01821nas a2200181   4500008004100000245005100041210005000092300001500142490000800157520128700165100001901452700001701471700001801488700001801506700001601524700001701540856008201557       2006                        eng d00aModular experimental riffle-pool stream system0 aModular experimental rifflepool stream system  a1559 -15660 v1353 aWe describe a modular method for building a large, outdoor experimental stream system that has great flexibility for research projects in fish ecology, behavior, conservation, or management. The system has been in use for more than a decade at the University of Oklahoma Biological Station (Kingston, Oklahoma) and has been used with modification at four other research facilities in the Midwest. Here, we document the system in detail, including specifications for construction of the original system and modifications or improvements at other sites. The system uses commercially available, customized fiberglass round tank and trough units that can be configured in many different ways to create flowing pool and riffle habitats. The system appears to be a good mimic of small natural streams based on system flow rates, establishment of natural substrates and cover, stream chemistry relative to that of a natural creek, and fish behaviors. At least 39 fish species have been used successfully in 1–14-month experiments in these systems and approximately half have reproduced. The system offers great flexibility of design to experimenters, is cost effective, and may be of interest at other facilities that research basic biology, conservation, or management of stream fishes.1 aMatthews, W.J.1 aGido, K., B.1 aGarrett, G.P.1 aGelwick, F.P.1 aStewart, J.1 aSchaefer, J.  uhttp://knz.lternet.edu/content/modular-experimental-riffle-pool-stream-system02169nas a2200145   4500008004100000245006000041210005800101300001500159490000700174520170900181100001701890700001701907700001601924856008301940       2005                        eng d00aA test for community change using a null model approach0 atest for community change using a null model approach  a1761 -17710 v153 aQuantifying patterns of temporal or spatial change in community structure is critical for assessing the impact of disturbances on biological systems and the stability of ecosystems. Detecting change in communities can be problematic, however, because of the inherent variability of systems and limitations of commonly used methods, such as similarity indices and ordination that do not explicitly test a hypothesis. Here we present empirical data to show a strong relationship between species mean abundance and variability across three broad taxonomic groups (plants, zooplankton, and fish). These statistical relationships were then used to construct null models of expected community variability that were used to test against the observed temporal change of these communities. We evaluated the ability of this approach to detect significant temporal change above that associated with random variation with nine communities (three Midwestern stream fish, three north temperate zooplankton, and three tallgrass prairie plant), each having long-term data sets and different expected levels of change. Nonrandom change was detected in 21.3% of samples from the expected low-change communities, 52.6% in moderately changed communities, and 60.4% in high-change communities. Thus, this approach was effective in detecting change over time in those communities expected to change most. By using empirical relationships between species abundance and variability, this null model approach provides ecologists and resource managers an objective tool, which can be used along with existing community indices and statistical techniques to assess the type and magnitude of community change with limited data sets.1 aSchaefer, J.1 aGido, K., B.1 aSmith, M.D.  uhttp://knz.lternet.edu/content/test-community-change-using-null-model-approach