1,721,017 research outputs found
Understanding the natural variability of diatom assemblages in springs of the Adamello-Brenta Nature Park (south-eastern Alps) on a temporal scale
No full textIt is thought that long-term monitoring is an essential tool through which conservationists and managers (i) are alerted when the system departs from the natural state, (ii) can check their environmental policy, and (iii) can detect disturbance effects. However, while long-term studies are growing in number, the lack of information on the background rates of natural changes could lead to a biased interpretation of results. In this study we analyzed the diatom composition of yearly samples (14 -16 yrs) in four springs with the following goals: (1) to estimate the consequences of sampling-related processes on the species composition and relative abundance; (2) to determine the form of the assemblages' variation, evaluating whether the assemblages can be predicted by cyclic, directional, or stochastic changes; (3) to test if, and to what extent, the diatom variability (variation in species composition, relative abundance and diversity) on a temporal scale is driven by the environment; (4) to evaluate the degree of temporal concordance among the diatom assemblages inhabiting four springs. Results showed that because the effect of sampling was inversely proportional to the species abundances, the presence of the least abundant species over the years were mainly a result of chance. The analyses allowed us to discriminate between stochastic and directional patterns, revealing the ongoing changes in two out of four springs. Because the environmental variables did not explain a significant portion of this variability, other hypotheses are put forward. The assemblages' dynamics of species composition over time were significantly synchronous in two out of six couples of springs, and regardless of the environment. This result can suggest that internal, within springs, drivers may be more important than extrinsic forces operating over regional spatial scales. Overall, these results provide a benchmark of diatom variability over time and in natural conditions delimiting the "limits of acceptable changes". © 2011 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany
Spatial structure, rock type, and local environmental conditions drive moss and lichen distribution on calcareous boulders
No full textAlthough mosses and lichens are a relevant component of the biota of rock habitats targeted for biodiversity conservation in Europe, the ecological factors driving their distribution are still poorly known. In this work, we examined the epilithic moss and lichen assemblages colonizing boulders of different types of calcareous rocks co-occurring in the same area in the Italian Alps. The goals were: (1) to evaluate if and to what extent different calcareous rocks host different assemblages; (2) to identify species associated to each rock type; (3) to quantify the relative importance of rock type, local environmental factors, and habitat spatial structure in explaining species distribution. Our results demonstrated that different calcareous rocks host different moss and lichen assemblages with some typical species, indicating that each rock type contributes to the total diversity of both mosses and lichens. Local environmental conditions influenced mosses and not lichens whose distribution is mainly associated to rock type. The patterns of both organism groups were also significantly related to habitat spatial structure, species assemblages tending to have a patchy distribution, which may reflect dispersal dynamics. Our results have implications for conservation: (1) each rock type may play a relevant role in maintaining the overall diversity contributing with unique assemblages and typical species; (2) the patchy distribution of both moss and lichen assemblages should warn from considering rock patches as a monotonous repetition of the same habitat across space
The role of environmental variables in structuring epiphytic and epilithic diatom assemblages in springs and streams of the Dolomiti Bellunesi National Park (south-eastern Alps)
No full textDiatom assemblages were investigated in 16 springs and five streams of the Dolomiti Bellunesi National Park (south-eastern Alps, Italy), by collecting individual samples of the main substrata (stones, bryophytes, surface sediment), and measuring an extensive number of morphological, physical, and chemical variables. An empirical grouping of these aquatic ecosystems, based mainly on morphological features and physical parameters, mostly agreed with groupings produced by non-metric multidimensional scaling. Significant differences among the diatom assemblages were found among the groups identified; however, these differences were more significant in the epilithic than in the epiphytic assemblages. Epiphytic and epilithic diatoms differed significantly according to: a) the identity of several species, b) the relative abundance of some other species, c) the Bray-Curtis distance between the assemblages, and d) taxa richness and diversity index. However, on studying species composition by canonical analysis, with reference to environmental variables (here called macrohabitat) on the one hand, and the type of substrata (stones and mosses) on the other, it was shown that the macrohabitat was responsible for more than 40 % of the variability among diatom assemblages, whereas the microhabitat (i.e. different substrata) accounted for only 3 %. Multivariate analyses (CCA) showed that the environmental factors most influential in structuring diatom assemblages were substrate particle size (influenced in turn by current velocity), permanence of flow, shade, nitrates, and total phosphorus. Characteristic groups of species were identified in the different morphological and hydrological types of springs and streams. Stream sites were often affected to a certain extent by organic pollution, even within the protected area, and consequently colonized by cosmopolitan, eutraphentic or tolerant taxa. In springs, in addition to common and widely distributed species, many poorly known, rare, or Red List species were found, in particular among the less abundant taxa. Our study therefore highlights the important role of springs as valuable habitats for the conservation of aquatic biodiversity. © 2009 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart
Criticità nella determinazione del Deflusso Ecologico in Italia mediante gli invertebrati bentonici
No full textNel Decreto n. 30/STA del 13.02.2017 si definiscono le Linee Guida per l’aggiornamento dei metodi di determinazione del Deflusso Minimo Vitale e Deflusso Ecologico. La disamina del metodo basato sugli invertebrati bentonici rileva una serie di problematicità che il presente lavoro identifica e discute. 1) Relazione tra STAR_ICMi e portata: le due variabili vanno correlate attraverso un terzo fattore (LRD: Lentic-lotic River Descriptor) che è a sua volta composto da 7 metriche le quali sono ricodificate in maniera arbitraria, e alcune di queste non hanno una relazione diretta con la portata. Si suggerisce di adottare metodi che pongano in relazione diretta STAR_ICMi e portata, senza passare attraverso campagne di misura delle portate che richiedano applicazione del protocollo CARAVAGGIO; 2) Metodo di ponderazione dell’indice STAR_ICMi per ridurre l’abbondanza del benthos in funzione della riduzione dell’habitat: la correzione non agisce sulla presunta riduzione dell’abbondanza assoluta degli organismi bentonici, ma modifica direttamente il valore dell’indice STAR_ICMi. La correzione dell’indice non ha quindi basi ecologiche sostenibili teoricamente; 3) Correzione dell’indice STAR_ICMi per corpi idrici in stato ecologico elevato/buono, verificato applicandolo a dati reali: la correzione, oltre ad non avere presupposti ecologici, non è efficace in quanto i valori risultanti sono compresi nell’intervallo di confidenza stesso dell’indice; 4) Applicabilità delle metriche nOCH e AB/BaSi, non adatte al contesto alpino a causa della scarsa presenza dei taxa inclusi nella metrica. È auspicabile che a livello nazionale si avvii una riflessione più ampia e partecipata, che coinvolga non solo gli Enti di Ricerca predisposti alla definizione delle metriche, ma anche ricercatori e Agenzie per l’Ambiente, in modo da non mettere in campo metodiche e procedure che potrebbero rivelarsi molto presto non idonee a definire i DE secondo le indicazioni fornite nelle Guidance europee.The decree n. 30/STA, 13.02.2017 defines the Guidelines to identify the methods useful to determine the Ecological Flows. In this paper we discuss the method based on benthic macroinvertebrates and identify several critical issues: 1) Relationship between the STAR_ICMi and discharge: these two variables should be related through a third factor (LRD: Lentic-lotic River Descriptor), which is in turn composed by 7 metrics, coded arbitrarily to attribute a final; moreover, some of the LRD metrics are not directly related to discharge. We suggest adopting method based on the direct relationship between STAR_ICMi and discharge, without the need to add discharge surveys based on the CARAVAGGIO method; 2) Correction of the STAR_ICMi index when habitat availability decreases: the correction does not act on the supposed reduction of the absolute abundance of benthic organisms, but instead it modifies the value of the STAR_ICMi index. Therefore, this correction cannot be ecologically supported, 3) Correction of the STAR_ICMi for waterbodies in high/good ecological status, verified using real data: the correction, besides not being ecologically-supported, is ineffective, as the resulting values are within the confidence interval of the index; 4) Applicability of the nOCH and AB/BaSi metrics, which are unsuitable for the Alpine streams because based on rare/absent taxa. We hope to open up a debate involving not only the research institutes in charge of the development of the specific methods, but also scientists and Environmental Agencies. This could prevent to adopt methods and procedures that could prove inappropriate to define the e-flow according to the European Guidelines
Relative importance of space and time in determining the biotic structure in the upper part of spring-fed streams
No full textAn increasing number of recent investigations of a wide range of species have considerably changed perspectives in spring ecology. However, relatively little is known about the differences between the eucrenon and assemblages in downstream habitats. We studied changes in environmental conditions and in 4 taxonomic groups along a downstream continuum. Assemblages of diatoms, other benthic macroalgae including cyanobacteria, macroinvertebrates, and bryophytes were compared among eucrenal, hypocrenal, and epirhithral stations in 2 spring-fed streams of the southeastern Italian Alps. Environmental factors were less variable at the eucrenal station than at downstream stations, but this pattern was not reflected by an equivalent response of biotic assemblages. The eucrenon clearly differed from assemblages at downstream stations in ways that varied between taxonomic groups and time. Diatom and macroinvertebrate assemblage compositions were more variable at the eucrenal station than at downstream stations. Space was a more important factor than time for diatoms and benthic macroalgae, whereas space and time were almost equally important for macroinvertebrates. Downstream changes were inconsistent between taxonomic groups, and a larger number of spring-fed streams must be studied to detect more generally valid patterns in downstream variation of different taxonomic groups. © 2012 The Society for Freshwater Science
Niche partitioning, shape of species response, and diversity in the phytobenthos across the rocky shoreline of a large peri-Alpine lake
No full textBy colonizing a particular depth zone across the transition from aquatic to terrestrial habitats, littoral species may exhibit specific physiological and ecological adaptations, as well as characteristic responses to the gradient of conditions across the ecotone. The objectives of the study were: (i) to identify the depth zone (location in relation to average water level) where the replacement of species occurs most rapidly; (ii) to test whether and to what extent the occurrence of species, their abundance and their response to the gradient evolves over time; and (iii) to assess the shape of the species' response to the gradient, calculating the niche overlap of the dominant species. Results showed that the diversity of species peaked at a depth between 18 and 48. cm, in a zone thought to be of intermediate disturbance (the transect depth was, on average, 103. cm). The main macroalgal species (the red alga, Bangia atropurpurea and the green algae, Jaoa bullata, and Cladophora glomerata), showed a variety of response shapes to the gradient: monotonic, symmetrical and skewed, depending on the stage of seasonal growth. The efficient regulation of growth of B. atropurpurea along the fluctuating gradient was interpreted as an adaptive trait giving it an advantage over more slowly reacting species. The spatial and temporal niches of B. atropurpurea and Jaoa bullata overlapped widely only in early spring, whereas later their optimal habitats were clearly differentiated. This suggested partial niche segregation between these two species, and a potential seasonal interaction. © 2012 Elsevier B.V
Patterns of bryophyte life-forms are predictable across land cover types
No full textBryophytes are promising indicators for detecting the impact of rapid global change. However, despite their great potential, they are still largely neglected, and their patterns across wide areas and environmental gradients are still poorly explored. Here we tested the capacity of bryophyte life-forms to respond to the main environmental and anthropogenic factors using an herbarium collection of high quality. The database consists of over 40,000 records referred to an Alpine area (Bolzano province, Northern Italy). The main aim of the work was to assess the relationship between bryophyte life-forms and different Corine Land Cover types which spans a wide elevational gradient and land uses. Results showed a broad match between similar land cover types and life-forms composition. For example, there was a positive relationship between plagiotropic forms and coniferous forests and between cushion- turf forms and natural grasslands. Anthropogenic habitats like vineyards and urban areas showed a high proportion of dendroid and thallose forms whereas plagiotropic species were underrepresented. Our results indicate that patterns of bryophyte life-forms are predictable across land cover types and altitude thus providing a direct link between the organism and the environmental conditions
STRUCTURAL EQUATION MODELLING DETECTS UNEXPECTED DIFFERENCES BETWEEN BRYOPHYTE AND VASCULAR PLANT RICHNESS ALONG MULTIPLE ENVIRONMENTAL GRADIENTS.
No full textAim. The aim of this study was to develop and evaluate a structural equationmodel explaining the species richness of bryophytes and vascular plants along multiple environmental gradients. Our primary interests in developing this model were: (1) to evaluate the effect of tree canopy along an altitudinal gradient on bryophyte and vascular plant richness; (2) to determine to what extent lithology was able to explain richness in the two groups of plants; (3) to assess whether anthropogenic disturbances decrease richness; and (4) to explore, comparing competing models, the causal links connecting spring area, discharge and spring complexity and to assess how these variables are related to richness.
Location. Eighty-six springs were sampled in the south-eastern Alps of Italy, from the lowlands to high-mountain regions, and on different lithologies.
Methods. A structural equation model (SEM) was used to test certain hypotheses about the direct and indirect effects of altitude, canopy, lithology, disturbance, spring complexity, discharge and spring area on bryophyte and vascular plant richness. Competing models were evaluated and bootstrap simulation was used to determine the stability of parameter estimates.
Results. SEM analysis made it possible to disentangle the different effects of canopy and lithology on bryophyte and vascular plant richness: for the former it was demonstrated that the increased richness with altitude was related primarily to lithology, whereas the latter increased because of the reduction of canopy cover. In addition, the model predicted that spring discharge determined the size of the spring area and even the complexity of the spring; these latter two variables influenced to different degrees both bryophyte and vascular plant richness. Anthropogenic disturbances affected the richness of bryophytes more than that ofthe vascular plants.
Main conclusions. Our study demonstrates that several similarities in the patterns of bryophyte and vascular plant richness are in fact induced by different environmental variables
Urbanization effects on shoreline phytobenthos: A multiscale approach at lake extent
No full textTo understand how littoral biota respond to anthropogenic disturbances, limnologists seek to detect the scale at which patterns and processes occur. We conducted an extensive study on the shoreline phytobenthos of Lake Garda (Italy) with the following main objectives: (i) to examine the importance of urbanization for species distribution within a set of hierarchical spatial scales (101-104 m), and then (ii) to test the spatio-temporal interactions on a reduced set of scales (101-102 m, and 101-102 days). Results showed that most of the variation in most abundant species and habitat characteristics occurred at the spatial scale of 101-102 m. Species richness was positively related with microheterogeneity, but the relationship occurred only at low urbanization and not at highly-urbanized sites where artificial shores were less heterogeneous. The similarity of species assemblages was regulated by two interacting processes, one operating at a fine spatial scale (102 m), reflecting the physical-habitat requirements of the species, and the other one operating at a broader scale (104 m) in relation to the N-S nitrogen gradient. Overall, time explained 73 % of the total variation of species assemblages, space 7 %, and 20 % was explained by the interaction between space and time (the patch scale, 10s of m, and area scale, 100s of m, interacted with the finest temporal scale, 10s of days). This interaction might be explained by the process of species recruitment operating at different rates at the two spatial scales. Since the largest variation in species assemblages was at the temporal scale (due to the seasonal succession of phytobenthos), we recommend collecting at least one sample per season when monitoring littoral habitats. © 2013 Springer Basel
Competition between a planktonic diatom and a dinoflagellate during enclosure experiments in a mountain lake
No full textLake Tovel (Trentino, Brenta Dolomites, NE Italy) was renowned for red blooms due to the dinoflagellate Glenodinium sanguineum. These blooms suddenly ceased in 1964. Responses of the summer phytoplankton communities to nutrient enrichments, analysed experimentally in enclosures, identified phosphorus as the factor limiting both G. sanguineum and a dominant Fragilaria tenera. Competitive interactions suggested that the dinoflagellates were favoured by higher temperatures, whereas the diatoms were limited by silica reduction. The ratio between the biovolumes of the two algae was an important parameter for predicting which species would benefit from the phosphorus additions and outcompete the other one under the experimental condition
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