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In lotic ecosystems, a higher availability of allochthonous food resources is expected during floods and rainfall events, which may yield a higher consumption of these resources by consumers. However, allochthonous input and seasonality in environmental conditions are locally dependent. Thus, dietary responses of freshwater consumers to seasonality should also be locally dependent. Herein, we applied a meta‐analytical approach to identify the spatial and seasonal environmental variables associated with the relative consumption of allochthonous food resources by fishes from tropical lotic ecosystems in different seasons.We gathered 566 observations of the diet of fish populations (i.e., restricted to the same sampling event) from 38 studies conducted in 70 localities across the tropics during flood and drought periods (hereafter, high‐water and low‐water periods, respectively). We retrieved latitude, seasonal channel width, elevation and two proxies for allochthonous input for each locality: terrestrial biomass (without considering seasonality) and the normalised difference vegetation index (NDVI; considering seasonality). Then, we applied meta‐regression models using these environmental variables as predictors and the proportion of allochthonous food resources in each consumer's diet (%Allo) as the response variable.Our models revealed that the diet of fishes from tropical lotic ecosystems is mostly autochthonous‐based, independent of the hydrological period (high‐water or low‐water), and aquatic invertebrates were the most consumed food items. Terrestrial vegetation biomass and elevation predicted increasing allochthony in the diet of tropical fishes for high‐water, but only terrestrial biomass predicted allochthony at low‐water periods. We found no relationship between latitude, channel width or NDVI with allochthony.Our study highlights the importance of considering the hierarchical level of biological organisation and fish trophic guilds for understanding seasonal patterns of relative consumption of allochthonous and autochthonous food resources by fishes. We also argue that variations in seasonality across the tropics are likely to have undermined its influence on allochthony in fish diets. The absence of a non‐relationship between channel width and allochthony provides evidence that the River Continuum Concept is better suited to temperate lotic ecosystems.Our results provide novel insights and the big‐picture of seasonal pattern in the diets of tropical fishes for use in future local empirical studies, improving forecasting of the relationship between the factors underpinning the availability of allochthonous and autochthonous food resources, and the diet of freshwater fishes. [ABSTRACT FROM AUTHOR]

Context: The collapse of a tailings dam in Brumadinho (Brazil) is considered one of the largest mining disasters worldwide. The mine tailings polluted the water and sediment of the Paraopeba River downstream of the collapsed dam. The effects of the tailings on biological communities remain unknown. Aims: We evaluated the effects of the tailings dam collapse on aquatic macroinvertebrate assemblages in the Paraopeba River and highlighted a potential bioindicator for the cumulative effects of the mine tailings spill. Methods: We sampled the macroinvertebrates upstream and downstream of the collapsed dam during the first dry and wet seasons following the collapse. Key results: We found that turbidity (likely non-related to the tailings) negatively affected the macroinvertebrates' abundance, but the richness was negatively affected by the presence of the mine tailings. The riparian land use negatively affected the macroinvertebrate richness and composition. We identified Helicopsyche spp. as a bioindicator. Conclusions: We provide circumstantial evidence of the effects of mine tailings on aquatic macroinvertebrates, suggesting that it may have affected their richness and caused the loss of Helicopsyche spp. in the most affected sites. Implications: We suggest that the richness and Helicopsyche spp. are potential biomonitoring tools for evaluating the effects of the tailings dam collapse on the macroinvertebrate assemblages. Aquatic macroinvertebrates can change their abundances, the number of 'species' and their presence in rivers because of environmental changes. The mud spill in the Paraopeba River is a major environmental change in this ecosystem. We observed that that mud spill might have reduced the number of 'species' of aquatic macroinvertebrates and induced the disappearance of a caddisfly 'species'. [ABSTRACT FROM AUTHOR]

Autochthonous biomass is heterogeneously distributed within freshwater ecosystems, shaping community structure and ecosystem functioning, yet few studies have evaluated how the spatial heterogeneity in the availability of the autochthonous resource affects its contribution to the diets of aquatic consumers. To fill this gap, we conducted a field survey to test whether the spatial heterogeneity of the autochthonous resource within freshwater ecosystems formed in tank bromeliads determines its contribution to the diet of aquatic consumers. Tank bromeliads are Neotropical plants with densely arranged leaves in a rosette shape that accumulate rainwater and terrestrial plant material, providing suitable habitat for a diversity of aquatic invertebrates. We sampled 3 regions (north, central, and south) of the bromeliad ecosystem to provide a natural gradient in the availability of the autochthonous resource (i.e., algae biomass). To trace the diets of aquatic consumers, we used stable isotope analysis of hydrogen coupled with Bayesian stable isotope mixing models. The availability of the autochthonous resource varied among the tank-bromeliad regions with light availability, but it was not related to its relative contribution to the diets of aquatic consumers. Instead, aquatic consumers from all regions showed similarly high degrees of autochthony. The capacity of aquatic consumers to move within the plant did not affect the contribution of the autochthonous resource to their diets. We reason that the contribution of the autochthonous resource to the diets of consumers is not related to its spatial distribution because aquatic consumers preferentially feed on this resource, even when its stocks are limited. In addition, water flow among tanks could provide a subsidy of the autochthonous resource from more productive to less productive regions. We conclude that spatial heterogeneity in the availability of the autochthonous resource does not limit its contribution to the diet of aquatic consumers because of active foraging on the autochthonous resource and the flux of this resource among compartments in freshwater tank-bromeliad ecosystems. [ABSTRACT FROM AUTHOR]

Climate change will alter the distribution of rainfall, with potential consequences for the hydrological dynamics of aquatic habitats. Hydrological stability can be an important determinant of diversity in temporary aquatic habitats, affecting species persistence and the importance of predation on community dynamics. As such, prey are not only affected by drought-induced mortality but also the risk of predation [a non-consumptive effect ( NCE)] and actual consumption by predators [a consumptive effect ( CE)]. Climate-induced changes in rainfall may directly, or via altered hydrological stability, affect predator-prey interactions and their cascading effects on the food web, but this has rarely been explored, especially in natural food webs. To address this question, we performed a field experiment using tank bromeliads and their aquatic food web, composed of predatory damselfly larvae, macroinvertebrate prey and bacteria. We manipulated the presence and consumption ability of damselfly larvae under three rainfall scenarios (ambient, few large rainfall events and several small rainfall events), recorded the hydrological dynamics within bromeliads and examined the effects on macroinvertebrate colonization, nutrient cycling and bacterial biomass and turnover. Despite our large perturbations of rainfall, rainfall scenario had no effect on the hydrological dynamics of bromeliads. As a result, macroinvertebrate colonization and nutrient cycling depended on the hydrological stability of bromeliads, with no direct effect of rainfall or predation. In contrast, rainfall scenario determined the direction of the indirect effects of predators on bacteria, driven by both predator CEs and NCEs. These results suggest that rainfall and the hydrological stability of bromeliads had indirect effects on the food web through changes in the CEs and NCEs of predators. We suggest that future studies should consider the importance of the variability in hydrological dynamics among habitats as well as the biological mechanisms underlying the ecological responses to climate change. [ABSTRACT FROM AUTHOR]