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Community Ecology
Authors:
C. Ricotta
,
E. Ari
,
G. Bonanomi
,
F. Giannino
,
D. Heathfield
,
S. Mazzoleni
, and
J. Podani

. Functional trait and phylogenetic tests of community assembly across spatial scales in an Amazonian forest . Ecol. Monog. 80 : 401 – 422 . Law , R. , Illian , J. , Burslem , D

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405 220 227 Gering, J.C., T.O. Crist and J.A. Veech. 2003. Additive partitioning of species diversity across multiple spatial scales: implications

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: the importance of spatial scale in species assemblages. Abstr. Bot. 17: 289–302. Bartha S. Pattern, area and diversity: the importance of spatial scale in species assemblages

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The recovery process of a Dutch heathland after fire is investigated. The study area, 12 m x 20 m, has been surveyed yearly between 1963 and 1993. Previous work has shown that a stationary Markov chain models the observed recovery process well. However, the Markov model fails to capture an important observation, the existence of a phase structure. The process begins deterministically, but small random (non-Markov) effects accumulate through time and at some point the process suddenly becomes noisy. Here we make use of the spatial information contained in vegetation maps to examine dynamics at a fine spatial scale. We find that the phases observed at a large spatial scale separate themselves out distinctly at finer spatial scales. This spatial information allows us to investigate hypotheses about the mechanisms governing deterministic versus noisy vegetation dynamics.

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Rarefaction has long represented a powerful tool for detecting species richness and its variation across spatial scales. Some authors recently reintroduced the mathematical expression for calculating sample-based rarefaction curves. While some of them did not claim any advances, others presented this formula as a new analytical solution. We provide evidence about formulations of the sample-based rarefaction formula older than those recently proposed in ecological literature.

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Due to the difficulties of field-based species data collection at wide spatial scales, remotely sensed spectral diversity has been advocated as one of the most effective proxies of ecosystem and species diversity. It is widely accepted that the relationship between species and spectral diversity is scale dependent. However, few studies have evaluated the impacts of scale on species diversity estimates from remote sensing data. In this paper we tested the species versus spectral relationship over very large scales (extents) with a varying spatial grain using floristic data of North America. Spectral diversity explained a low amount of variance while spatial extent of the sampling units (floras) explained a high amount of variance based on results from our variance partitioning analyses. This leads to the conclusion that spectral diversity must be carefully related to species diversity, explicitly taking into account potential area effects.

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Tree species richness is remarkably high in many tropical forests, even at very fine spatial scales. However, the study of fine-scale richness is complicated by the rarefaction effect: that is, a trivial correlation between the number of individuals and the number of species. We developed null models to test whether fine-scale species richness differs from random expectation, and applied these models to a dataset of 1170 100 m2circular plots in the old-growth portion of La Selva Biological Station in the Atlantic Lowlands of Costa Rica. Although species richness in these plots was close to its theoretical maximum, we found that it was frequently lower than null expectation. This was a result of slightly clumped distributions within species. We found no relationships between species richness at the 100 m2scale and soil type or topography, after accounting for the effects of density

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We analyzed long-term data related to temporal and spatial variation in fish assemblages from five sites along the Suquía River Basin (Córdoba, Argentina). We aimed at determining whether water quality variations generate changes in fish assemblage structure and composition along the river. Despite deterioration of water quality recorded along the basin, fish assemblages were characterized as qualitatively persistent and quantitatively stable, indicating that the specific composition were relatively constant over time. However, on a temporal scale, fish assemblages from the most polluted areas responded to the water quality degradation with a greater variation of species abundance than those from pristine sites. On a spatial scale, changes in fish assemblage structure were related with watershed disturbance gradient and indicated a strong association between fish species distribution and water quality variation. The alterations found in our study suggest a potential imbalance of fish assemblage structure in the long term.

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Abstract  

Two complimentary spectroscopic techniques, X-ray absorption and fluorescence spectroscopy have been conducted at spatial scales of 1 to 25 μm on uranium contaminated soil sediments collected from two former nuclear materials processing facilities of the DOE: Fernald, OH and Savannah River Site, SC. A method of imbedding particles in a non-reactive Si polymer was developed such that individual particles could be examined before and after extraction with a wide range of chemicals typically used in sequential extraction techniques and others proposed forex situ chemical intervention technologies. Using both the micro-X-ray fluorescence (XRF) and micro-X-ray Absorption Near Edge Structure (XANES) techniques, both elemental and oxidation state distribution maps were generated on individual particles before and following chemical extraction. XANES can determine the relative proportion of U(VI) and U(IV) in phases comprising individual particles before and after extraction and showed that greater than 85% of the uranium existed as hexavalent U(VI). Fluorescence spectra of contaminated particles containing mainly U(VI) revealed populations of uranyl hydroxide phases and demonstrated the relative efficacy and specificity of each extraction method. Correlation of XAS and fluorescence data at micron scales provides information of U oxidation state as well as chemical form in heterogeneous samples.

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The bryophyte vegetation of three acidophilous forest communities of four habitats on radiolarian bedrock were investigated in the Bükk Mts. The bryophyte layers of Deschampsio-Fagetum sylvaticae Soó 1962, Genisto pilosae-Quercetum petraeae Zólyomi et al. 1958 and Genisto tinctoriae-Quercetum petraeae Klika 1932 were compared on the basis of the dominance and frequency of 15 bryophyte species in the communities using ordination and cluster analysis methods. The soil pH and the photosynthetically active radiation (PAR) values in the four sampling areas were also compared. The results refer to a strong connection of the bryophyte species composition considering the dominance values and frequency of the species with the community type in different spatial scale. The soil pH values do not differ significantly in the habitats and they refer to a high amount of hidden acidity which is the effect of the radiolarian bedrock type. The PAR values have been statistically analysed and represent the homogeneity or the heterogeneity of the canopy layer and the effect of the exposition. The results show significant difference in the variances of PAR values between Genisto pilosae-Quercetum and the other two community types and the mean PAR value of Deschampsio-Fagetum sylvaticae differ significantly from the mean values of the two Genisto tinctoriae-Quercetum petraeae stands.

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