排序方式: 共有40条查询结果,搜索用时 421 毫秒
1.
Egbert Kanis Ab F. Groen Karel H. De Greef 《Journal of Agricultural and Environmental Ethics》2003,16(2):137-162
Pork producers in Western Europe moreand more encounter a variety of societalconcerns about pork and pork production. Sofar, however, producers predominantly focusedon low consumer prices, therewith addressingjust one concern. This resulted in an intensiveand large-scale production system, decreasinglyrelated to the area of farm land, andaccompanied with increasing concerns aboutsafety and healthiness of pork, animal welfare,environmental pollution, and others.An overview was given of possible concernsabout West-European pork production with theconsumers, citizens, and producers, and thoseconcerns are traced back to the pork productionsystem. The various kinds and qualities ofinformation about the pork production system onwhich possible concerns are based have beenworked out extensively in this paper. Knowledgeabout the aspects of pork production that cangive rise to concerns can be used in two ways.First, the communication about those aspectstowards consumers and citizens can be adjustedor extended to give them better possibilitiesto make food choices or to develop their ownopinions about pork production. Second,producers could change the pork productionsystem such that it better satisfies consumersand citizens. Such adaptations are wellpossible, as three pork quality schemes, whichhave been evaluated, illustrate. However, mostof these adaptations can only be carried out atthe cost of the present low consumer prices andwill not occur spontaneously on a large scale.Therefore, accounting for the type andrelevance of the concerns, legislation isnecessary to address societal concerns in abalanced way such that pork production systemsbecome acceptable for the majority of oursociety. 相似文献
2.
Assessment of Soil Erodibility Indices for Conservation Reserve Program Lands in Southwestern Kansas Using Satellite Imagery and GIS Techniques 总被引:2,自引:0,他引:2
The soil erodibility index (EI) of Conservation Reserve Program (CRP) lands, which was the major criterion for CRP enrollment,
was assessed for six counties in southwestern Kansas using USGS seamless digital elevation model data and Geographical Informational
System techniques. The proportion of land areas with EI values of 8 or lower was less than 1% of the entire study area and
most of the land areas (72.5%) were concentrated on EI values between 8 and 24. Although land acreage with EI values of 24
or higher decreased dramatically, the proportion of CRP lands to the other land-use types did not change much from low to
high EI levels. The soil EI and physical soil characteristics of the CRP lands were compared to those of other land-use types.
In general, the mean EI values of the land-use types were strongly correlated with physical soil properties, including organic
matter content, clay content, available water capacity, permeability, and texture. CRP lands were compared in detail with
cropland in terms of their soil characteristics to infer the pivotal cause of the land transformation. Although there was
no significant statistical difference in EI between cropland and CRP soils, soil texture, soil family, and permeability were
statistically different between the two. Statistical analyses of these three variables showed that CRP soils had coarser texture
and higher permeability on average than cropland soils, indicating that CRP lands in the study area are drier than cropland
soils. Therefore, soil moisture characteristics, not necessarily soil erosion potential, might have been the key factor for
CRP enrollment in the study area. 相似文献
3.
Lifjeld JT Kleven O Jacobsen F McGraw KJ Safran RJ Robertson RJ 《Behavioral ecology and sociobiology》2011,65(9):1687-1697
When males become more ornamented and reproduce more successfully as they grow older, phenotypic correlations between ornament
exaggeration and reproductive success can be confounded with age effects in cross-sectional studies, and thus say relatively
little about sexual selection on these traits. This is exemplified here in a correlative study of male fertilization success
in a large colony of American barn swallows (Hirundo rustica erythrogaster). Previous studies of this species have indicated that two sexually dimorphic traits, tail length and ventral plumage coloration,
are positively correlated with male fertilization success, and a mechanism of sexual selection by female choice has been invoked.
However, these studies did not control for potential age-related variation in trait expression. Here, we show that male fertilization
success was positively correlated with male tail length but not with plumage coloration. We also show that 1-year-old males
had shorter tails and lower fertilization success than older males. This age effect accounted for much of the covariance between
tail length and fertilization success. Still, there was a positive relationship between tail length and fertilization success
among older males. But as this group consisted of males from different age classes, an age effect may be hidden in this relationship
as well. Our data also revealed a longitudinal increase in both tail length and fertilization success for individual males.
We argue that age-dependent ornament expression and reproductive performance in males complicate inferences about female preferences
and sexual selection. 相似文献
4.
5.
Ecosystems close to a critical threshold lose resilience, in the sense that perturbations can more easily push them into an alternative state. Recently, it has been proposed that such loss of resilience may be detected from elevated autocorrelation and variance in the fluctuations of the state of an ecosystem due to critical slowing down; the underlying generic phenomenon that occurs at critical thresholds. Here we explore the robustness of autocorrelation and variance as indicators of imminent critical transitions. We show both analytically and in simulations that variance may sometimes decrease close to a transition. This can happen when environmental factors fluctuate stochastically and the ecosystem becomes less sensitive to these factors near the threshold, or when critical slowing down reduces the ecosystem's capacity to follow high-frequency fluctuations in the environment. In addition, when available data is limited, variance can be systematically underestimated due to the prevalence of low frequencies close to a transition. By contrast, autocorrelation always increases toward critical transitions in our analyses. To exemplify this point, we provide cases of rising autocorrelation and increasing or decreasing variance in time series prior to past climate transitions. 相似文献
6.
Testosterone upregulates lipoprotein status to control sexual attractiveness in a colorful songbird 总被引:4,自引:0,他引:4
Kevin J. McGraw Stephanie M. Correa Elizabeth Adkins-Regan 《Behavioral ecology and sociobiology》2006,60(2):117-122
A salient feature of many secondary sexual characteristics in animals is that their expression is controlled by sex-steroid hormones. However, for only a few types of ornaments do we know the precise molecular mechanism by which androgens like testosterone (T) enhance trait production. We studied the red carotenoid-based beak of male zebra finches (Taeniopygia guttata), which serves as a sexually selected trait and is thought to be T dependent. In previous research, we demonstrated that the extent to which male finches produce lipoproteins in the bloodstream, which bind carotenoid pigments acquired from the diet and transport them to peripheral tissues, regulates the accumulation of carotenoids in the body and beak pigmentation. Here we show that T acts to upregulate lipoprotein production and allows male zebra finches to display flashy, sexually attractive coloration. Levels of circulating T in blood positively and significantly predicted lipoprotein profile (as measured by cholesterol levels), blood carotenoid concentration, and beak color. Exogenous T administration elevated cholesterol and carotenoid status as well as beak redness. Last, experimental inhibition of T (using the anti-androgen flutamide) downregulated lipoprotein production and carotenoid circulation and faded the beak. This androgen- and lipoprotein-mediated system represents one of the more detailed physiological mechanisms underlying the development of a sex-steroid-dependent trait in animals. 相似文献
7.
Melissa G. Meadows Nathan I. Morehouse Ronald L. Rutowski Jonathan M. Douglas Kevin J. McGraw 《Behavioral ecology and sociobiology》2011,65(6):1317-1327
Quantification of animal colors is important to a variety of fields of research, especially those dealing with visual communication
and sexual selection. Most animal colors are easily measured using well-established spectrophotometric techniques. However,
the unique characteristics of iridescent colors present particular challenges and opportunities to quantify novel color metrics.
Due to the fine-scale angle dependence of iridescent coloration, color metrics, such as hue and brightness, must be measured
using methods that allow for repeatable comparison across individuals (e.g., by carefully controlling and measuring viewing
geometry). Here, we explain how the optical characteristics of iridescent colors should be considered when developing measurement
techniques, describe the pitfalls of some commonly used techniques, and recommend improved methods and metrics (angular degree
of color change and breadth of reflectance) for quantifying iridescent color. In particular, most studies of iridescent birds
to date have used less than ideal procedures and have not provided repeatability estimates for their methods. For example,
we demonstrate here that measuring coloration from overlapping patches of iridescent feathers may be problematic, and we argue
against methods that do not carefully control viewing geometry. We recommend measuring iridescence at maximal reflectance
angles using an apparatus that allows for sample rotation, and we compare this technique to some other commonly used methods
using iridescent gorget and crown feathers from Anna’s hummingbirds (Calypte anna). Our apparatus allows for the quantification of angular color change, and we found that maximal reflectance measurements
using single feathers are highly repeatable both within feather samples and among samples within an individual. 相似文献
8.
9.
Michael W. Butler Matthew B. Toomey Kevin J. McGraw 《Behavioral ecology and sociobiology》2011,65(2):401-413
For a variety of technical and conceptual reasons, biologists have come to use several different methods to quantify the colors
of animals. However, the relative abilities of these different color-scoring procedures to capture variation in the actual
color-generating mechanisms—pigment or structural composition of the integument—have never been tested systematically. Here,
we examined which commonly employed color metrics predict carotenoid content of ornaments in three avian species (house finch
Carpodacus mexicanus, mallard duck Anas platyrhynchos, and zebra finch Taeniopygia guttata). We used spectrophotometry to measure reflectance spectra from beak and feather tissue, calculated numerous color metrics
(e.g., hue, chroma, brightness, principal components, and tetrahedral color space position) from these spectra, and determined
carotenoid content at the site of color measurement with high-performance liquid chromatography. We found that several principal
component, tristimulus, and avian visual model metrics significantly correlated with carotenoid content of house finch feathers
and duck beaks. Carotenoid content of mallard beaks was most closely correlated with brightness and saturation metrics, whereas
in house finch feathers, carotenoid concentration was best captured by hue and saturation metrics. According to tristimulus
scores and visual models, we found that the ultraviolet portion of the spectrum was not an essential predictor of variation
in carotenoid content. Also, visual model chromatic contrasts generally were not significant predictors of carotenoid content,
although some achromatic contrasts and tetrahedral color space vector parameters were. Our results indicate that numerous
methods, especially tristimulus scores, are suitable for capturing pigment-based color variation in two carotenoid-containing
ornaments, and we discuss the merits and shortcomings of these different approaches. In contrast, there were no significant
relationships between any color metrics and the carotenoid content of zebra finch beaks, suggesting that other color-generating
mechanisms besides carotenoids may contribute to color variability in this species. 相似文献
10.
The role of detrital quantity and quality in forest floor N leaching was investigated in a litter manipulation experiment at a deciduous forest under chronic N deposition. Dissolved inorganic nitrogen (DIN) comprised the bulk of nitrogen leaching from the control except a short period following autumn litterfall. The dominance of DIN was strengthened by litter exclusion, whereas the addition of glucose or fresh litter led to a small increase in dissolved organic nitrogen (DON) and either a temporary or gradual reduction in NO(3)(-) release, respectively. Changes in soluble organic C and microbial C in the forest floor implied that increased availability of C sources might have enhanced microbial immobilization of DIN, either temporarily following glucose application or over the longer term following litter addition. The results suggest that detrital quantity and quality can play a crucial role in determining the balance between DIN and DON in N-enriched forest soils. 相似文献