5/18/2015  |   13:30 - 13:45   |  102DE

INVASIVE BIGHEAD CARP ALTER ORGANIC MATTER EXCHANGES WITHIN AND BETWEEN ECOSYSTEMS Bighead carp are a highly productive and invasive fish species. Curiously, little is known of the ecological impacts of juvenile bighead carp. We conducted an additive experiment to evaluate the direct and indirect effects of juvenile bighead carp within and between ecosystems. Ponds (0.04 ha.) were stocked with a native fish community (control, n=5) and native fishes plus juvenile bighead carp (treatment, n=5). Food web responses were quantified through time. Bighead carp greatly reduced zooplankton abundance, with indirect and cascading increases in chlorophyll-a levels. Direct competition between bighead carp and two families of shiners resulted in their reduced growth and survival. Additionally, bighead carp reduced filamentous algae and turbidity. Direct utilization of pelagic resources by bighead carp resulted in increased secondary production and rates of egestion, translocating organic matter from pelagic to benthic habitats. Consequently, increased flux of adult Chironomidae midges was observed in carp treatments. In contrast, bighead carp reduced the emergence of adult Chaoborus midges. Our experiment indicated that bighead carp could greatly alter the exchange of organic matter within and between aquatic and terrestrial ecosystems.

Scott Collins (Primary Presenter/Author), Texas Tech University, Scott.Collins@ttu.edu;


David Wahl (Co-Presenter/Co-Author), University of Illinois, d-wahl@illinois.edu;

5/18/2015  |   13:45 - 14:00   |  102DE

EFFECT OF FOREST CONDITION ON FOOD WEB STRUCTURE IN HEADWATER STREAMS IN DIFFERENT REGIONS OF CANADA An important ecosystem service provided to headwater stream communities by forests is the provision of allochthonous energy to support biodiversity. Forest disturbance can significantly affect this subsidization, but the mechanisms are poorly understood. To address this we are studying how forest management affects food web structure (via stable isotopes and ecological stoichiometry of macroinvertebrates and their food resources) in headwater streams differing in degree of disturbance and consequent forest condition across Canada. Streams with a range in watershed disturbance were sampled in Ontario (3 logged, 3 burned, 3 reference), British Columbia (6 clearcut, 1 thinned, 3 reference) and New Brunswick (15 with 0 to 69% of the watershed planted). Nitrogen isotope data from Ontario indicate longer food webs in streams with burned and logged watersheds compared to reference streams (33 and 17% longer, respectively). Carbon isotope data indicate that shredders feed on leaves, but that scrapers are not feeding on biofilm as anticipated. Linking food web results to forest condition may be crucial to understanding factors driving differences in food web structure among headwater streams.

Maitane Erdozain (Primary Presenter/Author), University of New Brunswick, maitane.erdozain@gmail.com;


Karen Kidd (Co-Presenter/Co-Author), McMaster University, karenkidd@mcmaster.ca;


David Kreutzweiser (Co-Presenter/Co-Author), Great Lakes Forestry Centre, Canadian Forest Service, dave.kreutzweiser@canada.ca;


Paul Sibley (Co-Presenter/Co-Author), University of Guelph, psibley@uoguelph.ca ;

5/18/2015  |   14:15 - 14:30   |  102DE

THE IMPORTANCE OF TERRESTRIAL SUBSIDIES IN STREAM FOOD WEBS VARIES ALONG A STREAM SIZE GRADIENT Energy and material subsidies can comprise a substantial fraction of food web fluxes in some ecosystems, especially when primary production is strongly limited. We explored whether assimilation of terrestrial energy varied within consumers collected from streams of different sizes and resource availabilities. Since headwater streams are often unproductive, we expected that inputs from surrounding terrestrial systems would be an important food source for consumers, while mid-size rivers would have more open canopies and higher amounts of primary production available for consumers. We collected basal resources, invertebrates, and fish along stream size gradients in both tropical and temperate sites and analyzed each sample for hydrogen stable isotopes (a proxy for material derived from allochthonous sources). Allochthonous energy use was positively correlated with canopy cover in both regions, with consumers from small, shaded streams having a more allochthonous signal than individuals collected from larger streams with open canopies. Our results demonstrate that the importance of terrestrial subsidies can vary markedly, with some taxa that range from being entirely allochthonous to entirely autochthonous, and others that are relatively fixed in their energy source.

Sarah M Collins (Primary Presenter/Author), University of Wyoming, sarah.collins@uwyo.edu;


Tyler Kohler (Co-Presenter/Co-Author), École Polytechnique Fédérale de Lausanne, Switzerland, tyler.j.kohler@gmail.com;


Steven Thomas (Co-Presenter/Co-Author), University of Alabama, sathomas16@ua.edu;


William Fetzer (Co-Presenter/Co-Author), Michigan State University, wwfetzer@gmail.com;


Alexander Flecker (Co-Presenter/Co-Author), Cornell University, Ithaca, NY, USA, asf3@cornell.edu;

5/18/2015  |   14:30 - 14:45   |  102DE

FLUXES OF CARBON AND NITROGEN FROM ISOTOPICALLY-ENRICHED LEAF LITTER TO A SHREDDING CADDISFLY REVEAL DIFFERENCES IN LITTER QUALITY Leaf litter is a crucial energy base for most headwater food webs. Although leaf litter from different trees varies in multiple chemical and physical traits, it is difficult to determine how these differences affect assimilation of carbon and nitrogen from leaves to aquatic macroinvertebrates. Rates of leaf decomposition are sometimes viewed as a proxy for food quality, with fast-decomposing litter thought to provide more nutrients to decomposers. We tested this hypothesis by comparing assimilation rates using leaf litter from four riparian tree species enriched with heavy carbon and nitrogen isotopes. Enriched leaf litter was incubated in a headwater stream in bags containing a shredding caddisfly Hesperophylax designatus. Three patterns emerged: (1) caddisflies assimilated carbon at the highest rates from slow-decomposing leaf litter. (2) Caddisflies assimilated nitrogen at the highest rates from fast-decomposing leaf litter. (3) The C:N ratio of assimilate was lowest for fast-decomposing leaf litter. These results demonstrate that nutrient fluxes vary by litter species, with fast-decomposing litter supporting higher nitrogen assimilation rates.

Adam Siders (Primary Presenter/Author), University of Florida, asiders@ufl.edu;


Zacchaeus Compson (Co-Presenter/Co-Author), University of North Texas, zacchaeus.compson@unt.edu;


Jane Marks (Co-Presenter/Co-Author), Northern Arizona University, jane.marks@nau.edu;

5/18/2015  |   14:45 - 15:00   |  102DE

DOES RECALCITRANT LEAF LITTER PROVIDE MORE ENERGY TO THE MACROSCOPIC FOOD WEB? A TEST USING THE POPULUS HYBRIDIZING SYSTEM We examined the hypothesis that slow-decomposing, recalcitrant leaf litter would better support the macroscopic food web than fast-decomposing, labile leaf litter, which runs contrary to the prevalent idea that fast-decomposing litter is a higher “quality” resource. Using lab mesocosm studies and a field study with double-labeled litter (13C and 15N), we measured preference, processing, assimilation, and growth rates of Hesperophylax designatus when given litter of different chemical and physical phenotypes from cottonwood species, cross types, and genotypes. Five patterns emerged. (1) H. designatus initially chose more labile leaf litter types, but preference changed quickly to more recalcitrant litter. (2) H. designatus processed more recalcitrant leaf litter (higher % lignin and % condensed tannins). (3) Carbon and nitrogen fluxes from leaf litter to H. designatus were higher for recalcitrant (higher % lignin) compared to labile (lower % lignin) litter types. (4) H. designatus growth rates were higher on recalcitrant leaf litter. Collectively, these results suggest that recalcitrant leaf litter is a more stable, slow-release resource that provides more energy to the macroscopic food web.

Zacchaeus Compson (Primary Presenter/Author), University of North Texas, zacchaeus.compson@unt.edu;


Bruce Hungate (Co-Presenter/Co-Author), Northern Arizona University, bruce.hungate@nau.edu;


Thomas Whitham (Co-Presenter/Co-Author), Northern Arizona University, Thomas.Whitham@nau.edu;


George Koch (Co-Presenter/Co-Author), Northern Arizona University, George.Koch@nau.edu;


David Rakestraw (Co-Presenter/Co-Author), Northern Arizona University, dnr34@nau.edu;


Alexa Schuettenberg (Co-Presenter/Co-Author), Northern Arizona University, aas322@nau.edu;


Ryan Jacobs (Co-Presenter/Co-Author), Northern Arizona University, rj238@nau.edu;


Kiel Allred (Co-Presenter/Co-Author), Northern Arizona University, kiel.allred23@gmail.com;


Chelsea Sayer (Co-Presenter/Co-Author), Northern Arizona University, cs333@nau.edu;


Jesse Maestas (Co-Presenter/Co-Author), Northern Arizona University, jmm479@nau.edu;


Jane Marks (Co-Presenter/Co-Author), Northern Arizona University, jane.marks@nau.edu;