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141.
Abstract An experiment, involving 2000 members of the public, determined the identity of nest predators in urban environments. Experimental nests of halved tennis balls covered with coconut fibre and wool were manufactured to resemble the nests of willie wagtails, Rhipidura leucophrys. The identity of predators was determined by analysis of imprints left in artificial eggs made of coloured modelling clay. Sixty-four per cent of nests were preyed upon, with most predation being the result of large birds. Direct observations of predation (n = 134) indicated that pied currawongs were the most common large bird, accounting for 52% of all predation. Predation incidence was higher in gardens with more trees and in which kookaburras, Dacelo novaeguineae, were fed frequently. Among nests placed in trees, nest predation was correlated with nest height. Eggs camouflaged by speckling experienced a similar incidence of predation to plain eggs. This study provides evidence to support the contention that pied currawongs are a major threat to the persistence of small birds in Australian urban environments. 相似文献
142.
CLAIRE G. WILLIAMS KAREN L. JOYNER LISA D. AUCKLAND SPENCER JOHNSTON H. JAMES PRICE 《Biological journal of the Linnean Society. Linnean Society of London》2002,75(4):503-508
Strong karotypic orthoselection does not fully account for genome size variation in pines. Adult F1 interspecific pine hybrids are fertile and the genomic consequences of hybridization can be studied using haploid female megagametophytes. Greater variation in genome size was hypothesized to occur in hybrids compared to their parental species and the variation was thought to be positively related to the phylogenetic distance between the parental species. Nuclear 1C DNA content of megagametophytes from four sets of fertile Pinus spp. F1 hybrids and their parents was determined using a laser flow cytometer. Fertile F1 hybrids included two sets of hard pine hybrid Pinus elliottii Engelm. x P. caribaea var. hondurensis Morelet and two Asian x New World soft pine hybrids P. wallichiana A.B. Jacks. x P. strobus L. (hybrid is known as P. x schwerinii ) and P. lambertiana Dougl. x P. armandii Franchlet. Fertile, adult F1 produce haploid megagametophytes with nuclear DNA contents comparable to the parents or parental species. One genomic consequence of hybridization in pines is stability in nuclear DNA content. Hybrid genomes neither increased or decreased DNA content regardless of the phylogenetic distance between parents. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 503–508. 相似文献
143.
The distribution of free sugars and organic acids between theepidermis and mesophyll of Tulipa gesneriana L., Vicia fabaL., and Commelina communis L. leaves was studied using mainlygas-liquid chromatography. Fructose, glucose, sucrose, and myo-inositol were found in theepidermis and mesophyll of all three species. In T. geenerianaleaf tissues arabinose (trace levels), stachyose, tuliposidesA and B (mainly in the mesophyll), and xylose (trace levelsalso in V. faba tissues) were also detected. The acids were more difficult to detect and identify, beingat considerably lower concentrations than the sugars in bothtissues. Fumaric, citric, malic, ascorbic (trace levels), andan unidentified acid were common to the epidermis and mesophyllof all three species. Of special interest was the detectionof large amounts of glyceric acid in the epidermis and mesophyllof V. faba; this acid was not detected in the tissues from theother species. Fumaric acid was also very abundant in the epidermisof V.faba. A special study was made of the compartmentation of acids andsugars between the epidermis and mesophyll of T. geenerianaleaves after light and dark treatments. No changes in free acidor sugar levels were detected in the epidermis or mesophyllafter these treatments. Except for suceinic acid (P < 0·05),there were no statistically significant differences in acidlevels between the epidermis and mesophyll but for most of thesugars (myo-inositol, arabinose, and xylose being exceptions)differences were highly significant (P < 0·001), highestlevels occurring in the mesophyll. The differences in sugarlevels and the similarity in acid levels between epidermis andmesophyll of tulip leaves were considered to be essentiallydue to the different CO2 fixing mechanisms and capacities ofthe two tissues. The energy source for the essentially non-greenepidermal tissue was discussed. 相似文献
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DAN E. CHAMBERLAIN JULIET A. VICKERY DAVID E. GLUE ROBERT A. ROBINSON GREG J. CONWAY RICHARD J. W. WOODBURN & ANDREW R. CANNON 《Ibis》2005,147(3):563-575
Provision of bird food in gardens is a common activity that may provide an alternative food source to birds in winter. Long-term survey data recording the weekly presence of all bird species using garden feeders in the winter were analysed to see if there was any evidence of trends in feeder use between 1970 and 2000 and whether these trends were correlated with breeding bird population trends. Of 41 species analysed, 21 showed significant increases in occurrence at garden feeders between 1970 and 2000. Many of these increases were evident only in the last 10 years. Several species showed significant positive correlations between trends in winter garden use and trends in relative population size in the previous breeding season. This was especially the case for species with population change (either increase or decrease) of the greatest magnitude. There was no evidence that seasonal shifts in garden feeder use were associated with population change in any species. Temperature was an important predictor of garden use but could not explain the year-to-year trends. However, as the number of feeding stations had increased over time the response of birds to the greater food availability in gardens may have been responsible for the widespread increases in occurrence of several species. 相似文献
147.
Lack of trade-off between direct and indirect defence against grape powdery mildew in riverbank grape 总被引:1,自引:0,他引:1
Abstract. 1. The hypothesis that plants that invest more in an indirect defence will invest less in direct mechanisms was tested using genotypes of the riverbank grape Vitis riparia that varied in expression of acarodomatia, tufts of non-glandular trichomes on underside of leaves that are frequently occupied by mycophagous mites. Mycophagous mites in this system have been shown to protect vines from grape powdery mildew caused by the fungus Uncinula necator .
2. Multiple cane cuttings from 24 genotypes of V. riparia , a species native to North America, were obtained from the USDA grape genetics repository and planted out in a common garden.
3. Genotypes varied in size of acarodomatia by threefold and varied in density of mycophagous mites by over 10-fold. Genotypes originating from the western part of the distribution had smaller acarodomatia and fewer mycophagous mites than genotypes from the eastern part of the distribution. There was a positive genetic correlation between acarodomatia size and mite density.
4. In a separate experiment, where vines were kept free of mycophagous mites, genotypes showed 10-fold variation in percentage leaf surface colonised by mildew. There was, however, no relationship between mildew on leaves and size of acarodomatia. Mildew did not vary depending on origin of genotype, although female vines tended to have greater levels than males.
5. No evidence was found for a trade-off between investment in an indirect defence mediated through acarodomatia and investment in direct defence against grape powdery mildew. Mite/plant defence mutualisms are contrasted with ant/plant defence mutualisms where there is better evidence for trade-offs under field conditions. 相似文献
2. Multiple cane cuttings from 24 genotypes of V. riparia , a species native to North America, were obtained from the USDA grape genetics repository and planted out in a common garden.
3. Genotypes varied in size of acarodomatia by threefold and varied in density of mycophagous mites by over 10-fold. Genotypes originating from the western part of the distribution had smaller acarodomatia and fewer mycophagous mites than genotypes from the eastern part of the distribution. There was a positive genetic correlation between acarodomatia size and mite density.
4. In a separate experiment, where vines were kept free of mycophagous mites, genotypes showed 10-fold variation in percentage leaf surface colonised by mildew. There was, however, no relationship between mildew on leaves and size of acarodomatia. Mildew did not vary depending on origin of genotype, although female vines tended to have greater levels than males.
5. No evidence was found for a trade-off between investment in an indirect defence mediated through acarodomatia and investment in direct defence against grape powdery mildew. Mite/plant defence mutualisms are contrasted with ant/plant defence mutualisms where there is better evidence for trade-offs under field conditions. 相似文献
148.
PATRICK C. TOBIN SUDHA NAGARKATTI† GREG LOEB‡ MICHAEL C. SAUNDERS† 《Global Change Biology》2008,14(5):951-957
Climate change can cause major changes to the dynamics of individual species and to those communities in which they interact. One effect of increasing temperatures is on insect voltinism, with the logical assumption that increases in surface temperatures would permit multivoltine species to increase the number of generations per year. Though insect development is primarily driven by temperature, most multivoltine insect species rely on photoperiodic cues, which do not change from year‐to‐year or in response to climate warming, to initiate diapause. Thus, the relationship between climate change and voltinism could be complex. We use a phenology model for grape berry moth, Paralobesia viteana (Clemens), which incorporates temperature‐dependent development and diapause termination, and photoperiod‐dependent diapause induction, to explore historical patterns in year‐to‐year voltinism fluctuations. We then extend this model to predict voltinism under varying scenarios of climate change to show the importance of both the quality and quantity of accumulated heat units. We also illustrate that increases in mean surface temperatures > 2 °C can have dramatic effects on insect voltinism by causing a shift in the ovipositional period that currently is subject to diapause‐inducing photoperiods. 相似文献
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