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981.
Taxonomic composition and structure of the phytoplankton were studied in the lowland rivers of the upper Ob basin: Barnaulka, Bol’shaya Losikha, and lower Inya. It has been shown that the phytoplankton of a large river system in Eurasia, exemplified by the Ob basin, is characterized by spatial heterogeneity in its taxonomic composition. 相似文献
982.
Gabriela Pastuch-Gawolek Tadeusz Bieg Wieslaw Szeja Jakub Flasz 《Bioorganic chemistry》2009,37(3):77-83
We present the synthesis of 1-thioglycosyl derivatives of uridine, which were designed to act as potential donor substrates for glycosyltransferases. We constructed such analogs using 5-amino-2-pyridyl 1-thioglycosides as glycosyl units which were connected to uridine via succinic linker. For preparation of the amide bonds we applied different condensation procedures. 相似文献
983.
Biological control has been attracting an increasing attention over the last two decades as an environmentally friendly alternative
to the more traditional chemical-based control. In this paper, we address robustness of the biological control strategy with
respect to fluctuations in the controlling species density. Specifically, we consider a pest being kept under control by its
predator. The predator response is assumed to be of Holling type III, which makes the system’s kinetics “excitable.” The system
is studied by means of mathematical modeling and extensive numerical simulations. We show that the system response to perturbations
in the predator density can be completely different in spatial and non-spatial systems. In the nonspatial system, an overcritical
perturbation of the population density results in a pest outbreak that will eventually decay with time, which can be regarded
as a success of the biological control strategy. However, in the spatial system, a similar perturbation can drive the system
into a self-sustained regime of spatiotemporal pattern formation with a high pest density, which is clearly a biological control
failure. We then identify the parameter range where the biological control can still be successful and describe the corresponding
regime of the system dynamics. Finally, we identify the main scenarios of the system response to the population density perturbations
and reveal the corresponding structure of the parameter space of the system.
A. Morozov is on leave from Shirshov Institute of Oceanology, Russian Academy of Science, Nakhimovsky Prosp. 36, Moscow 117218,
Russia. 相似文献
984.
Ernesto Hernández-Zapata Luciano Martínez-Balbuena Iván Santamaría-Holek 《Journal of biological physics》2009,35(3):297-308
We propose a free energy expression accounting for the formation of spherical vesicles from planar lipid membranes and derive
a Fokker–Planck equation for the probability distribution describing the dynamics of vesicle formation. We find that formation
may occur as an activated process for small membranes and as a transport process for sufficiently large membranes. We give
explicit expressions for the transition rates and the characteristic time of vesicle formation in terms of the relevant physical
parameters. 相似文献
985.
We review winner-loser models, the currently popular explanation for the occurrence of linear dominance hierarchies, via a
three-part approach. (1) We isolate the two most significant components of the mathematical formulation of three of the most
widely-cited models and rigorously evaluate the components’ predictions against data collected on hierarchy formation in groups
of hens. (2) We evaluate the experimental support in the literature for the basic assumptions contained in winner-loser models.
(3) We apply new techniques to the hen data to uncover several behavioral dynamics of hierarchy formation not previously described.
The mathematical formulations of these models do not show satisfactory agreement with the hen data, and key model assumptions
have either little or no conclusive support from experimental findings in the literature. In agreement with the latest experimental
results concerning social cognition, the new behavioral dynamics of hierarchy formation discovered in the hen data suggest
that members of groups are intensely aware both of their own interactions as well as interactions occurring among other members of their group. We suggest that
more adequate models of hierarchy formation should be based upon behavioral dynamics that reflect more sophisticated levels
of social cognition. 相似文献
986.
Rock-degrading endophytic bacteria in cacti 总被引:1,自引:1,他引:0
A plant–bacterium association of the cardon cactus (Pachycereus pringlei) and endophytic bacteria promotes establishment of seedlings and growth on igneous rocks without soil. These bacteria weather several rock types and minerals, unbind significant amounts of useful minerals for plants from the rocks, fix in vitro N2, produce volatile and non-volatile organic acids, and reduce rock particle size to form mineral soil. This study revealed the presence of large populations of culturable endophytic bacteria inside the seeds extracted from wild plants, from seeds extracted from the guano of bats feeding on cactus fruit, in seedlings growing from these seeds, in the pulp of fruit, and in small, mature wild plants, and are comparable in size to populations of endophytic populations in some agricultural crops. The dominant culturable endophytes were isolates of the genera Bacillus spp., Klebsiella spp., Staphylococcus spp., and Pseudomonas spp. Based on partial sequencing of the 16s rRNA gene, the isolated strains had low similarity to known strains in these genera. However, these strains have higher molecular similarity among endophytes obtained from seeds, endophytes from roots, and some bacterial strains from the rhizoplane. Seedlings developed from seeds with endophytes contain the similar species of endophytes in their shoots, possibly derived from the seeds. This study shows the involvement of endophytic bacteria in rock weathering by cacti in a hot, subtropical desert and their possible contribution to primary colonization of barren rock. This study proposes that cacti capable of acquiring diverse populations of endophytes may give them an evolutionary advantage to gain a foothold on highly uncompromising terrain. 相似文献
987.
Leonardo Tavares Salgado Leonardo Paes Cinelli Nathan Bessa Viana Rodrigo Tomazetto de Carvalho Paulo Antônio De Souza Mourão Valéria Laneuville Teixeira Marcos Farina And Gilberto Menezes Amado Filho 《Journal of phycology》2009,45(1):193-202
The interaction between phenolic substances (PS) and alginates (ALG) has been suggested to play a role in the structure of the cell walls of brown seaweeds. However, no clear evidence for this interaction was reported. Vanadium bromoperoxidase (VBPO) has been proposed as a possible catalyst for the binding of PS to ALG. In this work, we studied the interaction between PS and ALG from brown algae using size exclusion chromatography (SEC) and optical tweezers microscopy. The analysis by SEC revealed that ALG forms a high‐molecular‐weight complex with PS. To study the formation of this molecular complex, we investigated the in vitro interaction of purified ALG from Fucus vesiculosus L. with purified PS from Padina gymnospora (Kütz.) Sond., in the presence or absence of VBPO. The interaction between PS and ALG only occurred when VBPO was added, indicating that the enzyme is essential for the binding process. The interaction of these molecules led to a reduction in ALG viscosity. We propose that VBPO promotes the binding of PS molecules to the ALG uronic acids residues, and we also suggest that PS are components of the brown algal cell walls. 相似文献
988.
Based on a non-equilibrium mechanism for spatial pattern formation we study how position information can be controlled by locally coupled discrete dynamical networks, similar to gene regulation networks of cells in a developing multicellular organism. As an example we study the developmental problems of domain formation and proportion regulation in the presence of noise, as well as in the presence of cell flow. We find that networks that solve this task exhibit a hierarchical structure of information processing and are of similar complexity as developmental circuits of living cells. Proportion regulation is scalable with system size and leads to sharp, precisely localized boundaries of gene expression domains, even for large numbers of cells. A detailed analysis of noise-induced dynamics, using a mean-field approximation, shows that noise in gene expression states stabilizes (rather than disrupts) the spatial pattern in the presence of cell movements, both for stationary as well as growing systems. Finally, we discuss how this mechanism could be realized in the highly dynamic environment of growing tissues in multicellular organisms. 相似文献
989.
1. Spatial heterogeneity of resources may influence competition among individuals and thus have a fundamental role in shaping population dynamics and carrying capacity. In the present study, we identify shelter opportunities as a limiting resource for juvenile Atlantic salmon (Salmo salar L.). Experimental and field studies are combined in order to demonstrate how the spatial distribution of shelters may influence population dynamics on both within and among population scales. 2. In closed experimental streams, fish performance scaled negatively with decreasing shelter availability and increasing densities. In contrast, the fish in open stream channels dispersed according to shelter availability and performance of fish remaining in the streams did not depend on initial density or shelters. 3. The field study confirmed that spatial variation in densities of 1-year-old juveniles was governed both by initial recruit density and shelter availability. Strength of density-dependent population regulation, measured as carrying capacity, increased with decreasing number of shelters. 4. Nine rivers were surveyed for spatial variation in shelter availability and increased shelter heterogeneity tended to decrease maximum observed population size (measured using catch statistics of adult salmon as a proxy). 5. Our studies highlight the importance of small-scale within-population spatial structure in population dynamics and demonstrate that not only the absolute amount of limiting resources but also their spatial arrangement can be an important factor influencing population carrying capacity. 相似文献
990.