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171.
The Russian River-Cooper Lake-Resurrection River trail system, on the Kenai Peninsula, Alaska, traverses essential brown bear
habitat. To set management guidelines for this area, the trail system was monitored using questionnaire cards and electronic
trail counters from 1984 through 1987. This helped to determine the extent and type of human use and human-bear encounters
in the area. Management recommendations were intended to reduce the potential displacement of brown bears by hikers and to
inform wilderness users of the proper camping techniques to avoid attracting bears to the campsite. An average of 5800 visitors
hiked or camped along the trail system each year. Encounters between hikers and brown bears averaged 7/yr while encounters
with black bears averaged 35/yr. Minor problems occurred with both the electronic trail counters and the questionnaire. Modilications
to these methods are discussed. A Limits of Acceptable Change format should be considered for the trail system to determine
the character and future direction of recreational activities and monitoring of the trail system should continue in the future. 相似文献
172.
周润清 《湖南环境生物职业技术学院学报》2002,8(1):61-64
本文提出了人类社会生产的两个方面即物质生产、人口生产,指出人口生产必须与社会经济发展相一致,如果人口生产过多人口增长过快,就会影响社会经济的发展,因此我国必须对人口进行控制,实行计划生育. 相似文献
173.
Jill M. Mateo 《Behavioral ecology and sociobiology》2007,62(1):37-49
Predator–prey relationships provide an excellent opportunity to study coevolved adaptations. Decades of theoretical and empirical
research have illuminated the various behavioral adaptations exhibited by prey animals to avoid detection and capture, and
recent work has begun to characterize physiological adaptations, such as immune reactions, metabolic changes, and hormonal
responses to predators or their cues. A 2-year study quantified the activity budgets and antipredator responses of adult Belding’s
ground squirrels (Spermophilus beldingi) living in three different California habitats and likely experiencing different predation pressures. At one of these sites,
which is visually closed and predators and escape burrows are difficult to see, animals responding to alarm calls remain alert
longer and show more exaggerated responses than adults living in two populations that likely experience less intense predation
pressure. They also spend more time alert and less time foraging than adults at the other two sites. A 4-year study using
noninvasive fecal sampling of cortisol metabolites revealed that S. beldingi living in the closed site also have lower corticoid levels than adults at the other two sites. The lower corticoids likely
reflect that predation risk at this closed site is predictable, and might allow animals to mount large acute cortisol responses,
facilitating escape from predators and enhanced vigilance while also promoting glucose storage for the approaching hibernation.
Collectively, these data demonstrate that local environments and perceived predation risk influence not only foraging, vigilance,
and antipredator behaviors, but adrenal functioning as well, which may be especially important for obligate hibernators that
face competing demands on glucose storage and mobilization. 相似文献
174.
Corn buntings Miliaria calandra were abundant throughout arable agricultural landscapes in Europe, but have catastrophically declined since the mid 1970s with changes in farming practice and now give serious conservation cause for concern. Corn buntings declined in Denmark during 1976–1993, but (almost unique in Europe) have since increased (by up to 11% per annum) in some areas without specific conservation recovery actions. Based on breeding bird surveys in the mid 1990s, highest corn bunting densities occurred on mixed agriculture in west Denmark (Jylland); the species was rarer or absent in regions of highest arable land cover. Corn bunting density and extent of rotational and permanent grassland were correlated, but not with spring sown barley (all known to constitute important corn bunting winter habitat). The extent of spring barley rapidly declined in Denmark during the 1980s, but since 1990, most counties have since shown 2–3% annual increases in this crop, except in Nordjylland, where high densities of corn buntings have remained stable. Elsewhere in Jylland, corn buntings have increased in counties supporting highest densities during the mid 1990s, contrasting stable or declining trends in south and east Denmark where densities were originally lower. After dramatic decreases everywhere in Denmark, corn buntings retain highest breeding densities associated with mixed agriculture, especially where grassland and spring sown barley remained in greatest extent. Although purely based on land use correlation and bird surveillance, these results show an association between mixed farming and favourable conservation status of a species now red-listed throughout much of Europe. Further investigations of habitat use at small spatial scales and throughout the annual cycle are urgently required to better enlighten specific recommendations for wider applicability of guidelines for corn bunting recovery actions elsewhere. 相似文献
175.
Panayiotis Pafilis Shai Meiri Johannes Foufopoulos Efstratios Valakos 《Die Naturwissenschaften》2009,96(9):1107-1113
Resource availability, competition, and predation commonly drive body size evolution. We assess the impact of high food availability
and the consequent increased intraspecific competition, as expressed by tail injuries and cannibalism, on body size in Skyros
wall lizards (Podarcis gaigeae). Lizard populations on islets surrounding Skyros (Aegean Sea) all have fewer predators and competitors than on Skyros but
differ in the numbers of nesting seabirds. We predicted the following: (1) the presence of breeding seabirds (providing nutrients)
will increase lizard population densities; (2) dense lizard populations will experience stronger intraspecific competition;
and (3) such aggression, will be associated with larger average body size. We found a positive correlation between seabird
and lizard densities. Cannibalism and tail injuries were considerably higher in dense populations. Increases in cannibalism
and tail loss were associated with large body sizes. Adult cannibalism on juveniles may select for rapid growth, fuelled by
high food abundance, setting thus the stage for the evolution of gigantism. 相似文献
176.
Demographic factors such as operational sex ratio (OSR) and local population density (LPD) are temporally and spatially dynamic in the natural environment but the influence of these variables on male mating success and the mechanisms behind it are still poorly understood and highly controversial. Here, we manipulated the OSR and LPD of a seed bug, Nysius huttoni, and carried out a series of mating trials to test how these variables affected male mating success. The two demographic factors had no significant interactions, suggesting that they affect male mating success independently in N. huttoni. In this species male mating success was significantly higher in both male- and female-biased OSR than in even OSR. It is suggested that, in male-biased OSR, the increased intensity of competition and interference does not result in lower male mating success; rather, males may make more effort in courting and females may have more chance to encounter better males, resulting in higher male mating success. In female-biased OSR, females may become less choosy and less likely to reject male mating attempt, leading to the higher male mating success. Lower male mating success in N. huttoni in high LPD may be due to increased interference between males and/or delayed female receptiveness for mating. OSR had a stronger effect on male mating success than LPD in N. huttoni, suggesting that OSR and LPD affect mating success in different ways and intensities. 相似文献
177.
Split-plot field experiments, with variety as the main plot, were designed to analyze the microclimate and character of R498 (curved panicle) and R499 (erect panicle) varieties of rice during the full heading day and on the 20th day after full heading. The planting densities assigned to the subplots were 0.23 m (line spacing) × 0.12 m (hole spacing), 0.27 m × 0.14 m, 0.33 m × 0.17 m, 0.38 m × 0.20 m, and 0.40 m × 0.21 m. The results showed that for all the planting densities, the maximum temperature of R499 increased by 1.52 ℃ on an average during the full heading stage, but decreased by 0.66 ℃ on the 20th day after full heading, in comparison to those of R498. The mean daily light intensities of R498 and R499 in sparse planting (0.38 m × 0.20 m, 0.40 m × 0.21 m) were higher than those of other planting density treatments during the full heading stage, being 43.56% and 16.22% higher, respectively, than that of the lowest daily light intensity. The daily light intensity of R498 was hindered by close planting (0.23 m × 0.12 m, 0.27 m × 0.14 m) while that of R499 was inhibited by sparse planting on the 20th day after the full heading stage. The rates of decrease of vertical light intensity of R498 and R499 in sparse planting were the highest among all the planting density treatments, their rates of decrease being 97.96% and 92.56%, respectively, during the full heading stage, and 94.81% and 91.10%, respectively, on the 20th day after the full heading stage. When the planting density was decreased, the variability of plant height, tiller number, and panicle curvature were greater for R499 than those of R498. The rates of incidence of sheath blight for R498 and R499 in the planting specification of 0.38 m × 0.20 m were 66.67% and 68.89%, respectively, which was the most serious among all the planting density treatments. On increasing the effective spike number and panicle weight, both R498 and R499 produced the highest yields with the planting specification of 0.27 m × 0.14 m, among all the planting density treatments. Even when the density was excessively reduced, the value of yield components did not increase any further. Thus, it is better to plant rice with curved panicles (R498) in a reasonable planting density (neither too close nor too sparse), and to plant rice with erect panicles in a reasonably close planting density. © 2018 Science Press. All rights reserved. 相似文献
178.
In this paper, we present a three-step methodological framework, including location identification, bias modification, and out-of-sample validation, so as to promote human mobility analysis with social media data. More specifically, we propose ways of identifying personal activity-specific places and commuting patterns in Beijing, China, based on Weibo (China’s Twitter) check-in records, as well as modifying sample bias of check-in data with population synthesis technique. An independent citywide travel logistic survey is used as the benchmark for validating the results. Obvious differences are discerned from Weibo users’ and survey respondents’ activity-mobility patterns, while there is a large variation of population representativeness between data from the two sources. After bias modification, the similarity coefficient between commuting distance distributions of Weibo data and survey observations increases substantially from 23% to 63%. Synthetic data proves to be a satisfactory cost-effective alternative source of mobility information. The proposed framework can inform many applications related to human mobility, ranging from transportation, through urban planning to transport emission modeling. 相似文献
179.
Philippa Douglas Daniela Fecht Deborah Jarvis 《Frontiers of Environmental Science & Engineering》2021,15(3):40
180.
The main aim of the present work is to discuss the methodological approaches that underpin the “contaminant migration–population effects” models for the evaluation of the detriment to populations of moving organisms in environmental systems with spatial and time dependent pollution levels. A technique to couple the equations controlling the population dynamics and the pollutant dispersion is described and discussed. The domain of application and the limitations of the methodology are analysed and illustrated by some examples. Possible alternative approaches are briefly presented. 相似文献