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排序方式: 共有57条查询结果,搜索用时 15 毫秒
1.
Ectoparasites of house sparrows (Passer domesticus): an experimental test of the immunocompetence handicap hypothesis and a new model 总被引:2,自引:0,他引:2
Conspicuous secondary sexual traits may have evolved as handicap-revealing signals or as badges of status. We present results
of an experiment using males of the sexually dimorphic house sparrow (Passer domesticus), that support the idea that the male-specific bib can be both a handicap-revealing signal and a reliable badge indicating
the physical condition of the bird. In a test of the immunocompetence handicap hypothesis, wild-caught adult male house sparrows
were studied in captivity. Birds implanted with elevated doses of testosterone were more dominant, had higher circulating
levels of both testosterone and corticosterone and they also harboured relatively larger ectoparasite loads. Higher parasite
loads were also associated with individuals showing lower immunocompetence and larger changes in bib size. A new model for
immunocompetence effects in sexual selection is introduced, integrating actions that the hypothalamopituitary axis exerts
on gonads, adrenals and the thyroid gland. The ”integrated immunocompetence model” synthesizes both the ”handicap” (i.e. survival-decreasing)
and ”badge of status” (i.e. survival- enhancing) models for evolution of secondary sexual traits.
Received: 15 May 1999 / Received in revised form: 2 November 1999 / Accepted: 6 November 1999 相似文献
2.
Kevon Rhiney Anton Eitzinger Aidan D. Farrell Steven D. Prager 《Regional Environmental Change》2018,18(8):2313-2327
Despite recent calls to limit future increases in the global average temperature to well below 2 °C, little is known about how different climatic thresholds will impact human society. Future warming trends have significant global food security implications, particularly for small island developing states (SIDS) that are recognized as being among the most vulnerable to global climate change. In the case of the Caribbean, any significant change in the region’s climate is likely to have significant adverse effects on the agriculture sector. This paper explores the potential biophysical impacts of a +?1.5 °C warming scenario on several economically important crops grown in the Caribbean island of Jamaica. Also, it explores differences to a >?2.0 °C warming scenario, which is more likely, if the current policy agreements cannot be complied with by the international community. We use the ECOCROP niche model to estimate how predicted changes in future climate could affect the growing conditions of several commonly cultivated crops from both future scenarios. We then discuss some key policy considerations for Jamaica’s agriculture sector, specifically related to the challenges posed to future adaptation pathways amidst growing climate uncertainty and complexity. Our model results show that even an increase less than +?1.5 °C is expected to have an overall negative impact on crop suitability and a general reduction in the range of crops available to Jamaican farmers. This observation is instructive as increases above the +?1.5 °C threshold would likely lead to even more irreversible and potentially catastrophic changes to the sustainability of Jamaica’s agriculture sector. The paper concludes by outlining some key considerations for future action, paying keen attention to the policy relevance of a +?1.5 °C temperature limit. Given little room for optimism with respect to the imminent changes that SIDS will need to confront in the near future, broad-based policy engagement by stakeholders in these geographies is paramount, irrespective of the climate warming scenario. 相似文献
3.
In this study, we analyze the evolution of Canada's mining industry from 1929 to 2006, focussing on the determinants of the number of firms in the industry and why this number changed over that period. Most empirical studies of industry evolution have focused on manufacturing industries that share similar structural characteristics. Perhaps because of this, extant models of industry evolution tend to ignore industry-specific and national-specific factors that can cause atypical trajectories, that is, heterogeneous industry evolution. Initial inspection of the Canadian mining industry shows that it is atypical in that it exhibits “negative skew” over time in the number of firms rather than the typical “positive skew.” We review two dominant theoretical approaches to industry evolution: the density-dependence theory and variants of industrial organization economics. We also consider possible sources of industry evolution heterogeneity, focussing particularly on “regulatory punctuation”. Using Canadian mining data, we find that the traditional models do not fully explain the changes in population size in Canada's mining industry. As a result, we introduce a number of hybrid models. The results from these hybrid models suggest that Canadian-specific regulatory punctuations, particularly the introduction of significant new taxes, environmental legislation, and incentives have shaped the trajectory of mining firm participation. 相似文献
4.
Nigel J. Tapper Aidan W. Sudbury 《Journal of the Air & Waste Management Association (1995)》2013,63(4):433-441
Odor is acknowledged as a major community air pollution nuisance, but the problems of analysis, particularly in Identifying the origin of odor, are also well recognised. One approach to the problem has been the development of computational schemes which use wind directions at the times of odor observations to locate the likely source of odor. An earlier technique, PONG, has now been superseded by a more sophisticated version, PONG2, which incorporates Gaussian plume modeling techniques. This paper describes the operation of PONG2 in the odor source mapping mode and provides an analysis of the Insensitivity of the technique to errors in input. Then, using specific Australian examples of community odor nuisance emanating from a large sewage treatment complex near Melbourne, and an irrigated golf course within metropolitan Darwin, the paper outlines the utility of PONG2 in resolving problem odor sources at a range of scales and levels of complexity. 相似文献
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Evaluating factors influencing groundwater vulnerability to nitrate pollution: developing the potential of GIS 总被引:14,自引:0,他引:14
Lake IR Lovett AA Hiscock KM Betson M Foley A Sünnenberg G Evers S Fletcher S 《Journal of environmental management》2003,68(3):315-328
The 1991 EU Nitrate Directive was designed to reduce water pollution from agriculturally derived nitrates. England and Wales implemented this Directive by controlling agricultural activities within their most vulnerable areas termed Nitrate Vulnerable Zones. These were designated by identifying drinking water catchments (surface and groundwater), at risk from nitrate pollution. However, this method contravened the Nitrate Directive because it only protected drinking water and not all waters. In this paper, a GIS was used to identify all areas of groundwater vulnerable to nitrate pollution. This was achieved by constructing a model containing data on four characteristics: the quality of the water leaving the root zone of a piece of land; soil information; presence of low permeability superficial (drift) material; and aquifer properties. These were combined in a GIS and the various combinations converted into a measure of vulnerability using expert knowledge. Several model variants were produced using different estimates of the quality of the water leaving the root zone and contrasting methods of weighting the input data. When the final models were assessed all produced similar spatial patterns and, when verified by comparison with trend data derived from monitored nitrate concentrations, all the models were statistically significant predictors of groundwater nitrate concentrations. The best predictive model contained a model of nitrate leaching but no land use information, implying that changes in land use will not affect designations based upon this model. The relationship between nitrate levels and borehole intake depths was investigated since there was concern that the observed contrasts in nitrate levels between vulnerability categories might be reflecting differences in borehole intake depths and not actual vulnerability. However, this was not found to be statistically important. Our preferred model provides the basis for developing a new set of groundwater Nitrate Vulnerable Zones that should help England and Wales to comply with the EU Nitrate Directive. 相似文献
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8.
Andrew D. M. Dobson E. J. Milner-Gulland Colin M. Beale Harriet Ibbett Aidan Keane 《Conservation biology》2019,33(3):665-675
The threat posed to protected areas by the illegal killing of wildlife is countered principally by ranger patrols that aim to detect and deter potential offenders. Deterring poaching is a fundamental conservation objective, but its achievement is difficult to identify, especially when the prime source of information comes in the form of the patrols’ own records, which inevitably contain biases. The most common metric of deterrence is a plot of illegal activities detected per unit of patrol effort (CPUE) against patrol effort (CPUE-E). We devised a simple, mechanistic model of law breaking and law enforcement in which we simulated deterrence alongside exogenous changes in the frequency of offences under different temporal patterns of enforcement effort. The CPUE-E plots were not reliable indicators of deterrence. However, plots of change in CPUE over change in effort (ΔCPUE-ΔE) reliably identified deterrence, regardless of the temporal distribution of effort or any exogenous change in illegal activity levels as long as the time lag between patrol effort and subsequent behavioral change among offenders was approximately known. The ΔCPUE-ΔE plots offered a robust, simple metric for monitoring patrol effectiveness; were no more conceptually complicated than the basic CPUE-E plots; and required no specialist knowledge or software to produce. Our findings demonstrate the need to account for temporal autocorrelation in patrol data and to consider appropriate (and poaching-activity-specific) intervals for aggregation. They also reveal important gaps in understanding of deterrence in this context, especially the mechanisms by which it occurs. In practical applications, we recommend the use of ΔCPUE-ΔE plots in preference to other basic metrics and advise that deterrence should be suspected only if there is a clear negative slope. Distinct types of illegal activity should not be grouped together for analysis, especially if the signs of their occurrence have different persistence times in the environment. 相似文献
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