Importance Of Resource Competition Research Articles

Whole cell biophysical modeling of codon-tRNA competition reveals novel insights related to translation dynamics.

The importance of mRNA translation models has been demonstrated across many fields of science and biotechnology. However, a whole cell model with codon resolution and biophysical dynamics is still lacking. We describe a whole cell model of translation for E. coli. The model simulates all major translation components in the cell: ribosomes, mRNAs and tRNAs. It also includes, for the first time, fundamental aspects of translation, such as competition for ribosomes and tRNAs at a codon resolution while considering tRNAs wobble interactions and tRNA recycling. The model uses parameters that are tightly inferred from large scale measurements of translation. Furthermore, we demonstrate a robust modelling approach which relies on state-of-the-art practices of translation modelling and also provides a framework for easy generalizations. This novel approach allows simulation of thousands of mRNAs that undergo translation in the same cell with common resources such as ribosomes and tRNAs in feasible time. Based on this model, we demonstrate, for the first time, the direct importance of competition for resources on translation and its accurate modelling. An effective supply-demand ratio (ESDR) measure, which is related to translation factors such as tRNAs, has been devised and utilized to show superior predictive power in complex scenarios of heterologous gene expression. The devised model is not only more accurate than the existing models, but, more importantly, provides a framework for analyzing complex whole cell translation problems and variables that haven't been explored before, making it important in various biomedical fields.

Seed development following reciprocal crossing among autotetraploid and diploid Acacia mangium and diploid A. auriculiformis

As part of a program to breed sterile triploid varieties of tropical Acacia, a series of inter-and intra-specific crosses were made among clones of neo-tetraploid A. mangium (AM-4x) and diploid A. mangium (AM-2x) and A. auriculiformis (AA-2x). The present paper reports variation in seed-crop development from anthesis to harvest, in comparison with that after open pollination of the respective parent trees. Abscission of spikes and pods within spikes commenced soon after anthesis and was more rapid in inter-cytotype crosses than in open-pollinated controls. Less than 12% of spikes were retained to maturity in either cytotype, emphasising the likely importance of resource competition during development. Inter-cytotype crosses showed higher levels of abnormal ovule development at 7 weeks after pollination and more undeveloped seeds in those pods which did develop to maturity. No inter-cytotype combination produced more than one viable seed per pod on average, and all needed to be germinated in vitro to survive. A directional effect was apparent in the inter-cytotype crosses within AM but this was not obvious when the cross was inter-specific. The study contributes new knowledge of the post-anthesis timeline for ovule, pod and spike abscission and discusses the likely genetic and environmental causes of observed differences between inter-and intra-cytotype crosses as well as the implications for breeding.

Does the relative importance of resource competition and architectural effect in floral variation vary with stages of floral ontogeny?

Abstract Variation in floral allocation within inflorescences has been attributed to resource competition and/or architectural effect. The two hypotheses were extensively studied and both hypotheses were partly supported by previous studies. However, the relative importance of resource competition and architectural effect may vary with stages of floral ontogeny in a species. To detect the effects of ontogenetic stages on floral variation, we manipulated the 6-flowered inflorescences of Adenophora jasionifolia (Campanulaceae) by early, late, and non-thinning flowers. Our results indicated that pollen and ovule production of the remaining flowers were not significantly different between early and late thinning manipulations, suggesting that floral sex allocation was determined far before flowering, in support of the architectural effect hypothesis. Under hand-pollination treatments, early thinning but not late thinning resulted in a significant increase in seed number and seed set of the remaining flowers. Therefore, the increase in seed production of the remaining flowers related to the floral ontogeny. The resource competition for floral allocation was significant under early thinning rather than late thinning manipulation. Our results suggest that studies on floral variation within inflorescences should take into account the stages of floral ontogeny.

Top-down and bottom-up consequences of unchecked ungulate browsing on plant and animal diversity in temperate forests: lessons from a deer introduction

Debate on the relative importance of competition for resources and trophic interactions in shaping the biological diversity of living communities remains unsettled after almost a century. Recently, dramatic increases in ungulate populations have provided a useful quasi-experiment on the effects of unrestrained ungulates on forest ecology. The islands of Haida Gwaii (Canada) offer a unique situation to investigate the potential of large herbivores to control temperate forest community structure and diversity. Black-tailed deer Odocoileus hemionus Merriam, native to adjacent mainland areas of British Columbia, were introduced in 1878 and spread to all but a few islands. Because deer were not native to the archipelago, islands that still lack deer provide a rare instance of temperate forest vegetation and fauna that developed in the absence of large herbivores. The colonisation of different islands at different times, and the absence of significant predation allow us to assess whether and how a large herbivore can exert “top-down” control on vegetation and its associated fauna. We studied plant communities in forest interior and shoreline, on seven small islands of varying browse history. Three islands were untouched by deer, deer had been resident for about 15 years on two, and on another two deer had been present for more than 50 years. Without deer, vegetation in the understorey and/or shrub layer was dense or very dense. Structure and composition varied markedly within and between shoreline and interior communities. Without deer, shoreline communities were dominated by species absent from islands with deer. Where deer had been present for less than 20 years most plant species characteristic of shorelines on islands without deer were already absent or scarce, but in the forest interior species richness was less affected and extensive shrub thickets remained. On islands where deer had been present for >50 years vegetation below the browse line was extremely simplified, converging in both forest interior and shoreline towards an open assemblage of a few deer-tolerant species, basically two coniferous trees. This top down effect on the plant community reflected up the food chain so that understorey invertebrate and shrub-dependent songbird communities became simplified. In contrast, species densities of litter arthropods (especially weevils and millipedes) were highest where deer were present for >50 years. Canopy birds were unaffected by deer presence. In the absence of predators, major climatic stress or other means to control the herbivore, deer browsing created greatly simplified plant and animal communities.

Experimental clipping of sagebrush inhibits seed germination of neighbours

Current views of plant communities emphasize the importance of competition for resources and colonization ability in determining seedling establishment and plant distributions. Many desert shrubs are surrounded by bare zones that lack other plants or have different suites of species beneath them compared with the open desert surrounding them. Releases of biochemicals as volatiles from leaves, leachates from litter, or exudates from roots have been proposed as mechanisms for this pattern, but such phytotoxicity has been controversial. I tested the hypothesis that experimental clipping of sagebrush foliage enhances its effect as a germination inhibitor. Germination of native forbs and grasses was reduced in association with clipped, compared with unclipped, sagebrush foliage in lath house and field experiments. Sagebrush seeds were not significantly affected. Air contact was required for this inhibition of germination. Soil contact and leaf litter were not required and added little inhibition of germination. These results suggest a potentially large, indirect, and previously overlooked role for interactions between herbivory and germination that could affect plant community structure.

COMPETITIVE INTERACTIONS BETWEEN THE INVASIVE EUROPEAN HONEY BEE AND NATIVE BUMBLE BEES

Biological invasions represent both an increasingly important applied problem and a tool for gaining insight into the structure of ecological communities. Although competitive interactions between invasive and native species are considered among the most important mechanisms driving invasion dynamics, such interactions are in general poorly understood. The European honey bee (Apis mellifera) is a widespread and economically important invader long suspected to competitively suppress many native bee species. Yet the extent to which this introduced species alters native communities remains controversial, reflecting ongoing debate over the importance of resource competition in regulating pollinator populations. I experimentally tested the effects of competition with Apis on colony foraging behavior and reproductive success of a native eusocial bee, Bombus occidentalis Greene, in coastal California. B. occidentalis colonies located near experimentally introduced Apis hives had lower mean rates of forager return and a lower ratio of foraging trips for pollen relative to nectar. Both male and female reproductive success of B. occidentalis were also reduced with greater proximity to introduced Apis hives. Reproductive success correlated significantly with measures of colony foraging behavior, most strongly with the relative allocation of foraging effort to pollen collection. This pattern suggests that B. occidentalis colonies exposed to competition with Apis experienced increased nectar scarcity and responded by reallocating foragers from pollen to nectar collection, resulting in lowered rates of larval production. These results provide evidence that Apis competitively suppresses a native social bee known to be an important pollinator, with the potential for cascading effects on native plant communities. This work also contributes to a greater understanding of the role competitive interactions play in pollinator communities, particularly for social bees.

Reproduction and survival in Melanoplus sanguinipes (Orthoptera: Acrididae) in response to resource availability and population density: the role of exploitative competition

AbstractThe relative importance of exploitative competition for resources on grasshopper reproductive allocation has not been fully examined. Given the large fluctuations in grasshopper densities that periodically occur in western North America, an increased understanding of how grasshopper survival and reproduction vary in response to intraspecific densities and per capita resource availability is important. I examined if exploitative resource competition could explain variation in reproductive allocation in Melanoplus sanguinipes (Fabricius) in response to resource availability and grasshopper population density. I also examined whether individual differences in competitive ability resulted in increased variance in egg production with low per capita resource availability. As expected with exploitative resource competition, per capita resource availability explained a significant amount of the variation in all reproductive characteristics examined. There was no effect of per capita resource availability on survival. Residuals of the regressions of egg production and vitellogenesis versus per capita resource availability did not differ for resource or density treatments, indicating that exploitative competition for resources played a more important role than interference competition in determining reproductive allocation in M. sanguinipes. Individual differences were evident, as variation around the mean of egg production increased with resource limitation. Exploitative competition for resources was important in determining both individual and population-level reproductive responses of grasshoppers to resource availability.