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Tropical floodplains secure the protein supply of millions of people, but only sound management can ensure the long‐term continuity of such ecosystem services. Overfishing is a widespread threat to multitrophic systems, but how it affects ecosystem functioning is poorly understood, particularly in tropical freshwater food webs. Models based on temperate lakes frequently assume that primary producers are mostly bottom‐up controlled by nutrient and light limitations, with negligible effects of top‐down forces. Yet this assumption remains untested in complex tropical freshwater systems experiencing marked spatiotemporal variation.We use consolidated community‐based fisheries management practices and spatial zoning to test the relative importance of bottom‐up versus top‐down drivers of phytoplankton biomass, controlling for the influence of local to landscape heterogeneity. Our study focuses on 58 large Amazonian floodplain lakes under different management regimes that resulted in a gradient of apex‐predator abundance. These lakes, distributed along ~600 km of a major tributary of the Amazon River, varied widely in size, structure, landscape context, and hydrological seasonality.Using generalised linear models, we show that community‐based fisheries management, which controls the density of apex predators, is the strongest predictor of phytoplankton biomass during the dry season, when lakes become discrete landscape units. Water transparency also emerges as an important bottom‐up factor, but phosphorus, nitrogen and several lake and landscape metrics had minor or no effects on phytoplankton biomass. During the wet‐season food pulse, when lakes become connected to adjacent water bodies and homogenise the landscape, only lake depth explained phytoplankton biomass.Synthesis and applications. Tropical freshwaters fisheries typically assume that fish biomass is controlled by bottom‐up mechanisms, so that overexploitation of large predators would not affect overall ecosystem productivity. Our results, however, show that top‐down forces are important drivers of primary productivity in tropical lakes, above and beyond the effects of bottom‐up factors. This helps us to understand the enormous success of community‐based 'fishing agreements' in the Amazon. Multiple stakeholders should embrace socio‐ecological management practices that shape both bottom‐up and top‐down forces to ensure biodiversity protection, sustainable fisheries yields and food security for local communities and regional economies. [ABSTRACT FROM AUTHOR]

Involving communities in sustainable wildlife management in tropical forests can ensure food security and livelihoods of millions of forest dwellers that depend on wild meat, and also safeguard hunted species. Mathematical models have been developed to assess hunting sustainability; but these require empirical information on reproductive parameters of the prey species, often challenging to obtain.Here, we suggest that if local people can accurately identify the reproductive status of hunted animals in the field, these data could fill the existing knowledge gap regarding species' life‐history traits and enable better assessments of hunting impacts.We first tested whether local people in 15 rural communities in three Amazonian sites could accurately diagnose, before and after training, the pregnancy status of hunted pacas Cuniculus paca, which we use as our model. We then applied the results from these tests to correct reproductive status data of hunted specimens, voluntarily collected over 17 years (2002–2018) as part of a citizen-science project in one of our study sites. We ran generalized additive models to contrast these corrected reproductive rates with those obtained from the direct analysis of genitalia by researchers, and with indices describing game extraction levels (catch‐per‐unit‐effort, CPUE, and age structure of hunted individuals).Before training, interviewees correctly diagnosed pregnancy in 72.5% of tests, but after training, interviewees accurately diagnosed pregnancy in 88.2% of tests, with high improvements especially for earlier pregnancy stages. Monthly pregnancy rates determined by hunters and by researchers were similar. Reported annual pregnancy rates were negatively correlated with CPUE, and positively correlated with the percentage of immatures in the hunted population, in accordance with an expected density‐dependent response to variations in hunting levels.Synthesis and applications. We show that the voluntary diagnosis of game species' reproductive status by local people is a feasible method to obtain accurate life‐history parameters for hunted tropical species, and to assess hunting effects on game populations. Given that almost half of the protected areas in the world are co‐managed by local people, our results confirm the potential of integrating local communities in citizen-science initiatives to ensure faster, low‐cost and more accurate data collection for wildlife management. [ABSTRACT FROM AUTHOR]