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71.
Abstract Frog populations are rapidly disappearing throughout the world. An important issue for ecologists to resolve is why some frog species are more susceptible to decline than others. Here, we performed a comparative study of the endemic Australian frog fauna to determine whether the life history and ecology of declining species have predisposed them to extinction. Decline was consistently found to be correlated with geographical range size across contemporary species and in analyses based on phylogenetically independent contrasts (PICs). Species with narrow geographical ranges have been disproportionately more susceptible to decline. Across species, decline was also correlated with large body size and a high proportion of the geographical range overlapping with the distribution of cane toads and landscape stress (e.g. land clearing). We show that with the exception of range size, however, correlates of decline across species are underpinned by a small number of evolutionary events. Hence, the suite of traits that correlate with decline in the cross‐species analysis is only relevant to a small number of clades. We also found that clutch size, testes mass, ova size and distributional overlap with feral pigs were not significantly related to decline. In the ongoing search for life‐history and ecological correlates of decline and extinction, our results highlight the importance of performing analyses across contemporary species and using PICs. 相似文献
72.
The successful production of interspecific hybrids between membersof the dysploid chromosome series inDahlia offers a unique opportunityto investigate chromosome evolution. Analysis of meiotic metaphaseI in these hybrids using genomic in situ hybridization (GISH)has shown that pairing occurs both between and within parentalgenomes. These results have provided clear evidence for theallotetraploid origin of Dahlia species with 2n=32 and suggeststhat species with 2n=34 and 2n=36 have also arisen via allopolyploidy.A bivalent promoting mechanism proposed for species with 2n=32also appears to be present in Dahlia species with 2n=34 and2n=36 .Copyright 1999 Annals of Botany Company Dahlia , GISH, dysploidy, chromosome pairing, karyotype analysis, polyploidy. 相似文献
73.
To develop further the methods for estimation of NOx absorption by plants supplied with 15 N-labelled fertilizer, we proposed a new calculation method, total N fixed method (TNF), and compared with the 15 N dilution method and the classical mass balance method (MB).
Hydroponically grown soybean plants were supplied with15 N-labelled nitrate and exposed to 200–250 nl l−1 NO2 for 7 d. The proportions of the N derived from NO2 to total N in exposed plants were estimated by the three methods.
The reported rates of NO2 absorption by several plant species, estimated by the 15 N dilution method, were recalculated using the TNF method. The results of the two methods were compared and showed that: (1) The 15 N dilution method overestimated the content of NO2 -N in exposed plants compared with the MB method whilst the TNF method produced estimations of NO2 -N closer to those by the MB method when the plants were supplied with 5 m M nitrate. (2) The differences in estimations between the MB method and either the 15 N dilution method or the TNF method increased with decreasing supply of 15 N-labelled nitrate to roots. 相似文献
Hydroponically grown soybean plants were supplied with
The reported rates of NO
74.
75.
DENNIS L. MURRAY TODD D. STEURY JAMES D. ROTH 《The Journal of wildlife management》2008,72(7):1463-1472
Abstract The ecology of Canada lynx (Lynx canadensis) and their main prey, snowshoe hares (Lepus americanus), is poorly understood in southern Canada and the contiguous United States compared to the boreal forest of Canada and Alaska, USA, where both species are well studied. However, given recent listing of lynx under the Endangered Species Act, accurate understanding of lynx and snowshoe hare ecology and conservation requirements in the United States is a high priority. We critically examined unchallenged perceptions and important research needs related to lynx and hare ecology and conservation at the southern extent of their range. Contrary to popular dogma, lynx do not require old-growth forest for denning, but further research on lynx and hare use of fragmented landscapes at lower latitudes is required. The contention that southern lynx are subject to higher interference or exploitative competition compared to their northern counterparts remains without strong empirical support. Lynx rely more on red squirrels (Tamiasciurus hudsonicus) and possibly other alternate prey at lower latitudes, but hares are the predominant food type for lynx across their range. Southern lynx and hare populations do not exhibit periodic cyclicity, but harvest statistics suggest that lynx abundance in the southern range is highly variable, implying that numerical fluctuations likely are fueled by immigration from Canada. Southern lynx population viability in the absence of ingress is suspect and thus maintaining connectivity with northern areas of occupancy should be a priority. Successful conservation of lynx populations in the contiguous United States will require 1) improved understanding of lynx population and habitat ecology at lower latitudes, 2) protection and management of large tracts of lynx and snowshoe hare habitat, and 3) ensured connectivity between lynx populations at the core and periphery of the species' range. However, in light of the numerous challenges facing conservation of populations of many species at their southern distributional limit, the long-term prognosis for lynx in the southern range currently is uncertain. 相似文献
76.
JOHN G. CONRAN V. GUNTA JAUDZEMS NEIL D. HALLAM 《Botanical journal of the Linnean Society. Linnean Society of London》1997,123(3):211-223
The Droseraceae exhibit a range of"germination patterns which are of possible taxonomic usefulness at the sectional and higher levels. Three patterns were observed in the family: phanerocotylar ( Drosera subgen. Drosera and Regia ); cryptocotylar (subgen. Ergaleium and Rorella ); and a new category, hemi-cryptocotylar, where both cotyledon apices remain in the seed coat, but the remainder emerges forming a photosynthetic cotyledon loop ( Dionaea, Drosophyllum and Drosera adelae ). Subgenus Drosera , especially sect. Drosera , is heterogenous for germination, and other features, with Drosera indica , sect. Lasiocephala and D. neocaledonica anomalous on current placements, and in need of further study. Conversely, the merger of sects Psycophila and Stelogyne and subgenl Ptycnostigma with subgen. Drosera sect. Drosera is supported by their germination features. Further studies are needed to determine the significance of environmental effects on the germination characteristics, although because the results of this study largely agree with recent morphological and molecular studies, this suggests that germination characteristics are useful at the sectional level, potentially providing additional characters for phylogenetic investigations within the Droseraceae. 相似文献
77.
78.
Spontaneous <Emphasis Type="Italic">in vitro</Emphasis> Hybridization of LDH Homopolymers in the Undenatured State 总被引:1,自引:0,他引:1
UNTIL now, there has been no totally satisfactory hypothesis proposed for the hybridization of lactate dehydrogenase in vivo, This is because hybridization in vitro, the only experimental approach, has usually been accomplished by chaotropic agents: freeze-thaw1, guanidine2, 3, urea3, or acid denaturation4. Whatever means the cell uses, it follows5–8 that it is susceptible to environmental influences. We now describe a gentle hybridization between heart and muscle types which can occur in more physiological conditions and which mimics many observations in vivo. 相似文献
79.
Photomorphogenesis, Photosynthesis, and Early Growth of Primary Leaves of Phaseolus vulgaris 总被引:1,自引:0,他引:1
The response of leaf tissue to white, blue, red, and far-redlight has been examined. Leaves on plants grown in darknessshow increased cell number, cell volume, and area when exposedto long periods (up to 48 h) of low-intensity red, blue, orfar-red radiation. This is believed to be a photomorphogenicresponse which does not involve photosynthesis. Leaves fromplants exposed to white light during germination do not usuallyrespond to red, blue, or far-red light. An exception to thiswas found for leaf discs which showed a larger increase in areathan the dark controls following exposure to far-red light for24 h. Leaf tissue from light-grown plants responds to high-intensitywhite light, probably through photosynthesis. Discs cut fromdark-grown plants and cultured in white light grow equally wellin air and CO2-free conditions. Application of the photosyntheticinhibitor DCMU reduces growth and chlorophyll formation, however. It is concluded that light, perhaps acting through the phytochromemechanism, has initially a number of morphogenic effects includinginitiation of development of the photosynthetic apparatus. Theresponses to photomorphogenically active radiation do not persistand light effects through photosynthesis are rapidly initiatedand dominate the later stages of leaf growth. 相似文献
80.
MURRAY SHEILAH; WOODBINE MALCOLM; WALKER THOMAS KENNEDY 《Journal of experimental botany》1953,4(2):251-256
1. Forty-three strains of moulds, selected from ten species,were examined to ascertain their capabilities as producers offat, when grown in four different solutions of nutrient inorganicsalts together with sucrose. The three highest yields of feltwere given by Penicillium javanicum van Beyma, P. Soppi Zaleski,and Aspergillus nidulans Eidam, in that order. The fat contenton felt weight was maximal at 34·8 per cent, with P.Soppi, at 28·4 per cent. with Fusarium lini(1), and at25·8 per cent. with A. nidulans; on sugar utilized itwas maximal at 11·4 per cent. with P. Soppi, at 7·9per cent, with A. nidulans, and at 5·6 per cent. withF. lini(1). 2. Other moulds considered worthy of further trial were P. spinulosum,P. aurantiobrunneum, F. graminearum, A. flavus, F. oxysporum,A. clavatus, and P. oxalicum. 相似文献