Transmission of employment shocks before and after the Oklahoma City tornado

This study examined the economic impact of the May 3, 1999 Oklahoma tornado outbreak on the labor markets of Oklahoma City (OK), Wichita (KS), and Kansas City (MO). In particular, this article examines the transmission of shocks to employment growth across these different labor markets. Using monthly employment data from January 1990 to December 2004, we provide empirical evidence on the cross-market relationships that existed before and after the Oklahoma City tornado. The results suggest that the impact of the wind event may have altered labor market dynamics in Oklahoma City, as well as Wichita and Kansas City.     

Decision support in urban water management based on generic scenarios: The example of NoMix technology

Urine source separation (NoMix technology) followed by processing the concentrated nutrient solution has the potential to become a cost-efficient alternative to conventional end-of-pipe nutrient elimination. A choice of processing technologies can only be made for specific scenarios, and there is currently no methodology for analyzing generic situations. In setting up a formalized decision-support methodology (based on STEEPLED analysis), we discuss how to create such generic scenarios, how to couple them with process engineering objectives, how to define the technology requirements, and finally how to produce a realistic subset of technology alternatives. The methodology is tested in five real scenarios. We also touch on the criteria for a final choice of technology taking into account large uncertainties about the performance of real technologies. We conclude that technology development is one of the most important requirements for implementing urine source separation in practice. There is an urgent need to develop cost-efficient processing technologies that satisfy the requirements of stakeholders.     

Empirical evaluation of neutral theory

We describe a general framework for testing neutral theory. We summarize similarities and differences between ten different versions of neutral theory. Two central predictions of neutral theory are that species abundance distributions will follow a zero-sum multinomial distribution and that community composition will change over space due to dispersal limitation. We review all published empirical tests of neutral theory. With the exception of one type of test, all tests fail to support neutral theory. We identify and perform several new tests. Specifically, we develop a set of best practices for testing the fit of the zero-sum multinomial (ZSM) vs. a lognormal null hypothesis and apply this to a data set, concluding that the lognormal outperforms neutral theory on robust tests. We explore whether a priori parameterization of neutral theory is possible, and we conclude that it is not. We show that non-curve-fitting predictions readily derived from neutral theory are easily falsifiable. In toto, there is a current overwhelming weight of evidence against neutral theory. We suggest some next steps for neutral theory.     

Habitat complexity impacts persistence and species interactions in an intertidal whelk

Although experiments have shown that habitat structure may influence the distribution of species and species interactions, these effects are still not commonly integrated into studies of community dynamics. Since habitat structure often varies within and among communities, this may limit our understanding of how various factors influence communities. Here, we examined how mussel bed complexity (the presence and thickness of mussel layers) influenced the persistence of whelks (Nucella emarginata) and interactions with a top predator (ochre sea stars, Pisaster ochraceus) and prey (mussels, Mytilus californianus). Results from a mark?Crecapture experiment indicate that whelk recapture rates are higher in more complex habitats, and laboratory experiments demonstrate that habitat complexity affects whelk feeding, growth, and nonconsumptive interactions with a keystone predator. Habitat complexity therefore has direct effects on species and also may lead to trade-offs among feeding, refuge, and other factors, potentially influencing the distribution of whelks and the effects of both whelks and sea stars on intertidal communities. These results demonstrate that habitat structure may play an important role in intertidal communities and other habitats and should be further considered in the experimental design of future studies of community dynamics.     

Simulating property exchange in estuarine ecosystem models at ecologically appropriate scales

A computational scheme has been developed and tested to simulate property exchange by advection and dispersion in estuaries at time and space scales that are well suited to ecological and management simulations, but are coarse relative to the demands of physical hydrodynamic models. An implementation of the Regional Ocean Model System (ROMS) for the Providence River and Narragansett Bay (RI, USA) was used to determine property exchanges between the spatial elements of an ecological box model. The basis for the method is the statistical tabulation of numerical dye experiments done with the full ROMS physical model. The ROMS model domain was subdivided into fifteen coarse boxes, each with two vertical layers, defining 30 elements that were used for the box model simulations. Dye concentrations were set to arbitrary initial concentrations for all ROMS grids in the large elements, and the ROMS model was run for 24 h. The final distribution of the dye among the elements was used as a tracer for property exchange over that day and was used to develop an exchange matrix. Box model predictions of salinity over 77 days in each element compared favorably with ROMS simulated salinity averaged over the same spatial elements, although the disparity was greater in areas where large river inflows caused strong gradients in ROMS within elements assumed to be homogeneous in the box model. The 77-day simulation included periods of high and low river flow. Despite the large size of the spatial elements, dispersion artifacts were small, much less than the modeled daily exchanges. While others have taken a similar approach, we found a number of theoretical and practical considerations deserved careful attention for this approach to perform satisfactorily. Whereas the full ROMS model takes 9 days on a powerful computing cluster to compute the physics simulation for 77 days, the box model simulates physics and biology for the same interval in 5 s on a personal computer, and a full year in under 1 min. The exchange matrix mixing model is a fast, cost effective, and convenient way to simulate daily variation of complex estuarine physics in ecological modeling at appropriate scales of space and time.     

Estimating digestion time in gelatinous predators: a methodological comparison with the scyphomedusa Aurelia aurita

In order to quantify the trophic impact of gelatinous predators, digestion time estimates are commonly applied to counts of prey in the guts. Three primary approaches are used, the Manual-feeding, Natural-feeding and Steady-state methods; these differ in methodology and their underlying assumptions. The criteria used to define the end-point of digestion, and the resolution at which digestion progress is observed, also vary across studies. To understand the impact of such differences, we estimate digestion times of the scyphomedusa Aurelia aurita fed adult females of the copepod Acartia tonsa using these various approaches. We find ~fourfold differences which can be attributed to bias towards the slowest rates of digestion by some end-point criteria, and overestimation from low observation resolution. Artificial manipulation and the degree to which swimming and feeding behaviour are natural may also influence estimates. We provide recommendations for those quantifying digestion times of Aurelia aurita medusae and gelatinous predators.     

Leading from the front? Social networks in navigating groups

In many group-living animals, leadership by only a fraction of the group members can be important for group navigation. It has been shown that subgroups of informed individuals can steer the remainder of the group without direct communication, resolving conflicts of interest through individual-to-individual interactions. We present a model for the navigation of collectively moving groups that includes preferential interactions between individuals as a way of imposing social network structures, known to be present in many species. We show that effective leadership can occur when leaders do not occupy frontal spatial positions and when navigation tendency is appropriately balanced with social position. Our model also shows that small minorities can dominate movement decisions if they have navigational knowledge combined with influential social network positions. Our findings highlight the mechanistic importance of social networks for the movement decisions of animal groups. We discuss the implications of our research for interpreting empirical observations.     

The On-Ranch Economics of Riparian Zone Cattle Grazing Management

A simulation model of a cattle ranch based in southern Alberta, Canada was developed to evaluate the on-ranch economics of adopting different grazing management strategies to improve riparian grazing capacity in natural grass rangeland. Under low-cost scenarios, there are positive economic incentives to adopt strategies to maintain riparian zones that already have high grazing capacity. However, riparian zones that have declined to moderate or low grazing capacity may require additional economic incentives to encourage ranches to adopt more costly management strategies to improve the grazing capacity. The economic incentives to adopt costly management strategies are highly sensitive to the size and shape of the riparian zone and rates of grazing capacity decline or improvement.