Cooperative Fish and Wildlife Research Units Program: Arkansas
Education, Research and Technical Assistance for Managing Our Natural Resources

Arkansas Project

Influence of Flow Regime and Land Use on Food Web Dynamics in Streams

August 2018 - May 2022


Participating Agencies

  • Arkansas Game and Fish Commission
  • University of Arkansas

Food chain length, or the maximum trophic position within a food web, is an important aspect of food webs and community dynamics. Food chain length indicatestells the number of trophic transfers that occur from the basal resources to the top predator (1) and it. The length of the food chain determines the amount of energy movement with the system (2). Additionally, the food chain length can impact the amount of carbon fixation by the system, with top predators determining and altering biogeochemical processes and atmospheric interactions (3), and nutrient cycling (4). One theory for the length of food webs is that they are determined by the stability of the system, with systems showingwith frequent or extreme disturbances hypothesized to have shorter food webs (5). Streams are a dynamic systems with varying amounts of disturbance. Based on the dynamic stability hypothesis, streams with less stable flow regimes should have shorter food chain lengths than more stable flow regimes. Understanding the impact of disturbance on food webs and community stability is essential as climatic patterns shift and anthropogenic disturbance becomes more intensive. Studies on examining the dynamic stability hypothesis have found inconsistent results, including that the trophic position of fish has decreased with disturbance (6), high flow and low flow events reduced food chain length (7), and that while the trophic base of food webs shifted, food chain length did not differ due to flow intermittency (8). In addition, the streams in these studies had different compositions, including: a combination of streams with non-piscivorous fish and no fish (6), perennial streams having piscivorous fish and intermittent streams having small fish or invertebrates as the top predator (7), and no streams having fish (8). The propsedis research will examine food chain length in runoff flashy and groundwater flashying streams along a gradient of land uses. Runoff flashy and groundwater flashy streams have similar mean daily flows, keeping ecosystem size similar (9). However, runoff flashy streams are characterized by having a greater variability in daily flow, a higher maximum 30-day mean flow, and a greater flood frequency, which are major variables is stream disturbance (9). Piscivorous fish will be present in all streams included in the study. Basal resources, invertebrate, and fish samples have been obtained from 10 sites (5 runoff flashy and 5 groundwater flashy streams) in Northern Arkansas, Western Oklahoma, and Southern Missouri. Sample streams represent a gradient of anthropogenic land uses. Stable isotope analysis will be run onf samples to determine basal resource use and food web length in each stream and determine the impact disturbance due toinfluence of flow regime has on food chain length. In addition, food chain length with be analyzed in relation to land use in order to determine if land use impacts food chain length and if that impact differs with hydrologic disturbance.