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61.
Species richness and evenness are components of biological diversity that may or may not be correlated with one another and with patterns of species abundance. We compared these attributes among flowering plants, grasshoppers, butterflies, lizards, summer birds, winter birds, and rodents across 48 plots in the grasslands and mesquite-oak savannas of southeastern Arizona. Species richness and evenness were uncorrelated or weakly negatively correlated for each taxonomic group, supporting the conclusion that richness alone is an incomplete measure of diversity. In each case, richness was positively correlated with one or more measures of abundance. By contrast, evenness usually was negatively correlated with the abundance variables, reflecting the fact that plots with high evenness generally were those where all species present were about equally uncommon. Therefore richness, but not evenness, usually was a positive predictor of places of conservation value, if these are defined as places where species of interest are especially abundant. Species diversity was more positively correlated with evenness than with richness among grasshoppers and flowering plants, in contrast to the other taxonomic groups, and the positive correlations between richness and abundance were comparatively weak for grasshoppers and plants as well. Both of these differences can be attributed to the fact that assemblages of plants and grasshoppers were numerically dominated by small subsets of common species (grasses and certain spur-throated grasshoppers) whose abundances differed greatly among plots in ways unrelated to species richness of the groups as a whole. 相似文献
62.
63.
We have found that foraging bumblebees (Bombus hortorum, B. pascuorum, B. pratorum and B.␣terrestris) not only avoid flowers of Symphytum officinale that have recently been visited by conspecifics but also those that have been recently visited by heterospecifics. We propose
that the decision whether to reject or accept a flower is influenced by a chemical odour that is left on the corolla by a
forager, which temporarily repels subsequent foragers. Honeybees and carpenter bees have previously been shown to use similar
repellent forage-marking scents. We found that flowers were repellent to other bumblebee foragers for approximately 20 min
and also that after this time nectar levels in S. officinale flowers had largely replenished. Thus bumblebees could forage more efficiently by avoiding flowers with low rewards. Flowers
to which extracts of tarsal components were applied were more often rejected by wild B. terrestris workers than flowers that had head extracts applied, which in turn were more often rejected than flowers that had body extracts
applied. Extracts from four Bombus species were equally repellent to foragers. The sites of production of the repellent scent and its evolutionary origins are
discussed.
Received: 24 November 1997 / Accepted after revision: 8 March 1998 相似文献
64.
Marion Valeix Hervé Fritz Andrew J. Loveridge Zeke Davidson Jane E. Hunt Felix Murindagomo David W. Macdonald 《Behavioral ecology and sociobiology》2009,63(10):1483-1494
A central question in the study of predator–prey relationships is to what extent prey behaviour is determined by avoidance
of predators. Here, we test whether the long-term risk of encountering lions and the presence of lions in the vicinity influence
the behaviour of large African herbivores at waterholes through avoidance of high-risk areas, increases in group size, changes
in temporal niche or changes in the time spent in waterhole areas. In Hwange National Park, Zimbabwe, we monitored waterholes
to study the behaviour of nine herbivore species under different risks of encountering lions. We radio-collared 26 lions in
the study area which provided the opportunity to monitor whether lions were present during observation sessions and to map
longer-term seasonal landscapes of risk of encountering lions. Our results show that the preferred prey species for lions
(buffalo, kudu and giraffe) avoided risky waterholes. Group size increased as encounter risk increased for only two species
(wildebeest and zebra), but this effect was not strong. Interestingly, buffalo avoided the hours of the day which are dangerous
when the long-term and short-term risks of encountering lions were high, and all species showed avoidance of waterhole use
at night times when lions were in the vicinity. This illustrates well how prey can make temporal adjustments to avoid dangerous
periods coinciding with predator hunting. Additionally, many herbivores spent more time accessing water to drink when the
long- and short-term risks of encountering lions were high, and they showed longer potential drinking time when the long-term
risk of encountering lions was high, suggesting higher levels of vigilance. This study illustrates the diversity of behavioural
adjustments to the risk of encountering a predator and how prey respond differently to temporal variations in this risk. 相似文献
65.
Strong variability in bacterioplankton abundance and production in central and western Bay of Bengal
Veronica Fernandes Nagappa Ramaiah Jane T. Paul Sugandha Sardessai R. Jyoti Babu Mangesh Gauns 《Marine Biology》2008,153(5):975-985
With large influx of freshwater that decreases sea-surface salinities, weak wind forcing of <10 m s−1 and almost always warm (>28°C) sea-surface temperature that stratifies and shallows the mixed layer leading to low or no
nutrient injections into the surface, primary production in Bay of Bengal is reportedly low. As a consequence, the Bay of
Bengal is considered as a region of low biological productivity. Along with many biological parameters, bacterioplankton abundance
and production were measured in the Bay of Bengal during post monsoon (September–October 2002) along an open ocean transect,
in the central Bay (CB, 88°E) and the other transect in the western Bay (WB). The latter representing the coastal influenced
shelf/slope waters. Bacterioplankton abundances (<2 × 109cells l−1) were similar to those reported from the HNLC equatorial Pacific and the highly productive northern Arabian Sea. Yet, the
thymidine uptake rates along CB (average of 1.46 pM h−1) and WB (average of 1.40 pM h−1) were less than those from the northwestern Indian Ocean. These abundances and uptake rates were higher than those in the
oligotrophic northwestern Sargasso Sea (<7 × 108 cells l−1; av 1.0 pM h−1). Concentrations of chlorophyll a (chl a), primary production rates and total organic carbon (TOC) were also measured for a comparison of heterotrophic and autotrophic
production. In the WB, bacterioplankton carbon biomass equaled ∼ 95% of chl a carbon than just 31% in the CB. Average bacterial:primary production (BP:PP) ratios accounted for 29% in the CB and 31% in
the WB. This is mainly due to lower primary productivity (PP) in the WB (281 mg C m−2 d−1) than in the CB (306 mg C m−2 day−1). This study indicates that bacteria–phytoplankton relationship differs in the open (CB) and coastal waters (WB). Higher
abundance and contrastingly low bacterial production (BP) in WB may be because of the riverine bacteria, brought in through
discharges, becoming dormant and unable to reproduce in salinities of 28 or more psu. Heterotrophic bacteria appear to utilize
in situ DOC rather rapidly and their carbon demand is ∼50% of daily primary production. It is also apparent that allochthonous
organic matter, in particular in the western Bay, is important for meeting their carbon demand. 相似文献
66.
Shahid Parvez Glenn E. Rice Linda K. Teuschler Jane Ellen Simmons Thomas F. Speth Susan D. Richardson Richard J. Miltner E. Sidney Hunter III Jonathan G. Pressman Lillian F. Strader Gary R. Klinefelter Jerome M. Goldman Michael G. Narotsky 《环境科学学报(英文版)》2017,29(8):311-321
A method based on regression modeling was developed to discern the contribution of component chemicals to the toxicity of highly complex, environmentally realistic mixtures of disinfection byproducts(DBPs). Chemical disinfection of drinking water forms DBP mixtures.Because of concerns about possible reproductive and developmental toxicity, a whole mixture(WM) of DBPs produced by chlorination of a water concentrate was administered as drinking water to Sprague–Dawley(S–D) rats in a multigenerational study. Age of puberty acquisition,i.e., preputial separation(PPS) and vaginal opening(VO), was examined in male and female offspring, respectively. When compared to controls, a slight, but statistically significant delay in puberty acquisition was observed in females but not in males. WM-induced differences in the age at puberty acquisition were compared to those reported in S–D rats administered either a defined mixture(DM) of nine regulated DBPs or individual DBPs. Regression models were developed using individual animal data on age at PPS or VO from the DM study. Puberty acquisition data reported in the WM and individual DBP studies were then compared with the DM models. The delay in puberty acquisition observed in the WM-treated female rats could not be distinguished from delays predicted by the DM regression model, suggesting that the nine regulated DBPs in the DM might account for much of the delay observed in the WM. This method is applicable to mixtures of other types of chemicals and other endpoints. 相似文献
67.
When characterizing environmental radioactivity, whether in the soil or within concrete building structures undergoing remediation or decommissioning, it is highly desirable to know the radionuclide depth distribution. This is typically modeled using continuous analytical expressions, whose forms are believed to best represent the true source distributions. In situ gamma ray spectroscopic measurements are combined with these models to fully describe the source. Currently, the choice of analytical expressions is based upon prior experimental core sampling results at similar locations, any known site history, or radionuclide transport models. This paper presents a method, employing multiple in situ measurements at a single site, for determining the analytical form that best represents the true depth distribution present. The measurements can be made using a variety of geometries, each of which has a different sensitivity variation with source spatial distribution. Using non-linear least squares numerical optimization methods, the results can be fit to a collection of analytical models and the parameters of each model determined. The analytical expression that results in the fit with the lowest residual is selected as the most accurate representation. A cursory examination is made of the effects of measurement errors on the method. 相似文献
68.
Perceptions matter: household adaptive capacity and capability in two Australian coastal communities
Elrick-Barr Carmen E. Thomsen Dana C. Preston Benjamin L. Smith Timothy F. 《Regional Environmental Change》2017,17(4):1141-1151
Regional Environmental Change - This paper presents empirical data on household perceptions of capability to adapt to climate hazards and associated capacity needs. Households play an important... 相似文献
69.
Regional Environmental Change - Vulnerability assessment is fundamental for informing adaptation to climate change policy. The aim of this study is to evaluate the vulnerability of rural... 相似文献
70.
The use of pressure-volume-temperature (PVT) studies in processing of a biodegradable plastic composition made from soy protein
isolate and corn starch is described. The ability of PVT measurements to predict the combined effects of pressure, volume,
and temperature effects is demonstrated. The results show that the PVT relations of the plastic can be predicted by using
a regression analysis similar to the Tait equations of state. A change in slope of the PVT curves was observed at around 80‡C,
which is ascribed to the glass-transition process of the plastic. Evidence of onset of thermal degradation of the plastic
was observed at ca. 160‡C under 0 to 200 MPa isobaric pressure. This thermal degradation precluded determination of the crystal
melting point of the plastic. 相似文献