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101.
We examined the possible effects of heavy metal exposure on the quality and health of adult great tits (Parus major) at four study sites along a pollution gradient near a non-ferrous smelter in Belgium. Tarsus length, wing length, body mass and condition of great tits were compared with respect to study site, age (first-year and older great tits), sex and season (birds caught in winter and during breeding). Tarsus length did not differ significantly among study sites. The wing length of great tits was larger at the study site furthest from the smelter, especially for older great tits. The length of the outermost tail feathers, however, did not differ significantly among study sites. We found no signs of loss of body mass or condition towards the pollution source. The body mass and condition was lowest for female great tits at the site furthest from the smelter, especially during winter. Haematocrit values did not differ significantly among sites. Overall, we found no clear significant effects of heavy metal pollution on morphological measurements and health parameters of great tits. 相似文献
102.
The Gunnison River in the Black Canyon of the Gunnison National Park (BCNP) near Montrose, Colorado is a mixed gravel and
bedrock river with ephemeral side tributaries. Flow rates are controlled immediately upstream by a diversion tunnel and three
reservoirs. The management of the hydraulic control structures has decreased low-frequency, high-stage flows, which are the
dominant geomorphic force in bedrock channel systems. We developed a simple model to estimate the extent of sediment mobilization
at a given flow in the BCNP and to evaluate changes in the extent and frequency of sediment mobilization for flow regimes
before and after flow regulation in 1966. Our methodology provides a screening process for identifying and prioritizing areas
in terms of sediment mobility criteria when more precise systematic field data are unavailable. The model uses the ratio between
reach-averaged bed shear stress and critical shear stress to estimate when a particular grain size is mobilized for a given
reach. We used aerial photography from 1992, digital elevation models, and field surveys to identify individual reaches and
estimate reach-averaged hydraulic geometry. Pebble counts of talus and debris fan deposits were used to estimate regional
colluvial grain-size distributions. Our results show that the frequency of flows mobilizing river bank sediment along a majority
of the Gunnison River in the BCNP has significantly declined since 1966. The model results correspond well to those obtained
from more detailed, site-specific field studies carried out by other investigators. Decreases in the frequency of significant
sediment-mobilizing flows were more pronounced for regions within the BCNP where the channel gradient is lower. Implications
of these results for management include increased risk of encroachment of vegetation on the active channel and long-term channel
narrowing by colluvial deposits. It must be recognized that our methodology represents a screening of regional differences
in sediment mobility. More precise estimates of hydraulic and sediment parameters would likely be required for dictating quantitative
management objectives within the context of sediment mobility and sensitivity to changes in the flow regime. 相似文献
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Species with relatively narrow niches, such as plants restricted (endemic) to particular soils, may be especially vulnerable to extinction under a changing climate due to the enhanced difficulty they face in migrating to suitable new sites. To test for community-level effects of climate change, and to compare such effects in a highly endemic-rich flora on unproductive serpentine soils vs. the flora of normal (diorite) soils, in 2007 we resampled as closely as possible 108 sites originally studied by ecologist Robert H. Whittaker from 1949 to 1951 in the Siskiyou Mountains of southern Oregon, USA. We found sharp declines in herb cover and richness on both serpentine and diorite soils. Declines were strongest in species of northern biogeographic affinity, species endemic to the region (in serpentine communities only), and species endemic to serpentine soils. Consistent with climatic warming, herb communities have shifted from 1949-1951 to 2007 to more closely resemble communities found on xeric (warm, dry) south-facing slopes. The changes found in the Siskiyou herb flora suggest that biotas rich in narrowly distributed endemics may be particularly susceptible to the effects of a warming climate. 相似文献
107.
Landscape corridors, strips of habitat that connect otherwise isolated habitat patches, are commonly employed during management of fragmented landscapes. To date, most reported effects of corridors have been positive; however, there are long-standing concerns that corridors may have unintended consequences. Here, we address concerns over whether corridors promote propagation of disturbances such as fire. We collected data during prescribed fires in the world's largest and best replicated corridor experiment (Savannah River Site, South Carolina, USA), six -50-ha landscapes of open (shrubby/herbaceous) habitat within a pine plantation matrix, to test several mechanisms for how corridors might influence fire. Corridors altered patterns of fire temperature through a direct connectivity effect and an indirect edge effect. The connectivity effect was independent of fuel levels and was consistent with a hypothesized wind-driven "bellows effect." Edges, a consequence of corridor implementation, elevated leaf litter (fuel) input from matrix pine trees, which in turn increased fire temperatures. We found no evidence for corridors or edges impacting patterns of fire spread: plots across all landscape positions burned with similar probability. Impacts of edges and connectivity on fire temperature led to changes in vegetation: hotter-burning plots supported higher bunch grass cover during the field season after burning, suggesting implications for woody/herbaceous species coexistence. To our knowledge, this represents the first experimental evidence that corridors can modify landscape-scale patterns of fire intensity. Corridor impacts on fire should be carefully considered during landscape management, both in the context of how corridors connect or break distributions of fuels and the desired role of fire as a disturbance, which may range from a management tool to an agent to be suppressed. In our focal ecosystem, longleaf pine woodland, corridors might provide a previously unrecognized benefit during prescribed burning activities, by promoting fire intensity, which may assist in promoting plant biodiversity. 相似文献
108.
Nicola Ellen 《生态毒理学报》2004,26(1):19
Safeway是英国第4大超级市场连锁店,在全国有480家连锁店,年销售额约为90亿英镑,另外还有与英国石油公司(BP)合营的50家庭院便利店. 相似文献
109.
Two groups of part-time employees were compared to full-time employees on several organizationally relevant reactions and behaviours in order to replicate and extend research on potential employment status differences. After controlling for demographics, it was found that there were mean differences between the groups; however, no evidence was found for differences in how the various groups ‘process’ organizational experience. Based on the results, implications for managing part-versus full-time employees are discussed. 相似文献
110.
Arne Aar?s Gunnar Horgen Ola Ro Ellen L?ken Geir Mathiasen Hans-Henrik Bj?rset Stig Larsen Magne Thoresen 《International journal of occupational safety and ergonomics》2005,11(1):25-47
The Norwegian MEPS (musculoskeletal--visual--psychosocial--stress) study included 3 groups: data entry, data dialogue (female) and data dialogue (male). Before intervention, the data entry group reported significantly more symptoms and signs of musculoskeletal illness and had longer periods in front of the video display terminal (VDT) without a break. The ergonomic intervention consisted mainly of ergonomic information and training. After intervention, the data dialogue female group reported a significant reduction in shoulder pain in parallel with a reduction in trapezius load. Increasing the understanding in how to adjust the work stand and chair may have been contributing factors to reducing the pain level. There was a significant reduction in eye problems in all groups; the greatest reduction in eye symptoms was seen in the groups who had new optometric corrections. 相似文献