Resource movements across landscapes play vital roles in many food webs and ecosystems. Extensive work in aquatic food webs has revealed that nutrient and energy subsidies from external environments can profoundly impact the structure and function of recipient ecosystems. However, isolating subsidies’ effects on trophic structure remains challenging due to the many pathways linking most aquatic and terrestrial ecosystems, and the heterogeneity of autochthonous primary production. Aquatic caves provide compelling models for subsidy research due to their prevalent resource limitation and depleted taxon richness. Most aquatic cave communities rely entirely on intermittent subsidies of photosynthetic material from the surface, but some ecosystems are also supported by in situ chemosynthetic bacteria, which may contrast in their temporal availability. In order to test the importance of resource stability on community structure, we surveyed aquatic caves in Mexico and compared trophic structure and species richness between communities that depend entirely on intermittent subsidies and communities supported in part by more stable sources of chemosynthesis.
Results/Conclusions
We conducted visual surveys to assess macro crustacean community composition and species richness. Communities supported by chemosynthesis were more speciose than subsidy-dependent communities, but differences are largely due to the presence of more salt-tolerant taxa such as Xilbansus tulumensis and Bahalana mayana that were absent from subsidy-dependent communities due to patterns in groundwater chemistry. We used stable isotopes (δ13C and δ15N) to compare food web complexity, specialization, and basal resource use between communities. Our results reveal that utilization of photosynthetic and chemosynthetic material differs by taxon, and that both resources play an important role in shaping community structure. Broadly, this work advances our understanding of how resource predictability influences community structure.