155 research outputs found
Zero-sum, the niche,and metacommunities: long-term dynamics of community assembly
Recent models of community assembly, structure, and dynamics have incorporated, to varying degrees, three mechanistic processes: resource limitation and interspecific competition, niche requirements of species, and exchanges between a local community and a regional species pool. Synthesizing 30 years of data from an intensively studied desert rodent community, we show that all of these processes, separately and in combination, have influenced the structural organization of this community and affected its dynamical response to both natural environmental changes and experimental perturbations. In addition, our analyses suggest that zero-sum constraints, niche differences, and metacommunity processes are inextricably linked in the ways that they affect the structure and dynamics of this system. Explicit consideration of the interaction of these processes should yield a deeper understanding of the assembly and dynamics of other ecological communities. This synthesis highlights the role that long-term data, especially when coupled with experimental manipulations, can play in assessing the fundamental processes that govern the structure and function of ecological communities
Longâterm monitoring and experimental manipulation of a Chihuahuan desert ecosystem near Portal, Arizona (1977â2013)
Desert ecosystems have long served as model systems in the study of ecological concepts (e.g., competition, resource pulses, topâdown/bottomâup dynamics). However, the inherent variability of resource availability in deserts, and hence consumer dynamics, can also make them challenging ecosystems to understand. Study of a Chihuahuan desert ecosystem near Portal, Arizona began in 1977. At this site, 24 experimental plots were established and divided among controls and experimental manipulations. Experimental manipulations over the years include removal of all or some rodent species, all or some ants, seed additions, and various alterations of the annual plant community. This dataset includes data previously available through an older data publication and adds 11Â years of data. It also includes additional ant and weather data not previously available. These data have been used in a variety of publications documenting the effects of the experimental manipulations as well as the response of populations and communities to longâterm changes in climate and habitat. Sampling is ongoing and additional data will be published in the future.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146431/1/ecy1360.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146431/2/ecy1360_am.pd
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Vapor space characterization of waste Tank 241-C-104: Results from samples collected on 2/17/94 and 3/3/94
This report describes inorganic and organic analyses results from samples obtained from the headspace of the Hanford waste storage Tank 241-C-104 (referred to as Tank C-104). The results described here were obtained to support safety and toxicological evaluations. A summary of the results for inorganic and organic analytes is listed in Summary Table 1. Detailed descriptions of the results appear in the text. Quantitative results were obtained for the inorganic compounds ammonia (NH{sub 3}), nitrogen dioxide (NO{sub 2}), nitric oxide (NO), sulfur oxides (SO{sub x}), and water vapor (H{sub 2}O). Organic compounds were also quantitatively determined. Occupational Safety and Health Administration (OSHA) versatile sampler (OVS) tubes were analyzed for tributyl phosphate. Twenty-four organic tentatively identified compounds (TICs) were observed above the detection limit of (ca.) 10 ppbv, but standards for most of these were not available at the time of analysis, and the reported concentrations are semiquantitative estimates. In addition, the authors looked for the 40 standard TO-14 analytes. Of these, two were observed above the 2-ppbv calibrated instrument detection limit. The 10 organic analytes with the highest estimated concentrations are listed in Summary Table 1. These 10 analytes account for approximately 88% of the total organic components in Tank C 104. Tank C-104 is not on any of the Watch Lists
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Apparent Competition, Lion Predation, and Managed Livestock Grazing: Can Conservation Value Be Enhanced?
Predator restorations often result in apparent competition, where co-occurring prey populations experience asymmetric predation pressure driven by predator preferences. In many rangeland ecosystems, livestock share the landscape with wildlife, including ungulates and the large carnivores that consume them. We examined whether apparent competition reorganized prey communities following restoration of lions (Panthera leo) to a savanna ecosystem, and whether and how livestock management could alter this indirect interaction between lions and their prey. Three lines of evidence supported the hypothesis that Jackson's hartebeest (Alcelaphus bucelaphus lelwel; an ungulate of conservation concern) are suppressed via lion-mediated apparent competition. First, hartebeest exhibited an Allee effect where they were exposed to lions, but displayed negative density-dependent population growth where they were protected from lions. Second, spatial overlap between plains zebra (Equus burchelli; the primary prey of lions) and hartebeest further exacerbated lion predation on hartebeest. Finally, hartebeest were killed selectively by lions, whereas zebra were killed by lions in proportion to their abundance. We then tested whether glades [nutrient-rich hotspots created by abandoned cattle (Bos indicus) corrals] could be used to manipulate top-down control of hartebeest via their influence on the spatial distribution of zebra. Zebra aggregated at glades, and survival of hartebeest increased with increasing distance from glades, suggesting that corrals may be placed on the landscape away from hartebeest to create spatial refuges from lions. Our findings demonstrate how informed placement of livestock corrals can be used to manipulate the spatial distribution of primary prey (zebra), thereby reducing apparent competition suffered by hartebeest. Our work further provides an example of how integrating apparent competition theory with proactive livestock management can improve conservation efforts in multiple-use landscapes
Socializing infants towards a cultural understanding of expressing negative affect:A Bakhtinian informed discursive psychology approach
Lessons Learned from a Decade of Sudden Oak Death in California: Evaluating Local Management
Sudden Oak Death has been impacting Californiaâs coastal forests for more than a decade. In that time, and in the absence of a centrally organized and coordinated set of mandatory management actions for this disease in Californiaâs wildlands and open spaces, many local communities have initiated their own management programs. We present five case studies to explore how local-level management has attempted to control this disease. From these case studies, we glean three lessons: connections count, scale matters, and building capacity is crucial. These lessons may help management, research, and education planning for future pest and disease outbreaks
Cryogenically preserved RBCs support gametocytogenesis of Plasmodium falciparum in vitro and gametogenesis in mosquitoes
Background: The malaria Eradication Research Agenda (malERA) has identified human-to-mosquito transmission of Plasmodium falciparum as a major target for eradication. The cornerstone for identifying and evaluating transmission in the laboratory is standard membrane feeding assays (SMFAs) where mature gametocytes of P. falciparum generated in vitro are offered to mosquitoes as part of a blood-meal. However, propagation of "infectious" gametocytes requires 10-12 days with considerable physico-chemical demands imposed on host RBCs and thus, "fresh" RBCs that are †1-week old post-collection are generally recommended. However, in addition to the costs, physico-chemical characteristics unique to RBC donors may confound reproducibility and interpretation of SMFAs. Cryogenic storage of RBCs ("cryo-preserved RBCs") is accepted by European and US FDAs as an alternative to refrigeration (4 °C) for preserving RBC "quality" and while cryo-preserved RBCs have been used for in vitro cultures of other Plasmodia and the asexual stages of P. falciparum, none of the studies required RBCs to support parasite development for > 4 days. Results: Using the standard laboratory strain, P. falciparum NF54, 11 SMFAs were performed with RBCs from four separate donors to demonstrate that RBCs cryo-preserved in the gaseous phase of liquid nitrogen (- 196 °C) supported gametocytogenesis in vitro and subsequent gametogenesis in Anopheles stephensi mosquitoes. Overall levels of sporogony in the mosquito, as measured by oocyst and sporozoite prevalence, as well as oocyst burden, from each of the four donors thawed after varying intervals of cryopreservation (1, 4, 8, and 12 weeks) were comparable to using †1-week old refrigerated RBCs. Lastly, the potential for cryo-preserved RBCs to serve as a suitable alternative substrate is demonstrated for a Cambodian isolate of P. falciparum across two independent SMFAs. Conclusions: Basic guidelines are presented for integrating cryo-preserved RBCs into an existing laboratory/insectary framework for P. falciparum SMFAs with significant potential for reducing running costs while achieving greater reliability. Lastly, scenarios are discussed where cryo-preserved RBCs may be especially useful in enhancing the understanding and/or providing novel insights into the patterns and processes underlying human-to-mosquito transmission
Elemental sulfur as a versatile low-mass-range calibration standard for laser desorption ionization mass spectrometry
Effects of body size on estimation of mammalian area requirements.
Accurately quantifying species' area requirements is a prerequisite for effective area-based conservation. This typically involves collecting tracking data on species of interest and then conducting home range analyses. Problematically, autocorrelation in tracking data can result in space needs being severely underestimated. Based on the previous work, we hypothesized the magnitude of underestimation varies with body mass, a relationship that could have serious conservation implications. To evaluate this hypothesis for terrestrial mammals, we estimated home-range areas with global positioning system (GPS) locations from 757 individuals across 61 globally distributed mammalian species with body masses ranging from 0.4 to 4000 kg. We then applied blockcross validation to quantify bias in empirical home range estimates. Area requirements of mammals 1, meaning the scaling of the relationship changedsubstantially at the upper end of the mass spectrum
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