Ecosystem engineering across ecosystems: do engineer species sharing common features have generalized or idiosyncratic effects on species diversity?

Aim  To integrate the effects of ecosystem engineers (organisms that create, maintain or destroy habitat for other species) sharing the same archetype on species diversity, and assess whether different engineer species have generalized or idiosyncratic effects across environmentally similar ecosystems.
Location  High-Andean habitats of Chile and Argentina, from 23° S to 41° S.
Methods  We measured and compared the effects of eight alpine plants with cushion growth-form on species richness, species diversity (measured as the Shannon–Wiener index) and evenness of vascular plant assemblages across four high-Andean ecosystems of Chile and Argentina.
Results  The presence of cushion plants always increased the species richness, diversity (measured as the Shannon–Wiener index) and evenness of high-Andean plant assemblages. However, while the presence of different cushion species within the same ecosystem controlled species diversity in the same way, these effects varied between cushion species from different ecosystems.
Main conclusions  Results consistently supported the idea that increases in habitat complexity due to the presence of ecosystem engineers, in this case cushion plants, would lead to higher community diversity. Results also indicate that effects of the presence of different cushion species within the same ecosystem could be generalized, while the effects of cushion species from different ecosystems should be considered idiosyncratic.     

Seasonal variation in the abundance, biomass and biodiversity of earthworms in soils contaminated with metal emissions from a primary smelting works

1. Earthworms (Annelida: Oligochaeta) were sampled on four occasions (spring, summer, autumn and winter) at 14 sites along two transects from a primary lead/ zinc/cadmium smelting works at Avonmouth, UK.
2. Total abundance and biomass of earthworms decreased with proximity to the smelter. No worms were collected from the two sites closest to the factory (<0·6 km) and catches were significantly lower than controls at a further five sites (<3 km).
3. Seasonal composition of sampled communities differed only for summer with lower numbers of individuals and species collected at all sites. Reduced catches in the summer sample is a response to drought.
4. Species richness was lowest at sites close to the factory. For example, worms such as Aporrectodea caliginosa (Savigny) and Allolobophora chlorotica (Savigny) that were dominant at relatively clean sites further from the smelter are absent from the most contaminated soils.
5. Reduced species richness resulted in lower Shannon–Weiner diversity and higher Berger–Parker dominance. Multivariate cluster analysis for spring, summer and winter indicated that sites could be split into three groups based upon relative species composition. In autumn, two clusters were identified.
6. The absence of sensitive species from sites close to the smelting works supports the inclusion of earthworms as a key group in a terrestrial prediction and classification scheme for quantifying the effects of pollutants on soil biodiversity. However, sampling should be carried out in spring or autumn to obtain an accurate picture of community structure.     

Quantifying individual‐ and community‐level effects of competition using experimentally‐determined null species pools

Abstract. The effects of competition on individual fitness and species diversity were investigated in a first‐year old field by comparing the natural community to an experimentally‐determined null community. The species pool for the null community was estimated from low‐density plots, and hypothetical sample plots in the null community were constructed by random sampling from the species pool. Individual plants were larger in low‐density plots than control plots, indicating that competition reduced individual fitness. Competition appeared to reduce diversity in half the plots (i.e. species richness and diversity were lower than in hypothetical null community plots with the same number of individuals), but did not affect diversity in the other plots. However, the reduction in diversity could be explained as an artifact caused by spatial aggregation in control plots. The magnitude of the effects of competition on diversity did not change with plot density, and no species consistently increased or decreased in relative abundance as plot density increased. We conclude that competition had no effect on diversity in this community, despite the strong effect on individual growth.     

Estimating species – area relationships by modeling abundance and frequency subject to incomplete sampling

Models and data used to describe species–area relationships confound sampling with ecological process as they fail to acknowledge that estimates of species richness arise due to sampling. This compromises our ability to make ecological inferences from and about species–area relationships. We develop and illustrate hierarchical community models of abundance and frequency to estimate species richness. The models we propose separate sampling from ecological processes by explicitly accounting for the fact that sampled patches are seldom completely covered by sampling plots and that individuals present in the sampling plots are imperfectly detected. We propose a multispecies abundance model in which community assembly is treated as the summation of an ensemble of species‐level Poisson processes and estimate patch‐level species richness as a derived parameter. We use sampling process models appropriate for specific survey methods. We propose a multispecies frequency model that treats the number of plots in which a species occurs as a binomial process. We illustrate these models using data collected in surveys of early‐successional bird species and plants in young forest plantation patches. Results indicate that only mature forest plant species deviated from the constant density hypothesis, but the null model suggested that the deviations were too small to alter the form of species–area relationships. Nevertheless, results from simulations clearly show that the aggregate pattern of individual species density–area relationships and occurrence probability–area relationships can alter the form of species–area relationships. The plant community model estimated that only half of the species present in the regional species pool were encountered during the survey. The modeling framework we propose explicitly accounts for sampling processes so that ecological processes can be examined free of sampling artefacts. Our modeling approach is extensible and could be applied to a variety of study designs and allows the inclusion of additional environmental covariates.     

Incorporating functional dissimilarities into sample‐based rarefaction curves: from taxon resampling to functional resampling

Question: Indices of functional diversity have been seen as the key for integrating information on species richness with measures that focus on those components of community composition related to ecosystem functioning. For comparing species richness among habitats on an equal‐effort basis, so‐called sample‐based rarefaction curves may be used. Given a study area that is sampled for species presence and absence in N plots, sample‐based rarefaction generates the expected number of accumulated species as the number of sampled plots increases from 1 to N. Accordingly, the question for this study is: can we construct a ‘functional rarefaction curve’ that summarizes the expected functional dissimilarity between species when n plots are drawn at random from a larger pool of N plots? Methods: In this paper, we propose a parametric measure of functional diversity that is obtained by combining sample‐based rarefaction techniques that are usually applied to species richness with Rao's quadratic diversity. For a given set of N presence/absence plots, the resulting measure summarizes the expected functional dissimilarity at an increasingly larger cumulative number of plots n (n≤N). Results and Conclusions: Due to its parametric nature, the proposed measure is progressively more sensitive to rare species with increasing plot number, thus rendering this measure adequate for comparing the functional diversity of species assemblages that have been sampled with variable effort.     

Organic versus conventional management in an apple orchard: effects of fertilization and tree-row management on ground-dwelling predaceous arthropods

1 Organic and conventional management of apple orchards may have a different effect on arthropod communities.
2 We conducted a 3-year study to assess the effect of two strategies of fertilizer treatment (organic versus chemical) and three tree-row management systems (straw mulching, tillage and herbicide) on activity-density and biodiversity of epigeic predators. Ground beetles (Carabidae), rove beetles (Staphylinidae), ants (Formicidae) and spiders (Araneae) were sampled monthly with pitfall traps in the same apple orchard during 2003, 2004 and 2005.
3 A total of 4978 individuals were collected. Carabids (56.8% of the total catches) were the most abundant taxonomic group, followed by spiders (20.7%), ants (14.8%) and rove beetles (7.7%). Tree-row management had a greater influence on predator catches than fertilizer treatment. Total predator catches were lower under the mulch. Mulching also reduced carabid abundance, but increased staphylinid catches.
4 Tree row management also had a significant effect on biodiversity parameters. Species richness did not significantly differ among treatments for ants, spiders or the total catches, but was higher on herbicide-treated plots for carabids and on mulched plots for staphylinids. Shannon–Wiener's diversity index was significantly greater in the mulched and herbicide treated plots for total predators and carabids. For staphylinids, this index was significantly greater on the mulched plots. Fertilizer application strategy only influenced the species richness of rove beetles, which was greater in the chemically-treated plots.
5 The results showed that a change from conventional to organic fertilizer treatment of apple trees may be performed without differential effects on predator activity-density or biodiversity. However, a change from herbicide treatment to mulching or mechanical weed control may be significant, depending on the taxonomic group.     

Species diversity in spatial and temporal dimensions of fruit-feeding butterflies from two Ecuadorian rainforests

To test the hypotheses that butterflies in an intact lowland rainforest are randomly distributed in space and time, a guild of nymphalid butterflies was sampled at monthly intervals for one year by trapping 883 individuals of 91 species in the canopy and understory of four contiguous, intact forest plots and one naturally occurring lake edge. The overall species abundance distribution was well described by a log-normal distribution. Total species diversity (γ-diversity) was partitioned into additive components within and among community subdivisions (α-diversity and β-diversity) in vertical, horizontal and temporal dimensions. Although community subdivisions showed high similarity (l-β-diversity/γ-diversity), significant β-diversity existed in each dimension. Individual abundance and observed species richness were lower in the canopy man in the understory, but rarefaction analysis suggested that the underlying species richness was similar in both canopy and understory. Observed species richness varied among four contiguous forest plots, and was lowest in the lake edge plot. Rarefaction and species accumulation curves showed that one forest plot and the lake edge had significantly lower species richness than other forest plots. Within any given month, only a small fraction of total sample species richness was represented by a single plot and height (canopy or understory). Comparison of this study to a similar one done in disturbed forest showed diat butterfly diversity at a naturally occurring lake edge differed strongly from a pasture-forest edge. Further comparison showed that species abundance distributions from intact and disturbed forest areas had variances that differed significandy, suggesting mat in addition to extrapolation, rarefaction and species accumulation techniques, the shapes of species abundance distributions are fundamental to assessing diversity among sites. This study shows the necessity for long-term sampling of diverse communities in space and time to assess tropical insect diversity among different areas, and the need of such studies is discussed in relation to tropical ecology and quick surveys in conservation biology.     

Microclimate and tree community linked to differences in lepidopteran larval communities between forest fragments and continuous forest

Aim  We aim to assess the impact of forest fragmentation on lepidopteran larval community and study the associations of microclimate and tree community with lepidopteran assemblage.
Location  Kibale National Park, Uganda.
Methods  We investigated the effects of forest fragmentation on leaf herbivory, density of lepidopteran caterpillars, species richness and diversity as well as the composition of herbivorous lepidopteran larval community. Microclimate, size of the fragment, distance to the continuous forest, and tree diversity were studied as possible explanatory factors. We sampled 10 Neoboutonia macrocalyx Pax. (Euphorbiaceae) trees in each fragment during dry and rainy season, total of four times, in a year to cover the seasonal variation.
Results  The rates of herbivory, total larval density and species richness were significantly lower in the forest fragments than in the continuous forest but species diversity expressed as Fisher's alpha did not differ. The dominance structure and community composition of the larval communities in the fragments was different from that of the continuous forest. None of the differences we observed were related to the fragment area or distance to the continuous forest. Instead, we found an indication of association between the herbivore and the tree communities. The fragments had significantly lower humidity during most of the day and higher temperature during the afternoons (14–17 h), which might partially explain the differences in lepidopteran larval communities.
Main conclusions  Decreased larval density and species richness as well as differences in the community composition and structure all highlight the importance of large continuous forest areas for maintaining larval biodiversity.     

施肥和放牧对青藏高原高寒草甸物种丰富度的影响

在草地生态系统中, 施肥通常会导致生物多样性下降, 但是关于引起生物多样性下降的机制还存在着很大的争议。该研究基于一个4年的施肥实验, 试图通过个体大小的不整齐性和单位植物氮含量, 定性地揭示青藏高原东部高寒草甸施肥后多样性下降的原因。研究显示: 在封育地, 施肥致使个体大小不整齐性增加了15%, 并不同程度地增加了物种的高度。同时, 施肥使物种间单位植物氮含量存在显著差异的数目降低了65%。施肥后光竞争加剧, 导致大个体植物排斥小个体植物, 进而引起了物种丰富度下降29.6%。与封育地不同, 放牧地施肥并没有改变个体大小不整齐性和物种的高度, 而是使物种间单位植物氮含量存在显著差异的数目增加了11.4%。施肥并没有改变放牧地的光竞争强度, 而是增加了物种间对土壤营养元素氮的竞争强度, 进而引起了物种丰富度下降17.3%。该研究还发现, 放牧施肥地的物种丰富度下降速度和等级显著低于封育施肥地的物种丰富度下降速度和等级, 这表明放牧减缓了施肥对物种丰富度的影响力。     

Terrestrial isopod diversity in the wadi Moula‐Bouterfess catchment area (Kroumirie,north‐west of Tunisia)

We assessed the diversity of terrestrial isopods according to habitat and altitude in the wadi of Moula‐Bouterfess catchment area. The most representative habitat types for the area were selected within altitudinal range from 6 to 550 m a.s.l. In total nine sites were sampled: four with maquis and garrigue vegetation, one at a meadow and four sites with forest vegetation. In each sampled habitat, individuals were collected by hand in April 2005 using 30 replicates of a quadrate of 0.5 × 0.5 m. During the study, 582 individuals belonging to 11 terrestrial isopod species from five families were collected. Among these, three species were newly mentioned in Tunisia. The genus Armadillidium was the most abundant genus (60% of the total number of collected specimens) and P. variabilis was the most common species as it was sampled in eight of the nine studied habitats. Terrestrial isopod community structure differs among the nine sampling habitats. Abundance and species richness values are low in the different studied habitats. The Shannon–Wiener H′ varied from 0.67 to 2.06. The Canonical Correspondence Analysis (CCA) applied to our data showed that the majority of terrestrial isopod species seem to be more sensitive to vegetal associations than to altitude. No relationship was found between species richness/diversity (Shannon–Wiener index H’) and altitude. The studied sites were separated into open and closed areas based on the Bray–Curtis index for similarity.     

Community-based processes behind species richness gradients: contrasting abundance–extinction dynamics and sampling effects in areas of low and high productivity

Aim  To consider the role of local colonization and extinction rates in explaining the generation and maintenance of species richness gradients at the regional scale.
Location  A Mediterranean biome (oak forests, deciduous forests, shrublands, pinewoods, firwoods, alpine heathlands, crops) in Catalonia, Spain.
Methods  We analysed the relative importance of direct and indirect effects of community size in explaining species richness gradients. Direct sampling effects of community size on species richness are predicted by Hubbell's neutral theory of biodiversity and biogeography. The greater the number of individuals in a locality, the greater the number of species expected by random direct sampling effects. Indirect effects are predicted by the abundance–extinction hypothesis, which states that in more productive sites increased population densities and reduced extinction rates may lead to high species richness. The study system was an altitudinal gradient of forest bird species richness.
Results  We found significant support for the existence of both direct and indirect effects of community size in species richness. Thus, both the neutral and the abundance–extinction hypotheses were supported for the altitudinal species richness gradient of forest birds in Catalonia. However, these mechanisms seem to drive variation in species richness only in low-productivity areas; in high-productivity areas, species richness was uncorrelated with community size and productivity measures.
Main conclusions  Our results support the existence of a geographical mosaic of community-based processes behind species richness gradients, with contrasting abundance–extinction dynamics and sampling effects in areas of low and high productivity.     

Response of grassland soil arthropod community to biological and conventional control of a native moth: using Beauveria bassiana and lambda-cyhalothrin for Dalaca pallens (Lepidoptera: Hepialidae) suppression

Conventional and biological control of a native moth, Dalaca pallens (Blanchard) (Lepidoptera: Hepialidae), were evaluated in Southern Chile in relation to changes on community metrics (diversity, species richness, evenness and dominance) of a soil-dwelling invertebrate assemblage. Two experiments were conducted (in winter and spring) to compare non-target effects of Beauveria bassiana (Balsamo) Vuillemin and lambda-cyhalothrin insecticide. The invertebrate community was sampled before and after spraying by extracting soil cores. Estimates of diversity (Shannon index), species richness, evenness (Hurlbert’s Probability of Interspecific Encounter) and dominance indicated that the invertebrate assemblage was strongly disturbed by lambda-cyhalothrin treatment but not by B. bassiana applied in winter, over the sampling period (40 days). Spring results revealed that diversity and evenness at control and at B. bassiana plots were similar between them and higher than at lambda-cyhalothrin plots, while there were no differences between sites 30 days after treatment in species richness. Inundative biological control using B. bassiana strain QU-B931 was considered to pose lower ecological risk than lambda-cyhalothrin, currently one of the most frequently used insecticides for D. pallens control.     

Recovery of Bird Species in Minimally Restored Indonesian Tin Strip Mines

Bird species richness and individual abundances were recorded in old, unrestored tin strip mine plots, in mined plots restored 1, 2, and 3 years before the study, and in adjacent, unmined, natural secondary forest plots on the 11,340‐km² Indonesian island of Bangka (2°S, 106°E). The objective was to assess the ecological recovery of unrestored and minimally restored mine plots compared with surrounding reference forest. Unrestored mines had not been mined or used for any other purpose for 14–30 years; plots in their first, second, and third year since restoration were old mines planted with Acacia mangium (Leguminosae) at a density of 400 trees/ha. Natural secondary forest plots 20 or more years since the last disturbance were immediately adjacent to both unrestored and restored plots. Bird surveys on 4‐ha plots were performed during the 1995 breeding season. A comparison of data from unrestored plots of widely varying ages showed no significant differences among them for species richness, diversity (Shannon–Wiener index, H′), or individual abundance, indicating that little natural bird community recovery had occurred over time in the plots. However, increases did occur in restored sites over only 3 years for both species richness (r ² = 0.29, p = 0.04) and diversity (r ² = 0.45, p = 0.009). All values for third‐year restored plots, however, were still significantly lower than corresponding values for adjacent natural secondary forest plots. The quick return of bird activity on the plots after minimal efforts at restoration supports the idea that simple, inexpensive restoration can be effective for “jump starting” degraded systems at large scales. Such a restoration strategy might be of particular value for degraded land in developing nations, where scientific, professional, and financial resources might be in short supply. Using this strategy, a small number of restoration professionals could mobilize the labor of many local people in many areas, serving to both improve ecological systems and to educate and engage local populations in restoration and conservation projects.     

Bias in vegetation databases? A comparison of stratified‐random and preferential sampling

Aim: Vegetation plots collected since the early 20th century and stored in large vegetation databases are an important source of ecological information. These databases are used for analyses of vegetation diversity and estimation of vegetation parameters, however such analyses can be biased due to preferential sampling of the original data. In contrast, modern vegetation survey increasingly uses stratified‐random instead of preferential sampling. To explore how these two sampling schemes affect vegetation analyses, we compare parameters of vegetation diversity based on preferentially sampled plots from a large vegetation database with those based on stratified‐random sampling. Location: Moravian Karst and Silesia, Czech Republic. Methods: We compared two parallel analyses of forest vegetation, one based on preferentially sampled plots taken from a national vegetation database and the other on plots sampled in the field according to a stratified‐random design. We repeated this comparison for two different regions in the Czech Republic. We focussed on vegetation properties commonly analysed using data from large vegetation databases, including alpha (within‐plot) diversity, cover and participation of different species groups, such as endangered and alien species within plots, total species richness of data sets, beta diversity and ordination patterns. Results: The preferentially sampled data sets obtained from the database contained more endangered species and had higher beta diversity, whereas estimates of alpha diversity and representation of alien species were not consistently different between preferentially and stratified‐randomly sampled data sets. In ordinations, plots from the preferential samples tended to be more common at margins of plot scatters. Conclusions: Vegetation data stored in large databases are influenced by researcher subjectivity in plot positioning, but we demonstrated that not all of their properties necessarily differ from data sets obtained by stratified‐random sampling. This indicates the value of vegetation databases for use in biodiversity studies; however, some analyses based on these databases are clearly biased and their results must be interpreted with caution.     

Parasite species richness in carnivores: effects of host body mass, latitude, geographical range and population density

Aim  Comparative studies have revealed strong links between ecological factors and the number of parasite species harboured by different hosts, but studies of different taxonomic host groups have produced inconsistent results. As a step towards understanding the general patterns of parasite species richness, we present results from a new comprehensive data base of over 7000 host–parasite combinations representing 146 species of carnivores (Mammalia: Carnivora) and 980 species of parasites.
Methods  We used both phylogenetic and non-phylogenetic comparative methods while controlling for unequal sampling effort within a multivariate framework to ascertain the main determinants of parasite species richness in carnivores.
Results  We found that body mass, population density, geographical range size and distance from the equator are correlated with overall parasite species richness in fissiped carnivores. When parasites are classified by transmission mode, body mass and home range area are the main determinants of the richness of parasites spread by close contact between hosts, and population density, geographical range size and distance from the equator account for the diversity of parasites that are not dependent on close contact. For generalist parasites, population density, geographical range size and latitude are the primary predictors of parasite species richness. We found no significant ecological correlates for the richness of specialist or vector-borne parasites.
Main conclusions  Although we found that parasite species richness increases instead of decreases with distance from the equator, other comparative patterns in carnivores support previous findings in primates, suggesting that similar ecological factors operate in both these independent evolutionary lineages.     

浑善达克沙地不同微地形的土壤物理性质和草本群落分布及其相关性分析

采用样方调查和室内检测相结合法对内蒙古浑善达克沙地迎风坡、坡顶、背风坡和丘间地不同土层(0~10、10~20和20~40 cm)的土壤物理性质(包括含水量、田间持水量、容重、总孔隙度和毛管孔隙度)及草本群落的生产力(包括盖度和地上部生物量)和物种多样性(包括Margalef丰富度指数、Simpson多样性指数、Shannon-Wiener多样性指数和Pielou均匀度指数)进行比较分析;在此基础上,采用Pearson相关性分析法对不同微地形的土壤物理性质与草本群落各指标间以及草本群落生产力与物种多样性各指标间的相关性进行分析.结果表明:4种微地形的土壤物理性质总体上差异显著,但不同土层的土壤物理性质总体上无明显差异;从丘间地、背风坡、坡顶到迎风坡,土壤的含水量、田间持水量、总孔隙度和毛管孔隙度依次递减,而土壤容重则依次递增,说明迎风坡的土壤结构较差且水分散失较多,而丘间地的土壤结构和水分状况均相对较好.不同微地形间草本群落生产力和物种多样性总体上也存在明显差异,从背风坡、丘间地、坡顶到迎风坡,草本群落的生产力和物种多样性依次递减,仅Margalef丰富度指数表现为在丘间地最高、在迎风坡最低,说明迎风坡的草本群落物种多样性较低,群落稳定性差,而背风坡和丘间地的草本群落物种多样性和生产力水平均较高,群落稳定性较好.相关性分析结果表明:该区域的草本群落生产力和物种多样性与土壤容重呈负相关,与土壤的其他物理性状呈正相关,但仅部分指标间有显著或极显著相关性;草本群落生产力与物种多样性各指标间呈正相关,但多数指标间的相关性并不显著.研究结果显示:微地形能够显著影响浑善达克沙地的土壤物理性质和草本群落的分布特征,气候和人为干扰使该沙地的土壤物理性质受到严重破坏,导致草本群落生产力降低并处于不稳定状态.     

海南五指山热带山地雨林植物物种多样性研究

王指山热带山地雨林的物种种类十分丰富,在１ｈｍ＾２样地中共出现５４个科,１００个属的乔木树种１７７种,１３３７个个体。区系地理分析表明属的分布区类型以热带分布型成分占优,为８９．０％,充分体现了五指山山地雨林的热带性质。多样性指数分析结果为：样地１Ｍａｒｇａｌｅｆ指数１７．８２２,Ｓｈａｎｎｏｎ－Ｗｉｅｎｅｒ指数５．６２１,均匀度０．８２３,Ｓｉｍｐｓｏｎ指数０．０５０,均匀度６．７７５,表明五指     

Species diversity in vertical, horizontal, and temporal dimensions of a fruit-feeding butterfly community in an Ecuadorian rainforest

To test the hypotheses that fruit-feeding nymphalid butterflies are randomly distributed in space and time, a community of fruit-feeding nymphalid butterflies was sampled at monthly intervals for one year by trapping 6690 individuals of 130 species in the canopy and understory of four forest habitats: primary, higraded, secondary, and edge. The overall species abundance distribution was well described by a lognormal distribution. Total species diversity (γ-diversity) was partitioned into additive components within and among community subdivisions (α-diversity and β-diversity) in vertical, horizontal and temporal dimensions. Although community subdivisions showed high similarity (1 —β-diversity/γ-diversity), significant β-diversity existed in each dimension. Individual abundance and observed species richness was lower in the canopy than in the understory. However, rarefaction analysis and species accumulation curves revealed that canopy had higher species richness than understory. Observed species richness was roughly equal in all habitats, but individual abundance was much greater in edge, largely due to a single, specialist species. Rarefaction analysis and species accumulation curves showed that edge had significantly lower species richness than all other habitats. Samples from a single habitat, height and time contained only a small fraction of the total community species richness. This study demonstrates the feasibility, and necessity, of large-scale, long-term sampling in multiple dimensions for accurately measuring species richness and diversity in tropical forest communities. We discuss the importance of such studies in conservation biology.     

贵州省典型汞铊矿区周边农田土壤跳虫群落特征

大量的采矿活动导致矿区周边土壤重金属污染, 严重危害土壤生物安全。汞、铊等重金属元素毒性强, 相关污染的土壤生态风险鲜有研究。跳虫作为土壤环境变化指示生物, 能很好地反映土壤质量的健康状况。本研究以贵州省某汞铊矿区周边的农田土壤为研究对象, 按离矿区距离和作物类型设置4个采样区, 每个采样区种植2种作物, 每种作物农田设置3个样方。研究土壤跳虫群落结构和多样性及其影响因子。结果表明, 调查区内跳虫平均密度为12,000 ind./m²; 采样区距离矿区越近, 土壤重金属污染程度越大, 综合污染指数越高, 跳虫种数、密度、多样性和丰富度指数均呈先增加再降低的趋势; 环境因子分析表明重金属显著影响跳虫群落结构: Folsomides americanus、Isotomiella minor和Protaphorura encarpatus数量与汞、铊和砷含量呈负相关。高有机质含量能缓解重金属对土壤跳虫的影响, 但作物类型(玉米与薏仁)对土壤跳虫群落结构的影响无显著差异。本研究结果表明土壤有机质或能反向调节重金属污染对土壤跳虫群落的影响。     

Effects of additional illumination and fertilization on seasonal changes in fine-scale grassland community structure

Abstract. Fine-scale structure of a species-rich grassland was examined for seasonal changes caused by manipulated changes in the availability of above and below-ground resources (additional illumination with the help of mirrors and fertilization) in a field experiment. If changes induced by fertilization — which are expected to lead to a reduction in small-scale diversity —are due to intensified light competition, they should be compensated for by additional light input. Permanent plots of 40 cm × 40 cm were sampled by the point quadrat method at three angles (60°, 90° and 120° from the horizontal North-South direction), using a laser beam to position the quadrats, in early July and early September. The applied treatments did not cause apparent changes in plant leaf orientation. The degree of spatial aggregation of biomass increased seasonally in fertilized, non-illuminated plots: greater productivity at a constant light supply led to a faster growth rate of potentially dominant species, as compared to the subordinate ones. Additional illumination mitigated this effect of fertilization, indicating that the observed changes in biomass aggregation were due to increased light competition. There was a considerable seasonal decrease of variance ratio (ratio of observed variance of richness at a point and variance expected at random) in fertilized only and in illuminated only plots. In fertilized plots this was due to the positive relationship between biomass aggregation and expected variance of richness. Biomass constancy occurs to be inversely related to deficit in variance of richness. In illuminated plots, in contrast, only the observed variance of richness decreased seasonally, indicating a more uniform use of space by different species. Evidently, a deficit in variance of richness can be caused by drastically different processes, showing that the variance ratio statistic may not have a significant explanatory value in fine-scale community studies.