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Community Ecology
Authors:
H.L. Buckley
,
J.H. Burns
,
J.M. Kneitel
,
E.L. Walters
,
P. Munguia
, and
E. Miller

Addicott, J. F. 1974. Predation and prey community structure: an experimental study of the effect of mosquito larvae on the protozoan communities of pitcher plants. Ecology 55

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The aim of the present work was to compare the microbial communities of a mesophilic and a thermophilic pilot scale anaerobe sludge digester. For studying the communities cultivation independent chemotaxonomical methods (RQ and PLFA analyses) and T-RFLP were applied. Microbial communities of the mesophilic and thermophilic pilot digesters showed considerable differences, both concerning the species present, and their abundance. A Methanosarcina sp. dominated the thermophilic, while a Methanosaeta sp. the mesophilic digester among Archaea. Species diversity of Bacteria was reduced in the thermophilic digester. Based on the quinone patterns in both digesters the dominance of sulphate reducing respiratory bacteria could be detected. The PLFA profiles of the digester communities were similar though in minor components characteristic differences were shown. Level of branched chain fatty acids is slightly lower in the thermophilic digester that reports less Gram positive bacteria. The relative ratio of fatty acids characteristic to Enterobacteriaceae, Bacteroidetes and Clostridia shows differences between the two digesters: their importance generally decreased under thermophilic conditions. The sulphate reducer marker (15:1 and 17:1) fatty acids are present in low quantity in both digesters.

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Acta Microbiologica et Immunologica Hungarica
Authors:
M. Peterka
,
Katarina Tepšič
,
T. Accetto
,
R. Kostanjšek
,
Andreja Ramšak
,
L. Lipoglavšek
, and
G. Avguštin

Recently developed molecular biology approaches make possible the detailed genetic, taxonomic and ecological examination of microorganisms from various habitats. Animal gut represents one of the most complex microbial ecosystems with a large degree of microbial biodiversity present. Bacteria inhabiting the gut usually play important roles in metabolic transformations of substrates and sometimes, e.g. in ruminants, they make the basis for an obligate symbiosis with the host. Here we discuss molecular microbiology as a strategy for examination of gut bacteria, concentrating on a typical and in such environment dominant group of strictly anaerobic Gram-negative bacteria from the phylogenetic group Cytophaga/Flexibacter/Bacteroides. The bacteria from the genus Prevotella are the most abundant Gram-negative bacteria in the rumen and form a distinctive phylogenetic cluster, clearly separated from prevotellas isolated from other ecological niches. They may represent a good choice for a model organism in genetic manipulation experiments and for studies of gene transfer mechanisms taking place in the gut. The molecular tools for detection and monitoring of ruminal prevotellas are discussed.

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

. Reynolds , H.L. , Packer , A. , Bever , J.D. and Clay , K. 2003 . Grassroots ecology: plant-microbe-soil interactions as drivers of plant community structure and dynamics . Ecology 84 : 2281 – 2291

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The contribution of local (e.g., competition) and regional (e.g., dispersal) processes in the structure of communities remains an unresolved issue. In general, a tendency to assume local processes to be deterministic and regional to be stochastic dominates, although it is challenged. Fortunately, it can be cast as a testable proposition: if correct, the degree of determinism in the final community structure might indicate which process is more prominent in the control of community structure. However, recent findings have also suggested that stochastic patterns can arise from local processes and that dispersal can homogenize communities, which would make them appear deterministic irrespective of the mechanism involved. To evaluate these competing expectations we conducted an experiment where the initial communities had the same composition and species abundances. We hypothesized that if local processes dominate, then arrays of communities will show divergence of community structures whether connected by dispersal or not (i.e., being fully isolated). Alternatively, if regional processes dominate, the dispersal connected communities should converge while isolated ones should not. We found, however, that both groups of experimental communities showed similar patterns of change - a decline in similarity and a tendency to diverge. This suggests that biological interactions, demographic stochasticity, or both, exert noticeable control over community structure such that they reduce similarity among replicate communities and diversify their final states. We speculate that these mechanisms enhance potential for species additions, particularly in conjunction with factors such as dispersal and the size of the regional species pool.

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Dispersal allows species to immigrate and emigrate to and from habitat patches and is an important factor in determining community structure. The influence of species dispersal in a metacommunity is poorly understood, particularly its effect at the local community level. We aimed to address this deficiency by evaluating the potential influence of dispersal on local community structure in a rock pool metacommunity. Short term dispersal was quantified over an 11 day period by intercepting propagules dispersing via overflowing pool water and via wind. The composition of dispersing organisms was compared to natural local communities in the rock pools surveyed annually on 11 occasions. On average, the composition and abundance of dispersing species was approximately 54.1 ± 9.3% (mean ± SD) similar to the established pool community. Some species were more abundant among dispersers than they were in the pool community. This may be attributed to several factors including a variation in tolerance to environmental conditions, dispersal capacity, and local scale species interactions (predation and competition). In general, we found considerable similarity between short term dispersal and long term local community structure across a metacommunity. Differences in abundance patterns between the resident rock pool community and the dispersal assemblage emphasize that dispersal, a regional process, must interact with local factors in structuring communities.

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Five distinct habitats along salinity gradient were explored for plant ecological attributes including soil plant interaction, vegetation composition and species distribution in the Cholistan desert. Higher saline sites supported Sporobolus ioclados with Aeluropus lagopoides, Cymbopogonjwarancusa, Ochthochloa compressa, Haloxylon recurvum and Suaeda fruticosa , whereas moderately saline habitats supported predominantly Fagonia indica, C. jwarancusa and O. compressa . The community structure and composition of each habitat type were very specific, the most dominant component being S. ioclados . Each species has very specific relation to different environmental variables, and this reflects the habitat status, ecological adaptations and stress tolerance degree of the individual species. On the whole, it can be concluded that salinity alone was not responsible for the distribution of species at salt affected habitats.

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Climate change brings along trend-like changes as well as changes in the temporal variations in environmental conditions which interact with the biological dynamics of ecological systems. Therefore, only studies covering several decades may unveil long term trends in ecological systems, such as in animal communities. To demonstrate if recent climatic changes have caused fundamental changes in the structure of a key arthropod community, I studied the long-term dynamics of ant colonies for 37 years on a sandy grassland in central Hungary. To be able to monitor colonies – the natural units of ant communities – with the possible least disturbance, I applied two grids of a total of 80 slate plates as artificial nesting sites. Prior to the presented study, a well-defined spatial ant community structure had been identified in the studied habitat, which consisted of three species groups (dune top, transitional and dune slack groups), occupying different habitat patches. During the study period 2813 nests of 11 ant species were recorded under the slates. Over the 37 years, community pattern markedly changed, dune slack species disappeared from the studied plots, while the frequency of drought-tolerant dune top species increased by a significant trend. No significant trend was observed in the case of the transitional species group. On the species population level, two species, Lasius niger and Formica cunicularia, showed an intensive population decline; while the Plagiolepis taurica population significantly increased and spatially joined the transitional species group in the dune slack in the second half of the project. These changes led to a major decline in species richness and a homogenization of species composition across habitat patches. Multiple correlation analyses revealed that the depletion of groundwater had the strongest relationship with these population trends. The study indicates that climate change can be linked to a fundamental change in the community structure of major ecosystem actors.

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J. Bryol 12 403 459 Hairston, N.G., F.E. Smith, and L.B. Slobodkin. 1960. Community structure

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same levels of status, respectively. Different sets of attributes are considered in order to assess the salience of different factors for community structure: institution, research specialty and RAE rating. For research specialty, for instance

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