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Edward J. Brooks David W. Sims Andy J. Danylchuk Katherine A. Sloman 《Marine Biology》2013,160(10):2535-2546
The Caribbean reef shark (Carcharhinus perezi), an abundant coral-reef-associated apex predator, is one of the most economically and ecologically important, yet least studied species of large shark in the greater Caribbean region. The relative abundance and population structure of C. perezi off Cape Eleuthera, The Bahamas, was surveyed by standardised longline surveys from May 2008 to October 2011, which resulted in the capture of 331 sharks. Abundance peaked in the summer and was lowest during the winter. Females were 1.6 times more abundant than males and the assemblage was dominated by immature female sharks (45.5 %). The abundance of mature male and female sharks peaked a month apart in June and August, respectively. All 331 sharks were tagged and released with 15.4 % being recaptured after periods at liberty between 5 and 1,159 days (Mean = 333.4 ± 42.7 SE). The mean distance between tagging and recapture was 1.77 km for recaptures in excess of 6 months, indicating seasonally stratified philopatry in this species. C. perezi inhabiting Bahamian waters have developed complex habitat use patterns that are both spatiotemporally and demographically segregated, most probably in response to the large and diverse habitat mosaic available on the Bahamas Banks compared to contemporary study sites. This study represents an important step in understanding the spatiotemporal population structure of C. perezi and illustrates the potential for studies examining behavioural plasticity in response to environmental variation and anthropogenic disturbance. 相似文献
235.
The fate of manure nutrients in beef cattle (Bos taurus) feedlots is influenced by handling treatment, yet few data are available in western Canada comparing traditional practices (fresh handling, stockpiling) with newer ones (composting). This study examined the influence of handling treatment (fresh, stockpiled, or composted) on nutrient levels and mass balance estimates of feedlot manure at Lethbridge, Alberta, and Brandon, Manitoba. Total carbon (TC) concentration of compost (161 kg Mg(-1)) was lower (P < 0.001) than stockpiled (248 kg Mg(-1)), which was in turn lower (P < 0.001) than fresh manure (314 kg Mg(-1)). Total nitrogen (TN) concentration was not affected by handling treatment while total phosphorus (TP) concentration increased with composting at Lethbridge. The percent inorganic nitrogen (PIN) was lower (P < 0.01) for compost (5.1%) than both fresh (24.7%) and stockpiled (28.9%) manure. Composting led to higher (P < 0.05) dry matter (DM) losses (39.8%) compared to stockpiling (22.5%) and higher (P < 0.05) total mass (water + DM) losses (65.6 vs. 35.2%). Carbon (C) losses were higher (P < 0.01) with composting (66.9% of initial) than with stockpiling (37.5%), as were nitrogen (N) losses (46.3 vs. 22.5%, P < 0.05). Composting allowed transport of two times as much P as fresh manure and 1.4 times as much P as stockpiled manure (P < 0.001) on an "as is" basis. Our study looked at one aspect of manure management (i.e., handling treatment effects on nutrient concentrations and mass balance estimates) and, as such, should be viewed as one component in the larger context of a life cycle assessment. 相似文献
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Sholtz RI McLaughlin KR Cirillo PM Petreas M Park JS Wolff MS Factor-Litvak P Eskenazi B Krigbaum N Cohn BA 《Environment international》2011,37(4):709-714
Conserving irreplaceable, archived serum samples may sometimes conflict with the objective of minimizing measurement error due to laboratory effects. We sought to determine whether we could successfully combine assay results for DDT-related compounds and polychlorinated biphenyls (PCBs) in serum from the same birth cohort obtained from different laboratories over time. Using the Child Health and Development Studies (CHDS) serum archive, we compared variability for assays of a quality control pool to variability for assays of subject serum. The quality control pool was created from native archived serum samples that were pooled, then aliquoted, blinded and inserted pair-wise into assay batches along with the subject serum for 5 studies using CHDS samples conducted over a 13year period by three different laboratories. We found that the variability between laboratory and over time within laboratory was small relative to inter-individual variability for p,p'-DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane), p,p'-DDE (1,1'-dichloro-2,2'-bis(p-chlorophenyl)ethylene) and o,p'-DDT (1,1,1-trichloro-2-(p-chlorophenyl)-2-(o-chlorophenyl)-ethane). Results were also consistent for most PCB congeners which were detectable in 85% or more of samples. Our results suggest that it is possible to combine assays for DDT and PCB congeners measured at positive levels as they are accumulated for cohort subjects without risking meaningful misclassification due to variation stemming from laboratory or time period. This has significant implications for future study costs, conservation of irreplaceable archived samples and for leveraging past investments for future research. For PCB congeners with very low levels, findings caution against pooling of assays without further exploration. 相似文献
238.
Katherine A. Jones John R. Krebs Mark J. Whittingham 《Behavioral ecology and sociobiology》2009,63(9):1319-1329
The relationship between body mass and reactions speed in response to a predatory threat is poorly understood. Theory predicts
that different vigilance patterns are optimal for the detection of different predator types. We suggest that birds of different
individual state might also differ in their speed of response dependent upon predator type. We used laboratory trials of wild
caught chaffinches (Fringilla coelebs) to determine how between individual differences in chaffinch behaviour and state correlate with latency to react to a ground
predator model (domestic cat), thus providing a comparison with previous work in the same model system using aerial predator
models. In experiment 1, we observed chaffinch responses to a moving cat model, simulating a stalking predator. In experiment
2, we used a camouflaged cat model simulating an ambush predator. Both experiments show evidence suggesting heavier individuals
(which previous literature has linked to impaired flight performance) responded more quickly to the model cat. Heavier individuals
also had shorter interscan intervals. In contrast to a previous study, both experiments found individuals with a higher intake
rate were not faster at responding to the cat model. In addition, individuals in experiment 1 that head turned more while
scanning were slower to respond to the stalking cat model. Our work suggests that although heavier individuals may have impaired escape performance
they appear to show behavioural compensation by allocating more attention to anti-predator behaviour and by modifying their
interscan intervals, resulting in faster response times to a ground predator. We suggest more experiments investigating response
time to different predatory types and explicitly manipulating state to elucidate cause and effect. 相似文献
239.
Katherine Skalak James Pizzuto David D. Hart 《Journal of the American Water Resources Association》2009,45(1):97-109
Abstract: We evaluate the effects of small dams (11 of 15 sites less than 4 m high) on downstream channels at 15 sites in Maryland and Pennsylvania by using a reach upstream of the reservoir at each site to represent the downstream reach before dam construction. A semi‐quantitative geomorphic characterization demonstrates that upstream reaches occupy similar geomorphic settings as downstream reaches. Survey data indicate that dams have had no measurable influence on the water surface slope, width, and the percentages of exposed bedrock or boulders on the streambed. The median grain diameter (D50) is increased slightly by dam construction, but D50 remains within the pebble size class. The percentage of sand and silt and clay on the bed averages about 35% before dam construction, but typically decreases to around 20% after dam construction. The presence of the dam has therefore only influenced the fraction of finer‐grained sediment on the bed, and has not caused other measurable changes in fluvial morphology. The absence of measurable geomorphic change from dam impacts is explicable given the extent of geologic control at these study sites. We speculate that potential changes that could have been induced by dam construction have been resisted by inerodible bedrock, relatively immobile boulders, well‐vegetated and cohesive banks, and low rates of bed material supply and transport. If the dams of our study are removed, we argue that long‐term changes (those that remain after a period of transient adjustment) will be limited to increases in the percentage of sand and silt and clay on the bed. Thus, dam removal in streams similar to those of our study area should not result in significant long‐term geomorphic changes. 相似文献
240.
Open-plan offices are equipped with barriers such as panels and bookshelves to induce the perception of a private workspace. Despite perceived privacy, irrelevant speech contributes to mental workload, poor performance, stress, and fatigue. Certain dispositional variables related to sustained attention might exacerbate the effects of speech-related noise. This study used a 3 × 3 × 2 mixed factor design to determine the effects of two forms of irrelevant speech and individual differences on performance of a real-world verbal task and mental workload. The Expanded Tellegen Absorption Scale (ETAS) based upon Tellegen and Atkinson's scale was used to assess individual differences in focused attention. The NASA Task Load Index was administered to assess mental workload. Main effects of noise were found on performance and mental workload. Irrelevant speech appeared to increase false alarms and completion rates. Workload ratings were higher in the irrelevant speech conditions. Other differences found were among High and Low Task and Imaginative Absorbers, as measured by the ETAS. Recommendations to reduce the impact of irrelevant speech and future research suggestions are provided. 相似文献