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Global change drivers including eutrophication, hydrological disturbance, climate change, chemical pollution, overexploitation, invasive species, and land-use change are affecting the function and ...

Unravelling the effect of climate variability on species biology has been one of the main goals of ecological studies. Environmental factors such as river discharge and temperature have being proposed as triggers of reproductive cycle in fish. In temperate climates, fish reproduction is affected mainly by temperature, while is influenced by flood pulses in large tropical rivers. We evaluated the influence of temperature and river discharge as triggers of Iheringichthys labrosus’ reproduction. We studied the following reproductive variables: gonadosomatic index (GSI), hepatosomatic index (HSI) and condition factor (K). Females of I. labrosus were examined in a time series of ten years along three sites located in Lower Uruguay River at the beginning (last week of November‐first week of December, spring) and by the end of the reproductive period (middle‐end of April, autumn). Generalised linear models detected a positive effect of mean winter temperature and site on the spring mature female GSI. Site was significant in addition to the interaction between temperature and site. Moreover, the effect of winter temperature was stronger than water discharge in triggering reproductive timing of I. labrosus, contrary to the model proposed for other species in tropical systems. Additionally, a literature review suggested a latitudinal gradient on reproduction, occurring earlier and prolonged with decreasing latitude (and increasing temperature). In this study, we stated the effect of temperature on the life history in a Neotropical fish using a multifaceted approach, particularly important in the current context of global climate warming.

Forest change is a major environmental problem worldwide. Forest streams, with their large aquatic–terrestrial interface and strong dependence on terrestrially derived organic matter, are highly sensitive to forest changes. Fast-wood plantations can be particularly threatening if they markedly differ from native forests. Eucalyptus plantations, in particular, cover large areas worldwide (> 20 million ha, mostly from 35°S to 35°N), but their effects on stream functioning have been addressed mostly in the Iberian Peninsula, which limits generalization to other regions. We assessed the effect of eucalyptus plantations on total (microbial decomposers and macroinvertebrates; in coarse mesh bags) and microbial-driven (in fine mesh bags) leaf litter decomposition by comparing streams flowing through native forests and eucalyptus plantations in seven regions in the Iberian Peninsula, Central Africa and South America. We found an overall significant inhibition of total litter decomposition by 23%. The effect did not significantly differ across regions, although a significant inhibition was found for Spain (− 41%), South Brazil (− 31%) and Uruguay (− 36%) (Portugal had a marginally nonsignificant inhibition by 50%) but not for other regions, suggesting that the effects of plantations in temperate climates are mediated through effects on macroinvertebrate communities. Contrarily, the overall effect for microbial-driven litter decomposition was non-significant, but it significantly differed across regions with a significant stimulation in Central Brazil (110%) and Uruguay (32%), and nonsignificant effects for other regions (Kenya had a marginally nonsignificant inhibition by 48%), suggesting that functional redundancy among microbial communities is not general and effects can occur if plantations induce changes in nutrient availability, solar irradiation or litter characteristics.

Sudden increases in temperature and turbidity in aquatic ecosystems are expected for different regions in the future, as a result of the more frequent extreme climatic events that are predicted. The consequences of these abrupt changes in the outcomes of predator&ndash, prey interactions are unknown. Here, we tested the effects of a heat wave and a turbidity pulse on the foraging success of a subtropical cichlid fish (Gymnogeophagus terrapurpura) on amphipods (Hyalella curvispina). We carried out a short-term experiment combining treatments of turbidity (3 and 100 nephelometric turbidity units [NTU]) and water temperature (19.2, 22.2, 25.2 and 27.0 &deg, C), considering potential differences given by fish length. Changes in water temperature did not promote significant changes in prey consumption. Higher turbidity, in contrast, decreased prey consumption. Also, we found that fish with different body lengths consumed a similar amount of prey under clear waters, but, in turbid waters, bigger individuals were more efficient than the smaller individuals. This finding is an empirical demonstration that the effect of increased turbidity on predation rate depends upon predator body size, and it suggests that bigger body sizes may help overcome turbidity-associated limitations in finding and capturing prey. Our short-term results suggest that, if turbidity pulses and heat waves become more frequent in the future, the outcome of fish&ndash, invertebrate interaction can be affected by local characteristics such as fish population size distribution.

This article belongs to the Special Issue Trophic Interactions in Warm Freshwater Ecosystems The Neotropics represent a hotspot for freshwater biodiversity with vast number of fish species of scarce ecological knowledge. This holds true for the Uruguay River, where fish assemblages and their diets remain unexplored. Fish assemblages were surveyed in 14 sites along the river main course, from headwaters to mouth (approximately 1800 km), with the aim to identify the trophic roles of fishes and to describe trophic structure of these assemblages, following standardized sampling campaigns and laboratory procedures. One hundred species (2309 gut contents) were analysed and classified into four trophic groups subdivided into eight lower-level groups: Piscivore, piscivore-invertivore, detritivore, omnivore-detritivore, omnivore-invertivore, omnivore-planktivore and omnivore-herbivore. The trophic structure of the assemblages varied along the river, with the relative species richness of fish consuming terrestrial invertebrates increasing towards the middle river section, probably driven by the large floodplains in that areas, supporting global theories such as the flood pulse concept. This study describes the feeding habits of fish along the Uruguay River, being the first dietary description for 29 species. This knowledge is essential for management and conservation, serving as baseline in the context of future environmental changes while generating novel evidence on the functioning of ecosystems in this scarcely studied climatic region.

The trophic structure of fish assemblages often varies seasonally, following the changes in food availability and supposedly water temperature. To unveil potential drivers of trophic shifts, we studied changes in fish trophic structure at both whole-assemblage and species levels at contrasting food availability and water temperatures in a subtropical stream. We analysed the diet of the most abundant omnivorous species (Bryconamericus iheringii) monthly along the year, searching for relationships with environmental variables changing seasonally (i.e. temperature and water level) and with fish reproductive stage. We ran a single-species food choice field experiment with fixed animal and vegetal food availability in contrasting seasons to test food availability as driver of diet shifts. At the assemblage level, we found a higher consumption of vegetal during summer, reflecting the increased proportion of vegetal in the diet of omnivores, which dominated the assemblage. At the species level, the enhanced vegetal consumption was related to increases in temperature and reduction in water level. Moreover, fish selected for vegetal during summer and for animal food in winter under experimental conditions. Our findings support the role of temperature driving food web dynamics by increasing fish herbivory towards warmer scenarios, with potential strong implications for whole-assemblage trophic structure.