Warming is among the major drivers of changes in biotic interactions and, in turn, ecosystem functioning. The decomposition process occurs in a chain of facilitative interactions between detritivores and microorganisms. It remains unclear, however, what effect warming may have on the interrelations between detritivores and microorganisms, and the consequences for the functioning of natural freshwater ecosystems. To address these gaps, we performed a field experiment using tank bromeliads and their associated aquatic fauna. We manipulated the presence of bacteria and detritivorous macroinvertebrates (control, "bacteria," and "bacteria + macroinvertebrates") under ambient and warming scenarios, and analyzed the effects on the microorganisms and ecosystem functioning (detritus mass loss, colored dissolved organic matter, and nitrogen flux). We applied antibiotic solution to eliminate or reduce bacteria from control bromeliads. After 60 days incubation, bacterial density was higher in the presence than in the absence of macroinvertebrates. In the absence of macroinvertebrates, temperature did not influence bacterial density. However, in the presence of macroinvertebrates, bacterial density decreased by 54% with warming. The magnitude of the effects of organisms on ecosystem functioning was higher in the combined presence of bacteria and macroinvertebrates. However, warming reduced the overall positive effects of detritivores on bacterial density, which in turn, cascaded down to ecosystem functioning by decreasing decomposition and nitrogen flux. These results show the existence of facilitative mechanisms between bacteria and detritivores in the decomposition process, which might collapse due to warming. Detritivores seem to contribute to nutrient cycling as they facilitate bacterial populations, probably by increasing nutrient input (feces) in the ecosystem. However, increased temperature mitigated these beneficial effects. Our results add to a growing research body that shows that warming can affect the structure of aquatic communities, and highlight the importance of considering the interactive effects between facilitation and climatic drivers on the functioning of freshwater ecosystems.

1. Non‐trophic interactions between plants and animals can affect community structure and species trait composition. However, it is unclear how changes in intra‐ and interspecific morphological traits of plant species affect non‐trophic interactions at a metacommunity scale. Additionally, whether plant evolutionary history determines taxonomic and functional diversity of plant‐dwelling predators is an open question. 2. To address these gaps, this study used a published dataset with spiders dwelling exclusively on bromeliads to investigate if: (i) intra‐ and interspecific variability in host plant morphological traits affects spider taxonomic and functional diversity; and (ii) bromeliad trait evolution determines present‐day patterns of spider trait diversity. 3. Spider and bromeliad traits were measured, and a new statistical framework was used to quantify the response of spider beta diversity to intra‐ and interspecific variation in bromeliad traits. In addition, bromeliad traits were decomposed across its phylogenetic tree to check whether the current variation in morphological traits of bromeliads is a result of either ancestral or recent diversification. 4. Bromeliad intraspecific variation did not affect spiders, but leaf length variation between bromeliad species had a positive effect on spider functional beta diversity. Interestingly, the most ancestral split between two subfamilies explained most of the variation in bromeliad species, which suggests that spider functional diversity could represent an outcome of bromeliad evolutionary history. 5. Overall, the results of this study suggest that interactions between plants and organisms that do not feed directly on their tissues could be shaped by plant evolutionary history, which in turn suggests that non‐trophic interactions can be maintained over time.

1.A key challenge in the study of mutualistic interactions is understanding sources of variation that strengthen or weaken these interactions. In spider-plant mutualisms, spiders benefit plants by improving plant nutrition and protecting plants from herbivory. Although the benefits of plants to spider growth and survival are often claimed, they are rarely demonstrated.2. In this study, empirical evidence is provided that bromeliads (Bromelia balansae, Bromeliaceae) are essential for the resilience of the mutualistic bromeliad-living jumping spider populations (Psecas chapoda, Salticidae) after a fire event, sheltering spiders from the heat of the flames.3. Spider populations were compared before and after a natural fire event and it was shown that spiders of different ages survived the fire. The survival of such individuals allowed the population of P. chapoda spiders to recover rapidly, returning to pre-fire levels in 5 months.4. Bromeliads reduced the susceptibility of P. chapoda spiders to burning, and this mutualistic relationship contributed to the resilience of the spider population after a fire event. It is suggested that frequent fires in fire-prone landscapes may have strengthened this spider-plant relationship, contributing to the maintenance and evolution of this association.