Contaminants in fish tissue from US lakes and reservoirs: a national probabilistic study

An unequal probability design was used to develop national estimates for 268 persistent, bioaccumulative, and toxic chemicals in fish tissue from lakes and reservoirs of the conterminous United States (excluding the Laurentian Great Lakes and Great Salt Lake). Predator (fillet) and bottom-dweller (whole body) composites were collected from 500 lakes selected randomly from the target population of 147,343 lakes in the lower 48 states. Each of these composite types comprised nationally representative samples whose results were extrapolated to the sampled population of an estimated 76,559 lakes for predators and 46,190 lakes for bottom dwellers. Mercury and PCBs were detected in all fish samples. Dioxins and furans were detected in 81% and 99% of predator and bottom-dweller samples, respectively. Cumulative frequency distributions showed that mercury concentrations exceeded the EPA 300 ppb mercury fish tissue criterion at nearly half of the lakes in the sampled population. Total PCB concentrations exceeded a 12 ppb human health risk-based consumption limit at nearly 17% of lakes, and dioxins and furans exceeded a 0.15 ppt (toxic equivalent or TEQ) risk-based threshold at nearly 8% of lakes in the sampled population. In contrast, 43 target chemicals were not detected in any samples. No detections were reported for nine organophosphate pesticides, one PCB congener, 16 polycyclic aromatic hydrocarbons, or 17 other semivolatile organic chemicals.     

Personality and social networks in organizations: A review and future directions

Recent research linking individuals' personality characteristics to their social networks has brought a new understanding of how individual patterns of behavior affect networks in organizations. This review summarizes the major advancements in the three areas of social network research relevant to organizational behavior: (a) brokerage and structural holes; (b) network centrality and network size; and (c) strength of ties. This review also provides an agenda outlining three key opportunities for future research. These opportunities involve personality and social network change, bidirectional and dyadic processes, and the potential effect of network position on personality expression. Copyright © 2015 John Wiley & Sons, Ltd.     

Imperfectly optimal animals

Summary We consider models of behavior that apply to two different problems: when a predator should leave a foraging site and how a female should choose the best available male. In each case we derive rules for an optimal solution to the problem. We also derive models based on very simple, plausible rules of behavior that we suspect animals may actually use. Although the expected payoffs from optimality models always exceed the expected payoffs from our simpler behavioral models, under certain conditions the difference is not large. When good foraging sites last but a short time and when females' mobility in their habitat is limited, the results of simple models and optimal models are very close indeed.Because of the difficulty of distinguishing between the results of each type of model and because natural selection will presumably provide a best mix of solutions to a range of problems rather than a best solution to any one problem, we suggest that behavioral ecologists expend more effort on simple, plausible models of animal behavior. Such models provide ready-made testable hypotheses about the animal's approximation to optimality and about the actual mechanisms of behavior.     

An assessment of household willingness to pay for curbside recycling: a comparison of payment card and referendum approaches

Curbside recycling is a tool that communities use to reduce the need for landfill space. This study provides contingent valuation estimates of household willingness to pay (WTP) to continue a curbside recycling program in the face of budget cuts. Comparisons of two forms of the contingent valuation method (CVM) are provided: a single bounded referendum and a payment card. Neither approach emerges as unambiguously superior. Response rates were virtually identical. Both approaches show that support for curbside recycling is highly sensitive to price. Regression results from the payment card provided a more thorough identification of socio-demographic variables associated with WTP than the referendum, but the explanatory power of the two regressions did not differ significantly. The referendum estimates of mean WTP exceed those from the payment card, although the disparities are less than those typically reported in the CVM literature. Local policy makers cited the CVM results as influencing their decisions regarding funding options for the future of the program, and seemed to appreciate the fact that the two approaches provided a fairly narrow range of estimates of WTP. In an era when more of the burden of financing of environmental programs is being shifted to the local level, use of CVM to estimate the WTP of consumers for highly disaggregated goods and services designed to achieve environmental improvement will likely become more relevant to local decision makers who are interested in understanding their constituents' views.     

Natural attenuation of a plume from an emplaced coal tar creosote source over 14 years

An emplaced source of coal tar creosote within the sandy Borden research aquifer has documented the long-term (5140 days) natural attenuation for this complex mixture. Plumes of dissolved chemicals were produced by the essentially horizontal groundwater flowing at about 9 cm/day. Eleven chemicals have been extensively sampled seven times using a monitoring network of approximately 280, 14-point multilevel samplers. A model of source dissolution using Raoult's Law adequately predicted the dissolution of 9 of 11 compounds. Mass transformation has limited the extent of the plumes as groundwater has flowed more than 500 m, yet the plumes are no longer than 50 m. Phenol and xylenes have been removed and naphthalene has attenuated from its maximum extent on day 1357. Some compound plumes have reached an apparent steady state and the plumes of other compounds (dibenzofuran and phenanthrene) are expected to continue to expand due to an increasing mass flux and limited degradation potential. Biotransformation is the major process controlling natural attenuation at the site. The greatest organic mass lost is associated with the high solubility compounds. However, the majority of the mass loss for most compounds has occurred in the source zone. Oxygen is the main electron acceptor, yet the amount of organics lost cannot be accounted for by aerobic mineralization or partial mineralization alone. The complex evolution of these plumes has been well documented but understanding the controlling biotransformation processes is still elusive. This study has shown that anticipating bioattenuation patterns should only be considered at the broadest scale. Generally, the greatest mass loss is associated with those compounds that have a high solubility and low partitioning coefficients.     

The role of individual behavior type in mediating indirect interactions

Trait-mediated indirect interactions (TMII) play an important role in structuring natural communities, and numerous studies have experimentally demonstrated their presence in a variety of systems. However, these studies have largely examined the presence or absence of traits that are responsible for these interactions, without considering natural variation between individuals in the extent to which these traits are manifested. We used a well-documented TMII to investigate the importance of individual behavior type for determining the strength of the TMII. The toadfish Opsanus tau has an indirect positive influence on bivalve survival because the mud crab Panopeus herbstii, a consumer of bivalves, reduces foraging effort in the presence of toadfish. We quantified variation in the strength of persistent individual mud crab responses to toadfish and resulting variation in the strength of TMII. We demonstrate that the strength of this TMII is strongly influenced by mud crab size and behavior type, strengthening with the intensity of response of individual mud crabs to toadfish predator cues. Further, we demonstrate that the spatial distribution within intertidal oyster reefs of crabs with different behavior types is not random; mud crabs inhabiting subtidal areas, where predator cues are more persistent, are significantly less responsive to toadfish cues than mud crabs from intertidal areas. This spatial behavioral structure should lead to spatial variation in the strength of TMII. Given the widespread importance of TMII and the broad occurrence of individual personality or behavior types across numerous taxa, these results should be generally applicable. The distribution of behavior types within a population may therefore be a useful metric for improving our ability to predict the strength of TMII.     

Species invasion shifts the importance of predator dependence

The strength of interference between foraging individuals can influence per capita consumption rates, with important consequences for predator and prey populations and system stability. Here we demonstrate how the replacement of a previously established invader, the predatory crab Carcinus maenas, by the recently invading predatory crab Hemigrapsus sanguineus shifts predation from a species that experiences strong predator interference (strong predator dependence) to one that experiences weak predator interference (weak predator dependence). We demonstrate using field experiments that differences in the strength of predator dependence persist for these species both when they forage on a single focal prey species only (the mussel Mytilus edulis) and when they forage more broadly across the entire prey community. This shift in predator dependence with species replacement may be altering the biomass across trophic levels, consistent with theoretical predictions, as we show that H. sanguineus populations are much larger than C. maenas populations throughout their invaded ranges. Our study highlights that predator dependence may differ among predator species and demonstrates that different predatory impacts of two conspicuous invasive predators may be explained at least in part by different strengths of predator dependence.