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11.
Abstract. 60 of the 75 Banksia species are confined to southwestern Australia where five or six species often coexist. We explored the role of regional species richness, niche differentiation, and habitat specialization in structuring banksia assemblages. The diversity of growth forms and categories of seed production and response to fire were assessed in actual assemblages at 40 sites throughout southwestern Australia. Diversity indices at each site were compared with those from null communities assembled on the basis of the abundance and sociability of taxa in regional species pools. The relationship between local and regional species richness suggests that processes at the scale of 100-m2 quadrats limit local richness and therefore coexistence. However, there was no consistent evidence that taxa are differentiated by growth form or regeneration strategy. No particular biological profile makes a banksia adept at coexisting with a wide range of other taxa. Habitat specialization is an important factor contributing to lower local richness than would be predicted from niche differentiation of taxa in regional pools. There is recent empirical evidence of several mechanisms whereby the number of coexisting banksias is increased beyond the limits suggested by simple niche theories. Variability in the fire regime also provides a mechanism for maintaining local species richness because different fires favour recruitment of different taxa. 相似文献
12.
All individuals of all known populations of Banksia goodii were assessed for seed production. Small populations produced no or only a few seeds per unit canopy area. Effects of population size on seed production per unit area and seed production per plant were present over the whole range of population sizes, indicating that even in large populations seed production may still not be at its maximum. Resource differences could not explain this disproportionate decrease in seed production with decline in population size, because there were no differences in soil properties and understorey or overstorey cover between the small and large populations. Although plants in small and large populations were similar in size, seed production per plant was much lower in small populations. This was not because plants in small populations produced fewer cones but because the fraction of these cones that was fertile was much lower. Five of the nine smallest populations (<200 m2) produced no fertile cones over the last 10 years. The number of seeds per fertile cone did not depend on population size. The results are discussed in relation to pollination biology. 相似文献
13.
Niraj Shrestha Pallavi Chaturvedi Xiaoyun Zhu Michael J. Dee Varghese George Christopher Janney Jack O. Egan Bai Liu Mark Foster Lynne Marsala Pamela Wong Celia C. Cubitt Jennifer A. Foltz Jennifer Tran Timothy Schappe Karin Hsiao Gilles M. Leclerc Lijing You Christian Echeverri Catherine Spanoudis Ana Carvalho Leah Kanakaraj Crystal Gilkes Nicole Encalada Lin Kong Meng Wang Byron Fang Zheng Wang Jin-an Jiao Gabriela J. Muniz Emily K. Jeng Nicole Valdivieso Liying Li Richard Deth Melissa M. Berrien-Elliott Todd A. Fehniger Peter R. Rhode Hing C. Wong 《Aging cell》2023,22(5):e13806
14.
David M. Richardson Richard M. Cowling Byron B. Lamont 《Biodiversity and Conservation》1996,5(9):1035-1046
This paper explores the determinants of extinction of endemic plant taxa in mediterranean-climate regions in South Africa and southwestern Australia. Major threats to biodiversity in these areas include agriculture, deforestation, fragmentation, invasive alien organisms and urbanization. Case studies from the two regions show that synergisms between factors can lead to discontinuous, or non-linear, responses that have increased extinction rates (or threaten to) beyond predictions based on simple deterministic processes. 相似文献
15.
John J. Malinowski Bruce L. Grasberger Gary Trakshel Edward E. Huston Tracey M. Banks Patricia G. Brake Richard B. Ciccarelli Barry N. Jones James A. Koehn Diane Kratz Nicole Lundberg Panayiotis E. Stevis Carla T. Helaszek Mark A. Ator Angela M. Small Wood Travis Stams Byron Rubin Richard S. Alexander 《Protein science : a publication of the Protein Society》1995,4(10):2149-2155
16.
Relationship Between Substrate Concentration and Fermentation Product Ratios in Clostridium thermocellum Cultures 总被引:2,自引:1,他引:1 下载免费PDF全文
Growth of Clostridium thermocellum in batch cultures was studied over a broad range of cellobiose concentrations. Cultures displayed important differences in their substrate metabolism as determined by the end product yields. Bacterial growth was severely limited when the initial cellobiose concentration was 0.2 (wt/vol), was maximal at substrate concentrations between 0.5 and 2.0%, and did not occur at 5.0% cellobiose. Ethanol accumulated maximally (38.3 μmol/109 cells) in cultures with an initial cellobiose concentration of 0.8%, whereas cultures in 2.0% cellobiose accumulated only 17.3 μmol, and substrate-limited cultures (0.2% cellobiose) accumulated little, if any, ethanol beyond that initially detected (8.3 μmol/109 cells). In a medium with 0.8% cellobiose, ethanol was produced at a constant rate of approximately 1.1 μmol/109 cells per h from late-logarithmic phase (16 h) of growth well into stationary phase (44 h). When ethanol was added exogenously at levels more than twice the maximum produced by the cultures themselves (0.5% [vol/vol]), neither the extent of growth (maximum Klett units, 150) nor the amounts of ethanol produced (~0.17%) by the culture was affected. The ratio of ethanol to acetate was highest (2.8) when cells were grown in 0.8% cellobiose and lowest (1.2) when cells were grown in 0.2% cellobiose. 相似文献
17.
The heart of what's the matter The semantics of illness in Iran 总被引:2,自引:0,他引:2
Byron J. Good 《Culture, medicine and psychiatry》1977,1(1):25-58
Our understanding of the psychosocial and cultural dimensions of disease and illness is limited not merely by a lack of empirical knowledge but also by an inadequate medical semantics. The empiricist theories of medical language commonly employed both by comparative ethnosemantic studies and by medical theory are unable to account for the integration of illness and the language of high medical traditions into distinctive social and symbolic contexts. A semantic network analysis conceives the meaning of illness categories to be constituted not primarily as an ostensive relationship between signs and natural disease entities but as a syndrome of symbols and experiences which typically run together for the members of a society. Such analysis dirests our attention to the patterns of associations which provide meaning to elements of a medical lexicon and to the constitution of that meaning through the use of medical discourse to articulate distinctive configurations of social stress and to negotiate relief for the sufferer. This paper provides a critical discussion of medical semantics and develops a semantic network analysis of heart distress, a folk illness in Iran. 相似文献
18.
Helena C. Kraemer Byron Alexander Cathy Clark Curt Busse David Riss 《Primates; journal of primatology》1977,18(4):825-833
A method is suggested to evaluate on an empirical basis sampling plans for the longitudinal study of primate behavior in those
very common situations in which the mathematical structure of behavior is unknown. The method is based on a randomization
procedure applied to a pilot sample of the behavior organized so that cost of implementation of a sampling plan can be evaluated
vis á vis the sampling error intrinsic to the plan. 相似文献
19.
Examination of two diastereomeric analogs of somatostatin differing in stereochemistry at the tryptophan residue has revealed a high field resonance in the
-Trp isomer which is assigned to the γ-methylene of Lys9. The extent of correlation of this shift with biologic activity for a series of analogs of somatostatin is discussed. From comparison of close analogs, it is suggested that the biologically active conformation of somatostatin at the receptor controlling insulin release is not the major conformation of this hormone in solution. It is suggested that the conformation of somatostatin at this receptor resembles more closely the solution conformation of analogs having tryptophan in the
-configuration. This latter conformation places the Trp8-Lys9 side chains in close proximity, thus shifting the γ-methylene protons of Lys9 upfield. 相似文献
20.
Activation of MAP kinases by calcium-dependent and calcium-independent pathways. Stimulation by thapsigargin and epidermal growth factor. 总被引:5,自引:0,他引:5
T S Chao K L Byron K M Lee M Villereal M R Rosner 《The Journal of biological chemistry》1992,267(28):19876-19883
In order to determine the effect of calcium mobilization on mitogen-activated protein (MAP) kinase activation, we have treated human foreskin fibroblasts (HSWP cells) and human epidermal carcinoma (A431) cells with thapsigargin. Intracellular free calcium was monitored by single cell image analysis using fura-2 and correlated with MAP kinase stimulation as assessed by immunoprecipitation, kinase renaturation assays and immunoblotting. Thapsigargin stimulated the 44- and 42-kDa MAP kinase isozymes in both cell types with kinetics that were slightly delayed relative to enzyme stimulated by epidermal growth factor. Removal of external calcium did not significantly affect the activation of the MAP kinases by thapsigargin, indicating that intracellular calcium mobilization is sufficient to stimulate the enzymes. However, treatment of cells with EGTA under conditions which deplete both intra- and extracellular calcium inhibited stimulation by thapsigargin but not epidermal growth factor. Stimulation of the MAP kinases by the calcium ionophore ionomycin paralleled the activation observed with thapsigargin in both calcium-containing and calcium-free conditions. These results indicate that there are at least two independent pathways for stimulation of MAP kinase: one that is dependent on intracellular calcium mobilization, and one that is mediated by the tyrosine kinase epidermal growth factor receptor and is calcium-independent. 相似文献