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1.
Summary We evaluated three methods for the analysis of functional response data by asking whether a given method could discriminate among functional responses and whether it could accurately identify regions of positive density-dependent predation. We evaluated comparative curve fitting with foraging models, linear least-squares analysis using the angular transformation, and logit analysis. Using data from nature and simulations, we found that the analyses of predation rates with the angular transformation and logit analysis were best at consistently determining the true functional response, i.e. the model used to generate simulated data. These methods also produced the most accurate estimates of the true regions of density dependence. Of these two methods, functional response data best fulfill the assumptions of logit analysis. Angularly transformed predation rates only approximate the assumptions of linear leastsquares analysis for predation rates between 0.1 and 0.9. Lack-of-fit statistics can reveal inadequate fit of a model to a data set where simple regression statistics might erroneously suggest a good match. 相似文献
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3.
Hardies SC; Martin SL; Voliva CF; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1986,3(2):109-125
4.
The lateral pectoral composite flap in one-stage reconstruction of the irradiated mandible 总被引:1,自引:0,他引:1
We present a composite flap based on the musculature of the anterolateral thorax that allows immediate reconstruction of the mandible through the interposition of vascularized bony fifth rib. While the vascular pedicle remains the pectoral branch of the thoracoacromial artery, the pectoralis major muscle can be spared largely intact. The lateral position of the composite rib segment ensures a purely bony composition, while the lateral skin island remains largely hairless. Despite the unfavorable conditions of massive tumor size and prior irradiation attending the clinical cases presented, the complication rate was acceptable, with only one flap loss, and this followed technical error. 相似文献
5.
Summary An electrogenic K+–Na+ symport with a high affinity for K+ has been found inChara (Smith & Walker, 1989). Under voltage-clamp conditions, the symport shows up as a change in membrane current upon adding either K+ or Na+ to the bathing medium in the presence of the other. Estimation of kinetic parameters for this transport has been difficult when using intact cells, since K+–Na+ current changes show a rapid falling off with time at K+ concentrations above 50 m. Cytoplasm-enriched cell fragments are used to overcome this difficulty since they do not show the rapid falling off of current change seen with intact cells. Current-voltage curves for the membrane in the absence or presence of either K+ or Na+ are obtained, yielding difference current-voltage curves which isolate the symport currents from other transport processes. The kinetic parameters describing this transport are found to be voltage dependent, withK
m
for K+ ranging from 30 down to 2 m as membrane potential varies from –140 to –400 mV, andK
m
for Na+ ranging between 470 and 700 m over a membrane potential range of –140 to –310 mV.Two different models for this transport system have been investigated. One of these involves the simultaneous transport of both the driver and substrate ions across the membrane, while the other allows for the possibility of the two ions being transported consecutively in two distinct reaction steps. The experimental results are shown to be consistent with either of these cotransport models, but they do suggest that binding of K+ occurs before that of Na+, and that movement of charge across the membrane (the voltage-dependent step) occurs when the transport protein has neither K+ nor Na+ bound to it. 相似文献
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Increasingly electronic communication and a variety of electronic resources are accessible to a larger group of people within the scientific community. This paper outlines the range of resources that are available, and comments on their current and future value to the phycological community. Resources discussed include mailing lists and newsgroups. These are useful tools for rapid, informal, targeted communication, although the technology employed places limitations on the type and format of information which may be distributed. The World Wide Web (WWW) has the potential to overcome these limitations, the quality, complexity and value to the phycological community of the sites on the WWW are extremely variable, with some material being of dubious quality. However, it is possible to access high quality resources including culture collection catalogues, high quality images and microbial and molecular databases. As well as some of the current resources, this paper discusses some possible directions for the future of phycology on the internet.http://wiua.nwi.ac.uk/ 相似文献
8.
Pamela D. Arora Kathryn J. Bibby Christopher A. G. McCulloch 《Journal of cellular physiology》1994,161(2):187-200
Calcium transients in single, human gingival fibroblasts were studied after mechanical stretching of flexible culture substrates. A model system was developed to reproducibly stretch and rapidly (< 1 sec) refocus cells in the same focal plane so that changes in the concentration of free intracellular calcium ions ([Ca2+]i) were monitored without delay. Attached cells were grown on flexible bottom Petriperm dishes, loaded with fura-2/AM, and stretched by 1% or 2.8% of substrate area. The stretch caused no significant cell detachment or membrane lesions. A 1% stretch induced no calcium response, but a 2.8% stretch stimulated an initial calcium transient and the subsequent generation of [Ca2+]i oscillations of up to 2,000 sec. At 1% stretch, there was no calcium response. Cell shape and plating time were important determinants in the calcium response to mechanical stimulation: the responder cells were small and round without long processes. Major calcium transients were inhibited completely by 5 mM EGTA or by 10 μM gadolinium ions, by 50 μM nifedipine, or 250 μM verapamil, suggesting an influx of calcium through stretch-activated (SA) channels and L-type calcium channels. Depolarization by high KCl (144 mM) in the extracellular medium enhanced the amplitude of calcium transients by 54%. Calcium oscillations were not inhibited by preincubation with thapsigargin, caffeine, cholera toxin, staurosporine or 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), indicating that IP3 sensitive pools, IP3 insensitive pools, G5α subunits, and protein kinase C, respectively, were not involved in the generation of calcium oscillations. Pretreatment with genistein, a specific tyrosine kinase inhibitor or cytochalasin D, an inhibitor of actin polymerization, or pertussis toxin, an inhibitor of Giα and Goα subunits, completely abolished calcium transients and oscillations. These results indicate that Ca2+ flux due to mechanical stretching is likely mediated through SA ion channe s and is dependent on tyrosine kinases, pertussis toxin-sensitive subunits of G-proteins, and actin filaments. © 1994 Wiley-Liss, Inc. 相似文献
9.
10.
A major difference between the divergence patterns within the lines-1 families in mice and voles 总被引:3,自引:0,他引:3
Vanlerberghe F; Bonhomme F; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1993,10(4):719-731
L1 retroposons are represented in mice by subfamilies of interspersed
sequences of varied abundance. Previous analyses have indicated that
subfamilies are generated by duplicative transposition of a small number of
members of the L1 family, the progeny of which then become a major
component of the murine L1 population, and are not due to any active
processes generating homology within preexisting groups of elements in a
particular species. In mice, more than a third of the L1 elements belong to
a clade that became active approximately 5 Mya and whose elements are >
or = 95% identical. We have collected sequence information from 13 L1
elements isolated from two species of voles (Rodentia: Microtinae: Microtus
and Arvicola) and have found that divergence within the vole L1 population
is quite different from that in mice, in that there is no abundant
subfamily of homologous elements. Individual L1 elements from voles are
very divergent from one another and belong to a clade that began a period
of elevated duplicative transposition approximately 13 Mya. Sequence
analyses of portions of these divergent L1 elements (approximately 250 bp
each) gave no evidence for concerted evolution having acted on the vole L1
elements since the split of the two vole lineages approximately 3.5 Mya;
that is, the observed interspecific divergence (6.7%-24.7%) is not larger
than the intraspecific divergence (7.9%-27.2%), and phylogenetic analyses
showed no clustering into Arvicola and Microtus clades.
相似文献