Plant species diversity and tree population structure of a humid tropical forest in Tamil Nadu, India

Vegetation structure and species composition of tropical ecosystems were studied through nine transects at Veerapuli and Kalamalai reserve forests in the Western Ghats of Tamil Nadu, India. Species diversity, dominance, species richness and evenness indices of plant communities and also population structure of woody plants were enumerated. A total of 244 species (183 genera and 76 families) were recorded. Species richness (number of species) were 82,142 and 96 species per 0.3 ha respectively for the study areas of low-elevation forest (LEF), mid-elevation forest (MEF) and high elevation forest (HEF). Species diversity indices were greater in MEF compared to the other two forests except juveniles. In contrast, greater dominance value indices were recorded in LEF than other forests. Density and basal area of the MEF were twice greater than the LEF, while HEF showed greater tree density and low basal area when compared to LEF. The stem density and species richness (number of species) decreased with increased size classes of trees observed in the present study indicated good regeneration status. Population structure of juveniles and seedlings also reflects good regeneration status. Terminalia paniculata (IVI of 99.9) and Hopea parviflora (IVI of 103.8) were dominant tree species respectively in LEF and MEF whereas in HEF Agrostistachys meeboldii (63.65), Cullenia excelsa (63.67) and Drypetes oblongifolia (39.67) share the dominance. Past damage (anthropogenic perturbation) may be one of the reasons for single species dominance in LEF and MEF. Occurrence of alien species such as Eupatorium odoratum and Ageratum conyzoides also indicated the past disturbance in LEF. The variations in plant diversity and population structure are largely due to anthropogenic perturbation and other abiotic factors.     

Patterns of planktonic foraminiferal abundance and diversity in surface sediments of the western North Atlantic

Seventy-two core tops and grab samples from the western North Atlantic were analyzed to determine what aspects of planktonic foraminiferal abundance and diversity are most closely related to ocean circulation. Some species appear to be reliable indicators of the Gulf Stream, a warm surface current. Both Globorotalia menardii and Globigerinoides sacculifer have their highest abundances under the main trend of the Gulf Stream. Globorotalia inflata reaches high abundances in the cold slope water north of the Gulf Stream but its distribution is not as continuous as the Gulf Stream indicators.Contoured values of species diversity, the Shannon diversity index, and species equitability also reflect surface circulation. A plot of species diversity (number of species) shows a poorly defined region of high diversity beneath the major trend of the Gulf Stream. Use of the Shannon diversity index enhances and clarifies this region of high diversity. A map of species equitability shows a broad belt of low species dominance (high equitability) beneath the Gulf Stream. North of the Gulf Stream, a tongue of high dominance (low equitability) corresponds to the increased relative abundance of Globorotalia inflata.High diversity of planktonic foraminifera in bottom sediments characterizes the warm shifting surface currents of the Gulf Stream; low diversity is typical of slope and Sargasso Sea waters. Low equitability (high species dominance) indicates either cold currents or gyre center waters. Maps of foraminiferal diversity and equitability for other intervals of geologic time may be useful in tracing the evolution of ocean circulation.     

陕西吴起县生态恢复区直翅目昆虫的多样性

应用多样性指数、主成分分析及多元逐步回归等方法,对陕西吴起县生态恢复区直翅目昆虫的群落结构,植被因素与直翅目昆虫群落特征的相关性进行研究。共获得标本1 155号,隶属于10科17属,共计20种。黄胫小车蝗Oedaleus infernalis Saussure,宽翅曲背蝗Pararcyptera microptera meridionalis,短星翅蝗Calliptamus abbreviatusIkonn分别占总数量的17.58%,15.15%和14.89%,共同构成该地区直翅目昆虫的优势类群。多样性的变化趋势是县城>白豹>周湾>王洼。对各生境植被因素和直翅目昆虫群落所进行的主成分分析,两维主成分的累计方差贡献率分别达到了95.299%和86.304%。影响直翅目昆虫种类和数量变化的植被因素有草本植物高度多样性、草本植物种数、菊科优势度、禾本科优势度、其他科优势度。     

Disturbance effects on plant community diversity: spatial scales and dominance hierarchies

It is proposed that evaluations of disturbance effects upon community diversity will be influenced by two factors currently overlooked in models addressing disturbance-diversity relationships: (1) the spatial scale of inquiry, and (2) the level of the species abundance (dominance) hierarchy at which the search for diversity is done. We analyzed how two disturbance types—cattle grazing and large flooding—affected community diversity at two spatial scales (stand and patch) and three levels of species dominance in a grassland of the Flooding Pampa, Argentina. The effect of disturbance interaction was also examined. Species diversity at the stand scale was reduced by either grazing or flooding. Both disturbances decreased community spatial heterogeneity. At the patch scale, diversity declined with flooding but was enhanced by grazing. Flooding increased diversity under grazing conditions. However, stand diversity was highest in the undisturbed grassland; pattern diversity was the salient feature in this condition. The combination of disturbances yielded the highest patch-scale diversity; grazing increased richness whilst flooding enhanced evenness. Comparisons among grassland conditions appeared scale-dependent. Moreover the extent of disturbance effects varied with the level of dominance hierarchy considered. We point out the relevance of site history and initial conditions, encompassing the possibility of disturbances interaction, to the patters produced by disturbance events. Effects perceived at different spatial scales, or in species positioned at separate dominance levels, may parallel meaningful changes in the relative importance of factors controlling species coexistence and community organization.     

Allelopathy prevents competitive exclusion and promotes phytoplankton biodiversity

It has been hypothesized that allelopathy can prevent competitive exclusion and promote phytoplankton diversity in aquatic ecosystems, where numerous species coexist on a limited number of resources. However, experimental proof‐of‐principle is not available to support this hypothesis. Here we present the first experimental evidence to support this hypothesis by demonstrating that allelopathy promotes the coexistence of two phytoplankton species, Ankistrodesmus falcatus and Oscillatoria sp., that compete for a single limiting nutrient. By performing long‐term competition experiments in nitrate‐limited continuous cultures, and by describing the population dynamics using a mechanistic model, we demonstrate that when allelopathy comes into play, one of the following outcomes is possible depending on the relative initial abundances of the species: dominance of the stronger competitor for nitrate (the non‐allelopathic species), oscillatory coexistence, or dominance of the weaker competitor (the allelopathic species). Our model analysis revealed that sustained oscillatory coexistence of the two species would be a common outcome of this experiment. Our study confirms for the first time, based on laboratory experiments combined with mechanistic models, that allelopathy can alter the predicted outcome of inter‐specific competition in a nutrient‐limited environment and increase the potential for the coexistence of more species than resources, thereby contributing to the identification of endogenous mechanisms that explain the extreme diversity of phytoplankton communities.     

鸡公山自然保护区蝶类多样性及其影响因素

2019年4-10月,在鸡公山自然保护区的核心区和实验区内不同生境、不同人为干扰程度的区域选取6条样线,对蝶类群落进行了观测研究.共记录蝴蝶3431头,隶属于10科79属127种;其中蛱蝶科Nymphalidae的种类数最多,共23属36种;粉蝶科Pieridae和灰蝶科Lycaenidae为保护区优势科,菜粉蝶Pie...     

Average seasonal phytomass: a temporally independent index of herbaceous plant dominance

Diversity, similarity and dominance in plant communities are usually assessed from data collected at a single date. Herbaceous species have differing periods of growth, making phytomass or cover-weighted indices of diversity, similarity or dominance highly dependent on the timing of data collection. A new way of mathematically expressing residence time is presented. Average seasonal phytomass values can be used to better express dominance throughout a growing season. A similar approach could be used for cover or any other dynamic property of plant growth. These values could then be used in dominance-weighted indices of community similarity and diversity. Acknowledgements: J. Watkins-Williams assisted in the field and laboratory. R. L. Bayn, Jr. assisted in data processing. This study was supported in part by Grant DEB-78-05328 from the National Science Foundation to J. A. MacMahon.     

Mechanisms linking diversity,productivity and invasibility in experimental bacterial communities

Decreasing species diversity is thought to both reduce community productivity and increase invasibility to other species. However, it remains unclear whether identical mechanisms drive both diversity-productivity and diversity-invasibility relationships. We found a positive diversity-productivity relationship and negative diversity-invasibility and productivity-invasibility relationships using microcosm communities constructed from spatial niche specialist genotypes of the bacterium Pseudomonas fluorescens. The primary mechanism driving these relationships was a dominance (or selection) effect: more diverse communities were more likely to contain the most productive and least invasible type. Statistical elimination of the dominance effect greatly weakened the diversity-invasibility relationship and eliminated the diversity-productivity relationship, but also revealed the operation of additional mechanisms (niche complementarity, positive and negative interactions) for particular combinations of niche specialists. However, these mechanisms differed for invasibility and productivity responses, resulting in the invasibility-productivity relationship changing from strongly negative to weakly positive. In the absence of the dominance effect, which may be an experimental artefact, decreasing diversity can have unexpected or no effects on ecosystem properties.     

新疆农田系统瓢虫资源调查与多样性研究

为全面了解新疆农田系统瓢虫资源组成以及多样性结构差异,本研究采用网捕法于2018年、2019年连续两年对新疆11个地州50个县/市/区15种农作物生境的406个采集点开展了瓢虫资源系统调查.结果表明:共获7001号瓢虫标本,隶属3亚科13属26种,其中多异瓢虫Hippodamia variegata为绝对优势种类,其个...     

Species richness and evenness respond in a different manner to propagule density in developing prairie microcosm communities

Diversity has two basic components: richness, or number of species in a given area, and evenness, or how relative abundance or biomass is distributed among species. Previously, we found that richness and evenness can be negatively related across plant communities and that evenness can account for more variation in Shannon’s diversity index (H′) than richness, which suggests that relationships among diversity components can be complex. Non-positive relationships between evenness and richness could arise due to the effects of migration rate or local species interactions, and relationships could vary depending on how these two processes structure local communities. Here we test whether diversity components are equally or differentially affected over time by changes in seed density (and associated effects on established plant density and competition) in greenhouse communities during the very early stages of community establishment. In our greenhouse experiment, we seeded prairie microcosms filled with bare field soil at three densities with draws from a mix of 22 grass and forb species to test if increased competition intensity or seedling density would affect the relationships among diversity components during early community establishment. Increased seed density treatments caused diversity components to respond in a different manner and to have different relationships with time. Richness increased linearly with seed density early in the experiment when seedling emergence was high, but was unrelated to density later in the experiment. Evenness decreased log-linearly with seed densities on all sampling dates due to a greater dominance by Rudbeckia hirta with higher densities. Early in the experiment, diversity indices weakly reflected differences in richness, but later, after the competitive effects of Rudbeckia hirta became more intense, diversity indices more strongly reflected differences in evenness. This suggests that species evenness and diversity indices do not always positively covary with richness. Based on these results, we suggest that evenness and richness can be influenced by different processes, with richness being more influenced by the number of emerging seedlings and evenness more by species interactions like competition. These results suggest that both diversity components should be measured in plant diversity studies whenever it is possible.     

Tree Diversity Explains Variation in Ecosystem Function in a Neotropical Forest in Panama

Many experimental studies show that a decline in species number has a negative effect on ecosystem function, however less is known about this pattern in natural communities. We examined the relative importance of environment, space, and diversity on ecosystem function, specifically tree carbon storage in four plant types (understory/canopy; trees/palms), in a tropical forest in central Panama. The objectives of this study were to detect the relationship between tree diversity and carbon storage given the environmental and spatial variation that occur in natural forests and to determine which species diversity measure is more important to tree carbon storage: richness or dominance. We used redundancy analyses to partition the effect of these sources of variation on tree carbon storage. We showed that together, environment, space, and diversity accounted for 43 percent of tree carbon storage, where diversity (19%) alone is the most important source of variation and explained more variation than space (13%) and environment (1%) together. Therefore, even in natural forests where substantial environment and spatial variation can be found, it is still possible to detect the effect of diversity on ecosystem function at scales relevant to conservation. Moreover, both richness and dominance are important to explain the variation on tree carbon storage in natural forests suggesting that these two diversity measures are complementary. Thus, tree diversity is important to predict tree carbon storage in hyperdiverse forests.     

Density compensation can cause no effect of biodiversity on ecosystem functioning

The role of density compensation (the decline of species density with increasing diversity), in the context of biodiversity and ecosystem functioning, has not been explicitly explored. I used aquatic microbial communities containing bacterivorous consumers (protozoans and rotifers) to investigate whether competition can lead to density compensation and whether density compensation can contribute to the relationship between biodiversity and ecosystem functioning. The experiment employed a nested design in which the consumer diversity gradient (0, 1, 2 or 4 species) was constructed by drawing all possible species or species combinations at each diversity level from a five-species pool. All consumer species coexisted but there was little evidence for overyielding or species dominance, suggesting weak complementarity and sampling effects. Rather, increasing number of consumer species resulted in community-wide density compensation, such that aggregate consumer biomass was unaffected by consumer diversity. Whereas culturable bacterial density declined as consumer diversity increased, total bacterial density showed no discernible response to changes in consumer diversity, a result probably due in part to heterogeneity in bacterial edibility. This study demonstrates the potential for density compensation to shape the relationship between biodiversity and ecosystem functioning.     

A heatwave increases turnover and regional dominance in microbenthic metacommunities

While the effect of the global biodiversity crisis on local species loss is still debated, there is empirical evidence for major changes in local biodiversity attributed to increased species turnover. In communities exposed to a climate stressor, species turnover can lead to increased dominance of well-adapted species and consequently to an overall decline in species diversity. Despite the known importance of species turnover for community dynamics and functioning, experimental results on the connection between biodiversity loss and species turnover are scarce. We still do not fully understand which specific factors increase the rate of change in species composition, especially when considering natural compared to artificially lab assembled communities. In the present study, we experimentally tested whether a heatwave and dispersal increased species turnover and decreased species diversity in natural benthic diatom communities with different initial species compositions. We found that on the local scale, dispersal had overall positive effects on species richness while the relationship between exposure to the heatwave, species turnover, and diversity depended on initial community composition. However, on the regional (i.e. metacommunity) scale, exposure to the heatwave and dispersal both increased turnover and decreased Shannon diversity by almost 50%. Turnover in these metacommunities was not caused by a loss of species, but rather by a change in dominance patterns leading to homogenization, and consequently decreased diversity. Our study shows that climate change can destabilize community composition and degrade species diversity, but still after ca. 15 generations does not decrease the number of species in the community, demonstrating that the response of species diversity and richness to changing conditions can be fundamentally decoupled on ecological time scales.     

Dominance–diversity relationships in ant communities differ with invasion

The relationship between levels of dominance and species richness is highly contentious, especially in ant communities. The dominance‐impoverishment rule states that high levels of dominance only occur in species‐poor communities, but there appear to be many cases of high levels of dominance in highly diverse communities. The extent to which dominant species limit local richness through competitive exclusion remains unclear, but such exclusion appears more apparent for non‐native rather than native dominant species. Here we perform the first global analysis of the relationship between behavioral dominance and species richness. We used data from 1,293 local assemblages of ground‐dwelling ants distributed across five continents to document the generality of the dominance‐impoverishment rule, and to identify the biotic and abiotic conditions under which it does and does not apply. We found that the behavioral dominance–diversity relationship varies greatly, and depends on whether dominant species are native or non‐native, whether dominance is considered as occurrence or relative abundance, and on variation in mean annual temperature. There were declines in diversity with increasing dominance in invaded communities, but diversity increased with increasing dominance in native communities. These patterns occur along the global temperature gradient. However, positive and negative relationships are strongest in the hottest sites. We also found that climate regulates the degree of behavioral dominance, but differently from how it shapes species richness. Our findings imply that, despite strong competitive interactions among ants, competitive exclusion is not a major driver of local richness in native ant communities. Although the dominance‐impoverishment rule applies to invaded communities, we propose an alternative dominance‐diversification rule for native communities.     

Species richness–decomposition relationships depend on species dominance

Human disturbances both decrease the number of species in ecosystems and change their relative abundances. Here we present field evidence demonstrating that shifts in species abundances can have effects on ecosystem functioning that are as great as those from shifts in species richness. We investigated spatial and temporal variability of leaf decomposition rates and community metrics of leaf‐eating invertebrates (shredders) in streams. The shredder community composition dramatically influenced the diversity–function relationship; decomposition was much higher for a given species richness at sites with high species dominance than at sites where dominance was low. Decomposition rates also markedly depended on the identity of the dominant species. Further, dominance effects on decomposition varied seasonally and the number of species required for maintaining decomposition increased with increasing evenness. These findings reveal important but less obvious aspects of the biodiversity–ecosystem functioning relationship.     

Invasion by mobile aquatic consumers enhances secondary production and increases top-down control of lower trophic levels

Increased biological diversity due to invasion by non-indigenous species (NIS) is a global phenomenon with potential effects on trophic interactions and ecosystem processes in the invaded habitat. We assessed the effects of resource availability and invasion of three non-indigenous invertebrate grazers (two crustaceans and a snail) on secondary production, relative dominance of NIS grazers and resource depletion in experimental freshwater mesocosms. The relative dominance of NIS grazers increased with increasing initial resource availability, although the effect was largest for one of the three species. The effect was due to the fact that all the included non-indigenous grazers were able to expand their populations quickly in response to resource addition. For the most dominating species, the increased grazer diversity due to invasion in turn resulted in higher production of grazer biomass and a more efficient depletion of the periphyton resource. The effect was largest at high initial resource availability, where NIS dominance was most pronounced. Our results show that an invasion-induced increase in species diversity can increase resource depletion and consequently production, but that the effect depends on identity of the introduced species. The results also suggest that properties of the recipient system, such as resource availability, can modulate ecosystem effects of NIS by affecting invader success and dominance.     

三工河流域琵琶柴群落特征与土壤因子的相关分析

琵琶柴(Reaumuria soongorica)是我国荒漠地区分布最广的地带性植被类型之一,对维系荒漠地区生态系统的稳定性具有重要作用。以三工河流域两个琵琶柴群落为对象,在2010年主要生长季节(6—10月),通过群落和土壤调查,采用土钻法、土柱法、地上收割法对两个琵琶柴群落的土壤性质、生物多样性、细根生物量、地上生物量、生物多样性与土壤性质的关系进行研究,结果表明:两个琵琶柴群落在冠幅、盖度、多度和物种多样性等方面均存在显著差异。在0—100 cm土壤层内,两个群落土壤电导率、pH值、容重、含水量存在显著差异。除土壤容重外,群落2各个土壤因子的值均大于群落1,并随土壤深度的增加表现出类似的趋势。两个群落物种多样性指数、地上生物量、细根生物量存在显著差异,从6月到10月呈现先下降再上升的趋势。由于7、8月群落1有大量夏雨型短命植物和类短命草本植物的出现,Shannon-Wiener多样性指数、Pielou均匀度指数急剧降低,Simpson指数表现出相反的变化趋势。群落2土壤电导率和pH值较高,草本植物鲜有出现,多样性指数和均匀度指数变化均较为平缓。两个群落的Sorenson相似性系数较低,群落差异明显。相关和回归分析表明土壤环境因子是导致两个琵琶柴群落特征、生物多样性和生物量不同的主要因素。较高的土壤含水量可以增加琵琶群落的生物多样性,较高的土壤容重抑制琵琶柴群落细根的生长,轻度的干旱胁迫促进地上生物量的积累,一定浓度的土壤pH值和土壤盐分可以促进琵琶柴群落细根的生长。     

科尔沁沙地植被恢复系列上群落演替与物种多样性的恢复动态

通过对科尔沁沙地植被恢复系列上不同阶段的群落取样,研究了植被恢复过程中群落物种组成、物种多样性的变化过程.在演替时间分别为1年、3年、5年、12年、20年和30年的群落中,物种丰富度分别为7、11、17、14、28和30种,而物种多样性指数分别为1.458 8、2.610 0、3.108 4、1.696 8、3.738 6、3.639 6.在生活型结构上,一年生植物的种类数量占绝对优势,但随着演替进展,多年生植物的种类数量增加且单种植物的优势度超过了一年生植物,表明多年生植物在群落功能维持中占据重要地位.随演替进展,来自不同科属的植物增加.藜科植物在演替过程中种类数量较为稳定,特别是在演替早期藜科植物占有很高的优势度.禾本科种类随演替进展不断增加,且在群落中的优势度逐渐上升.总体上,随演替进展群落种类组成与物种多样性增加,群落生态优势度下降,而均匀度增加,群落趋向稳定.     

Bamboo dominance reduces tree regeneration in a disturbed tropical forest

Human disturbance may change dominance hierarchies of plant communities, and may cause substantial changes in biotic environmental conditions if the new dominant species have properties that differ from the previous dominant species. We examined the effects of bamboos (Bambusa tulda and Cephalostachyum pergracile) and their litter on the overall woody seedling abundance, species richness and diversity in a mixed deciduous forest in northeastern Thailand. These bamboo species are gaining dominance after human disturbance. Our results show that seedling abundance and species richness were reduced by bamboo canopies. Seedling abundance and species diversity under bamboo canopies were affected by bamboo litter, whereas seedling abundance and species diversity outside bamboo canopies did not respond to the mixed-tree litter manipulation. Removal of bamboo litter increased seedling abundance and species diversity. However, bamboo litter addition did not affect seedling abundance or species diversity compared to either control or litter removal. This may indicate that the effect of natural amount of bamboo litter is as high as for litter addition in preventing seedling establishment by woody species and hence in minimizing resource competition. We conclude that undergrowth bamboos and their litter affect tree seedling regeneration differently from mixed-tree litter, causing changes in plant community composition and species diversity. Increased human disturbance, causing a shift in dominance structure of these forests, may result in a concomitant reduction in their overall woody species abundance, richness and diversity. Thus, management of bamboos by controlling their distribution in areas of high bamboo density can be an important forest restoration method.