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SFS Annual Meeting

Monday, May 20, 2019
14:00 - 15:30

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14:00 - 14:15: / 250 DE EXPERIMENTAL N AND P ADDITIONS RELIEVE STOICHIOMETRIC CONSTRAINTS ON ORGANIC-MATTER FLOWS THROUGH FIVE STREAM FOOD WEBS

5/20/2019  |   14:00 - 14:15   |  250 DE

EXPERIMENTAL N AND P ADDITIONS RELIEVE STOICHIOMETRIC CONSTRAINTS ON ORGANIC-MATTER FLOWS THROUGH FIVE STREAM FOOD WEBS Pervasive nutrient pollution is changing basal resource quality in food webs, thereby affecting rates and pathways of energy and material flow to higher trophic levels. We used the framework of ecological stoichiometry to investigate the effects of experimental N and P enrichment on the trophic basis of macroinvertebrate production and flows of dominant food resources to consumers in five headwater streams (target N:P of 2:1 to 128:1). Nutrient enrichment resulted in increased basal resource flows to consumers relative to reference conditions, with the greatest increases occurring among resources that experienced the largest reductions in C:P ratios. Flows of leaf detritus, diatoms and wood were all negatively related to resource C:P, indicating widespread P-limitation in these detritus-based food webs. However, increased basal resource flows did not uniformly result in greater material flows to predators. Invertebrates consumed a greater proportion of available leaf litter following nutrient enrichment, with that proportion increasing with decreasing leaf litter C:P. This study suggests that global increases in N and P supply will increase organic matter flows to consumers in detritus-based ecosystems by reducing stoichiometric constraints at the base of food webs.

Jonathan Benstead (Co-Presenter/Co-Author), University of Alabama, jbenstead@ua.ed;


Amy Rosemond (Co-Presenter/Co-Author), University of Georgia, rosemond@uga.edu;


Vlad Gulis (Co-Presenter/Co-Author), Coastal Carolina University, vgulis@coastal.edu;


John Maerz (Co-Presenter/Co-Author), University of Georgia, jcmaerz@uga.edu;


Lee Demi (Primary Presenter/Author), North Carolina State University, mickdemi@yahoo.com;


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14:15 - 14:30: / 250 DE FOOD WEB CONTROLS ON MERCURY FLUX AND FATE IN THE COLORADO RIVER, GRAND CANYON

5/20/2019  |   14:15 - 14:30   |  250 DE

FOOD WEB CONTROLS ON MERCURY FLUX AND FATE IN THE COLORADO RIVER, GRAND CANYON Mercury (Hg) accumulation in the environment is well studied, but less attention has focused on how species traits and trophic interactions affect the movement of Hg within food webs and between ecosystems. We quantified Hg flows in Colorado River food webs by coupling measures of animal production, gut contents, and tissue Hg concentrations over two years before and after an experimental flood. Hg fluxes to invertebrates were dominated by consumption of amorphous detritus and diatoms. Among aquatic invertebrates, Hg flux to mudsnails was the greatest, but this represented a Hg sink because mudsnails are predator resistant. Blackfly larvae biomass was just ~1% relative to mudsnail biomass, but they were the largest Hg source to fishes because they were preferred prey. Blackflies were also the dominant Hg source for terrestrial predators. However, the fate of Hg accumulated in blackfly tissue (aquatic vs. terrestrial), depended on the degree of match/mismatch between larval blackfly production and their predation rate by fish. By coupling ecotoxicological perspectives with ecosystem energetics, we provide an ecological basis for predicting contaminant fate within and across aquatic-riparian boundaries and new insights on how contaminant flux can govern wildlife exposure.

David Walters (Primary Presenter/Author), US Geological Survey, waltersd@usgs.gov;


Emma Rosi (Co-Presenter/Co-Author), Cary Institute of Ecosystem Studies, rosie@caryinstitute.org;


Wyatt Cross (Co-Presenter/Co-Author), Montana State University, wyatt.cross@montana.edu ;


Ted Kennedy (Co-Presenter/Co-Author), USGS Southwest Biological Science Center, Grand Canyon Monitoring and Research Center, tkennedy@usgs.gov;


Colden Baxter (Co-Presenter/Co-Author), Idaho State University, baxtcold@isu.edu;


Robert Hall (Co-Presenter/Co-Author), Flathead Lake Biological Station, University of Montana, bob.hall@flbs.umt.edu;


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14:30 - 14:45: / 250 DE DIVERSITY AND BIOMASS OF SHREDDER INSECTS ALONG AN ALTITUDINAL GRADIENT IN CENTRAL AMERICA

5/20/2019  |   14:30 - 14:45   |  250 DE

DIVERSITY AND BIOMASS OF SHREDDER INSECTS ALONG AN ALTITUDINAL GRADIENT IN CENTRAL AMERICA Shredder aquatic insects richness is generally low in tropical streams, possibly because of low quality leaf litter. However, richness varies highly among streams, suggesting that environmental filtering is driving shredders diversity. Here, we evaluate how much richness and biomass of shredder insects increase along an altitudinal gradient (170 - 2000 m asl). We conducted a quantitative sampling in first order streams, located in conserved catchments of Guatemalan basins. Vegetation ranges from rainy neotropical forest to cloud forest; however, leaf litter quality did not seem increase with altitude (SLA: 2.62 – 4.36 cm2 mg-1). Shredder insects richness was a low proportion of the assemblage (9 of 69 taxa), and increased with altitude. Although biomass in streams at lower altitude (8.32 mg AFDM m-2) was less than a 5% of the biomass at higher altitude (218.53 mg AFDM m-2), the highest biomass was in the stream at the middle of the gradient (291.23 mg AFDM m-2). Therefore, shredder richness seems not to respond to the change of vegetation, while variation in biomass suggests that this group may be responding to changes in water temperature, substrate size, and predators presence.

Pavel Garcia (Primary Presenter/Author), Organismal Biology, Ecology and Evolution Program, University of Montana, pavel.garciasoto@umontana.edu;


Robert Hall (Co-Presenter/Co-Author), Flathead Lake Biological Station, University of Montana, bob.hall@flbs.umt.edu;


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14:45 - 15:00: / 250 DE SEASONALITY IN FLOW FOOD WEBS: THE IMPORTANCE OF WINTER BASEFLOW IN ALPINE STREAMS

5/20/2019  |   14:45 - 15:00   |  250 DE

SEASONALITY IN FLOW FOOD WEBS: THE IMPORTANCE OF WINTER BASEFLOW IN ALPINE STREAMS Stream basal resources, both autochthonous (i.e., within-system; e.g., biofilm) and allochthonous (i.e., external; e.g., coarse benthic organic matter [CBOM]), support food webs, though their availability varies with environmental characteristics such as the hydrological regime. We sampled biofilm, CBOM, and macroinvertebrates in three catchments for biomass and stable isotopes approximately monthly for over a year. Biofilm showed seasonal trends with high biomass in winter months (Dec-Apr) while CBOM was aseasonal, both temporal patterns similar across catchments. Macroinvertebrate abundance generally tracked instream resources with high abundances in winter months (e.g., 100s of 1 mm individuals per m2), and was dominated by Plecoptera and Ephemeroptera. Preliminary results indicate higher reliance of Heptageniidae grazers on instream resources in winter months (higher ?13C values). However, size class distributions remained fairly constant during those winter months (e.g., Heptageniidae: peak 3 mm Oct-Mar). Combining estimates of monthly secondary production with stable isotope data will be needed to identify reliance on and importance of specific basal resources. Hydrological regime drives temporal patterns in basal resources and as a result likely affects flow food webs with winter baseflow critical for early instar growth and thus productivity in Alpine streams.

Janine Rüegg (Primary Presenter/Author), École Polytechnique Fédérale de Lausanne, janine.ruegg@unil.ch;


Tom Battin (Co-Presenter/Co-Author), Ecole Polytechnique Fédérale de Lausanne, tom.battin@epfl.ch;


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15:00 - 15:15: / 250 DE EFFECTS OF TEMPERATURE ON ENERGY FLUX THROUGH STREAM FOOD WEBS

5/20/2019  |   15:00 - 15:15   |  250 DE

EFFECTS OF TEMPERATURE ON ENERGY FLUX THROUGH STREAM FOOD WEBS Predicting how temperature influences fluxes of energy through food webs is challenging because of covariation between temperature and resource (e.g., light, food) availability. Further, responses of food web fluxes to warming will depend on both physiological changes to consumer metabolism, as well as, population-level shifts in species composition and life-history. We measured the influence of temperature on energy and material fluxes from basal resources to invertebrate consumers seasonally in six geothermally-influenced streams (temperature range: ~5–30°C). We predicted temperature-invariance of energy flows because of the opposing expectations for temperature dependence of standing biomass and energy demand. We found that total annual energy fluxes were positively related to temperature. However, seasonal patterns in light led to widely varying consumer biomass, strongly influencing the timing (late-summer peak) and magnitude (~15–70 fold differences) of consumer demand. In the warmest stream, peak consumer demand was out of phase with resource availability due to large reductions in demand as temperatures neared the thermal maximum for metazoans. Our results show that interactions between temperature and resource availability shape temporal patterns of energy flux in food webs and may constrain stream ecosystem responses to warming.

James Junker (Primary Presenter/Author), Montana State University, james.junker1@gmail.com;


Wyatt Cross (Co-Presenter/Co-Author), Montana State University, wyatt.cross@montana.edu ;


Jonathan Benstead (Co-Presenter/Co-Author), The University of Alabama, jbenstead@ua.edu;


James Hood (Co-Presenter/Co-Author), The Ohio State University, hood.211@osu.edu;


Alexander D. Huryn (Co-Presenter/Co-Author), The University of Alabama, huryn@ua.edu;


Gisli Gislason (Co-Presenter/Co-Author), University of Iceland, gisli@ui.is;


Daniel Nelson (Co-Presenter/Co-Author), University of Oklahoma, dnelson12@crimson.ua.edu;


Jon Olafsson (Co-Presenter/Co-Author), Iceland Marine and Freshwater Research Institute, jon.s.olafsson@hafogvatn.is;


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15:15 - 15:30: / 250 DE THERMAL NICHE AND TROPHIC REDUNDANCY COMBINE TO DRIVE NEUTRAL EFFECTS OF EXPERIMENTAL WARMING ON ORGANIC MATTER FLUX THROUGH A STREAM FOOD WEB

5/20/2019  |   15:15 - 15:30   |  250 DE

THERMAL NICHE AND TROPHIC REDUNDANCY COMBINE TO DRIVE NEUTRAL EFFECTS OF EXPERIMENTAL WARMING ON ORGANIC MATTER FLUX THROUGH A STREAM FOOD WEB Climate warming is predicted to alter flows of energy through food webs due to varied effects of temperature on physiological rates, community structure, and trophic dynamics. Few studies, however, have experimentally assessed the net effect of warming on energy flux and food web dynamics in natural intact communities. Here, we test how warming affects energy flux and the trophic basis of production in a natural invertebrate food web by experimentally heating a stream reach in southwest Iceland by ~4°C for two years and comparing its response to an unheated reference stream. Diatoms dominated the trophic basis of production in both study streams, contributing 80 – 91% to secondary production. Although warming shifted organic matter flows within the food web, total resource consumption did not increase as predicted. The neutral effect of warming on total energy flow through the food web was a result of taxon-level variation in responses to warming, a neutral effect on production, and strong trophic redundancy within the invertebrate assemblage. Thus, food webs characterized by a high degree of trophic redundancy may be more resistant to the effects of climate warming than those with more specialized consumers

Daniel Nelson (Primary Presenter/Author), University of Oklahoma, daniel.nelson79@gmail.com;


Jonathan Benstead (Co-Presenter/Co-Author), University of Alabama, jbenstead@ua.ed;


Wyatt Cross (Co-Presenter/Co-Author), Montana State University, wyatt.cross@montana.edu ;


Alexander D. Huryn (Co-Presenter/Co-Author), The University of Alabama, huryn@ua.edu;


James Hood (Co-Presenter/Co-Author), The Ohio State University, hood.211@osu.edu;


Philip Johnson (Co-Presenter/Co-Author), University of Alabama, pjohnson@eng.ua.edu;


James Junker (Co-Presenter/Co-Author), Montana State University, james.junker1@gmail.com;


Jon Olafsson (Co-Presenter/Co-Author), Iceland Marine and Freshwater Research Institute, jon.s.olafsson@hafogvatn.is;


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