Search Content

Matching Items (2)

Filtering by

All Subjects: flow regime
Creators: Grimm, Nancy

Food Webs Across the Stream-Riparian Boundary: Disentangling the Influence of Hydrologic Variability and Resource Dynamics

Description

Spatial and temporal patterns of biodiversity are shaped, in part, by the resources available to biota, the efficiency of resource transfer through the food web, and variation in environmental conditions. Stream and riparian zones are dynamic systems connected through reciprocal resource exchange and shaped by floods, droughts, and long-term patterns in the quantity, timing, and variability of streamflow (flow regime). The interdependent nature of the stream-riparian ecosystem defies the scope of any single discipline, requiring novel approaches to untangle the controls on ecological processes. In this dissertation, I explored multiple mechanisms through which streamflow and energy flow pathways maintain the community and trophic dynamics of desert stream and riparian food webs. I conducted seasonal sampling of Arizona streams on a gradient of flow regime variability to capture fluctuations in aquatic communities and ecosystem production. I found that flow regime shapes fish community structure and the trajectory of community response following short-term flow events by constraining the life history traits of communities, which fluctuate in prevalence following discrete events. Streamflow may additionally constrain the efficiency of energy flow from primary producers to consumers. I estimated annual food web efficiency and found that efficiency decreased with higher temperature and more variable flow regime. Surprisingly, fish production was not related to the rate of aquatic primary production. To understand the origin of resources supporting aquatic and riparian food webs, I studied the contribution of aquatic and terrestrial primary production to consumers in both habitats. I demonstrated that emergent insects “recycled” terrestrial primary production back to the riparian zone, reducing the proportion of aquatic primary production in emergent insect biomass and riparian predator diet. To expand the concept of stream and riparian zones as an integrated ecosystem connected by resource cycling through the food web, I introduced a quantitative framework describing reciprocal interconnections across spatial boundaries and demonstrated strong aquatic-riparian interdependencies along an Arizona river. In this dissertation, I develop a novel perspective on the stream-riparian ecosystem as an intertwined food web, which may be vulnerable to unforeseen impacts of global change if not considered in the context of streamflow and resource dynamics.

ContributorsBaruch, Ethan Max (Author) / Sabo, John (Thesis advisor) / Bateman, Heather (Committee member) / Cease, Arianne (Committee member) / Grimm, Nancy (Committee member) / Arizona State University (Publisher)

Created2021

Assessing the Response of Macroinvertebrate Communities to River Flow Dynamics in the Sonoran Desert

Description

Climate change is causing hydrologic intensification globally by increasing both the frequency and magnitude of floods and droughts. While environmental variation is a key regulator at all levels of ecological organization, such changes to the hydrological cycle that are beyond the normal range of variability can have strong impacts on stream and riparian ecosystems within sensitive landscapes, such as the American Southwest. The main objective of this study was to investigate how anomalous hydrologic variability influences macroinvertebrate communities in desert streams. I studied seasonal changes in aquatic macroinvertebrate abundances in eleven streams that encompass a hydrologic gradient across Arizona’s Sonoran Desert. This analysis was coupled with the quantification and assessment of stochastic hydrology to determine influences of flow regimes and discrete events on invertebrate community composition. I found high community variability within sites, illustrated by seasonal measures of beta diversity and nonmetric multidimensional scaling (NMDS) plots. I observed notable patterns of NMDS data points when invertebrate abundances were summarized by summer versus winter surveys. These results suggest that there is a difference within the communities between summer and winter seasons, irrespective of differences in site hydroclimate. Estimates of beta diversity were the best metric for summarizing and comparing diversity among sites, compared to richness difference and replacement. Seasonal measures of beta diversity either increased, decreased, or stayed constant across the study period, further demonstrating the high variation within and among study sites. Regime shifts, summarized by regime shift frequency (RSF) and mean net annual anomaly (NAA), and anomalous events, summarized by the power of blue noise (Maximum Blue Noise), were the best predictors of macroinvertebrate diversity, and thus should be more widely applied to ecological data. These results suggest that future studies of community composition in freshwater systems should focus on understanding the cause of variation in biodiversity gradients. This study highlights the importance of considering both flow regimes and discrete anomalous events when studying spatial and temporal variation in stream communities.

ContributorsSainz, Ruby (Author) / Sabo, John L (Thesis advisor) / Grimm, Nancy (Committee member) / Stampoulis, Dimitrios (Committee member) / Arizona State University (Publisher)

Created2021