1. The interspecific interactions within and between adjacent ecosystems strongly depend on the changes in their abiotic and biotic components. However, little is known about how climate change and biodiversity loss in a specific ecosystem can impact the multiple trophic interactions of different biological groups within and across ecosystems.
2. We used natural micro-ecosystems (tank-bromeliads) as a model system to investigate the main and interactive effects of aquatic warming and aquatic top predator loss (i.e., trophic downgrading) on trophic relationships in three integrated food web compartments: i) aquatic microorganisms, ii) aquatic macroorganisms, and iii) terrestrial predators (i.e., via cross ecosystem effects).
3. The aquatic top predator loss substantially impacted the three food web compartments. In the aquatic macrofauna compartment, trophic downgrading increased the filter-feeder richness and abundance directly and indirectly via an increase of detritivore richness, likely through a facilitative interaction. For the microbiota compartment, aquatic top predator loss had a negative effect on algae richness, probably via decreasing the input of nutrients from predator biological activities. Furthermore, the more active terrestrial predators responded more to aquatic top predator loss, via an increase of some components of aquatic macrofauna, than more stationary terrestrial predators. The aquatic trophic downgrading indirectly altered the richness and abundance of cursorial terrestrial predators, but these effects had different direction according to the aquatic functional group, filter-feeder or other detritivores. The web-building predators were indirectly affected by aquatic trophic downgrading due to increased filter-feeder richness. Aquatic warming did not affect the aquatic micro- or macro-organisms but did positively affect the abundance of web-building terrestrial predators.
4. These results allow us to raise a predictive framework of how different anthropogenic changes predicted for the next decades, such as aquatic warming and top predator loss, could differentially affect multiple biological groups through interactions within and across ecosystems.

We conducted the study at the Serra do Mar State Park, Nucleo Picinguaba, on the northern coast of the state of São Paulo, Brazil, from April to July 2014. The bromeliad species Neoregelia johannis (Carriere) LB Smith. (Bromeliaceae) were employed as a model system in the experiment. Our study investigated how aquatic warming and the loss of top aquatic predators affect the food web structure of aquatic macrofauna and microfauna, as well as multiple groups of terrestrial predators. Temperature manipulations here predicted warming for the next decades in the study site, i.e., an average projected for 2040 (2°C above ambient), and 2100 (4°C above ambient). To sample the aquatic microbiota organisms, we homogenized the bromeliad water, collected 2 ml, and fixed it with 5% Lugol for counting and identifying microscopic algae, protozoa, and metazoa (hereafter referred to as microbiota). To sample macrofauna organisms at the end of the experiment, we first sampled the terrestrial organisms foraging upon the experimental tank-bromeliads (e.g., spiders, centipeds, ants). After that, we dissected and washed the bromeliads. Then, we separated terrestrial and aquatic organisms found in the trays, counted, fixed, and later identified the organisms to the lowest possible taxonomic level and functional group (Antiqueira et al., 2018a). The details of the sampling and characterization of macrofauna and microfauna are described in Appendix 1 of the paper. The consumer-resource relationships between all the macrofauna and microbiota were determined according to specific literature and field observation.