THE MACROEVOLUTIONARY CONSEQUENCES OF ECOLOGICAL DIFFERENCES AMONG SPECIES

Abstract:  In this paper, I examine the dynamics of species richness in a model system in which multiple species compete in a metacommunity (multiple patches linked by dispersal). Patches lie along an environmental gradient, and new species are introduced into the system by speciation of existing species. This model is used to explore how the ecological similarity of species influences the patterns in community structure that result and to determine whether patterns in fossil and systematics data may be signatures for different types of community structure. Making species more similar overall along the entire gradient or making new species that have more similar optimal positions along the gradient to their progenitor both increase the time required to drive species extinction. As a result, making species more similar ecologically to one another increases overall species richness because of an increased frequency of transient species in the system. Having more transient species in systems shifted the longevity distributions of species in the fossil record towards having a greater frequency of shorter duration species, and the age distribution of extant species that would be estimated from molecular phylogenies also had a higher frequency of younger aged species. Comparisons of these results with species longevity distributions extracted from two data sets and with species ages derived from species-level molecular phylogenies strongly suggest that transient species are an important component of real biological communities.     

三个大豆品种光合特性的差异

不同氮浓度处理下早衰型大豆徐州424叶片净光合速率均比苏协1号和1138-2低。这种差异与比叶重、叶厚度、栅栏细胞形状及RuBP羧化酶活力有关。 离体叶片的失绿进程可分滞后期和对数期两个阶段。滞后期的长短与叶片光合功能期有一定关系,但与光合速率无关。滞后期以1138-2最长,苏协1号次之,徐州424最短。 在4m mol/L氮浓度以下,叶片净光合速率随氮处理浓度增加而上升,超过4m mol/L以后,上升缓慢或不再上升,这是一种两次形曲线的反映方式。但单株干物重则呈线性反应方式。叶片可溶性蛋白质含量与光合速率也呈线性关系。徐州424的净光合速率/可溶性蛋白质量之比为0.864,苏协1号和1138-2分别为1.103和1.144。     

用等电聚焦技术对三种马鸡亲缘关系的研究

本文用0.5mm薄层等电聚焦电泳技术对三种马鸡的卵清蛋白进行了比较分析。电泳谱和扫描结果表明,藏马鸡和蓝马鸡的亲缘关系比褐马鸡更近些。而且地理分布、骨骼和化石材料方面的分析结果和等电聚焦的结果是一致的。     

三种竞争种群的古典Gause-Lotka-Volterra系统

本文讨论了三种竞争种群的古典GLV系统．对系统所有非负平衡点的稳定性,进行了分析,给出了正平衡点全局稳定的充分条件,应用Hopf分支定理,我们给出了系统具有分支值的充分条件．     

植物竞争对3种移植树苗生长的影响

在植物幼苗生长过程中,总是受到包括地下根竞争在内的各种竞争影响。植物间的竞争主要同有效光辐射、水分和各种营养相关。当外来植物侵入森林群落时,可能受到群落中其它植物竞争的影响。该文通过移植尾叶桉(Eucalyptus urophylla)、大叶相思(Acacia auriculaeformis)两种外来种和本地种荷木(Schima superba)幼苗,挖沟排除根竞争和砍树创造林窗来排除地上竞争的野外实验,研究植物竞争对幼苗生长的影响。有根竞争时,荷木、尾叶桉和大叶相思幼苗的生物量和净初级生产力均小于没有根竞争时,可见地下根竞争对3种幼苗生长有抑制性影响。尾叶桉、大叶相思和荷木3种幼苗受到的总竞争强度分别是0.357 9、0.338 3和0.198 9,受到的地下根竞争强度则分别是0.104 3、0.053 04和0.118 8,受到的地上竞争强度则分别是0.285 1、0.277 0和0.090 85。尾叶桉和大叶相思两种幼苗受到的总竞争强度间的差异不显著,但都显著大于荷木;3种幼苗受到的地上竞争强度间的差异同总竞争强度情况相似;尾叶桉和荷木两种幼苗受到的地下根竞争强度间的差异不显著,但都显著大于大叶相思。地上竞争对阳性树种尾叶桉和大叶相思两种幼苗的生长影响大,而地下根竞争则对耐阴性强的荷木幼苗影响大。尾叶桉和大叶相思两种外来种幼苗受到的总竞争强度均大于本地种荷木幼苗,这反映了这两种外来树种侵入次生林这样的群落受到竞争影响大。     

IMPLICATIONS OF NUCLEOLAR DIFFERENCES IN THE ROOT EPIDERMIS AMONG SEVERAL GRASS SPECIES

The nucleolar sizes of root epidermal cells were determined in 10 species of the Gramineae. Festucoid and panicoid roots presented significantly larger nucleoli in hair-producing, as opposed to hairless, cells. The magnitude of the nucleolar size differences between cell types seemed to be species specific and was not related to the type of epidermal cellular pattern. There seemed to be some suggestion that meristematic nucleoli of festucoid species may generally be larger than those of panicoid types. There was also an indication that festucoid grasses might be characterized by a high percent of multinucleolate epidermal cells. In contrast, cells of panicoid roots contained a single nucleolus in most instances. Possible implications of these observations were briefly discussed in terms of development and systematics.     

COMPETITIVE EXCLUSION AMONG THREE PLANKTONIC BLUE-GREEN ALGAL SPECIES1,2

Although domination of 1 species in an algal community has often been attributed to toxic effects, nutrient exhaustion can also lead to competitive exclusion among algal species. The bacteria-associated blue-green algae Microcystis aeruginosa, Nostoc muscorum, and Phormidium foveolarum were cultivated in Zehnder-Gorham's medium No. 11 individually and in their combinations. The growth rates of Microcystis and of Nostoc were reduced by the presence of Phormidium. This detrimental effect was apparently not due to formation of any toxic or allelopathic matter. It was caused by the reduction of iron and trace metal concentrations in the medium by Phormidium to levels too low for normal growth of Microcystis and Nostoc. Work with the axenic forms of the 3 algal species also indicated a lowering of iron and trace element concentrations by Phormidium to levels not sufficient for sustained growth of Microcystis and Nostoc. Thus, bacteria played no significant role in this example of competitive exclusion.     

RAPID DIVERSIFICATION OF SPERM PRECEDENCE TRAITS AND PROCESSES AMONG THREE SIBLING DROSOPHILA SPECIES

Postcopulatory sexual selection is credited with driving rapid evolutionary diversification of reproductive traits and the formation of reproductive isolating barriers between species. This judgment, however, has largely been inferred rather than demonstrated due to general lack of knowledge about processes and traits underlying variation in competitive fertilization success. Here, we resolved processes determining sperm fate in twice‐mated females, using transgenic Drosophila simulans and Drosophila mauritiana populations with fluorescently labeled sperm heads. Comparisons among these two species and Drosophila melanogaster revealed a shared motif in the mechanisms of sperm precedence, with postcopulatory sexual selection potentially occurring during any of the three discrete stages: (1) insemination; (2) sperm storage; and (3) sperm use for fertilization, and involving four distinct phenomena: (1) sperm transfer; (2) sperm displacement; (3) sperm ejection; and (4) sperm selection for fertilizations. Yet, underlying the qualitative similarities were significant quantitative differences in nearly every relevant character and process. We evaluate these species differences in light of concurrent investigations of within‐population variation in competitive fertilization success and postmating/prezygotic reproductive isolation in hybrid matings between species to forge an understanding of the relationship between microevolutionary processes and macroevolutionary patterns as pertains to postcopulatory sexual selection in this group.     

POPULATION DIFFERENCES IN INDIGENOUS FUSARIUM SPECIES BY CORN CULTURE OF PRAIRIE SOIL

Six species of Fusarium were identified among approximately 7,000 cultures isolated from roots and soils collected from prairies and cornfields in southern Minnesota. In both soil sources, F. oxysporum and F. solani predominated, followed in order by F. roseum, F. episphaeria, F. tricinctum, and F. moniliforme. The same order was obtained for the 28 species of prairie grasses and forbs as for corn. From prairie plant and corn roots, respectively, F. oxysporum was isolated from 64 and 90%; F. solani, 26 and 80%; F. roseum, 8 and 35%; and F. tricinctum, 6 % each. In 10 of 17 companion soil pairs, populations of Fusarium species were higher in cornfield than in prairie soils. Populations of F. roseum and F. moniliforme especially, were higher in cornfield soils of sample pairs, but populations of F. solani were higher in prairie soils. Fusarium roseum ‘Equiseti’ was the predominant cultivar of this species in both prairie and cornfield soils. Thus all six species of Fusarium appeared to be indigenous to the prairie, and some, especially F. roseum, apparently had increased in prevalence in soil and roots by corn culture.     

SPATIAL PATTERNS OF SHELL SHAPE OF THREE SPECIES OF CO-EXISTING LITTORINID SNAILS IN NEW SOUTH WALES, AUSTRALIA

The shape and relative weight of the shell have been shown tovary intraspecifically and interspecifically in a number ofspecies of gastropods, including many different littorinids.These differences give rise to different shell forms in differenthabitats. In those species which have non-planktotrophic development,differences in shell form among shores have been usually explainedin terms of natural selection because exposure to waves supposedlyfavours light shells with large apertures, while predation bycrabs on sheltered shores favours elongated, thick shells withsmaller apertures. Differences in shell shape among speciesfound at different heights on the shore have been explainedin terms of resistance to desiccation and temperature. Suchvariables would tend to act on a relatively broad-scale, i.e.causing differences among heights on a shore or among shores.Rates of growth, which might vary at much smaller scales withina shore, have also been shown to affect the shapes of many shells. In this study, the shape and relative weight of shells of threespecies of co-existing littorinids (Littorina unifasciata, Bembiciumnanum and Nodilittorina pyramidalis) were measured. These speciesall haveplanktotrophic development and they are found on manyshores where there is no evidence that they are preyed uponby crabs. Before explanations of shell shape are proposed, itis necessary that patterns of variation, within different partsof ashore and among different shores are clearly documented.These patterns were measured at a number of different spatialscales within and among replicate shores with different amountsof wave exposure. Large and small specimens were included toallow intraspecific comparisons among snails of different sizesfound at different heights on the shore. The results showedsignificant differences among shores in shape and relative weightof shells, but these differences could not be explained by exposureto waves. In addition, snails of different sizes and differentspecies did not show the same patterns although they were collectedfrom the same sites. Importantly, the shell shape of Liuorinaunifasciata varied significantly among sites at approximatelythe same height within a shore. These differences could notbe clearly correlated with density, mean size nor exposure towaves. The only consistent pattern was a decrease in relativeaperture size in specimens living higher on the shore. Modelsthat have commonly been proposed to explain shape and relativeweight of shells in other species of gastropods are not adequateto explain the small- and large-scale variation of the measurementsdescribed here. It is proposed that any selective advantageof shell morphology and the effects of any variables on thedevelopment of shell morphology in these species can only beidentified after appropriately designed and replicated fieldexperiments. (Received 4 March 1994; accepted 13 September 1994)     

SOURCES OF INORGANIC CARBON FOR PHOTOSYNTHESIS BY THREE SPECIES OF MARINE DIATOM1

The utilization of inorganic carbon by three species of marine diatom, Skeletonema costatum (Grev.) Cleve. Ditylum brightwellii (West) Grun., and Chaetoceros calcitrans Paulsen was investigated using an inorganic carbon isotopic disequilibnum technique and inorganic carbon dose-response curves. Stable carbon isotope data of the diatoms are also presented. Observed rates of photosynthetic oxygen evolution were greater than could be accounted for by the theoretical rate of CO₂ supply from the uncatalyzed dehydration of HCO₃^? in the external medium, suggesting use of HCO₃^? as an inorganic carbon source. Data from the isotopic disequilibrium experiment demonstrate the use of both HCO₃^? and CO₂ for photosynthesis. Carbon isotope discrimination values support the use of HCO₃^? by the diatoms.     

三种食肉目动物的核型分析

本文报道了产于我国华北地区的艾鼬、貉和果子狸的核型。其中艾鼬2n=36。组型由20条双臂染色体、14条单臂染色体和一对性染色体组成。貉2n=65,它与wuster等报道过的貉的2n=42的核型表现出同种动物核型间的多态现象。果子狸2n=44,其c带带型中具有一对带有较大异染色质的中部着丝点染色体。     

ENZYME ELECTROPHORESIS AND EVOLUTIONARY RELATIONSHIPS AMONG THREE SPECIES OF LASTHENIA (ASTERACEAE: HELIANTHEAE)

Enzyme electrophoresis was used to examine variation at 18 gene loci in Lasthenia burkei, L. conjugens, and L. femontii. The species consist of diploid annuals restricted to vernal pools in California; a variety of data has indicated that they are closely related. Populations of the three species are similar at isozyme loci; L. conjugens and L. fremontii are most similar with a genetic identity of 0.965. Lasthenia conjugens and L. burkei are next most similar (0.934), while L. burkei and L. fremontii have an identity of 0.909. Lasthenia burkei and L. femontii each contain a different subset of the alleles found in L. conjugens. Electrophoretic data are concordant with the view that these three species are closely related, but do not support the hypothesis that L. burkei is a stabilized hybrid derivative of L. conjugens and L. fremontii because alleles unique to each of the latter two species are not combined in the former. Rather, distribution of alleles among the three species suggests two possible alternative hypotheses of evolutionary relationships. One hypothesis considers Lasthenia conjugens a hybrid derivative of L. burkei and L. fremontii while the alternative explanation views the latter two species as independent derivatives of the former. Neither of these hypotheses appears to be concordant with morphological data.     

INFLORESCENCE SIZE AND FRUIT DISTRIBUTION AMONG INDIVIDUALS IN THREE ORCHID SPECIES

Fruit distribution among individuals in populations of three orchid species was analyzed. Fruit set was low in the three species. The distribution of fruits in the non-autogamous species was skewed to the right, with high variance: mean ratios, and a moderate to high proportion of fruitless plants. Larger inflorescence size did not necessarily result in an increase in percent fruit set but tended to increase the probability to produce at least one fruit. Pollinator-mediated selection on inflorescence size through fruit production may be limited by the low overall level of visitation and the resulting uncertainty of pollination at the individual level.     

绿僵菌属的三个新种

作者从广东、贵州、北京等地收集的虫生真菌中,发现在我国具有绿僵菌属特征的真菌可分为四个种。根据菌落颜色、分生孢子团块大小、紧密和牢固程度、孢子链连接方式、分生孢子形状等,将我们收集的属于本属的菌株分为四个种。本文报道绿僵菌属三个新种的描述。金龟子绿僵菌Metarhizium anisopliae(Metsch.)Sorokin为最常见的甘蔗金龟子致病菌,是本属的模式种。平沙绿僵菌Metarhizium pingshaense Chen et Guo sp.nov.、柱孢绿僵菌Metarhizium cylindrosporae Chen et Guo sp.nov.和贵州绿僵菌Metarhizium guizhouense Chen et Guo sp.nov.是三个新种。