Changes in rainfall level and litter stoichiometry affect aquatic community and ecosystem processes in bromeliad phytotelmata

Abstract

Both N deposition and changes in precipitation amount are important components of global change and affect aquatic ecosystem functioning by altering the detrital quality and detrital processing rates by macroinvertebrates and microorganisms. Changes in precipitation pattern can also modify the physical structure of the ecosystem, determining habitat availability for aquatic organisms. Although these drivers can individually affect ecosystem structure and functioning, their interactive effects are poorly understood. To better understand the combined effects of detritus quality and precipitation regime on the structure and function of aquatic ecosystems we manipulated litter quality, by modifying N:P stoichiometry and rainfall amount on tropical natural aquatic microcosms (water‐holding epiphytic bromeliads). We performed an orthogonal manipulation of litter N:P ratio (natural N:P and high N:P) and rainfall levels (current level and predicted 40% increase for south‐eastern Brazil) Changes in litter quality affected the abundance of the aquatic organisms inhabiting bromeliads, including algae and bacteria. However, changes in litter quality combined with changes in precipitation levels affected only one group of macroinvertebrates, the Naididae worms (Oligochaeta) an important group of detritivores in the bromeliad systems. These combined drivers also affected the decomposition of organic matter by changing coloured organic matter concentrations, fine particulate matter biomass, and NH4+ concentrations in bromeliad tanks. The NH4+ concentration in bromeliad water was positively related with Naididae abundance, suggesting that these worms can act as ecosystem engineers by boosting N cycling. In both N:P treatments we observed a 50% decrease in N flux from litter to bromeliad leaves due to increases in nutrient leaching from the tanks caused by rainfall. The combined effects of litter quality and changes in precipitation regimes altered the decomposition process and nutrient cycling in tank bromeliads, probably through changes in the abundance of some keystone species (e.g. Naididae). Aquatic macroinvertebrate community structure remained similar after manipulating precipitation, despite changes in the abundance of some species. Although some microorganisms were washed out of the system, their abundance inside the bromeliads remained stable. We conclude that the abundance of individuals belonging to aquatic communities in bromeliad phytotelmata are generally stable and resistant to changes in rainfall levels, but are sensitive to changes in litter quality. This experiment showed that the interactive effects of increased precipitation and N concentrations differed from the effects of either factor alone. As responses to changes in these factors were complex rather than additive, caution is required in predicting the outcomes of changes in both factors in freshwater ecosystems.

Influence of Larval Habitat Environmental Characteristics on Culicidae Immature Abundance and Body Size of Adult Aedes aegypti

“…Here, the number of immature Culicidae was positively associated to the dissolved organic carbon (DOC) concentration in the larval habitat. A higher availability of organic matter usually results in a higher flow of energy via the food web (Benavides-Gordillo et al, 2019) and could have acted as an oviposition attractant for mosquito female (together with container size) and/or food source enabling increased immature survival. In addition, it might also serve as substrate for bacterial growth (Benavides-Gordillo et al, 2019).…”

Extreme rainfall events alter the trophic structure in bromeliad tanks across the Neotropics

“…Larger predators from these environments might be better adapted to drought, bouncing back quickly from perturbations. For such lentic ecosystems, flooding events seem to be at least as harmful as drought, as flooding can leach out important nutrients, basal resources (organic matter, microorganisms) 26,27 and even small macroinvertebrates (e.g., detritivores) 27 from the ecosystem. Indeed, we found turbidity, a measure that integrates organic and inorganic suspended matter in ecosystems, including free-living algae and particulate nutrients (C, N, P), resulting from detritivore activity, to be lower under more frequent rainfall conditions in our experiments ( Supplementary Fig.…”

“…Whereas detritivore standing stock exhibited strong sitespecific responses to extremes of rainfall frequency, mesopredators were not affected by rainfall or hydrological stability. The patterns observed for detritivores may be explained by the different ambient rainfall patterns among sites 12,25,27 , with indications that communities from some regions are more resistant to drought and flooding than others 26,27 . Conversely, mesopredators are known to be opportunistic species with generalized feeding and habitat requirements and are less sensitive to habitat features and climate change 24,31,32 .…”

“…1c). Conversely, an excessive amount of rainfall combined with higher frequency of rainfall among consecutive days could impact lower trophic levels through hydrodynamic perturbations, e.g., if important nutrients and basal resources (detrital organic matter and microorganisms) are lost to flooding 26,27 . Bigger predators could be more resistant to flooding, but their biomass could still decrease if they have fewer resources to support them.…”

Predators override rainfall effects on tropical food webs

“…The rainwater for this experiment was collected on site in buckets. Overflow normally flushes nutrients and bacteria from bromeliads (Benavides‐Gordillo et al, 2019); we simulated overflow by removing each day 5 ml of water from the 500 ml cups surrounding the 50 ml tubes, resulting in the passive movement of water out of the tubes without disturbing the insects (see Amundrud & Srivastava, 2016).…”