The functional importance of rare and dominant species in a Neotropical forest bird community

Bird communities in Tropical forests have high rate of rare species, but only recently some studies suggested their disproportional role for the overall functional diversity. We investigated data from bird communities monitored annually using point counts over ten years in Iguassu National Park, that is a large and protected area in the southern portion of the Atlantic Forest in Brazil. We aimed (1) to determine the rare and dominant species in the community based on their abundance over time; (2) to evaluate the impact of each class of rarity on the overall functional volume of the community; (3) to investigate the pattern of occupancy of the trait space filled by each dominance class, and (4) to assess the disparity in functional trait composition between classes of rarity. We defined dominant, intermediate, and rare species in communities using cluster analysis and data of relative abundance of species in five sections of 1-km in the forest interior. The number of clusters was defined in accordance with the silhouette criterion measures of cohesion and separation that range from −1 to 1, with values > 0.5 indicating high-quality clusters. Among total 138 bird species recorded, 107 were rare, 26 intermediates, and 5 dominants. Our data corroborate a functional disproportional importance of rare bird species in the community considering the functional space (FRic), but functional dispersion (FDis) was not significantly different between the rare and intermediate species. In fact, there is a large overlap of the functional volume occupied by rare in relation to dominant/intermediate species. The niche space occupied by rare species covers most of the space occupied by intermediate and dominant species. The low representativeness of functional turnover indicates that few functions are unique to the classes of higher dominance. Our data suggest the importance of rare bird species to the overall functional diversity but also highlights the potential use of dominants/intermediates species as indicators to select important forests areas for conservation, as certain forest fragments. Through these most abundant species it would be possible to assess which functions are heaviest in abundance, becoming core functions, in the context of each independent forest fragment.     

Functional traits predict drought performance and distribution of Mediterranean woody species

Water availability is one of the key environmental factors that affect plant establishment and distribution. In many regions water availability will decline with climate change, exposing small seedlings to a greater likelihood of drought. In this study, 17 leaves, stem, root, and whole-plant traits of ten woody Mediterranean species were measured under favourable growing conditions and seedling drought survival was evaluated during a simulated dry-down episode. The aims of this study were: i) to assess drought survival of different species, ii) to analyse which functional traits predict drought survival time, and iii) to explain species distribution in the field, based on species drought survival and drought strategies. Drought survival time varied ten-fold across species, from 19 to 192 days. Across species, drought survival was positively related to the rooting depth per leaf area, i.e., the ability to acquire water from deeper soil layers while reducing transpiring leaf area. Drought survival time was negatively related to species ability to grow quickly, as indicated by high relative growth and net assimilation rates. Drought survival also explained species distribution in the field. It was found that species were sorted along a continuum, ranging between two contrasting species functional extremes based on functional traits and drought performance. One extreme consisted of acquisitive fast-growing deciduous species, with thin, soft metabolically active leaves, with high resource use and vulnerability to drought. The opposite extreme consisted of conservative slow-growing evergreen species with sclerophyllous leaves, deep roots, a low transpiring area, and low water use, resulting in high drought survival and drought tolerance. The results show that these drought strategies shape species distribution in this Mediterranean area.     

Ecological indicators and functional groups of copepod assemblages

Copepods are important ecological indicators of ecosystem functioning. In this study, we analyzed the structure of copepod assemblages and cross-shelf patterns based on functional traits and indicator value analysis. Copepod samples were collected from 54 stations distributed along the inner, middle, and outer continental shelves covering a wide geographical area (20,100 km²). Overall, 38 species were identified: 20 Calanoida, 14 Cyclopoida, and 4 Harpacticoida. Copepod density was the highest in the inner shelf profile, with richness and diversity being higher on the outer shelf close to the shelf break. The results suggest that there is a gradient of zooplankton distribution even on narrow (<50 km) continental shelves. The cluster analysis of the stations showed a tendency to form three groups largely corresponding to physical location. Two major functional groups were identified, sorted by spawning strategy. These were subdivided according to the trophic regime and feeding strategy. Temora turbinata (alien species), Clausocalanus furcatus, and Ditrichocorycaeus amazonicus (native species) were found to be ecological indicators. These species have different functional traits and distinct cross-shelf distributions, where the alien species dominates the turbid coastal waters, and C. furcatus is an indicator of outer-shelf waters. Thus, these species can be considered ecological indicators of the different continental shelf waters. The results indicate that it is necessary to understand the functional diversity and ecological indicators of copepods, considering their importance for the basis of marine food webs.     

The effect of diversity and spatial arrangement on biomass of agricultural cultivars and native plant species

Various spatial arrangements can be found within natural grassland plant populations and communities. In contrast, spatial arrangement diversity is typically not observed in agroecosystems. Little is known about the influence of spatial arrangement on the productivity and success of agricultural or native plants. Such information is of interest to farmers who want to increase yield and restorationists working with native ecosystems. Agricultural and native plants were planted in two-way mixtures that included combinations of cultivars, species, genera, or functional groups. Each combination was arranged as a random mixture within rows, alternating rows of the different genotypes or species, and as alternating pairs of rows. Aboveground biomass was determined for each mixture component and compared to monoculture controls. Though plot composition had the most consistent influence on aboveground biomass, spatial arrangement appeared to have some influence among agricultural cultivars. Whether native or agricultural, biomass was greater for mixtures containing both a grass and a legume.     

The response of Paracoccidioides spp. to nitrosative stress

Paracoccidioidomycosis (PCM) is an endemic disease in Latin America caused by species belonging to the genus Paracoccidioides. During infection, immune cells present a variety of defense mechanisms against pathogens. One of these defensive strategies is the production and release of nitric oxide (NO) and S-nitroso thiols (e.g., S-nitrosoglutathione, GSNO), which produce reactive nitrogen species (RNS). This results in damage to DNA and membranes, inhibition of respiration and inactivation of cellular enzymes. In response to nitrosative stress, human pathogenic fungi possess defense mechanisms to prevent the adverse effects of NO, which helps them survive during initial contact with the host immune system. To understand how Paracoccidioides spp. respond to nitrosative stress, we conducted this study to identify genes and proteins that might contribute to this response. The results of proteomic analysis demonstrated that nitrosative stress induced a reduction in the expression of proteins related to the mitochondrial electron transport chain. This hypothesis was supported by the reduced mitochondrial activity observed in the presence of GSNO. Additionally, lipids and branched chain amino acid metabolism enzymes were altered. The role played by enzymes acting in oxidative stress in the RNS response was remarkable. This interface among enzymes acting in both stress responses was confirmed by using a RNA approach to silence the ccp gene in Paracoccidioides. It was observed that mutants with low expression of the ccp gene were more sensitive to nitrosative stress.     

Community impacts of two invasive crabs: the interactive roles of density, prey recruitment, and indirect effects

Assessing the implications of species invasion for native communities requires determining whether effects of invaders are novel, or are redundant with effects of species that are already present. Using a pair of field experiments conducted over two successive years, we examined factors that influence community impacts of a recent predatory crab invader (Hemigrapsus sanguineus) and a previously established invasive crab (Carcinus maenas) on New England coasts. We demonstrate that effects of these species differ temporally with changes in the ambient prey community, and are influenced by density differences between the two species and by different strengths and types of indirect effects that each elicits. Our study highlights the importance of including bottom-up processes (i.e., prey recruitment) when examining the redundancy of consumers.     

Identifying functional species pool of planktonic protozoa for discriminating water quality status in marine ecosystems

It is cost-effective protocol to identify a functional species pool for marine bioassessment by removing redundant species from a raw dataset. The feasibility of functional species pool for discriminating water quality status was studied based on a dataset of 120 samples of ciliated protozoa. From the full 60-species dataset of the whole ciliate communities, a 35-species subset was identified as a functional species pool, the species number, abundance and biodiversity indices of which were significantly correlated with those of the full species dataset. The spatial pattern of the subset was significantly related to the changes in nutrients soluble reactive phosphates (SRP), nitrate/nitrite nitrogen (NO₃-N/NO₂-N) and ammonium nitrogen (NH₄-N). Four indices of the taxonomic diversity (Δ), taxonomic distinctness (Δ*), average in taxonomic distinctness (Δ⁺) and the variation in taxonomic distinctness (Λ⁺) based on this small species pool were significantly correlated with the changes of nutrients NO₃-N and/or (NH₄-N). The paired indices Δ⁺ and Λ⁺ showed a clear decreasing trend of departure from the expected taxonomic pattern. These findings suggest that the 35-species functional species subset may be used as a feasible functional surrogate of ciliated protozoan assemblages for community-based bioassessment in marine ecosystems.     

Structure of ground-foraging ant assemblages in relation to land-use change in the northwestern Mediterranean region

The abandonment by humans of marginal and less productive zones signifies an important change in land use in North Mediterranean agroecosystems. Human perturbations have led to a highly diversified landscape, with a mosaic made up of patches of land at different stages of succession, from cultivated fields to closed forest. Our aim here is to characterize ant assemblages and their functional groups in response to these land-use changes. This progressive abandonment results in an initial increase in ant richness and abundance, which can reach high levels if the succession proceeds as far as woodland. In terms of the ant functional groups, this land-use change implies: (1) the appearance of Subordinate Camponotini; (2) an increase in Generalized Myrmicinae, Cryptics and Cold-climate specialists in terms of ant species richness, overall abundance and, for Generalized Myrmicinae and Cryptics, an increase in abundance percentage; (3) a decrease in percentage abundance of Opportunists; (4) a progressive decrease in species richness as well as overall and percentage abundance of Hot-climate Specialists throughout the transformation from crops to woodlands; and (5) an initial increase of Dominant Dolichoderinae followed by a decrease in ant species richness, overall abundance and percentage abundance. Using the ant functional group approach for the clearly separate stages of the regeneration process is a promising method for comparing responses of ant communities to human land use.     

Functional group classification and target species selection for Yancheng Nature Reserve, China

Yancheng Nature Reserve in east China is of great importance to the protection of biodiversity. It is a principal refuge for Red-crowned Cranes (Grus japonensis) and many other rare species, an important station for migrant waterfowls in the Asian Pacific, and a captive breeding base for Milu (Elaphurus davidianus). However, since the late 1980s, serious losses of biodiversity have been emerging in the protected area. In this study, to value objectively and improve management of the Yancheng Nature Reserve, a new approach for conservation management is proposed by virtue of the theories of self-organizing systems, functional group classification and target species selection. According to this approach, biological components in Yancheng Nature Reserve are classified into 10 supporting functional groups, eight target functional groups and 11 subordinate functional groups. Eight target species were selected from those target functional groups, i.e., G. japonensis, E. davidianus, Hydropotes inermis, Larus saundersi, Centropus toulou, Felis bengalensis, Paradoxornis heudei, and Platalea minor. Past observations in Yancheng Nature Reserve illustrate that the new approach is feasible, and this new approach will also benefit the management of the nature reserve.     

The induction of oxidative stress in cervix carcinoma cells by levoglucosenone derived 4-S-salicyl derivative and (1–4)-S-thio-disaccharides. Part 4

(1–4)-S-thiodisaccharides were shown to kill various cancer cell lines, including cervix, lung, mammary-gland and colon by unknown mechanisms. Here we identified two actions of levoglucosenone derived (1–4)-S-thiodisaccharides against cervix cancer cells: induction of oxidative stress and DNA damage. In consequence, (1–4)-S-thiodisaccharides lowered the cellular GSH level and changed the expression profile of genes encoding key proteins involved with oxidative stress response. We also observed that (1–4)-S-thiodisaccharides induced DNA damage and interfered with the thioredoxin (Trx) system. Both actions, as induced by FPC6, were stronger when dihedral angles of sulfur bridge were set to 110°, 100° and 109°, clearly indicating differences when compared to FPC8. These findings demonstrate that the 1–4-thio bridge of disaccharide is a powerful anticancer pharmacophore, and its potential use needs further studies.     

Commonness,rarity, and intraspecific variation in traits and performance in tropical tree seedlings

One of the few rules in ecology is that communities are composed of many rare and few common species. Trait‐based investigations of abundance distributions have generally focused on species‐mean trait values with mixed success. Here, using large tropical tree seedling datasets in China and Puerto Rico, we take an alternative approach that considers the magnitude of intraspecific variation in traits and growth as it relates to species abundance. We find that common species are less variable in their traits and growth. Common species also occupy core positions within community trait space indicating that they are finely tuned for the available conditions. Rare species are functionally peripheral and are likely transients struggling for success in the given environment. The work highlights the importance of considering intraspecific variation in trait‐based ecology and demonstrates asymmetry in the magnitude of intraspecific variation among species is critical for understanding of how traits are related to abundance.     

Measuring ecosystem degradation through half a century of fish species introductions and extirpations in a large isolated lake

The introduction of exotic species and the extirpation of native species that occurred during the past two centuries have strongly modified the structure of most plant and animal assemblages across the globe. Such a biotic change is particularly marked in isolated environments such as islands or isolated lakes. Most studies reported drastic changes between before and after human disturbances, but the dynamics of change in assemblage structure through the invasion and extirpation processes are rarely reported. Here we measured the aquatic ecosystem degradation through exotic species introduction and native species extirpation experienced by Lake Erhai (China) during the last 50 years using structural, functional and taxonomic distinctness biodiversity indices. Structural diversity (species richness) did not varied monotonically along the temporal gradient, due to an opposite trend between exotic species increase and a concomitant decline of native species richness. Functional diversity displayed unclear ascending trends driven by the introduction of exotic species having distinct functional traits than natives. Taxonomic distinctness indices exhibited an increase of the average taxonomic distinctness (Δ⁺), but a decrease of the variation in taxonomic distinctness (Λ⁺) through time. Structural, functional and distinctness indices providing complementary information on ecosystem degradation, we here proposed a new multifaceted degradation index integrating these three facets of biodiversity. Such an index provided an accurate representation of the faunistic changes experienced by Lake Erhai and might constitute a comprehensive way to measure ecosystem degradation through exotic fish species introductions and native fish species extirpations.     

植物群落的生物多样性及其可入侵性关系的实验研究

 生物入侵已经成为一个普遍性的环境问题,并为许多学者所关注。尽管一些理论研究和观察表明生物多样性丰富的群落不容易受到外来种的入侵,但后来有些实验研究并没能证实两者的负相关性,多样性 可入侵性假说仍然是入侵生态学领域争论比较多的一个焦点。人为构建不同物种多样性和物种功能群多样性（C3 禾本科植物、C4植物、非禾本科草本植物和豆科植物）梯度的小尺度群落,把其它影响可入侵性的外在因子和多样性效应隔离开来,研究入侵种喜旱莲子草(Alternanthera philoxeroides)在不同群落里的入侵过程来验证多样性 可入侵性及其相关假说。研究结果显示,物种功能群丰富的群落可入侵程度较低,功能群数目相同而物种多样性不同的群落可入侵性没有显著性差异,功能群特征不同的群落也表现出可入侵性的差异,生活史周期短的单一物种群落和有着生物固氮功能的豆科植物群落可入侵程度较高,与喜旱莲子草属于同一功能群且有着相似生态位的土著种莲子草(A. sessilis)对入侵的抵抗力最强。实验结果表明,物种多样性和群落可入侵性并没有很显著的负相关,而是与物种特性基础上的物种功能群多样性呈负相关,群落中留给入侵种生态位的机会很可能是决定群落可入侵性的一个关键因子。     

Functional redundancy in heterogeneous environments: implications for conservation

It has been argued that one of the best ways to conserve biological diversity is to maintain the integrity of functional processes within communities, and this can be accomplished by assessing how much ecological redundancy exists in communities. Evidence suggests, however, that the functional roles species play are subject to the influences of local environmental conditions. Species may appear to perform the same function (i.e. be redundant) under a restricted set of conditions, yet their functional roles may vary in naturally heterogeneous environments. Incorporating the environmental context into ecological experiments would provide a critical perspective for examining functional redundancy among species.     

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.     

Effect of long-term cutting versus abandonment on the vegetation of a mountain hay meadow (Polygono-Trisetion) in Central Europe

The aim of this study was to identify changes in the plant species richness, diversity and composition of a mountain hay meadow (alliance Polygono bistortae-Trisetion flavescentis) after abandonment in comparison with a control cut once per year. The experiment was carried out from 1999 to 2008 in a mountain hay meadow in the Bukovec nature reserve in the north-eastern part of the Jizera Mountains (Jizerské hory, Góry Izerskie, Isergebirge), Czech Republic.The number of vascular plants species with cover greater than or equal to 1% remained almost the same throughout the study period; however, the total number of vascular plants was higher in the cut treatment after the first four years of the study. The cover of Festuca rubra, Agrostis capillaris, Anthoxanthum odoratum, Briza media and Trifolium repens was positively affected by cutting. On the other hand, the cover of Cirsium heterophyllum, Geranium sylvaticum, Hypericum maculatum, Trisetum flavescens and Luzula luzuloides was higher on the abandoned treatment plots.The main effect of the abandonment on plant species composition was the shift in cover of the dominant species. Despite ten years of contrasting management, changes in the vegetation were relatively small with no shift to a different plant community. Therefore the cutting regime combined with several years of no management may be a suitable management strategy for the maintenance of Polygono-Trisetion grasslands and will not be detrimental to the preservation of the target vegetation.