Mass transfer limitation of sulfate in methanogenic aggregates

The role of mass transfer limitation of sulfate as a factor governing the competition between sulfate reducing and methane producing bacteria in methanogenic aggregates was theoretically evaluated by the calculation of steady-state sulfate microprofiles using a reference set of parameters obtained from the literature. The shooting method was used as a numerical technique for solving the mathematical model. The effect of the parameters on mass transport limitation was tested by varying each reference value of the parameters with a factor of 3. Sulfate limitation within granules prevailed at moderate (0.1 kg m(-3)) and low sulfate concentrations in the bulk liquid, at high maximum sulfate utilization rates (3.73 x 10(-5) kg SO(4) (2-) kg(-1) VSS S(-1) or biomass concentrations (40 KG VSS m(-3)), and in large aggregates (radius of 7.5 10(-4) m). The effective diffusion coefficient of sulfate and the affinity constant were less determinative for the penetration depth of sulfate within a granule. (c) 1994 John Wiley & Sons, Inc.     

Competitive habitat utilization in the damselfly,Mnais nawai (Zygoptera: Calopterygidae) coexisting with a related species,Mnais pruinosa

Reproductive behaviors related to habitat utilization were studied in males of the damsefly,Mnais nawai, which has two male forms, territorial orange-winged males (nawai) and non-territorial pale-orange-winged males (sahoi), at the upper part of a mountain stream where they partiallycoexist with a related species,Mnais pruinosa, which also has two male forms, territorial orange-winged males (esakii) and non-territorial hyaline-winged males (strigata). These two species showed parapatric distribution; the lower part of the stream was occupied byM. nawai, and the upper part byM. pruinosa. In the present study, cross-matings occurred between bothMnais species, although normal intraspecific matings occurred more frequently than cross-matings. Territorial males of both species copulated with conspecific females that entered their territory and guarded the ovipositing females, probably to avoid sperm displacement resulting from subsequent copulations. Severe competition for oviposition sites by territorial males even occurred between the two species. On the other hand, non-territorial males of both species have alternative mating strategies (including several tactics such as sneaking, takeover and interception). The possible benefits from conflict among territorial males of both species is discussed.     

Competing for blood: the ecology of parasite resource competition in human malaria–helminth co‐infections

Ecological theory suggests that co‐infecting parasite species can interact within hosts directly, via host immunity and/or via resource competition. In mice, competition for red blood cells (RBCs) between malaria and bloodsucking helminths can regulate malaria population dynamics, but the importance of RBC competition in human hosts was unknown. We analysed infection density (i.e. the concentration of parasites in infected hosts), from a 2‐year deworming study of over 4000 human subjects. After accounting for resource‐use differences among parasites, we find evidence of resource competition, priority effects and a competitive hierarchy within co‐infected individuals. For example reducing competition via deworming increased Plasmodium vivax densities 2.8‐fold, and this effect is limited to bloodsucking hookworms. Our ecological, resource‐based perspective sheds new light into decades of conflicting outcomes of malaria–helminth co‐infection studies with significant health and transmission consequences. Beyond blood, investigating within‐human resource competition may bring new insights for improving human health.     

金钟藤入侵群落的种间联结及生态位特征

金钟藤(Decalobanthus boisianus)是林业有害植物, 其暴发生长和扩散对森林生态系统造成了严重破坏。本文以海南岛48个金钟藤典型分布群落为研究对象, 用方差比率法和贡献定律法探究群落的稳定性; 用χ ²统计量、联结系数(AC)、共同出现百分率(PC)、Ochiai指数和Dice指数分析金钟藤与伴生物种的种间联结关系; 用生态位宽度、生态位相似性系数和生态位重叠指数研究群落中各物种的生态位特征, 以期为金钟藤生物防治的植物物种筛选提供借鉴。结果表明: (1)金钟藤所在48个群落共有156种伴生植物, 其中大戟科、茜草科、桑科、无患子科和樟科植物占优势; (2)群落中优势物种呈正联结关系, 植物种类累积倒数百分比与累积相对频度交点坐标为(44.53, 55.47), 远离稳定交点坐标(20, 80), 说明群落处于不稳定状态; (3)金钟藤与芳槁润楠(Machilus suaveolens)、黄椿木姜子(Litsea variabilis)、岭南山竹子(Garcinia oblongifolia)、显脉杜英(Elaeocarpus dubius)、鸭脚木(Schefflera octophylla)和银柴(Aporusa dioica)都紧密关联, 说明金钟藤与这些物种的资源利用方式较相似; (4)金钟藤的生态位宽度最大, 与伴生物种间的生态位重叠度较高, 但伴生物种间的生态位重叠度较低。金钟藤的入侵导致群落处于不稳定状态, 并与伴生物种间存在激烈的竞争关系。因此, 建议在金钟藤已入侵的群落中大量栽种芳槁润楠、黄椿木姜子、显脉杜英、鸭脚木和银柴, 以遏制其蔓延; 大量栽种翻白叶树(Pterospermum heterophyllum)、海南菜豆树(Radermachera hainanensis)、九节(Psychotria rubra)和肉实树(Sarcosperma laurinum)用于金钟藤入侵群落的植被恢复。     

GENOME‐WIDE INVESTIGATION OF REPRODUCTIVE ISOLATION IN EXPERIMENTAL LINEAGES AND NATURAL SPECIES OF NEUROSPORA: IDENTIFYING CANDIDATE REGIONS BY MICROARRAY‐BASED GENOTYPING AND MAPPING

Inherent incompatibilities between genetic components from genomes of different species may cause intrinsic reproductive isolation. In evolution experiments designed to instigate speciation in laboratory populations of the filamentous fungus Neurospora, we previously discovered a pair of incompatibility loci (dfe and dma) that interact negatively to cause severe defects in sexual reproduction. Here we show that the dfe‐dma incompatibility also is a significant cause of genetic isolation between two naturally occurring species of Neurospora (N. crassa and N. intermedia). The strong incompatibility interaction has a simple genetic basis (two biallelic loci) and antagonistic epistasis occurs between heterospecific alleles only, consistent with the Dobzhansky–Muller model of genic incompatibility. We developed microarray‐based, restriction‐site associated DNA (RAD) markers that identified ～1500 polymorphisms between the genomes of the two species, and constructed the first interspecific physical map of Neurospora. With this new mapping resource, the approximate genomic locations of the incompatibility loci were determined using three different approaches: genome scanning, bulk‐segregant analyses, and introgression. These population, quantitative, and classical genetics methods concordantly identified two candidate regions, narrowing the search for each incompatibility locus to only ～2% of the nuclear genome. This study demonstrates how advances in high‐throughput, genome‐wide genotyping can be applied to mapping reproductive isolation genes and speciation research.     

Cost of resistance and tolerance under competition: the defense-stress benefit hypothesis

Defense costs provide a major explanation for why plants in nature have not evolved to be better defended against pathogens and herbivores; however, evidence for defense costs is often lacking. Plants defend by deploying resistance traits that reduce damage, and tolerance traits that reduce the fitness effects of damage. We first tested the defense-stress cost (DSC) hypothesis that costs of defenses increase and become important under competitive stress. In a greenhouse experiment, uniparental maternal families of the host plant Arabis perennans were grown in the presence and absence of the bunch grass Bouteloua gracilis and the herbivore Plutella xylostella. Costs of resistance and tolerance manifest as reduced growth in the absence of herbivory were significant when A. perennans grew alone, but not in the competitive environment, in contrast to the DSC hypothesis. We then tested the defense-stress benefit (DSB) hypothesis that plant defenses may benefit plants in competitive situations thereby reducing net costs. For example, chemical resistance agents and tolerance may also have functions in competitive interactions. To test the DSB hypothesis, we compared differentially competitive populations for defense costs, assuming that poorer competitors from less dense habitats were less likely to have evolved defenses that also function in competition. Without competitive benefits of defenses, poorer competitors were expected to have higher net costs of defenses under competition in accordance with DSB. Populations of A. perennans and A. drummondii that differed dramatically in competitiveness were compared for costs, and as the DSB hypothesis predicts, only the poor competitor population showed costs of resistance under competition. However, cost of tolerance under competition did not differ among populations, suggesting that the poor competitors might have evolved a general stress tolerance. Although the DSC hypothesis may explain cases where defense costs increase under stress, the DSB hypothesis may explain some cases where costs decrease under competitive stress.     

Evolutionary analysis of life span, competition, and adaptive radiation, motivated by the Pacific rockfishes (Sebastes)

The Pacific rockfishes (Sebastes spp) are remarkable for both their diversity (on the order of 100 species) and range of maximum life span ( approximately 10 years for Calico rockfish to approximately 200 years for Rougheye rockfish). We describe the natural history and patterns of diversity and life span in these species and then use independent contrasts to explore correlates of these. When phylogenetic history is taken into account, maximum life span is explained by age at maturity, size at maturity, and the interaction of these two. We introduce a life-history model that allows insight into the origin of these correlations. We then describe a variety of mechanisms that may increase lifepans and diversity. These include fluctuating environments (in which organisms basically have to "wait out" bad periods to reproduce successfully), diversity, and longevity inspired by interspecific competition and physiological complexity in growth and accumulation of cellular damage. All of the results point toward the importance of flat or "indifferent" fitness surfaces as a key element in the evolution of diversity. We conclude that further development of the theory of flat or indifferent fitness surfaces as applied to diversity and life span is clearly warranted.     

Shift in competitive ability mediated by soil biota in an invasive plant

Understanding the shifts in competitive ability and its driving forces is key to predict the future of plant invasion. Changes in the competition environment and soil biota are two selective forces that impose remarkable influences on competitive ability. By far, evidence of the interactive effects of competition environment and soil biota on competitive ability of invasive species is rare. Here, we investigated their interactive effects using an invasive perennial vine, Mikania micrantha. The competitive performance of seven M. micrantha populations varying in their conspecific and heterospecific abundance were monitored in a greenhouse experiment, by manipulating soil biota (live and sterilized) and competition conditions (competition‐free, intraspecific, and interspecific competition). Our results showed that with increasing conspecific abundance and decreasing heterospecific abundance, (1) M. micrantha increased intraspecific competition tolerance and intra‐ vs. interspecific competitive ability but decreased interspecific competition tolerance; (2) M. micrantha increased tolerance of the negative soil biota effect; and (3) interspecific competition tolerance of M. micrantha was increasingly suppressed by the presence of soil biota, but intraspecific competition tolerance was less affected. These results highlight the importance of the soil biota effect on the evolution of competitive ability during the invasion process. To better control M. micrantha invasion, our results imply that introduction of competition‐tolerant native plants that align with conservation priorities may be effective where M. micrantha populations are long‐established and inferior in inter‐ vs. intraspecific competitive ability, whereas eradication may be effective where populations are newly invaded and fast‐growing.     

Competition between two aquatic detritivorous isopods – a laboratory study

The role of adult faeces in juvenile nutrition of two isopod species, Proasellus coxalis s.l. and Asellus aquaticus (L.), with similar trophic strategies and different reproductive output, has been studied in laboratory. Our aim was to consider the possible competitive mechanisms occurring at the beginning of the species coexistence using allopatric populations in single and mixed species experiments. Two series of competition experiments were performed. In the first, adult specimens were used for breeding and feeding trials. Both population dynamics and the percentage of ovigerous females and juveniles were evaluated during 10 months. Adult densities and juvenile percentage of A.aquaticus were lower in the presence of P. coxalis s.l. than when alone. At the end of the breeding experiments the dietary preferences of adults on a set of fungally conditioned leaf discs were not different among treatments. In the second series of experiments, the influence of coexistence on the feeding rates of young asellids and the relative importance of faeces and decaying plant material in their diet were investigated. Individual consumption by wild juveniles in multiple-choice laboratory experiments was measured by radioisotopes (^{32 2}P). Juveniles of P. coxalis s.l. showed the highest ingestion rates. In co-occurrence, contrary to A.aquaticus, they were able to further increase feeding on parental faeces. The role of parental faeces in the diet of the two species juveniles and the competitive dominance of P. coxalis s.l. are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interspecific Interactions Between Coptotermes formosanus and Reticulitermes flavipes (Isoptera: Rhinotermitidae) in Laboratory Bioassays

Experiments were conducted to examine competitive interactions between the Formosan subterranean termite, Coptotermes formosanus Shiraki (FST), and the eastern subterranean termite, Reticulitermes flavipes (Kollar) (EST), using groups of termites with different worker:soldier proportions. Experiments were conducted using three connected test chambers: an FST chamber, an unoccupied center chamber, and an EST chamber. When groups of FST were comprised of 20% soldiers versus 2% EST soldiers, only 8% of center chambers were occupied exclusively by EST. When groups of FST were comprised of 10% soldiers versus 1% EST soldiers, 44% of center chambers were occupied exclusively by EST. When the only food source was located in the center chamber, 60% of center chambers were occupied by both species. FST did not completely displace EST in any of these experiments.