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131.
Given recent focus on large rivers as conduits for excess nutrients to coastal zones, their role in processing and retaining nutrients has been overlooked and understudied. Empirical measurements of nutrient uptake in large rivers are lacking, despite a substantial body of knowledge on nutrient transport and removal in smaller streams. Researchers interested in nutrient transport by rivers (discharge >10000 L/s) are left to extrapolate riverine nutrient demand using a modeling framework or a mass balance approach. To begin to fill this knowledge gap, we present data using a pulse method to measure inorganic nitrogen. (N) transport and removal in the Upper Snake River, Wyoming, USA (seventh order, discharge 12000 L/s). We found that the Upper Snake had surprisingly high biotic demand relative to smaller streams in the same river network for both ammonium (NH4+) and nitrate (NO3-). Placed in the context of a meta-analysis of previously published nutrient uptake studies, these data suggest that large rivers may have similar biotic demand for N as smaller tributaries. We also found that demand for different forms of inorganic N (NH4+ vs. NO3-) scaled differently with stream size. Data from rivers like the Upper Snake and larger are essential for effective water quality management at the scale of river networks. Empirical measurements of solute dynamics in large rivers are needed to understand the role of whole river networks (as opposed to stream reaches) in patterns of nutrient export at regional and continental scales. 相似文献
132.
Honey bee foragers specialize on collecting pollen and nectar. Pollen foraging behavior is modulated by at least two stimuli
within the nest: the presence of brood pheromone and young larvae and the quantity of stored pollen. Genetic variation in
pollen foraging behavior has been demonstrated repeatedly. We used selected high and low pollen-hoarding strains of bees that
differ dramatically in the quantity of pollen collected to determine if the observed differences in foraging could be explained
by differential responses to brood stimuli. Workers from the high and low pollen-hoarding strains and wild-type bees were
co-fostered in colonies with either brood or no brood. As expected based on previous studies, returning high pollen-hoarding
foragers collected heavier pollen loads and lighter nectar loads than low pollen-hoarding bees. Effects of brood treatment
were also observed; bees exposed to brood collected heavier pollen loads and initiated foraging earlier than those from broodless
colonies. More specifically, brood treatment resulted in increased pollen foraging in high pollen-hoarding bees but did not
affect pollen foraging in low pollen-hoarding bees, suggesting that high pollen-hoarding bees are more sensitive to the presence
of brood. However, response to brood stimuli does not sufficiently explain the differences in foraging behavior between the
strains since these differences persisted even in the absence of brood. 相似文献
133.
Many benthic colonial invertebrates have the ability to fuse and form chimeras with compatible colonies. Botryllid ascidians
are model organisms for the study of the evolution of and molecular basis for allorecognition, and fusion rates have been
determined for different populations and species by random sampling and fusion testing between individuals. However, natural
fusion rates over time have not been documented. Nine settlement panels were deployed in Salem Harbor, Massachusetts, USA
and Botrylloides violaceus settlement, growth, and fusion monitored from July to mid-August 2007. Seventy-three percent of the recruits observed fused
with at least one other colony, while 4% neither fused nor were overgrown. Multifused colonies were not observed to grow faster
than single colonies when growth was calculated as increase in size beyond the summation of fused entities; however, they
were significantly larger. These results suggest that larvae settle in clumps of compatible individuals, and that large subtidal
colonies may be the result of high numbers of fusions between compatible colonies. 相似文献
134.
David Fowler Rognvald Smith Jennifer Muller John Neil Cape Mark Sutton Jan Willem Erisman Hilde Fagerli 《Water, Air, & Soil Pollution: Focus》2007,7(1-3):41-47
Emissions of sulphur and oxidized nitrogen compounds in Europe have been reduced following a series of control measures during
the last two decades. These changes have taken place during a period in which the primary gases and the wet deposition throughout
Europe were extensively monitored. Since the end of the 1970s, for example land based sulphur emissions declined by between
90 and 70% depending on the region. Over the same period the total deposition of sulphur and its partitioning into wet and
dry deposition have declined, but the spatial pattern in the reduction in deposition differs from that of emission and has
changed with time. Such non-linearities in the emission-deposition relationship are important to understand as they complicate
the process of assessing the effects of emission reduction strategies. Observed non-linearities in terrestrial sulphur emission-deposition
patterns have been identified in north west Europe due to increases in marine emissions, and are currently slowing the recovery
of freshwater ecosystems. Changes in the relative amounts of SO2 and NH3 in air over the last two decades have also changed the affinity of terrestrial surfaces for SO2 and have therefore changed the deposition velocity of SO2 over substantial areas. The consequence of this effect has been the very rapid reduction in ambient SO2 concentration in some of the major source areas of Europe, where NH3 did not change much. Interactions between the different pollutants, generating non-linearities are now being incorporated
in long-range transport models to simulate the effects of historical emission trends and to provide projections into the future.
This paper identifies non-linearities in emission deposition relationships for sulphur and nitrogen compounds in Europe using
data from the EMEP long-rang transport model and measured concentration fields of the major ions in precipitation and of SO2 and NO2 in surface air. 相似文献
135.
Christine E. Wilkinson Alex McInturff Jennifer R. B. Miller Veronica Yovovich Kaitlyn M. Gaynor Kendall Calhoun Harshad Karandikar Jeff Vance Martin Phoebe Parker-Shames Avery Shawler Amy Van Scoyoc Justin S. Brashares 《Conservation biology》2020,34(4):854-867
Carnivore predation on livestock is a complex management and policy challenge, yet it is also intrinsically an ecological interaction between predators and prey. Human–wildlife interactions occur in socioecological systems in which human and environmental processes are closely linked. However, underlying human–wildlife conflict and key to unpacking its complexity are concrete and identifiable ecological mechanisms that lead to predation events. To better understand how ecological theory accords with interactions between wild predators and domestic prey, we developed a framework to describe ecological drivers of predation on livestock. We based this framework on foundational ecological theory and current research on interactions between predators and domestic prey. We used this framework to examine ecological mechanisms (e.g., density-mediated effects, behaviorally mediated effects, and optimal foraging theory) through which specific management interventions operate, and we analyzed the ecological determinants of failure and success of management interventions in 3 case studies: snow leopards (Panthera uncia), wolves (Canis lupus), and cougars (Puma concolor). The varied, context-dependent successes and failures of the management interventions in these case studies demonstrated the utility of using an ecological framework to ground research and management of carnivore–livestock conflict. Mitigation of human–wildlife conflict appears to require an understanding of how fundamental ecological theories work within domestic predator–prey systems. 相似文献
136.
Team trust is gaining attention in research and practice due to its benefits for team performance, yet clarity about the intricacies of its measurement is needed. Therefore, we meta-analyzed 118 studies (N = 7,738) to untangle the role of measurement features by investigating the degree to which they influence the trust–performance relationship. Results showed that the trust–performance relationship is contingent upon time lag and source of measurement. Specifically, cross-sectional and single-source studies produced higher effect sizes than time-lagged and different-source studies. In contrast, the moderating roles of conceptualization–operationalization alignment and referent of trust measures were not supported. Post hoc analyses revealed that affective trust is more strongly related to global, versus specific team outcomes, and that mixed-referent items are particularly effective within intact teams, whereas the trust–performance relationship is constrained when direct consensus items are used within ad hoc teams. Furthermore, we provided a critical review that highlights the importance of composites, multilevel forces, and item content and wording. Finally, we clarified key gaps in the literature, calling for research where needed. This review serves as a bridge between conceptualization and measurement and lays the groundwork for advancing knowledge of team trust. 相似文献
137.
Matthew W. Rees Josie Carwardine Andrew Reeson Jennifer Firn 《Conservation biology》2020,34(4):843-853
Conservation strategies aimed at reducing threats to biodiversity can have significant implications for multiple sectors in a socioeconomic system, but these cobenefits are often poorly understood. For example, many of the threats to native species also impede agricultural production, yet agriculture is typically perceived as in competition with conservation objectives. Although a comprehensive, multiobjective decision analysis is usually beyond the scope and capacity of conservation decision makers, failing to incorporate key socioeconomic costs and benefits into conservation decision-making processes can result in missed opportunities for diversifying outcomes and creating cost-sharing multisectoral partnerships. We devised a straightforward and readily interpretable approach to incorporate cobenefits into a threat-management prioritization approach. We used it to analyze the agricultural cobenefits of implementing 9 invasive animal management strategies designed to ensure the persistence of 148 threatened species across Australia's Lake Eyre Basin over 50 years. A structured elicitation process with 24 participants (scientists, land managers, agriculturalists, and other stakeholders) was used to collect information on each strategy, including costs, technical and social feasibility, benefits to native threatened species, and cobenefits to agricultural production systems. The costs of targeted invasive animal management to save threatened species across the basin (AU$33 million/year) outweighed the overall benefits to the agricultural industry (estimated AU$226 million/year). The return on investment for these management strategies varied substantially when agricultural cobenefits were considered alongside threatened species benefits and showed synergies and challenges. Our approach demonstrates the value of incorporating cobenefits of conservation actions into cost-effectiveness analyses to guide potential investment and partnerships and to diversify implementation pathways. 相似文献
138.
139.
Kristiina A. Vogt Karen H. Beard Shira Hammann Jennifer O''''Hara Palmiotto Daniel J. Vogt Frederick N Scatena Brooke P. Hecht 《Ambio-人类环境杂志》2002,31(6):485-490
本研究运用满月时收获非木材林产品的当地实践如识,来证明控制叶片分解速率的化学物质随月亮周期而波动,并且这种现象可能已发展为一种植物一食草动物之间的相互关系.当地知识认为,满月期收获的叶片更为耐用.满月期收获的棕榈叶片具有较高的总碳量、半纤维素和碳化合物、而钙的浓度则较低.这些化学上的变化使棕榈叶在满月收获时对食草动物不太敏感且更为耐用.本研究提出了热带植物减少食叶功物食用及影响衰老叶片的分解速度和耐用性(尤其在满月期)的作用机制.本研究认为森林经营中有必要利用天然的生命周期,并为当地人的收获实践提供了科学依据. 相似文献
140.
Dr Theresa M. Marteau Rachel Cook Jane Kidd Susan Michie Marie Johnston Joan Slack Robert W. Shaw 《黑龙江环境通报》1992,12(3):205-214
The purpose of the study was to describe the impact of false-positive results from initial maternal serum alpha-fetoprotein (MS-AFP) screening. The analyses compared two groups of women, those receiving a negative result (n = 346) and those receiving an initial positive result (n = 26), over four time points—prior to testing, immediately after testing, later in pregnancy, and in the post-partum period. Receiving an abnormal result was associated with high levels of anxiety which were reflected in increased worry about the baby's health and a more negative attitude towards the pregnancy and the baby. Women who had an initial abnormal result were offered a variety of further tests. Those women who went on to have amniocentesis were less worried about their baby's health in the third trimester and also less anxious post-partum than those who did not have amniocentesis. In view of the increasing number of screening tests available, it is necessary to establish whether and how these levels of distress can best be reduced. 相似文献