Autotrophs are important contributors to benthic macroinvertebrate food webs in two tropical first‐order forest streams

Abstract

In tropical first‐order streams, the availability of basal resources changes according to tropical seasonality, i.e., dry and rainy seasons, with consequences for the food web structure. However, the seasonal variation in autotrophic and detrital pathways remains unclear. In this study, we aimed to establish whether the dominant pathway of the benthic macroinvertebrate food web in two tropical first‐order streams in the Lacandona rainforest, Mexico, relies on autotrophic or detrital food resources. We evaluated the assimilation of autotrophic and detrital food resources through carbon and nitrogen stable isotope (δ13C and δ15N) analysis. We included the biomass of the macroinvertebrates sustained by the autotrophic and detrital pathways and the food web structure—trophic position, size structure, and degree of omnivory. The biomass sustained by the detrital pathway remained similar throughout the year in both streams. In contrast, the biomass sustained by the autotrophic pathway was higher in the dry season than in the rainy season. The benthic macroinvertebrate food web had four levels, a poorly developed size structure, and an important degree of omnivory in both streams and in both seasons. It is likely that omnivory was a response to high resource variability and a strategy to reduce intraguild competition. Autotrophs had a relatively higher importance than detritus since a much lower algae biomass sustained an equal or higher macroinvertebrate biomass, particularly in the dry season when the biomass of autotrophs increased. Seasonality influenced the macroinvertebrate food web by modifying the food resource availability and transference to higher trophic levels. However, the high frequency of omnivory reduced the seasonal changes in the food web structure. Our results suggest that the autotrophic pathway plays an important role in maintaining the benthic macroinvertebrate food web in tropical streams. The relative importance of autotrophs in the macroinvertebrate food web is associated with seasonality, the rainfall pattern, and its effect on the stream hydrology.

Influence of Seasonal Water Level Fluctuations on Food Web Structure of a Large Floodplain Lake in China

“…In shallow lakes, autochthonous carbon sources, particularly aquatic macrophytes, are typically considered the most important carbon sources supporting consumer growth [16,17,32]. In our study area, the abundance and biomass of aquatic macrophytes are very low due to rapid flow and relatively high turbidity in the wet season [33].…”

“…On the other hand, seasonal fluctuations in the water level can provoke complicated changes in the community structure of the littoral area [9]. Most of the research concerning the response of aquatic systems to extreme water level fluctuation (i.e., flooding and drought) has taken place in arid climates [15] or focuses primarily on riverine systems [5,16,17]. Little attention has been paid to the ecological effects of water level fluctuations in naturally fluctuating floodplain lakes in subtropics [18].…”

Current Status of Omics in Biological Quality Elements for Freshwater Biomonitoring

“…These tools working together could be a favorable approach towards the modernization of freshwater biomonitoring since most of the biological levels and the interaction settings between them can be tackled. Isotopomics could be a direct extension of omics techniques into trace signals on certain processes associated with the optimal status of ecological functions, such as photosynthesis rate [193] or food web structure [194]. Nonetheless, isotopomics from traditional isotopic analysis executed in ecology differ greatly depending on the internal or external evaluation of metabolic backgrounds.…”