses. Clear compositional changes were observed as anthropogenic impacts increased from least-impacted to agricultural and urbanized sites. Taxonomic diversity was lowest at sites with morphological and water quality impairment (agricultural sites), whereas taxonomic identity (susceptible vs. generalist species) mainly changed due to water quality degradation (agricultural and urban sites) based on the SPEAR (pesticides) index. Using stable isotopes (δC, δN), a simplification in macroinvertebrate trophic structure was evident along the land use gradient. At a site receiving wastewater treatment effluent, stable isotopes also revealed trophic shifts in primary consumers that corresponded to changes in available food resources. Results further showed that some taxa losses, e.g., the mayfly Ecdyonurus, to land- use effects may be due to low trophic plasticity. The combination of analyses, including stable isotopes, provided an improved mechanistic understanding of community and population responses to land-use changes along river networks. [ABSTRACT FROM AUTHOR]

In some environments, species may exhibit trophic plasticity, which allows them to extend beyond their assigned functional group. For Gammarus minus, a freshwater amphipod classified as a shredder or detritivore, cave populations have been observed consuming heterotrophs as well as shredding leaves, and therefore may be exhibiting trophic plasticity. To test this possibility, we examined the C and N stable isotope and C/N ratios for cave and spring populations of G. minus. A 15-day feeding experiment using leaves and G. minus from a spring population established that the diet-tissue discrimination factor was 3.2 ‰ for δN. Cave G. minus were 8 ‰ higher in δN relative to cave leaves, indicating they did not derive nitrogen from leaves, whereas field collected spring populations were 2-3 ‰ higher than spring leaves, indicating that they did. Cave G. minus were 2.6 ‰ higher in δN than the cave isopod, Caecidotea holsingeri. Relative to spring populations, Organ Cave G. minus were N enriched by 6 ‰, suggesting they occupied a different trophic level, or incorporated an isotopically distinct N source. While stable isotopes cannot tell what the cave G. minus are eating, the isotopes certainly show that G. minus are not eating leaves and are trophically distinct form the surface populations. Differences in C/N ratios were observed, but reflect the size of the G. minus examined and not feeding group or habitat. The isotope data strongly support the hypothesis that cave populations of G. minus have become generalist or omnivorous by including animal protein in their diet. [ABSTRACT FROM AUTHOR]

Two phenotypes are present within the European eel population: broad-heads and narrow-heads. The expression of these phenotypes has been linked to several factors, such as diet and differential growth. The exact factors causing this dimorphism, however, are still unknown. In this study, we performed a feeding experiment on glass eels from the moment they start to feed. Eels were either fed a hard diet, which required biting and spinning behavior, or a soft diet, which required suction feeding. We found that the hard feeders develop a broader head and a larger adductor mandibulae region than eels that were fed a soft diet, implying that the hard feeders are capable of larger bite forces. Next to this, soft feeders develop a sharper and narrower head, which could reduce hydrodynamic drag, allowing more rapid strikes towards their prey. Both phenotypes were found in a control group, which were given a combination of both diets. These phenotypes were, however, not as extreme as the hard or the soft feeding group, indicating that some specimens are more likely to consume hard prey and others soft prey, but that they do not selectively eat one of both diets. In conclusion, we found that diet is a major factor influencing head shape in European eel and this ability to specialize in feeding on hard or soft prey could decrease intra-specific competition in European eel populations. [ABSTRACT FROM AUTHOR]

In this study, the feeding apparatus (gill rakers, GR) and the diet composition of European sardine Sardina pilchardus populations living in two contrasting environments were compared: the upwelling area off western Iberia and the comparatively less productive region of the north-western Mediterranean Sea. The importance of local adaptations in the trophic ecology of this species was estimated. Sardina pilchardus from the Atlantic Iberian coast and from the north-western Mediterranean Sea have clear differences in the feeding apparatus and diet compositions. Those from the Atlantic Iberian coast have significantly more GRs than S. pilchardus of the same size range in the Mediterranean Sea. While S. pilchardus from the Mediterranean Sea mostly depend on prey ranging between 750-1500 and 3000-4000 µm, corresponding mostly to cladocerans, decapods and copepods, those from the Atlantic depend on smaller prey (50-500 and 1000-1500 µm) that include phytoplankton and copepods, particularly during summer months, and S. pilchardus eggs during the winter. The marked difference between the trophic ecology of S. pilchardus in the two areas studied appears to have originated from different dietary strategies that the two populations have adopted in contrasting feeding environments. These differences are shown to profoundly affect the size and quality of prey consumed, and the effect of cannibalism on the populations. [ABSTRACT FROM AUTHOR]

We tested the hypothesis that the highly flexible feeding repertoire of juvenile Chaetodipterus faber reflects their trophic adaptability by quantifying the feeding behaviour of juveniles in situ, for the first time, in a northeastern Brazilian estuary. The fishes presented a preference for alga-rich habitats, irrespective of the substrate type chosen during feeding bouts. The analysis of stomach contents revealed omnivorous feeding habits, indicating that the ingestion of plant material occurs incidentally during foraging for benthic prey hidden under the alga. Particulate feeding in the water column was often as important as bottom feeding on alga-rich substrates. The results of this study are consistent with those of other ephippid species in different coastal environments, which typically exploit an ample diversity of food items from different substrates. Therefore, the flexibility observed in the feeding behavior of the most ephippid species may be a fundamental determinant of the ecological success of this group. [ABSTRACT FROM AUTHOR]

Following up on previous investigations on the stress resistance of corals, this study assessed the trophic plasticity of the coral Stylophora subseriata in the Spermonde Archipelago (Indonesia) along an eutrophication gradient. Trophic plasticity was assessed in terms of lipid content and fatty acid composition in the holobiont relative to its plankton (50-300 μm) food as well as the zooxanthellae density, lipid, FA and chlorophyll a content. A cross-transplantation experiment was carried out for 1.5 months in order to assess the trophic potential of corals. Corals, which live in the eutrophied nearshore area showed higher zooxanthellae and chlorophyll a values and higher amounts of the dinoflagellate biomarker FA 18:4n-3. Their lipid contents were maintained at similar to levels from specimens further away from the anthropogenic impact source going up to 14.9 ± 0.9 %. A similarity percentage analysis of the groups holobiont, zooxanthellae and plankton >55 μm found that differences between the FA composition of the holobiont and zooxanthellae symbionts were more distinct in the site closer to the shore, thus heterotrophic feeding became more important. Transplanted corals attained very similar zooxanthellae, chlorophyll a and lipid values at all sites as the specimens originating from those sites, which indicates a high potential for trophic plasticity in the case of a change in food sources, which makes this species competitive and resistant to eutrophication. [ABSTRACT FROM AUTHOR]

1. Rainbow ( Oncorhynchus mykiss) and brown trout ( Salmo trutta) are widespread and invasive salmonids with important lethal effects as predators, although indirect effects are also possible. We used stable isotope analyses (δ15N, δ13C) to explore how the density of invasive trout in 25 Patagonian lakes alters the trophic niche (TN) of a widespread native fish, Galaxias platei (Galaxiidae). We also explored how the density of the galaxiid influences the TN of invasive trout. 2. We quantified two aspects of the TN: (i) the proportion of littoral carbon (PL) and (ii) trophic height (TH) (i.e. the 'height' at which the fish feeds in the food web). We related these measures of TN in a given species to the density of other species (as estimated by catch-per-unit-effort). 3. As G. platei body size increased, their PL increased (increasing littoral feeding) in several lakes. However, none of the fish species investigated showed changes in PL with increasing density of the other fish species. TH increased with body size in all three species. In addition, the TH of large G. platei declined with increasing trout density and, reciprocally, the TH of large S. trutta decreased with decreasing G. platei density. 4. The reciprocal effects of native and the invasive fish on TH were as large as a shift of one trophic level. This pattern is consistent with an exhaustion of galaxiid prey for both piscivorous G. platei and S. trutta in lakes with high trout density. 5. These finding support the suggested management strategy of culling trout from overpopulated lakes, which should simultaneously protect native fish and enhance a lucrative sport fishery for large trout. [ABSTRACT FROM AUTHOR]

The fish community of Lake Victoria, East Africa, has continued to exhibit an intriguing degree of resiliency despite stress from anthropogenic activities. Frequent environmental perturbations include wild fluctuations in fishing pressure, limnological conditions, and lake levels. Surprisingly, many of the endemic and other indigenous fishes have survived, and some have even increased in numbers in recent years. While a positive development, this resiliency is a red flag to scientists because we do not understand it, or know whether it can be expected to continue. Furthermore, besides issues of immediate human well-being, there remain grave concerns about long term resource sustainability. This paper explores possible reasons for ecological resilience in the Lake Victoria fish community, with a focus on omnivory and functional redundancy as possible explanations. The analysis used published data based on both traditional gut content analysis (GCA) and stable isotope analysis (SIA). Trophic plasticity is ubiquitous among the surviving fishes of Lake Victoria. This, combined with an overall simplification of the food web, contributed to the lake community's current resilience. [ABSTRACT FROM AUTHOR]

This study describes experimental herbivory and detritivory of three common native aquatic macrophyte species by the introduced Mozambique tilapia Oreochromis mossambicus (Peters) (Pisces: Cichlidae), and its physiological response to their consumption. There was a highly significant effect of fish herbivory on plant weight for each of the macrophyte species, but this effect was not influenced by any preference for periphyton. Despite the herbivory, there was a highly significant loss of fish body weight across all plant species and weight could only be maintained by supplementary feeding of a high protein fish flake. These results suggest that despite eating these plants, an alternative food resource may be needed for survival and may trigger trophic plasticity in O. mossambicus. [ABSTRACT FROM AUTHOR]

Experimental tanks were used to observe predatory effects in three different size classes of Mozambique tilapia Oreochromis mossambicus (one of the world's most widespread exotic species and generally regarded to be a herbivore or both herbivore and detritivore) when tested against 10 juvenile Australian freshwater fish species, and significant levels of predation against all were recorded. There was a general trend for larger O. mossambicus to kill more prey and this was also reflected in a separate series of experiments using juvenile barramundi Lates calcarifer over a range of size classes. Predatory effects by O. mossambicus broadly reflected the accepted models of predator–prey interactions, being that mortality (and survival) was closely related to relative body size and mouth gape limitation. Experimental evidence for piscivory in O. mossambicus was supported by field sampling that detected prey fish remains in 16% of all fish surveyed ( n = 176). The recognition of active piscivory by O. mossambicus in laboratory and field situations is the first such evidence, and suggests a need to re-evaluate the nature of their effects in introduced environments. [ABSTRACT FROM AUTHOR]