Population Dynamics of Culex restuans and Culex pipiens (Diptera: Culicidae) Related to Climatic Factors in Northwest Ohio.

Two species of Culex mosquitoes are common throughout much of North America. Culex restuans Theobold is a native species, whereas Culex pipiens L. is a European immigrant that has been in North America since the 1600s. Larvae of Cx. restuans are numerically dominant in spring and early summer but Cx. pipiens dominates by mid-summer. This transition is termed the "Culex crossover" and has been previously explored in larval populations, largely because Cx. pipiens is more likely to transfer West Nile virus to humans. Adult mosquitoes of both species were captured in 14 light traps in Lucas County, OH, between May and October 1980-2011. We examined this 31-yr, continuous record of adult populations for signs of a species crossover, relationships between abundances of both species and climate factors, and evidence of interspecific competition. The total cumulative degree-days (above 0°C), total cumulative precipitation, and total number of each species were calculated for each day of January-September (annual) and May-September (mosquito season) of each year. On average, adult Cx. pipiens became numerically dominant over Cx. restuans on day 175 ± 21 (June 24), consistent with the Culex crossover reported for their larvae. Pearson correlations showed that abundances of both species were related to temperature and precipitation, but Cx. pipiens tended to be positively related to climatic factors, whereas Cx. restuans showed negative correlations. Moreover, abundances of the two species were more positively than negatively related to one another, providing no evidence of interspecific competition.

Impact of light regimes on productivity patterns of benthic microbial mats in an antarctic lake: a modeling study.

Filamentous cyanobacteria often dominate benthic microbial communities of antarctic lakes and usually exhibit saturation of photosynthesis at light intensities approximately 100 microEinst m-2 s-1. Incident light regimes are controlled by ice and snow accumulations overlaying water columns during much of the year. Thus, light availability to microbial mats is often below saturation intensity and is strongly influenced by modest changes in climatic factors. A model of net primary production for benthic mat communities of the subantarctic Sombre Lake, Signy Island, was developed (1) to evaluate depth-specific productivities of mat communities, (2) to test the relative importances of model parameters to mat production, and (3) to explore the potential impacts of climate change on mat production as manifested through changes in light regime. Simulated rates of net primary production corresponded to observations on a daily basis (approximately 1-4 micrograms C fixed mg-1 ash-free DW of mat d-1) but were an order of magnitude lower than estimates of net annual production based on field measurements (< or = 3 vs. 11-45 g C m-2 yr-1, respectively). Close examination suggested that the simulated values were more plausible. A detailed sensitivity analysis of model behavior revealed that variations in the time of ice and snow melt in spring accounted for 40-60% of the total variation in model behavior, emphasizing the importance of climatic factors to net primary production of mat communities and the sensitivity of mat production to climate change.

Dynamic relationships between microbial biomass, respiration, inorganic nutrients and enzyme activities: informing enzyme-based decomposition models.

We re-examined data from a recent litter decay study to determine if additional insights could be gained to inform decomposition modeling. Rinkes et al. (2013) conducted 14-day laboratory incubations of sugar maple (Acer saccharum) or white oak (Quercus alba) leaves, mixed with sand (0.4% organic C content) or loam (4.1% organic C). They measured microbial biomass C, carbon dioxide efflux, soil ammonium, nitrate, and phosphate concentrations, and ß-glucosidase (BG), ß-N-acetyl-glucosaminidase (NAG), and acid phosphatase (AP) activities on days 1, 3, and 14. Analyses of relationships among variables yielded different insights than original analyses of individual variables. For example, although respiration rates per g soil were higher for loam than sand, rates per g soil C were actually higher for sand than loam, and rates per g microbial C showed little difference between treatments. Microbial biomass C peaked on day 3 when biomass-specific activities of enzymes were lowest, suggesting uptake of litter C without extracellular hydrolysis. This result refuted a common model assumption that all enzyme production is constitutive and thus proportional to biomass, and/or indicated that part of litter decay is independent of enzyme activity. The length and angle of vectors defined by ratios of enzyme activities (BG/NAG vs. BG/AP) represent relative microbial investments in C (length), and N and P (angle) acquiring enzymes. Shorter lengths on day 3 suggested low C limitation, whereas greater lengths on day 14 suggested an increase in C limitation with decay. The soils and litter in this study generally had stronger P limitation (angles >45°). Reductions in vector angles to <45° for sand by day 14 suggested a shift to N limitation. These relational variables inform enzyme-based models, and are usually much less ambiguous when obtained from a single study in which measurements were made on the same samples than when extrapolated from separate studies.