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71.
72.
The pink, tubular, nectariferous flowers of Melocactus intortus (Cactaceae) in Puerto Rico are visited by native hummingbirds (Anthracothorax dominicus), but also by invasive honeybees (Apis mellifera) and ants (Solenopsis sp.). We sought to determine if the bees and ants significantly alter the pollination of M. intortus by measuring pollinator effectiveness. Using traditional estimates of effectiveness (visitation rate and seed set), our results show that hummingbirds were the most effective pollinators as expected. Bees and ants were less effective, and their contributions were one‐fourth to one‐tenth of that observed for hummingbirds. We then modified this measure of effectiveness by adding two components, fitness of progeny and temporal availability of visitors, both of which refine estimates of flower visitor effectiveness. With these new estimations, we found that the effectiveness values of all three animal visitors decreased; however, the role of hummingbirds as the principal pollinator was maintained, whereas the effectiveness values of bees and ants approached zero. By these new measures of overall pollinator effectiveness, the invasive honeybees and ants have little effect on the reproductive success of M. intortus. 相似文献
73.
Host tree resistance against the polyphagous wood-boring beetle Anoplophora glabripennis 总被引:2,自引:0,他引:2
W.D. Morewood K. Hoover P.R. Neiner J.R. McNeil & J.C. Sellmer 《Entomologia Experimentalis et Applicata》2004,110(1):79-86
Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae: Lamiini) is an invasive wood‐boring beetle with an unusually broad host range and a proven ability to increase its host range as it colonizes new areas and encounters new tree species. The beetle is native to eastern Asia and has become an invasive pest in North America and Europe, stimulating interest in delineating host and non‐host tree species more clearly. When offered a choice among four species of living trees in a greenhouse, adult A. glabripennis fed more on golden‐rain tree (Koelreuteria paniculata Laxmann) and river birch (Betula nigra L.) than on London planetree (Platanus × acerifolia (Aiton) Willdenow) or callery pear (Pyrus calleryana Decaisne). Oviposition rate was highest in golden‐rain tree, but larval mortality was also high and larval growth was slowest in this tree species. Oviposition rate was lowest in callery pear, and larvae failed to survive in this tree species, whether they eclosed from eggs laid in the trees or were manually inserted into the trees. Adult beetles feeding on callery pear had a reduced longevity and females feeding only on callery pear failed to develop any eggs. The resistance of golden‐rain tree against the larvae appears to operate primarily through the physical mechanism of abundant sap flow. The resistance of callery pear against both larvae and adults appears to operate through the chemical composition of the tree, which may include compounds that are toxic or which otherwise interfere with normal growth and development of the beetle. Unlike river birch or London planetree, both golden‐rain tree and callery pear are present in the native range of A. glabripennis and may therefore have developed resistance to the beetle by virtue of exposure to attack during their evolutionary history. 相似文献
74.
Piotr Politański Elźbieta Rajkowska Marcin Brodecki Andrzej Bednarek Marek Zmyślony 《Bioelectromagnetics》2013,34(4):333-336
The aim of this study was to investigate the effect of static magnetic fields (SMF) on reactive oxygen species induced by X‐ray radiation. The experiments were performed on lymphocytes from male albino Wistar rats. After exposure to 3 Gy X‐ray radiation (with a dose rate of 560 mGy/min) the measurement of intracellular reactive oxygen species in lymphocytes, using a fluorescent probe, was done before exposure to the SMF, and after 15 min, 1 and 2 h of exposure to the SMF or a corresponding incubation time. For SMF exposure, 0 mT (50 µT magnetic field induction opposite to the geomagnetic field) and 5 mT fields were chosen. The trend of SMF effects for 0 mT was always opposite that of 5 mT. The first one decreased the rate of fluorescence change, while the latter one increased it. Bioelectromagnetics 34:333–336, 2013. © 2012 Wiley Periodicals, Inc. 相似文献
75.
This paper investigates the causal relationships between per capita CO2 emissions, gross domestic product (GDP), renewable and non-renewable energy consumption, and international trade for a panel of 25 OECD countries over the period 1980–2010. Short-run Granger causality tests show the existence of bidirectional causality between: renewable energy consumption and imports, renewable and non-renewable energy consumption, non-renewable energy and trade (exports or imports); and unidirectional causality running from: exports to renewable energy, trade to CO2 emissions, output to renewable energy. There are also long-run bidirectional causalities between all our considered variables. Our long-run fully modified ordinary least squares (FMOLS) and dynamic ordinary least squares (DOLS) estimates show that the inverted U-shaped environmental Kuznets curve (EKC) hypothesis is verified for this sample of OECD countries. They also show that increasing non-renewable energy increases CO2 emissions. Interestingly, increasing trade or renewable energy reduces CO2 emissions. According to these results, more trade and more use of renewable energy are efficient strategies to combat global warming in these countries. 相似文献
76.
77.
The Importance of Hydrodynamics for Protected and Endangered Biodiversity of Lowland Rivers 总被引:3,自引:3,他引:0
R. J. W. de Nooij W. C. E. P. Verberk H. J. R. Lenders R. S. E. W. Leuven P. H. Nienhuis 《Hydrobiologia》2006,565(1):153-162
This paper examines the relationship between protected and endangered riverine species (target species) and hydrodynamics
in river-floodplain ecosystems, combining ecological and policy-legal aspects of biodiversity conservation in river management.
The importance of different hydrodynamic conditions along a lateral gradient was quantified for various taxonomic groups.
Our results show that (i) target species require ecotopes along the entire hydrodynamic gradient; (ii) different parts of
the hydrodynamic gradient are important to different species, belonging to different taxonomic groups; (iii) in particular
low-dynamic parts are important for many species and (iv) species differ in their specificity for hydrodynamic conditions.
Many species of higher plants, fish and butterflies have a narrow range for hydrodynamics and many species of birds and mammals
use ecotopes along the entire gradient. Even when focussing only on target species, the entire natural hydrodynamic gradient
is important. This means that the riverine species assemblage as a whole can benefit from measures focussing on target species
only. River reconstruction and management should aim at re-establishing the entire hydrodynamic gradient, increasing the spatial
heterogeneity of hydrodynamic conditions. 相似文献
78.
Craig R. Allen Ahjond S. Garmestani Jill A. LaBram Amanda E. Peck Luanna B. Prevost 《Biological invasions》2006,8(2):169-176
Woodlots are forest islands embedded within an urban matrix, and often represent the only natural areas remaining in suburban
areas. Woodlots represent critical conservation areas for native plants, and are important habitat for wildlife in urban areas.
Invasion by non-indigenous (NIS) plants can alter ecological structure and function, and may be especially severe in remnant
forests where NIS propagule pressure is high. Woody shrubs in the Family Berberidaceae have been well documented as invaders
of the forest–urban matrix in North America. Mahonia bealei (Berberidaceae) is a clonal shrub native to China, and is a popular ornamental in the Southeastern United States. Mahoni bealei is listed as “present” on some local and state floras, but almost nothing is known regarding its invasion potential in the
United States. We sampled 15 woodlots in Clemson, South Carolina, to assess the invasion of M. bealei and other woody non-indigenous species (NIS). M. bealei invaded 87% of the woodlots surveyed and species richness of NIS on these woodlots varied from 5 to 14. Stepwise-multiple
regression indicated that less canopy cover and older M. bealei predicted greater abundance of M. bealei , and that not all subdivisions were equally invaded (P < 0.0001; r2 = 0.88). The impact of M. bealei on native flora and fauna may be considerable, and it is likely to continue to spread in the Southeastern United States.
M. bealei should be recognized as an aggressive invader in the Southeastern United States, with the potential for negative impacts
on native flora and fauna. 相似文献
79.
The aim of this study was to update figures for the presence of dioecy among the gymnosperms and investigate its correlation with climate, growth form, pollination and seed dispersal syndromes, and risk of extinction. Dioecy was found in almost 65% of contemporary gymnosperm species, a higher percentage than previous estimates. It dominates in 8 of the 12 families. As in angiosperms, dioecious gymnosperms are particularly common in climbers and are more commonly found in tropical climates. Analysis of the degree of threat using IUCN red list categories showed that the proportion of threatened species is higher in dioecious than in monoecious species only in temperate climate. The high sensitivity of dioecious species to environmental changes associated with human activity in temperate climate may explain this phenomenon. The monophyly of extant gymnosperms and the relatively small number of species (about 1000) create the possibility of treating them as a model group in investigating the evolution of sexual systems. 相似文献
80.
Oviposition behavior and offspring fitness of the parasitoid Aphidius gifuensis (Ashmead) were compared on three aphid species, Sitobion avenae F., Myzus persicae (Sulzer), and Aphis gossypii Glover using wasps collected from both S. avenae and M. persicae. A. gifuensis produced more mummies and adults on S. avenae and M. persicae than on A. gossypii regardless of the host of origin. Mummy production was influenced by attack rate and percentage of aphids superparasitized. The F1 generations from S. avenae and M. persicae were more female-biased and wasps were larger than those from A. gossypii. Although there were significant differences in development time of A. gifuensis in the three aphid species, the difference was generally shorter than one day. Fewer mummies were produced when A. gifuensis was transferred between S. avenae and M. persicae, but no significant difference was observed in emergence rate, percentage of female offspring, or body size. The effects of host species on A. gifuensis female performance and offspring fitness are discussed, along with the potential for using A. gifuensis to control M. persicae and A. gossypii. 相似文献