Oral Presentation Freshwater Sciences 2023

Stability in food webs connected across a complex braided river landscape. (#89)

Holly A L Harris 1 , Jonathan D Tonkin 1 , Tara Murray 2 , Angus R McIntosh 1
  1. University of Canterbury, Christchurch, CANTERBURY, New Zealand
  2. Department of Conservation, Dunedin, Otago, New Zealand

Food webs and food-web structure can give indications of ecosystem stability. For example, variation in resource pathways and interaction strength can dampen cascading species interactions that would otherwise destabilise populations within the food web. Moreover, connections by mobile predators in complex landscapes may alter food-web metrics at aggregate scales and integrate resources from the wider landscape. Hydrologically dynamic riverine systems such as braided rivers, have a significant amount of lateral and hydrological complexity and food webs across these landscapes are connected by mobile predators such as birds and fish. We applied stable isotope analysis to a braided river system to investigate changes in food-web structure across a lateral braidplain, and how these food webs may be integrated by mobile consumers. We expected food webs in the major channels of a braided river to have low resource breadth and smaller isotopic niche space, due to disturbance limited primary productivity, than food webs in the surrounding springs, upwellings, and stable lateral channels. We also expected these aggregated food-webs to form a meta-food web where the total niche space and resource breadth is larger, allowing opportunities for asymmetrical feeding links and spatial variation in interactions, and thus a stable meta-system structure. Results suggest channels with greater hydrological variability have a smaller isotopic niche space and resource breadth than stable areas, and mobile consumers can integrate these spatially separated food webs to form meta-food webs with more stable properties.  This spatial variation and connectivity could be critical in braided rivers, which are significantly threatened natural ecosystems where bed shifts and flooding occur frequently, and habitats can be affected at different rates by flooding disturbance or removed completely by terrestrial plant invasions and press disturbances.