柴达木盆地荒漠灌丛群落谱系结构研究

谱系信息是群落生态学和保育生物学研究的主要内容之一。为探究柴达木盆地荒漠灌丛群落谱系结构及其与环境因子的关系,该研究以柴达木盆地荒漠灌丛为对象,基于群落中物种存在与否的物种组成数据,使用R语言中picante软件包计算了灌丛群落谱系多样性指数和谱系结构指数,并且分析了谱系结构指数与年均温度、年均降水以及土壤含水量之间的关系,以揭示柴达木盆地灌丛群落物种之间的亲缘关系和群落生物多样性维持机制。结果表明:(1)柴达木盆地灌丛群落谱系结构与土壤含水量之间存在极显著相关性(P=2.77×10-6),随着土壤含水量的增加,群落谱系结构聚集程度逐渐降低,表现出生境过滤作用逐步减弱,生物间相互作用逐渐加强的变化趋势。(2)群落谱系结构与年均温度、年均降水之间无显著相关性。(3)典型荒漠生境灌丛和河谷(河漫滩)生境灌丛群落的谱系结构差异显著(P0.05),整体上分别表现为谱系聚集状态和谱系发散状态;河谷(河漫滩)生境灌丛群落的谱系多样性显著高于典型荒漠生境灌丛(P0.05)。(4)将群落谱系信息应用在生物多样性保护实践中,发现河谷(河漫滩)生境灌丛群落较典型荒漠生境的灌丛群落可能具有更高的保护价值。研究认为,将群落谱系研究与保育生物学理论结合将会使生物多样性保护策略更加科学有效。     

Indirect effects in a desert plant community: is competition among annuals more intense under shrub canopies?

An unresolved discussion in contemporary ecology deals with the relative importance of competition along environmental gradients. In deserts, local-scale differences in environmental productivity may be caused by the presence of shrubs, which represent a favorable habitat for annual populations within a nutrient-poor matrix. In this study, we attempted to test the hypothesis that facilitation of desert annuals by shrubs increase the intensity of competition among the annual plants. Such negative indirect effects have so far been ignored in studies about plant-plant interactions. We tested our hypothesis by measuring seedling survival and fecundity of four abundant annual plant species with and without neighbors in open areas and under shrub canopies in a sandy desert area. Our findings did not indicate indirect negative effects of shrubs on their understory annuals. Sensitivity to the presence of neighbors varied between species and surprisingly, the species with the smallest seeds was the only one which was not negatively affected by the presence of neighbors. In contrast to our hypothesis, there was no difference between the habitat types shrubs and openings in absolute and relative competition intensity. Our overall results suggest that negative indirect effects of shrubs are unimportant in determining demographic response of understory annual plants.     

The distribution of invertebrate communities in a small South African river

Monthly samples of macroinvertebrates were collected from the stony-bed and marginal-vegetation habitats of a small river in the south western Cape Province, South Africa. Cluster analyses of the samples revealed assemblages of invertebrates (here referred to as communities) with clear spatial and temporal distribution patterns in the muer. The species composition of the communities, and their distribution, are described. The relation of the macroinvertebrate distribution to changes in the physico-chemical environment was investigated using stepwise multiple discriminant analysis. The results indicated a strong correlation between the two.     

Testing for non-randomness in sizes and habitats of West Indian lizards: choice of species pool affects conclusions from null models

Summary Several null models are proposed for testing whether size or habitat differences in West IndianAnolis lizards are greater than expected by chance. The models differ primarily in choice of the pool from which species are sampled to form random communities. Regardless of choice of pool, size differences in the Lesser Antilles are greater than null models predict; the pool using species on the known source (Puerto Rico) gives a greater variance in ratios but about the same mean ratio (for males), or a greater mean ratio (for females), compared with the pool composed of species on the islands being tested (the Stronget al., 1979, Galápagos procedure). On satellite islands of the Greater Antilles, sizes do not differ more than expected from null models. Pools composed of mainland-source species give null communities with more small or more large ratios than those composed of island species, depending upon whether four-species islands are included or excluded, respectively. Colwell and Winkler's unmodified Narcissus hypothesis is contradicted by these results in procedures where species not likely to be able to occur on small islands are included in the species pool. Using the most biologically reasonable, but not other, choices of source pool, species on satellite islands of the Greater Antilles differ more in structural habitat then expected by chance. In contrast to some of the results on size, here mainland-source pools are more likely to produce a statistically significant difference between real and random communities, as predicted by the Narcissus hypothesis. However, exclusion of structural habitat categories not found on satellite islands is necessary to achieve this significance.     

Substitutions of the Conserved Thr42 Increased the Roles of the ε-Subunit of Maize CF1 as CF1 Inhibitor and Proton Gate

The conserved residue Thr42 of -subunit of the chloroplast ATP synthase of maize (Zea mays L.) was substituted with Cys, Arg, and Ile, respectively, through site-directed mutagenesis. The over-expressed and refolded -proteins were purified by chromatography on DEAE-cellulose and FPLC on mono-Q column, which were as biologically active (inhibiting Ca²⁺-ATPase activity and blocking proton gate) as the native subunit isolated from chloroplasts. The T42C and T42R showed higher inhibitory activities on the soluble CF₁(–) Ca²⁺-ATPase than the WT. The T42I inhibited the Ca²⁺-ATPase activity of soluble CF₁ and restored photophosphorylation activity of membrane-bound CF₁ deficient in the most efficiently. Far-ultraviolet CD spectra showed that the portions of -helix and -sheet structures of the three mutants were somewhat different from WT. Thus the conserved residue Thr42 may be important for maintaining the structure and function of the -subunit and the basic functions of the -subunit as far as an inhibitor of Ca²⁺-ATPase and the proton gate are related.     

Temporal variation in habitat structure and shrubsteppe bird dynamics

Summary We investigate the role of temporal variation in habitat physiognomy in influencing the dynamics of shrubsteppe bird populations and communities. During a 3-y (1977–1979) study of 14 sites in the northern Great Basin of North America, annual precipitation varied substantially, with one of the driest years on record followed by one of the wettest. This resulted in significant physiognomic variation (increasing height and coverage of vegetation, decreasing horizontal patchiness), mediated largely by changes in the annual elements of the flora, particularly forbs and grasses. Shrub species coverage values, on the other hand, demonstrated no statistically detectable year-to-year changes, nor were they correlated with any physiognomic variation. Despite large scale physiognomic changes, no bird species' abundance varied in a statistically significant fashion; neither could variation in bird abundances be correlated with variation in either physiognomy or shrub species coverages.Multivariate analyses revealed essentially the same patterns as the univariate analyses: substantial changes in physiognomy, few changes in shrub species coverages or bird species abundances, and little correlation of temporal variation among the three data sets. Calculation of the Euclidean distances that sites moved in multivariate physiognomic, bird species, or shrub species hyperspaces yields synthetic gradients of annual turnover of sites with respect to those data sets. Sites identified as demonstrating high physiognomic turnover were characterized by high coverage of grass and forbs, while low turnover sites had greater coverage of shrubs and higher shrub species diversity. Relatively high bird turnover sites had greater numbers of Western Meadowlarks and Black-throated Sparrows, while more stable sites had high numbers of Brewer's Sparrows. Physiognomically, high bird turnover sites were grassier and had greater total vegetation coverage, while low bird turnover sites had more bare ground and higher horizontal patchiness. A site's position on the avifauna turnover axis, however, was uncorrelated with its position on the physiognomic turnover axis. Shrub species showed virtually no annual turnover.Reanalysis of a previous Principal Components Analysis (PCA) of these same data sets that was applied without regard to year of sampling revealed that the first physiognomic component (41% of the total physiognomic variability) did in fact have a strong temporal element, and that this element was consistent with the changes in univariate characters noted above. No other physiognomic component could be associated with annual variation, nor could any components of parallel bird abundance or shrub species coverage PCA's.Regional patterns indicate that sites tended to be very consistent from year to year in their relationships to one another as defined by their relative locations in either physiognomic or shrub species hyperspaces, but varied independently of one another with respect to their bird species abundances and composition. Examination of the temporal consistency of site relationships between bird space and vegetation space reveals that bird communities are to a large degree independent of a site's physiognomic position, but instead are strongly associated with its position in shrub species hyperspace.The overall patterns that emerge from these analyses are consistent with the so-called checkerboard effect that results from the apparently random annual redistribution of individual birds, and leads to the conclusion that populations of shrubsteppe birds are not existing at maximum density or carrying capacity. Such observations are consistent with contentions that these populations lack close biological coupling with coexisting species and that interactions among these species (e.g. competition) are likely to play little if any role in the organization of their communities.     

An index of weed size for assessing the soil productivity of ancient crop fields

A method is presented for generating data on archaeological weed species relevant to soil productivity and consequently crop husbandry. Three plant attributes (maximum canopy height, maximum canopy spread and maximum dry leaf weight per node) which are functionally related to habitat productivity were measured for 161 British annual species. These three attributes were combined to produce an index of weed size. Index values were found to differ significantly between character species of phytosociological classes from fertile and infertile habitats and to provide an objective assessment of CSR (Competitor/Stress-tolerator/Ruderal) strategysensu Grime (1974, 1979). Further work is required, however, to distinguish medium-sized species that exploit highly disturbed and productive habitats from those of less disturbed and less productive situations.     

Plant response to variations in nitrogen availability in a desert shrubland community

Spatial variations in nitrogen availability were studied in a desert community codominated byLarrea tridentata (DC.) Cov. andProsopis glandulosa Torr. Measurements of natural ¹⁵N values in tissues suggested thatProsopis obtains approximately half of its nitrogen through direct symbiotic fixation. Soils were collected under 1)Prosopis shrubs, 2)Larrea shrubs 2 m fromProsopis (LP), and 3)Larrea 2 m from otherLarrea but> 5 m from the nearestProsopis (LL).Prosopis soils showed significantly higher rates of nitrogen mineralization than LL soils in both A and B horizons. Rates of mineralization in LP soils were significantly higher than rates in LL soils only in the B horizon and were not significantly different from rates inProsopis soils. Leaf nitrogen concentrations were significantly higher in LP shrubs (2.06%) than in LL shrubs (1.78%), although ¹⁵N values did not differ between the two shrub types. Nitrogen concentrations inPerezia nana Gray, a perennial herb, were greater in plants underProsopis shrubs (2.09%) than under LP shrubs (1.93%) or LL shrubs (1.67%). Despite apparent differences in nitrogen availability, biomass ofLarrea and density ofPerezia did not differ significantly among these sites.     

Plant distribution in relation to the length of the growing season in a snow-bed in the Taisetsu Mountains,northern Japan

The distribution pattern of plants was studied in an alpine snow-bed in six plots along a snow-melting gradient. Each plot consisted of two habitats with respect to the microtopography; the flat habitat and the mound habitat. The number of species per plot decreased with the shortened snow-free period. In the flat habitat, the dominant growth forms changed from the early exposed plots to the late exposed ones as follows; lichens evergreen and deciduous shrubs forbs graminoids bryophytes. In the mound habitat, evergreen and deciduous shrubs prevailed widely along the gradient because of the ability to exploit new habitat by creeping over exposed rocks. For shrubs, the existence of mounds contributed to the expansion of the distribution ranges. Forbs and graminoids shifted their distribution modes to the late exposed plots where shrubs decreased in cover. Deciduous shrubs and forbs completely disappeared in the latest exposed plot.     

Plant-soil Interactions in Deserts

Geostatistical analyses show that the distribution of soil N, P and K is strongly associated with the presence of shrubs in desert habitats. Shrubs concentrate the biogeochemical cycle of these elements in islands of fertility that are localized beneath their canopies, while adjacent barren, intershrub spaces are comparatively devoid of biotic activity. Both physical and biological processes are involved in the formation of shrub islands. Losses of semiarid grassland in favor of invading shrubs initiate these changes in the distribution of soil nutrients, which may promote the further invasion and persistence of shrubs and cause potential feedbacks between desertification and the Earth's climate system.     

Remarkable medium-term dynamics of leaf succulent Mesembryanthemaceae shrubs in the winter-rainfall desert of northwestern Namaqualand,South Africa

Populations of shrubs in a winter-rainfall (ca. 70 mm yr_-1 desert community (Succulent Karoo), dominated by leaf succulents, showed remarkable dynamics over a 17-yr period. After a severe drought in 1979, which caused high plant mortality, perennial species number in a permanent 10 m×10 m plot doubled between 1980 and 1996, when the maximum of 41 species was recorded. Numbers of individuals of evergreen, leaf succulent shrubs also doubled over the same period, but showed fluctuations in response to dry years during the monitoring period. Detailed observations on the four dominant leaf succulent shrubs (all members of the Mesembryanthemaceae) between 1983 and 1996, showed species-specific patterns in population turnover. Mortality of all observed individuals ranged between 60% and 85%, and the proportion of the population that was recruited over this period ranged from 62% to 89%. In only one species did individuals persist throughout the monitoring period. Mean ages of individuals, excluding seedlings with lifespans of <1 yr, and individuals observed at the beginning of the monitoring period, ranged from 4.6 yr to 5.6 yr. Patterns of mortality and recruitment showed substantial differences among species and were not all attributable to rainfall patterns. Overall, the turnover of the shrub populations over the 15-yr monitoring period was remarkably high for a system of desert perennials. These unusual population patterns may explain the unique structure of leaf succulent-dominated communities in the Succulent Karoo.     

Two gerbils of the Negev: A long-term investigation of optimal habitat selection and its consequences

Optimal foraging theory has entered a new phase. It is not so much tested as used. It helps behavioural ecologists discover the nature of the information in an animals brain. It helps population ecologists reveal coefficients of interaction and their patterns of density-dependent variation. And it helps community ecologists examine niche relationships. In our studies on two species of Negev desert gerbil, we have taken advantage of the second and third of these functions. Both these gerbils prefer semi-stabilized dune habitat, and both altered their selective use of this habitat and stabilized sand according to experimental changes we made in their populations. Their changes in selectivity agree with a type of optimal foraging theory called isoleg theory. Isoleg theories provide examples of dipswitch theories – bundles of articulated qualitative predictions – that are easier to falsify than single qualitative predictions. By linking behaviour to population dynamics through isoleg theory, we were able to use the behaviour of the gerbils to reveal the shapes of their competitive isoclines. These have the peculiar non-linear shapes predicted by optimal foraging theory. Finally, when owl predation threatens, the behaviour of Gerbillus allenbyi reveals the shape of their victim isocline. As has long been predicted by predation theory and laboratory experiments, it is unimodal.     

鄂尔多斯高原西部几种荒漠灌丛群落种间联结关系的研究

采用ＰＣ、ＰＣＣ、ＡＣ、Ｘ２和ｒ等公式对鄂尔多斯高原西部５种典型荒漠灌丛群落种间联结系数的求算,通过这些种间的相互关系,阐述了这些物种对生境要求的差异和分布特点,本文的研究结果对与建立在种群关系基础上的荒漠植被的研究具有重要的意义。     

鄂尔多斯高原西部几种荒漠灌丛群落种间联结关系的研究

采用PC、PCC、AC、X2和r等公式对鄂尔多斯高原西部5种典型荒漠灌丛群落种间联结系数的求算,通过这些种间的相互关系,阐述了这些物种对生境要求的差异和分布特点,本文的研究结果对与建立在种群关系基础上的荒漠植被的研究具有重要的意义。     

Broad-scale reciprocity in an avian seed dispersal mutualism

Aim Coevolved relationships between individual species of birds and plants rarely occur in seed dispersal mutualisms. This study evaluates whether reciprocal relationships may occur between assemblages of bird and plant species. Location Vancouver Island, British Columbia, Canada (48°50′‐N, 125°22′‐W). Methods The distribution and fruiting phenologies of seven shrub species were compared to seasonal changes in habitat selection and seed dispersal by six fruit‐eating bird species. Results Shrub species inhabiting forest understorey habitat had earlier fruiting phenologies than shrub species inhabiting forest edge habitat along lake and bog margins. Birds showed a parallel pattern in habitat selection, being more abundant in the forest understorey early in the fruiting season, and more abundant in the forest edge later in the season. Rates of seed deposition covaried with avian habitat selection, in such a way that birds directed seed dispersal into habitats preferred by shrubs. Conclusions These results depict a broad‐scale pattern in the abundance of birds and fruits indicative of reciprocal interactions. Seasonal changes in seed dispersal to each habitat appear to reinforce the relationship between shrub habitat affinities and fruiting phenologies. Phenological differences between habitats may also reinforce seasonal changes in avian habitat selection. Therefore, although reciprocal interactions between pairs of bird and plant species are rare, broad‐scale reciprocal relationships may occur between assemblages of bird and plant species.     

Influences of shrub vegetation on distribution and diversity of a ground beetle community in a Gobi desert ecosystem

In shrubland ecosystems, shrubs as ecosystem engineers play an important role in structuring ground beetle communities. However, the influence of shrub vegetation on the distribution and diversity of ground beetles remains unknown in Gobi desert, northwest China, where shrubland is a major biome type. Using Gobi shrubland dominated by shrub species Nitraria sphaerocarpa and Reaumuria soongorica as a model system, we sampled ground beetle communities using a pitfall trapping method under canopies of both shrubs and in intershrub bare areas during spring, summer and autumn corresponding to the main period of beetle activity. Simultaneously, physical environment of the three microhabitats and plant characteristics of both shrubs were measured. We determined whether shrubs and species identity influence ground beetle distribution and diversity patterns and whether the response of beetles to the presence and species of shrubs is consistent across species. At the community level, total beetle abundance and species richness were significantly greater under shrubs than in intershrub bare areas, whereas more beetles were captured under N. sphaerocarpa than under R. soongorica. At the population level, eight dominant beetle species responded differently to the presence and species of shrubs. The abundance of Anatolica sp., Carabus sp., Cyphogenia chinensis, Microdera sp. and Sternoplax setosa was consistently much greater under shrubs than in intershrub bare areas, whereas the abundance of Blaps gobiensis, Lethrus apterus and Pterocoma reitteri under shrubs was similar to that in intershrub bare areas. The shrub N. sphaerocarpa was commonly preferred by Anatolica sp., C. chinensis and S. setosa, whereas the shrub R. soongorica was commonly preferred by L. apterus, but the abundance of B. gobiensis, Carabus sp., Microdera sp. and P. reitteri was unaffected by shrub species. Differences in the abundance, species richness and composition of ground beetles among microhabitat types were largely related to among-microhabitat differences in the physical environment and resource availability. Our results suggest that shrubs and species identity play key roles in structuring ground beetle communities, but their influence differed between species. This study emphasizes the importance of protecting shrub habitats for the maintenances of beetle biodiversity in this Gobi desert ecosystem.     

Snake communities of moist rainforest and derived savanna sites of Nigeria: biodiversity patterns and conservation priorities

The taxonomic composition and the abundance of two communities of snakes were studied in two different areas of southern Nigeria. One community was studied in a derived savanna area (environs of Ejule, 06°54N, 07°23E), and one community was studied in a moist rainforest area (environs of Eket, 04°50N, 07°59E). Both the specific diversity and the mean frequency of observation of snakes were significantly higher in the forest area than in the savanna area, and the dominance index was higher in the savanna than in the forest site. However, most of the species were found in only one of the two areas, depending on their habitat requirements (e.g. Gastropyxis smaragdina, Dispholidus typus, Thelotornis kirtlandii, Dendroaspis jamesoni, Bitis nasicornis, Causus maculatus, etc). The forest community housed a significant number of arboreal and semiaquatic taxa, but in both sites most of the species were terrestrial. The commonest species in the forest area was an oviparous, semiaquatic, batracophagous natricine snake (Afronatrix anoscopus), whereas the commonest species in the savanna area was an oviparous terrestrial lacertophagous psammophine snake (Psammophis phillipsi). Some conservation implications of our biodiversity analyses are presented. It is suggested that the moist rainforest represents a critically endangered habitat, and should deserve special attention by the international scientific community. Oil industry activity is especially dangerous for snake communities, especially in the southernmost regions of Nigeria.     

Bird Communities of the Arctic Shrub Tundra of Yamal: Habitat Specialists and Generalists

Background

The ratio of habitat generalists to specialists in birds has been suggested as a good indicator of ecosystem changes due to e.g. climate change and other anthropogenic perturbations. Most studies focusing on this functional component of biodiversity originate, however, from temperate regions. The Eurasian Arctic tundra is currently experiencing an unprecedented combination of climate change, change in grazing pressure by domestic reindeer and growing human activity.

Methodology/Principal Findings

Here we monitored bird communities in a tundra landscape harbouring shrub and open habitats in order to analyse bird habitat relationships and quantify habitat specialization. We used ordination methods to analyse habitat associations and estimated the proportions of specialists in each of the main habitats. Correspondence Analysis identified three main bird communities, inhabiting upland, lowland and dense willow shrubs. We documented a stable structure of communities despite large multiannual variations of bird density (from 90 to 175 pairs/km²). Willow shrub thickets were a hotspot for bird density, but not for species richness. The thickets hosted many specialized species whose main distribution area was south of the tundra.

Conclusion/Significance

If current arctic changes result in a shrubification of the landscape as many studies suggested, we would expect an increase in the overall bird abundance together with an increase of local specialists, since they are associated with willow thickets. The majority of these species have a southern origin and their increase in abundance would represent a strengthening of the boreal component in the southern tundra, perhaps at the expense of species typical of the subarctic zone, which appear to be generalists within this zone.     

Comparisons of carbon isotope discrimination in populations of aridland plant species differing in lifespan

Summary Carbon isotope discrimination () was compared between populations of dominant perennial plant species, differing in life expectancy, in two deserts with contrasting vegetation types. In both deserts, plants of the shorter-lived species showed significantly higher and greater intrapopulation variance in this character compared to the long-lived species. These results indicate underlying differences in gas-exchange physiology, and suggest a positive correlation between water-use efficiency and lifespan in desert plants. Differences in variance for this character may reflect greater microenvironmental variation experienced by shorter-lived plants and/or different forms of selection acting on water-use traits. Spatial distributions were significantly clustered for the shorter-lived species and significantly uniform for the long-lived species, indicating that competition has been important in the development of the long-lived populations. The long-lived Larrea tridentata showed a significant, negative correlation between and Thiessen polygon area, suggesting a positive relationship between water-use efficiency and longevity within this species. This relationship was weakly supported in the other warm desert species, Encelia farinosa, but was not observed within populations of the cold desert species, Gutierrezia microcephala and Coleogyne ramosissima. These results suggest that reflects key aspects of plant metabolism related to lifespan; these differences may ultimately influence interactions among desert plants and the structure of desert plant communities.     

Examining differences in phylogenetic composition enhances understanding of the phylogenetic structure of the shrub community in the northeastern Qinghai‐Tibetan Plateau

Periodic climatic oscillations and species dispersal during the postglacial period are two important causes of plant assemblage and distribution on the Qinghai‐Tibet Plateau (QTP). To improve our understanding of the bio‐geological histories of shrub communities on the QTP, we tested two hypotheses. First, the intensity of climatic oscillations played a filtering role during community structuring. Second, species dispersal during the postglacial period contributed to the recovery of species and phylogenetic diversity and the emergence of phylogenetic overdispersion. To test these hypotheses, we investigated and compared the shrub communities in the alpine and desert habitats of the northeastern QTP. Notably, we observed higher levels of species and phylogenetic diversity in the alpine habitat than in the desert habitat, leading to phylogenetic overdispersion in the alpine shrub communities versus phylogenetic clustering in the desert shrub communities. This phylogenetic overdispersion increased with greater climate anomalies. These results suggest that (a) although climate anomalies strongly affect shrub communities, these phenomena do not act as a filter for shrub community structuring, and (b) species dispersal increases phylogenetic diversity and overdispersion in a community. Moreover, our investigation of the phylogenetic community composition revealed a larger number of plant clades in the alpine shrub communities than in the desert shrub communities, which provided insights into plant clade‐level differences in the phylogenetic structures of alpine and desert shrub communities in the northeastern QTP.