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21.
Tracy J. Baldyga Scott N. Miller Kenneth L. Driese Charles Maina Gichaba 《African Journal of Ecology》2008,46(1):46-54
Kenya's Rift Valley has been undergoing rapid land cover change for the past two decades, which has resulted in ecological and hydrological changes. An effort is under way to quantify the timing and rate of these changes in and around the River Njoro watershed located near the towns of Njoro and Nakuru using remote sensing and geographic information system (GIS) methods. Three Landsat TM images, representing a 17‐year period from 1986 to 2003 in which the area underwent a significant land cover transition, were classified and compared with one another. Vegetation diversity and temporal variability, common to tropical and sub‐tropical areas, posed several challenges in disaggregating classified data into sub‐classes. An iterative approach for the resolving challenges is presented that incorporates unsupervised and supervised classification routines in coordination with knowledge‐based spatial analyses. Changes are analysed at three spatial scales ranging from the highly impacted and deforested uplands to the watershed and landscape scales. Land cover transitions primarily occurred after 1995, and included large forest losses coupled with increases in mixed small‐scale agriculture and managed pastures and degraded areas. These changes in cover type are highly spatially variable and are theorized to have significant impacts on ecological and hydrologic systems with implications for environmental sustainability. 相似文献
22.
Mathara JM Schillinger U Kutima PM Mbugua SK Guigas C Franz C Holzapfel WH 《Current microbiology》2008,56(4):315-321
Lactobacillus plantarum was the major species among the lactic acid bacterial strains isolated from traditional fermented milk of the Maasai in Kenya.
Selected strains were characterized for their functional properties using in vitro standard procedures. All strains expressed
acid tolerance at pH 2.0 after 2-h exposure of values that ranged from 1% to 100%, while bile tolerance of acid-stressed cells
at 0.3% oxgal varied from 30% to 80%. In vitro adhesion to the mucus-secreting cell line HT 29 MTX and binding capacity to
extracellular protein matrices was demonstrated for several strains. The four strains tested in a simulated stomach duodenum
passage survived with recovery rates ranging from 17% to 100%. Strains were intrinsically resistant to several antibiotics
tested. From these in vitro studies, a number of Lb. plantarum strains isolated from the Maasai traditional fermented milk showed probiotic potential. The strains are good candidates for
multifunctional starter culture development. 相似文献
23.
Intra-plant versus Inter-plant Root Competition in Beans: avoidance,resource matching or tragedy of the commons 总被引:7,自引:0,他引:7
Root competition inhibits root proliferation. All else equal, a plant should invest roots in a nutrient patch devoid of roots rather than one already occupied by roots. Less clear is how a plant should respond to intra-plant versus inter-plant root competition. We consider three responses for how a plant may select habitats based on intra-versus inter-plant root competition: inter-plant avoidance, resource matching, or intra-plant avoidance. The first assumes that plants prefer to have their own space and preferentially proliferate roots away from neighboring plants. The second response, based on the ideal free distribution, assumes that plants invest so as to equalize average returns from roots, regardless of the identity of the neighboring roots. The third, based on game theory, assumes that the plant proliferates roots so as to maximize whole-plant fitness, in which case it is better to proliferate plants among a neighbor's roots than to continue proliferating amongst one's own roots. To test among these models we grew beans (Phaseolus varigaris, var. Kenya) in a greenhouse under two planting scenarios. Both scenario were tested under 0.5 and 0.1 strength of nutrient solution. Under scenario A (fence-sitters), two split-root plants each shared two patches by virtue of having roots in each. Under scenario B (owners) two plants each had their own patch. The results supported the game theory model of intra-plant avoidance (whole plant habitat selection). Fence-sitters produced 150% more root mass per individual than owners. Owners produced 90% more yield (dry mass of pods) than fence-sitters. Furthermore, owners had significantly higher shoot-root ratios than fence-sitters. These effects did not vary with high or low nutrient levels. The over-proliferation of roots under inter-plant competition (fence-sitters) was manifest by the tenth day after planting. In short, the fence-sitters engaged in a tragedy of the commons in which they competed with each other through root proliferation. At the ESS, the fitness maximizing strategy of the individual is to sacrifice collective yield in a quest to `steal' nutrients from its neighbor. The research has three implications. First, plants may be able to assess and respond to local opportunities in a manner that maximizes the good of the whole plant. Second, nutrient foraging as a game may provide a fresh perceptive for viewing root competition either intra-specifically or inter-specifically. Third, it may be possible to increase the yield of certain crop species by breeding more `docile' cultivars that do not overproduce roots in response to inter-plant competition. 相似文献
24.
Gradients of disturbance and environmental conditions shape coral community structure for south‐eastern Indian Ocean reefs 下载免费PDF全文
Jens Zinke James P. Gilmour Rebecca Fisher Marji Puotinen Joseph Maina Emily Darling Michael Stat Zoe T. Richards Timothy R. McClanahan Maria Beger Cordelia Moore Nicholas A. J. Graham Ming Feng Jean‐Paul A. Hobbs Scott N. Evans Stuart Field George Shedrawi Russ C. Babcock Shaun K. Wilson 《Diversity & distributions》2018,24(5):605-620
25.
Anastasia Nikolopoulou Theodosia Maina Petros Sotiriou Paul Cordopatis Berthold A. Nock 《Journal of peptide science》2006,12(2):124-131
Two somatostatin analogues, [99mTc]Demotide and [99mTc]Demotate 4, were compared with [99mTc]Demotate 1, a previously reported somatostatin receptor subtype 2 (sst2) targeting tracer. Conjugates were prepared by coupling an open‐chain tetraamine chelator to D ‐Phe1 of [Tyr3]‐octreotide or [Tyr3]‐octreotate, respectively, via a p‐benzylaminodiglycolic acid spacer adopting solid‐phase peptide synthesis techniques. Peptide conjugates were collected in a highly pure form after chromatographic purification. Eventually, [99mTc]Demotide and [99mTc]Demotate 4 were obtained in ~1 Ci/µmol specific activity and >96% purity after labeling under alkaline conditions. Demotide and Demotate 4 exhibited similar high binding affinities for the sst2 expressed in AR4‐2J cells with IC50 values 0.16 and 0.10 nM, respectively. The (radio)metallated analogues [99mTc]Demotide and [99mTc]Demotate 4 showed equally high affinities to the sst2 during saturation binding assays in AR4‐2J cell membranes (Kds 0.08 and 0.07 nM, respectively). During incubation at 37 °C with AR4‐2J cells, the radiopeptides internalized effectively via a receptor‐mediated process, with [99mTc]Demotate 4 exhibiting a faster internalization rate than [99mTc]Demotide. After injection in athymic mice bearing sst2‐expressing AR4‐2J tumors, the radiotracers showed high and specific uptake in the tumor (>25%ID/g at 1 h) and in the sst2–positive organs. However, both [99mTc]Demotide and [99mTc]Demotate 4 showed unfavorably higher background activity, especially in the abdomen, in comparison to [99mTc]Demotate 1 and are, therefore, less suited than [99mTc]Demotate 1 for sst2‐targeted tumor imaging in man. Copyright © 2005 European Peptide Society and John Wiley & Sons, Ltd. 相似文献
26.
Yoon JJ Chawla D Paal T Ndungu M Du Y Kurtkaya S Sun A Snyder JP Plemper RK 《Journal of biomolecular screening》2008,13(7):591-608
Several members of the paramyxovirus family constitute major human pathogens that, collectively, are responsible for major morbidity and mortality worldwide. In an effort to develop novel therapeutics against measles virus (MV), a prominent member of the paramyxovirus family, the authors report a high-throughput screening protocol that uses a nonrecombinant primary MV strain as targets. Implementation of the assay has yielded 60 hit candidates from a 137,500-entry library. Counterscreening and generation of dose-response curves narrows this pool to 35 compounds with active concentrations =15.3 microM against the MV-Alaska strain and specificity indices ranging from 36 to >500. Library mining for structural analogs of several confirmed hits combined with retesting of identified candidates reveals a high accuracy of primary hit identification. Eleven of the confirmed hits interfere with viral entry, whereas the remaining 24 compounds target postentry steps of the viral life cycle. Activity testing against selected members of the paramyxovirus family reveals 3 patterns of activity: 1) exclusively MV-specific blockers, 2) inhibitors of MV and related viruses of the same genus, and 3) broader range inhibitors with activity against a different Paramyxovirinae genus. Representatives of the last class may open avenues for the development of broad-range paramyxovirus inhibitors through hit-to-lead chemistry. ( Journal of Biomolecular Screening 2008:591-608). 相似文献
27.
Steinauer ML Hanelt B Mwangi IN Maina GM Agola LE Kinuthia JM Mutuku MW Mungai BN Wilson WD Mkoji GM Loker ES 《Molecular ecology》2008,17(23):5062-5074
Hybridization and introgression can have important consequences for the evolution, ecology and epidemiology of pathogenic organisms. We examined the dynamics of hybridization between a trematode parasite of humans, Schistosoma mansoni, and its sister species, S. rodhaini, a rodent parasite, in a natural hybrid zone in western Kenya. Using microsatellite markers, rDNA and mtDNA, we showed that hybrids between the two species occur in nature, are fertile and produce viable offspring through backcrosses with S. mansoni. Averaged across collection sites, individuals of hybrid ancestry comprised 7.2% of all schistosomes collected, which is a large proportion given that one of the parental species, S. rodhaini, comprised only 9.1% of the specimens. No F1 individuals were collected and all hybrids represented backcrosses with S. mansoni that were of the first or successive generations. The direction of introgression appears highly asymmetric, causing unidirectional gene flow from the rodent parasite, S. rodhaini, to the human parasite, S. mansoni. Hybrid occurrence was seasonal and most hybrids were collected during the month of September over a 2-year period, a time when S. rodhaini was also abundant. We also examined the sex ratios and phenotypic differences between the hybrids and parental species, including the number of infective stages produced in the snail host and the time of day the infective stages emerge. No statistical differences were found in any of these characteristics, and most of the hybrids showed an emergence pattern similar to that of S. mansoni. One individual, however, showed a bimodal emergence pattern that was characteristic of both parental species. In conclusion, these species maintain their identity despite hybridization, although introgression may cause important alterations of the biology and epidemiology of schistosomiasis in this region. 相似文献
28.
N. J. Cordeiro J. C. Lovett E. Mulungu G. G. Maina J. H. Gerstle 《Biodiversity and Conservation》2006,15(3):971-983
The Lower Kihansi Hydropower Project in southern Tanzania caused the diversion of the Kihansi River from the Kihansi Gorge
in the year 2000. By sampling the understorey avifauna prior to diversion, we examined (i) whether the adjacent Udagaje Gorge
was an adequate control for observations in the Kihansi Gorge; (ii) which species of conservation interest occurred; and,
(iii) which season best suited annual monitoring. Species composition and capture rates at three and two elevational transects
in the Kihansi Gorge and Udagaje Gorge, respectively, confirmed that Udagaje had a comparable avifaunal assemblage to Kihansi.
The cold season was most appropriate for population monitoring because >2 times more individuals were captured in the cold
than hot season at both gorges, and at least four altitudinal migrants were present in the cold but not hot season. Post-diversion
sampling revealed that only the Upper Kihansi transect suffered a significant decrease in number of individuals, a result
that was driven largely by a decline in the Little Greenbul, Andropadus virens. This transect is closest to the Kihansi waterfall and associated spray zone which were lost after river diversion. Lack
of differences in bird communities at other transects after diversion illustrates that early post-diversion effects on birds
are probably concentrated near the base of the main falls. Together with studies of other biota in Kihansi, we propose that
long-term monitoring is necessary to understand the factors that regulate changes in species composition of this threatened
forest site. 相似文献
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