When are fish sources versus sinks of nutrients in lake ecosystems?

Animals can be important in nutrient cycling through a variety of direct and indirect pathways. A high biomass of animals often represents a large pool of nutrients, leading some ecologists to argue that animal assemblages can represent nutrient sinks within ecosystems. The role of animals as sources vs. sinks of nutrients has been debated particularly extensively for freshwater fishes. We argue that a large pool size does not equate to a nutrient sink; rather, animals can be nutrient sinks when their biomass increases, when emigration rates are high, and/or when nutrients in animal carcasses are not remineralized. To further explore these ideas, we use a simple model to evaluate the conditions under which fish are phosphorus (P) sources or sinks at the ecosystem (lake) level, and at the habitat level (benthic and water column habitats). Our simulations suggest that, under most conditions, fish are sinks for benthic P but are net P sources to the water column. However, P source and sink strengths depend on fish feeding habits (proportion of P consumed from the benthos and water column), migration patterns, and especially the fate of carcass P. Of particular importance is the rate at which carcasses are mineralized and the relative importance of benthic vs. pelagic primary producers in taking up mineralized P (and excreted P). Higher proportional uptake of P by benthic primary producers increases the likelihood that fish are sinks for water column P. Carcass bones and scales are relatively recalcitrant and can represent a P sink even if fish biomass does not change over time. Thus, there is a need for better documentation of the fraction of carcass P that is remineralized, and the fate of this P, under natural conditions. We urge a more holistic perspective regarding the role of animals in nutrient cycling, with a focus on quantifying the rates at which animals consume, store, release, and transport nutrients under various conditions

Fish Distributions and Nutrient Cycling in Streams: Can Fish Create Biogeochemical Hotspots?

Rates of biogeochemical processes often vary widely in space and time, and characterizing this variation is critical for understanding ecosystem functioning. In streams, spatial hotspots of nutrient transformations are generally attributed to physical and microbial processes. Here we examine the potential for heterogeneous distributions of fish to generate hotspots of nutrient recycling. We measured nitrogen (N) and phosphorus (P) excretion rates of 47 species of fish in an N-limited Neotropical stream, and we combined these data with population densities in each of 49 stream channel units to estimate unit- and reach-scale nutrient recycling. Species varied widely in rates of N and P excretion as well as excreted N:P ratios (6–176 molar). At the reach scale, fish excretion could meet \u3e75% of ecosystem demand for dissolved inorganic N and turn over the ambient NH4 pool i

Male aggression varies with consortship rate and habitat in a dolphin social network

Coalitions and alliances exemplify the core elements of conflict and cooperation in animal societies. Ecological influences on alliance formation are more readily attributed to within-species variation where phylogenetic signals are muted. Remarkably, male Indo-Pacific bottlenose dolphins in Shark Bay, Western Australia, exhibit systematic spatial variation in alliance behavior, not simply within a species or population, but within a single social network. Moving SE-NW along Peron Peninsula in Shark Bay, males ally more often in trios than pairs, consort females more often, and exhibit greater seasonal movements. Ecological models predict more male-male conflict in the north, but sufficient observations of aggression are lacking. However, dolphins often incur marks, in the form of tooth rakes, during conflicts. Here we report that the incidence of new tooth rake marks varies systematically in the predicted pattern, with greater marking in the north, where males form more trios and consort females at a higher rate. While our previous work demonstrated that alliance complexity has an ecological component, we can now infer that ecological variation impacts the level of alliance-related conflict in Shark Bay

Fish Distributions And Nutrient Cycling In Streams: Can Fish Create Biogeochemical Hotspots

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/117137/1/ecy20088982335.pd

Multi-Institutional Outcomes of Minimally Invasive Harvest of Rectal Mucosa Graft for Anterior Urethral Reconstruction.

PurposeWe report multi-institutional outcomes in patients who underwent urethroplasty with a rectal mucosa graft.Materials and methodsWe used the TURNS (Trauma and Urologic Reconstructive Network of Surgeons) database to identify patients who underwent urethral reconstruction with transanal harvest of a rectal mucosa graft. We reviewed preoperative demographics, stricture etiology, previous management and patient outcomes.ResultsWe identified 13 patients from April 2013 to June 2017. Median age at surgery was 54 years. The stricture etiology was lichen sclerosus in 6 of 13 patients (46%), idiopathic in 2 (15%), hypospadias in 1 (7%), prior gender confirming surgery in 3 (23%) and rectourethral fistula after radiation for prostate cancer in 1 (7%). Prior procedures included failed urethroplasty with a buccal mucosa graft in 9 of 13 patients (69%), direct vision internal urethrotomy in 2 (15%) and none in 2 (15%). Median stricture length was 13 cm. Stricture location in the 9 cisgender patients was panurethral in 5 (56%), bulbopendulous in 2 (22%) and bulbar in 2 (22%). It was located at the junction of the fixed urethra extending into the neophallus in all 3 patients (100%) who underwent prior gender confirming surgery. Mean rectal mucosa graft length for urethroplasty was 10.6 cm (range 3 to 16). Repair types included dorsal or ventral onlay, or 2-stage repair. Stricture recurred at a median followup of 13.5 months in 2 of 13 patients (15%). Postoperative complications included glans dehiscence, urethrocutaneous fistula and compartment syndrome in 1 patient each (7%). No rectal or bowel related complications were reported.ConclusionsUrethral reconstruction with a transanal harvested rectal mucosa graft is a safe technique when a buccal mucosa graft is unavailable or not indicated

Linking Adult Reproduction and Larval Density of Invasive Carp in a Large River

Eeotogists increasingly recognize the need to understand how landscapes ami food webs interact. Reservoir ecosystems are heavily subsidized by nutrients and detritus from surrounding watersheds, and ofren contain abundant populations of gizzard shad, an omnivorous ftsh that consumes plankton and detritus. Gizzard shad link terrestrial landscapes ami pelagic reservoir food webs by consuming detritus, translocating nutrients from sedimctn detritus to the water column, and consuming zooplaukton. The abundance of gizzard shad increases with watershed agricuhuralization, most likely through n variety oj mechanisms npeniting on ttuvat and adult life stages. Gizzard shad have myriad effects on reservoirs, including impacts on nutrients, phytoplankton, zooplankton, and fish, and many of their effects vary with ecosystem productivity (i.e., watershed land use). Interactive feedbacks among watersheds, gizzard shad populations, and reservoir food webs operate to maintain dominance of gizzard shad in highly productive systems. Thus, effective stewardship of reservoir ecosystems must incorporate both watershed and food-web perspective