Criteria for the evaluation of dioxins in the environment

In FRG and other countries unequivocal criteria for the limitation of dioxins (PCDD's/PCDF's) in food like vegetables and fruits are lacking. These have to be directly associated with the limitation of dioxins in the soil and the deposition of particulate matter as the two main pathways for plant contamination. Based on recent investigations in the vicinity of cable-waste incinerators in Northrhine-Westphalia with comparatively high contents of dioxins in garden plants and soils and other sources of dioxins, considerations are given for the establishment of the criteria urgently needed.     

Streamwater phosphorus and nitrogen across a gradient in rural–agricultural land use intensity

This paper provides an overview of the impacts of rural land use on lowland streamwater phosphorus (P) and nitrogen (N) concentrations and P loads and sources in lowland streams. Based on weekly water quality monitoring, the impacts of agriculture on streamwater P and N hydrochemistry were examined along a gradient of rural–agricultural land use, by monitoring three sets of ‘paired’ (near-adjacent) rural headwater streams, draining catchments which are representative of the major geology, soil types and rural/agricultural land use types of large areas of lowland Britain. The magnitude and timing of P and N inputs were assessed and the load apportionment model (LAM) was applied to quantify ‘continuous’ (point) source and ‘flow-dependent’ (diffuse) source contributions of P to these headwater streams. The results show that intensive arable farming had only a comparatively small impact on streamwater total phosphorus (TP loads), with highly consistent stream diffuse-source TP yields of ca. 0.5 kg-P ha^?1 year^?1 for the predominantly arable catchments with both clay and loam soils, compared with 0.4 kg-P ha^?1 year^?1 for low agricultural intensity grassland/woodland on similar soil types. In contrast, intensive livestock farming on heavy clay soils resulted in dramatically higher stream diffuse-source TP yields of 2 kg-P ha^?1 year^?1. The streamwater hydrochemistry of the livestock-dominated catchment was characterised by high concentrations of organic P, C and N fractions, associated with manure and slurry sources. Across the study sites, the impacts of human settlement were clearly identifiable with effluent inputs from septic tanks and sewage treatment works resulting in large-scale increases in soluble reactive phosphorus (SRP) loads and concentrations. At sites heavily impacted by rural settlements, SRP concentrations under baseflow conditions reached several hundred μg-P L^?1. Load apportionment modelling demonstrated significant ‘point-source’ P inputs to the streams even where there were no sewage treatment works within the upstream catchment. This indicates that, even in sparsely populated rural headwater catchments, small settlements and even isolated groups of houses are sufficient to cause significant nutrient pollution and that septic tank systems serving these rural communities are actually operating as multiple point sources, rather than a diffuse input.     

Why we need theory in the organization sciences

To make the case that theory is a necessary part of research in the organization sciences, I develop three lines of argument. In the first, drawing upon Staw and Sutton's (1995, “What theory is not” Administrative Science Quarterly, 40, 371–384) classic piece, I outline the boundaries of theory and, using a recently published empirical article as an example, demonstrate how research based on literature references and line‐and‐box diagrams instead of explanatory theory can make only a limited contribution to the literature. I next discuss more generally the pitfalls of conducting research without first developing theory, citing the example of malaria. In the final section of the article, I defend the role of theory‐review articles, such as those published in the Academy of Management Review, and illustrate (again by reference to an example) how such articles are critical to advancing organizational research. Copyright © 2016 John Wiley & Sons, Ltd.     

Landscape-scale resources promote colony growth but not reproductive performance of bumble bees

Variation in the availability of food resources over space and time is a likely driver of how landscape structure and composition affect animal populations. Few studies, however, have directly assessed the spatiotemporal variation in resource availability that arises from landscape pattern, or its effect on populations and population dynamic parameters. We tested the effect of floral resource availability at the landscape scale on the numbers of worker, male, and queen offspring produced by bumble bee, Bombus vosnesen?kii, colonies experimentally placed within complex agricultural-natural landscapes. We quantified flower densities in all land use types at different times of the season and then used these data to calculate spatially explicit estimates of floral resources surrounding each colony. Floral availability strongly correlated with landscape structure, and different regions of the landscape showed distinct seasonal patterns of floral availability. The floral resources available in the landscape surrounding a colony positively affected the number of workers and males it produced. Production was more sensitive to early- than to later-season resources. Floral resources did not significantly affect queen production despite a strong correlation between worker number and queen number among colonies. No landscape produced high floral resources during both the early and late season, and seasonal consistency is likely required for greater queen production. Floral resources are important determinants of colony growth and likely affect the pollination services provided by bumble bees at a landscape scale. Spatiotemporal variation in floral resources across the landscape precludes a simple relationship between resources and reproductive success as measured by queens, but nonetheless likely influences the total abundance of bumble bees in our study region.     

Invasive species impacts on ecosystem structure and function: A comparison of Oneida Lake, New York, USA, before and after zebra mussel invasion

Exotic species invasion is widely considered to affect ecosystem structure and function. Yet, few contemporary approaches can assess the effects of exotic species invasion at such an inclusive level. Our research presents one of the first attempts to examine the effects of an exotic species at the ecosystem level in a quantifiable manner. We used ecological network analysis (ENA) and a social network analysis (SNA) method called cohesion analysis to examine the effect of zebra mussel (Dreissena polymorpha) invasion on the Oneida Lake, New York, USA, food web. We used ENA to quantify ecosystem function through an analysis of food web carbon transfer that explicitly incorporated flow over all food web paths (direct and indirect). The cohesion analysis assessed ecosystem structure through an organization of food web members into subgroups of strongly interacting predators and prey. Our analysis detected effects of zebra mussel invasion throughout the entire Oneida Lake food web, including changes in trophic flow efficiency (i.e., carbon flow among trophic levels) and alterations of food web organization (i.e., paths of carbon flow) and ecosystem activity (i.e., total carbon flow). ENA indicated that zebra mussels altered food web function by shunting carbon from pelagic to benthic pathways, increasing dissipative flow loss, and decreasing ecosystem activity. SNA revealed the strength of zebra mussel perturbation as evidenced by a reorganization of food web subgroup structure, with a decrease in importance of pelagic pathways, a concomitant rise of benthic pathways, and a reorganization of interactions between top predator fish. Together, these analyses allowed for a holistic understanding of the effects of zebra mussel invasion on the Oneida Lake food web.     

Plasticity in male courtship behaviour as a function of light intensity in guppies

The environment is profoundly important in shaping many aspects of animal phenotype, including courtship and mating behaviours. Courtship displays rely upon the transmission of visual information from the signaller to the receiver, which means they are likely to be less effective in visually poor conditions such as at low light or in turbid ecosystems. One might therefore predict that in visually poor environments it would be beneficial for individuals to plastically adjust their mating behaviour to maximise mating success. Here, we investigate the impact of the developmental and current visual environment (light intensity) upon male mating behaviour in the Trinidadian guppy Poecilia reticulata. Male guppies have two different mating tactics: They can court females with a visual sigmoid display or attempt to circumvent female choice by attempting a non-consensual copulation (gonapodium thrust). We reared juvenile guppies in low light and relatively high light intensities for 5 months before observing individual males for mating behaviour in both light conditions. We found that the current light environment is important in determining the frequency of both sigmoidal courtship displays and non-consensual copulation attempts. Males increase the frequency of sigmoidal displays at relatively high light and increase non-consensual mating attempts at low light, suggesting that males compensate for poor visual conditions via an adjustment in tactics. We also find a significant correlation in courtship effort between the different light environments, suggesting that there is individual consistency across time and context for this trait. Developmental environment was less important. However, we found that fish reared at lower light intensities continued to employ sigmoidal displays despite the poor current visual environment. Our data show that male mating behaviour is phenotypically plastic in response to recent light environment. This may have implications for understanding how animals cope with anthropogenic environmental change.