Food Webs and Trophic Interactions in Intermittent Rivers and Ephemeral Streams

The contraction of aquatic, and expansion of terrestrial, habitats in association with flow cessation and drying in intermittent rivers and ephemeral streams (IRES) fundamentally affect interactions among IRES organisms. Drying alters the relative contributions of autotrophy and heterotrophy to food webs because shredders, microbes, and autotrophs are affected, which often leads heterotrophy to become dominant. Changes in ecosystem dimensions, conditions, and resources fundamentally alter the types, sizes, and abundance of organisms present. Spatial and temporal fragmentation of habitats constrains, compresses, and sometimes expands trophic interactions, often substantially altering interaction strengths due to disproportional effects on large top predators. Drying and rewetting alter the trophic linking of aquatic and terrestrial habitats laterally, longitudinally, and vertically, with the form of food web modification in IRES related to regional differences in climate, biota, and riparian structure. Overall, drying reduces aquatic food chain length and trophic diversity, and often culminates in collapse of aquatic food webs; however, it can also trigger transitions toward terrestrial energy pathways and likely expands terrestrial food web dimensions. Given that hysteresis effects and strong, destabilizing interactions have been observed in drying stream food webs, global changes that exacerbate or produce unnatural drying are likely to have deleterious influences in IRES