Diversity-invasibility across an experimental disturbance gradient in Appalachian Forests

Research examining the relationship between community diversity and invasions by nonnative species has raised new questions about the theory and management of biological invasions. Ecological theory predicts, and small-scale experiments confirm, lower levels of nonnative species invasion into species-rich compared to species-poor communities, but observational studies across a wider range of scales often report positive relationships between native and nonnative species richness. This paradox has been attributed to the scale dependency of diversity-invasibility relationships and to differences between experimental and observational studies. Disturbance is widely recognized as an important factor determining invasibility of communities, but few studies have investigated the relative and interactive roles of diversity and disturbance on nonnative species invasion. Here, we report how the relationship between native and nonnative plant species richness responded to an experimentally applied disturbance gradient (from no disturbance up to clearcut) in oak-dominated forests. We consider whether results are consistent with various explanations of diversity-invasibility relationships including biotic resistance, resource availability, and the potential effects of scale (1 m2 to 2 ha). We found no correlation between native and nonnative species richness before disturbance except at the largest spatial scale, but a positive relationship after disturbance across scales and levels of disturbance. Post-disturbance richness of both native and nonnative species was positively correlated with disturbance intensity and with variability of residual basal area of trees. These results suggest that more nonnative plants may invade species-rich communities compared to species-poor communities following disturbance.     

Sensitivity of mesquite shrubland CO2 exchange to precipitation in contrasting landscape settings

In semiarid ecosystems, physiography (landscape setting) may interact with woody-plant and soil microbe communities to constrain seasonal exchanges of material and energy at the ecosystem scale. In an upland and riparian shrubland, we examined the seasonally dynamic linkage between ecosystem CO2 exchange, woody-plant water status and photosynthesis, and soil respiration responses to summer rainfall. At each site, we compared tower-based measurements of net ecosystem CO2 exchange (NEE) with ecophysiological measurements among velvet mesquite (Prosopis velutina Woot.) in three size classes and soil respiration in sub-canopy and inter-canopy micro-sites. Monsoonal rainfall influenced a greater shift in the magnitude of ecosystem CO2 assimilation in the upland shrubland than in the riparian shrubland. Mesquite water status and photosynthetic gas exchange were closely linked to the onset of the North American monsoon in the upland shrubland. In contrast, the presence of shallow alluvial groundwater in the riparian shrubland caused larger size classes of mesquite to be physiologically insensitive to monsoonal rains. In both shrublands, soil respiration was greatest beneath mesquite canopies and was coupled to shallow soil moisture abundance. Physiography, through its constraint on the physiological sensitivity of deeply rooted woody plants, may interact with plant-mediated rates of soil respiration to affect the sensitivity of semiarid-ecosystem carbon exchange in response to episodic rainfall.     

Determination of steroidal estrogens in flushed dairy manure wastewater by gas chromatography-mass spectrometry

There is a critical need to accurately measure the concentrations of natural steroidal estrogens in flushed dairy manure wastewater (FDMW) to assess any potential risk of waterway contamination resulting from land application. Estrogens are a concern because low concentrations (10-100 ng L-1) in water can adversely affect aquatic vertebrate species such as fish, turtles, and frogs by disrupting the normal function of their endocrine systems. The objective of this study was to develop a sample preparation method that permits the quantification of four natural steroidal estrogens (17alpha-estradiol, 17beta-estradiol, estrone, and estriol) in FDMW by gas chromatography-mass spectrometry (GC-MS). Solid-phase extraction with graphitized carbon black was used for the bulk extraction of estrogens from FDMW and additional sample purification was accomplished with C-18. The sample preparation method allowed estrogens to be detected accurately by GC-MS in FDMW. Spiked recovery experiments indicated that the method is satisfactory for measuring the estrogens of interest in FDMW with average recovery of >90%. As expected in FDMW, characterization of the estrogen profile revealed a large abundance of 17alpha-estradiol relative to 17beta-estradiol and estrone. Estriol was not detected in FDMW. The methodology developed in this research helps provide an analytical foundation for the quantification of steroidal estrogens in FDMW by GC-MS.     

Need for multiscale planning for conservation of urban bats

For over a century there have been continual efforts to incorporate nature into urban planning. These efforts (i.e., urban reconciliation) aim to manage and create habitats that support biodiversity within cities. Given that species select habitat at different spatial scales, understanding the scale at which urban species respond to their environment is critical to the success of urban reconciliation efforts. We assessed species–habitat relationships for common bat species at 50‐m, 500‐m, and 1 km spatial scales in the Chicago (U.S.A.) metropolitan area and predicted bat activity across the greater Chicago region. Habitat characteristics across all measured scales were important predictors of silver‐haired bat (Lasionycteris noctivagans) and eastern red bat (Lasiurus borealis) activity, and big brown bat (Eptesicus fuscus) activity was significantly lower at urban sites relative to rural sites. Open vegetation had a negative effect on silver‐haired bat activity at the 50‐m scale but a positive effect at the 500‐m scale, indicating potential shifts in the relative importance of some habitat characteristics at different scales. These results demonstrate that localized effects may be constrained by broader spatial patterns. Our findings highlight the importance of considering scale in urban reconciliation efforts and our landscape predictions provide information that can help prioritize urban conservation work.     

Delineation and Validation of River Network Spatial Scales for Water Resources and Fisheries Management

Identifying appropriate spatial scales is critically important for assessing health, attributing data, and guiding management actions for rivers. We describe a process for identifying a three-level hierarchy of spatial scales for Michigan rivers. Additionally, we conduct a variance decomposition of fish occurrence, abundance, and assemblage metric data to evaluate how much observed variability can be explained by the three spatial scales as a gage of their utility for water resources and fisheries management. The process involved the development of geographic information system programs, statistical models, modification by experienced biologists, and simplification to meet the needs of policy makers. Altogether, 28,889 reaches, 6,198 multiple-reach segments, and 11 segment classes were identified from Michigan river networks. The segment scale explained the greatest amount of variation in fish abundance and occurrence, followed by segment class, and reach. Segment scale also explained the greatest amount of variation in 13 of the 19 analyzed fish assemblage metrics, with segment class explaining the greatest amount of variation in the other six fish metrics. Segments appear to be a useful spatial scale/unit for measuring and synthesizing information for managing rivers and streams. Additionally, segment classes provide a useful typology for summarizing the numerous segments into a few categories. Reaches are the foundation for the identification of segments and segment classes and thus are integral elements of the overall spatial scale hierarchy despite reaches not explaining significant variation in fish assemblage data.     

Community wildfire protection planning in the American West: homogeneity within diversity?

As large wildfires have become common across the American West, federal policies such as the Healthy Forests Restoration Act have empowered local communities to plan for their own wildfire protection. Here, we present an analysis of 113 community wildfire protection plans from 10 western states where large fires have recently occurred. These plans contain wide diversity in terms of specific plan elements and dimensions, yet less diversity in the paradigms underlying their fire protection approaches. These patterns held true across both plans constructed solely by local actors as well as those constructed with the help of outside consultant expertise.     

Older can be better: physiological costs of paternal investment in the Florida scrub-jay

In species that undergo actuarial senescence, the value of current reproduction is predicted to increase relative to the value of future reproduction with age, as the probability of survival to another reproductive event is reduced. Therefore, life history theory predicts that aging animals should increase their investment in reproduction. However, an increase in reproductive investment may carry significant costs to the breeding individuals. We recorded provisioning rates of Florida scrub-jay male breeders, followed by their immediate capture to assess body condition and collect blood for an in vitro test of immunocompetence and an assay of baseline corticosterone for a measure of stress. Older males provisioned offspring and brooding mates at the highest rates. There was no evidence of any physiological deficits in males with high provisioning rates, independent of age. It appears that birds that survive to old age are high quality birds that maintain good physiological condition, which complements the value of experience and permits maximal investment in offspring.     

Regional source identification using Lagrangian stochastic particle dispersion and HYSPLIT backward-trajectory models

The main objective of this study was to investigate the capabilities of the receptor-oriented inverse mode Lagrangian Stochastic Particle Dispersion Model (LSPDM) with the 12-km resolution Mesoscale Model 5 (MM5) wind field input for the assessment of source identification from seven regions impacting two receptors located in the eastern United States. The LSPDM analysis was compared with a standard version of the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) single-particle backward-trajectory analysis using inputs from MM5 and the Eta Data Assimilation System (EDAS) with horizontal grid resolutions of 12 and 80 km, respectively. The analysis included four 7-day summertime events in 2002; residence times in the modeling domain were computed from the inverse LSPDM runs and HYPSLIT-simulated backward trajectories started from receptor-source heights of 100, 500, 1000, 1500, and 3000 m. Statistics were derived using normalized values of LSPDM- and HYSPLIT-predicted residence times versus Community Multiscale Air Quality model-predicted sulfate concentrations used as baseline information. From 40 cases considered, the LSPDM identified first- and second-ranked emission region influences in 37 cases, whereas HYSPLIT-MM5 (HYSPLIT-EDAS) identified the sources in 21 (16) cases. The LSPDM produced a higher overall correlation coefficient (0.89) compared with HYSPLIT (0.55-0.62). The improvement of using the LSPDM is also seen in the overall normalized root mean square error values of 0.17 for LSPDM compared with 0.30-0.32 for HYSPLIT. The HYSPLIT backward trajectories generally tend to underestimate near-receptor sources because of a lack of stochastic dispersion of the backward trajectories and to overestimate distant sources because of a lack of treatment of dispersion. Additionally, the HYSPLIT backward trajectories showed a lack of consistency in the results obtained from different single vertical levels for starting the backward trajectories. To alleviate problems due to selection of a backward-trajectory starting level within a large complex set of 3-dimensional winds, turbulence, and dispersion, results were averaged from all heights, which yielded uniform improvement against all individual cases.     

Microbial and plant ecology of a long-term TNT-contaminated site

The contamination of the environment with explosive residues presents a serious ecological problem at sites across the world, with the highly toxic compound trinitrotoluene (TNT) the most widespread contaminant. This study examines the soil microbial community composition across a long-term TNT-contaminated site. It also investigates the extent of nitroaromatic contamination and its effect on vegetation. Concentrations of TNT and its metabolites varied across the site and this was observed to dramatically impact on the extent and diversity of the vegetation, with the most heavily contaminated area completely devoid of vegetation. Bryophytes were seen to be particularly sensitive to TNT contamination. The microbial population experienced both a reduction in culturable bacterial numbers and a shift in composition at the high concentrations of TNT. DGGE and community-level physiological profiling (CLPP) revealed a clear change in both the genetic and functional diversity of the soil when soil was contaminated with TNT.     

Distribution of sulfamethazine, chlortetracycline and tylosin in manure and soil of Canadian feedlots after subtherapeutic use in cattle

Feedlots are potential point sources for the flow of antibiotics into the environment due to common use of antibiotics such as sulfamethazine, chlortetracycline and tylosin. Hence soils and manures originating from a grassland control, an experimental and a commercial feedlot were analyzed and mass balances were calculated for these antibiotics. Up to 9990 μg kg⁻¹ sulfamethazine and 401 μg kg⁻¹ chlortetracycline on a dry matter basis were determined in feedlot manure. Soil concentrations were two orders of magnitude smaller. This corresponds to 7-40% of the calculated residual amount. In the commercial feedlot chlortetracycline was found down to soil depths of −40 cm; sulfamethazine was still detectable 1 year after medication. Sulfamethazine and chlortetracycline were additionally determined in manure of a control treatment in the experimental feedlot where cattle never received antibiotics. This was attributed to runoff from upslope pens. Consequently, antibiotics partially persist within feedlots and may be dislocated into the surrounding environment by vertical transport and runoff.