@article {KNZ001851, title = {Top - down effects of a grazing, omnivorous minnow (Campostoma anomalum) on stream microbial communities}, journal = {Freshwater Science}, volume = {37}, year = {2018}, pages = {121-133}, abstract = {

Top\–down control exerted by macroconsumers can strongly affect lower trophic levels and ecosystem processes. Studies of effects on primary consumers in streams have been focused on algae, and effects on bacteria are largely unknown. We manipulated the density of an omnivorous, grazing minnow, the central stoneroller (Campostoma anomalum), in experimental stream mesocosms (treatments with 0, 1, 2, 3, 4, 5, 6, or 7 individuals) to understand consumer effects on algal and bacterial abundance (chlorophyll a [Chl a] extraction, bacterial cell counts, biomass measurements) and bacterial diversity and community composition (via Illumina MiSeq sequencing of the V4 region of the 16S ribosomal RNA gene). Increasing C. anomalum density reduced algal biomass until density reached ~2 fish (5 g fish biomass/m2), and higher fish densities did not affect algal biomass. Fish biomass did not affect bacterial cell counts. Biofilm organic matter decreased with increasing C. anomalum biomass. Bacterial community composition was not affected by fish biomass, but variation in community composition was correlated with shifts in bacterial abundances. Evenness of bacterial operational taxonomic units (OTUs) decreased with increasing C. anomalum biomass, indicating that bacterial communities exhibited a greater degree of OTU dominance when fish biomass was higher. These findings suggest that this grazing fish species reduces algal abundance and organic matter in low-nutrient streams until a threshold of moderate fish abundance is reached and that it reduces evenness of benthic bacterial communities but not bacterial biomass. Given the importance of biofilm bacteria for ecosystem processes and the ubiquity of grazing fishes in streams, future researchers should explore both top\–down and bottom\–up interactions in alternative environmental contexts and with other grazing fish species.

}, keywords = {LTER-KNZ}, doi = {10.1086/696292}, url = {https://www.journals.uchicago.edu/doi/abs/10.1086/696292}, author = {Veach, Allison M. and Troia, Matthew J. and A. Jumpponen and W. K. Dodds} } @article {KNZ001896, title = {Testing metabolic cold adaptation as a driver of warm-water fish species replacement along the river continuum}, journal = {Environmental Biology of Fishes}, volume = {100}, year = {2017}, pages = {265-279}, abstract = {

Hydrologic and thermal regimes vary along the upstream-to-downstream river continuum and drive the assembly of fish communities. The metabolic cold adaptation (MCA) hypothesis predicts that faster development is adaptive for species exposed to shorter growing seasons. Whether gradients of hydrologic variability and seasonal thermal regime associated with the river continuum operate as environmental filters on species with differing developmental rates remains an untested mechanism of community assembly. We analyzed daily records of stream discharge and modeled stream temperatures to quantify these two gradients of abiotic harshness in Kansas, USA. We then used laboratory experiments to compare temperature-dependent larval development rates among three congeneric cyprinid species that are most abundant in small tributaries (Pimephales promelas), medium tributaries (P. notatus), or river mainstems (P. vigilax). Growing season duration increased with stream size, with temperature exceedance thresholds of 22 and 26\ \°C lasting 1.4 and 270 times longer, respectively, in eighth order river mainstems compared to second order tributaries. The frequency of small flood pulses within the growing season peaked in mid-order streams, whereas the frequency of large flood pulses within the growing season peaked in low-order streams. Larval development rates increased with incubation temperature, but did not differ predictably among species. These findings, when viewed alongside a companion study, suggest that thermal adaptation and not MCA explains the replacements of Pimephales species along the river continuum. The prominent upstream-to-downstream gradient in growing season duration highlights the need for studies on the evolutionary and ecological significance of this infrequently explored characteristic of the river continuum.

}, keywords = {LTER-KNZ}, doi = {10.1007/s10641-017-0577-2}, url = {http://link.springer.com/10.1007/s10641-017-0577-2}, author = {Troia, Matthew J. and K. B. Gido} }