5/18/2015  |   10:30 - 10:45   |  102DE

SPATIAL SCALE VARIATION IN TOP-DOWN EFFECTS Most experiments examining top-down (consumer) control in stream ecosystems have focussed on only a single spatial scale, frequently < 1 m². The strength of top-down control is known to be context dependent and may vary with spatial scale. We conducted a 40 day consumer manipulation experiment (i.e. fish and shrimp removal) at the patch scale (1 m² exclusion cages) and at the reach scale (whole-reach exclusions ~20 m length), with the aim of examining top-down effects at multiple scales within three streams in the wet/dry tropics of northern Australia. At the reach scale strong top-down effects on benthic algal biomass and macroinvertebrate density were observed, with evidence of a trophic cascade. However, at the patch scale there was no evidence of top-down effects. Our findings suggest that whilst most top-down experiments are conducted at small spatial scales they may yield misleading results if interpolated to larger scales.

Erica Garcia (Primary Presenter/Author), Charles Darwin University, erica.garcia@cdu.edu.au;


Katherine Lacksen (Co-Presenter/Co-Author), Charles Darwin University, klacksen@mac.com;


Damien McMaster (Co-Presenter/Co-Author), Charles Darwin University, Damien.McMaster@cdu.edu.au;


Alison King (Co-Presenter/Co-Author), Charles Darwin University, Alison.King@cdu.edu.au;


Michael Douglas (Co-Presenter/Co-Author), Charles Darwin University, Michael.Douglas@cdu.edu.au;

5/18/2015  |   10:45 - 11:00   |  102DE

COLONISATION RATE AND ADAPTIVE FORAGING CONTROL THE EMERGENCE OF TROPHIC CASCADES Ecological communities are assembled and sustained by colonization. At the same time, predators make foraging decisions based on the local availability of potential resources, which reflects colonization. We combined field and laboratory experiments with mathematical models to demonstrate that a feedback between these two processes determines emergent patterns in community structure. Namely, our results show that prey colonization rate determines the strength of trophic cascades – a feature of virtually all ecosystems – by prompting behavioral shifts in adaptively-foraging omnivorous fish predators. Communities experiencing higher colonization rates were characterized by higher invertebrate prey biomass and richness. Consequently, fish functioned as predators when colonization rate was high, but as herbivores when colonization rate was low. Human land use is changing habitat connectivity worldwide. A deeper quantitative understanding of how spatial processes modify individual behavior, and how this scales to the community level, will be required to predict ecosystem responses to these changes.

Ashkaan Fahimipour (Co-Presenter/Co-Author), University of California, Riverside, ashkaan.fahimipour@email.ucr.edu;


Kurt Anderson (POC,Primary Presenter), University of California, Riverside, kurt.anderson@ucr.edu;

5/18/2015  |   11:00 - 11:15   |  102DE

THE EFFECTS OF PERIPHYTON FATTY ACIDS ON GRAZER LIPID COMPOSITION AND GROWTH IN SUBTROPICAL STREAMS Dietary polyunsaturated fatty acid (PUFA) compositions are important for herbivores, not only limiting somatic growth but also affecting energy transfer to higher trophic levels. In a study of subtropical streams in Australia, we manipulated four different food bases by inducing two light levels and two nutrient regimes to investigate the effect of periphyton PUFA on gazer lipid composition and growth. After 6 weeks, periphyton PUFA content changed considerably and differed in each food base. The alteration of gazer PUFA composition generally followed the pattern of periphyton PUFA. Both periphyton and grazers (Austrophlebioides and Helicopsyche) accumulated more linoleic acid (LIN) in food bases with high light levels, but increased their content of eicosapentaenoic acid (EPA) in food bases with low light intensity. An exception was observed in the food base with low light intensity and enriched nutrient where grazers grew faster compared with other bases. When dietary EPA increased, stream grazers tended to invest more in growth rather than retention. Our study indicated that even under food limited conditions, changes in grazer PUFA composition is still consistent with dietary PUFA pattern.

Fen Guo (Primary Presenter/Author), Australian Rivers Institute, Griffith University, Australia, fen.guo@griffithuni.edu.au;


Martin Kainz (Co-Presenter/Co-Author), WasserCluster Lunz – Inter-university Centre for Aquatic Ecosystem Research, Lunz am See, Austria, Martin.Kainz@donau-uni.ac.at;


Fran Sheldon (Co-Presenter/Co-Author), Australian Rivers Institute, Griffith University, Australia, f.sheldon@griffith.edu.au;


Stuart Bunn (Co-Presenter/Co-Author), Australian Rivers Institute, Griffith University, Australia, s.bunn@griffith.edu.au;

5/18/2015  |   11:15 - 11:30   |  102DE

RELATIONSHIP BETWEEN ECOLOGICAL STOICHIOMETRY AND BIOCHEMICAL COMPOSITION IN A LAKE PHYTOPLANKTON COMMUNITY. Elemental stoichiometry and biochemical composition both describe the nutritional quality of a food resource. While stoichiometry quantifies the elemental composition of the food source, usually with C:N, C:P, and N:P ratios, the biochemical composition refers to the protein, lipid, and carbohydrate contents as well as fatty acid (FA) composition. However, the relationship between these two metrics of nutritional quality is unclear, and understanding this link is key to fully understanding food web dynamics. Employing 21, 5400-liter lake mesocosms housed in the outdoor Experimental Lake Facility at Fordham University’s Calder Biological Field Station, we conducted a nutrient enrichment experiment with a phytoplankton assemblage. We added varying amounts of inorganic N and P to create seven treatments with target molar N:P supply ratios between 2.6 and 70. We predicted that changes in biochemical composition will mirror changes in elemental ratios: seston with the highest concentrations of proteins, lipids, and essential FAs will also have the lowest C:N and C:P ratios.

Catharina Grubaugh (Primary Presenter/Author), Louis Calder Center – Biological Field Station, Fordham University, cgrubaugh@fordham.edu;


John Wehr (Co-Presenter/Co-Author), Louis Calder Center - Fordham University, wehr@fordham.edu;
Professor of Biology at the Louis Calder Center, the biological field station of Fordham University. Directs freshwater ecology research lab. Supervised graduate, undergraduate and high school students in independent research. - Mentored 11 Masters and 7 PhD theses Editor, Freshwater Algae of North America (Academic Press) Specialties: - Phytoplankton and benthic algal identification - Phycology - Biostatistics - Stream ecology - Water chemistry

5/18/2015  |   11:30 - 11:45   |  102DE

EXPERIMENTAL NUTRIENT ENRICHMENT OF HEADWATER STREAMS ALTERS FOODWEB PATHWAYS TO LARVAL SALAMANDERS Bottom-up perturbations can influence predators indirectly via effects on their prey. We tested the effects of nutrient enrichment on larval salamander diets in five streams that received experimental nitrogen (N) and phosphorus (P) additions at moderate concentrations for two years. Nutrient enrichment altered diet composition of Desmognathus quadramaculatus (PERMANOVA P = 0.007). Little detectable changes were found for Eurycea wilderae (PERMANOVA P = 0.06), possibly due to microhabitat preferences. Changes in D. quadramaculatus diet composition, measured a functional group biomass of prey, were related to shifts in the basal resources of prey taxa. Biomass of shredder prey decreased, while that of biofilm consumers increased in salamander guts; these shifts were related to corresponding changes in the quanitity of respective primary food resources (leaves, P = 0.005, R2 = 0.47; biofilm, P = 0.08, R2 = 0.15). Although our study streams were detritus-based, small increases in biofilm availability with enrichment were linked to diet changes at the highest trophic level, altering energetic pathways to salamanders and likely contributing to the increased salamander growth rates observed with nutrient enrichment.

Phillip Bumpers (Primary Presenter/Author), University of Georgia, bumpersp@gmail.com;


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


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


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

5/18/2015  |   11:45 - 12:00   |  102DE

ASSESSING THE EFFECTS OF ALTERED LARVAL SALAMANDER DENSITY ON ECOSYSTEM PROCESSES IN A HEADWATER STREAM Larval salamanders are a dominant predator in headwater streams. While the southeastern United States is a current hotspot for salamander diversity, multiple stressors including climate change, land-use change, and invasive pathogens could reduce salamander densities. We used an enclosure experiment to assess potential consequences of altered larval salamander density in a headwater stream in the Coweeta LTER. We manipulated density of larval Desmognathus quadramaculatus, with treatments ranging from 0 to ~30 individuals·m^-2. We tested whether salamander density affected patch-scale measurements of ecosystem processes: primary productivity, respiration, and ammonium uptake. We predicted that salamander effects on our measurements were mediated by their effects on benthic leaf litter, and that litter breakdown rate would be inversely related to salamander density due to salamander predation on macroinvertebrate shredders. Preliminary results suggest that salamanders did not affect breakdown rates and that salamander density was not related to other measured processes. While some ecosystem functions in streams may be resilient to losses in a top consumer, understanding how to extrapolate our results to the reach-scale will also be important in predicting effects of consumer losses.

Kaitlin J. Farrell (Primary Presenter/Author), University of Georgia, farrellkj2@gmail.com;


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


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


Phillip Bumpers (Co-Presenter/Co-Author), University of Georgia, bumpersp@gmail.com;