1,721,012 research outputs found
Evaluation of syntaxonomic schemes of aquatic plant communities by cluster analysis
No full textNumerical classification methods can simulate strategies of intuitive classifications. This paper considers two different intuitive syntaxonomic schemes suggested for stagnant eutrophic fresh-water communities with a view to identifying which among the commonest numerical methods of classification fits the two intuitive schemes best. Comparison of classifications using an information function and discriminant analysis revealed that the different numerical methods simulate different intuitive schemes, but the results of the numerical classifications are always judged superior. Two new syntaxonomic schemes optimizing the sharpness between the syntaxa are proposed. © 1982 Dr W. Junk Publishers
Hill numbers everywhere. Does it make ecological sense?
Full text linkA supposed weakness of most diversity measures is their non-linearity with respect to species addition. Even for a community where all species have equal abundance, each added species usually leads to a smaller increment in the diversity measure than the species added before it. A recent proposal to solve this problem was to transform classical diversity measures to ‘effective numbers of species’ or ‘Hill numbers.’ For any community with diversity D, the effective number of species N is the number of equally abundant species that is needed to get a diversity value equal to D. The conversion of classical diversity measures to Hill numbers makes them linear with respect to species addition such that, given two equally large and completely distinct communities, each with diversity D, if these communities are pooled, the diversity of the pooled communities is 2D. According to this proposal, Hill numbers have been widely adopted in ecological literature as the ultimate solution for diversity analysis regardless of the scientific question at hand. In contrast, we believe that assuming a non-linear response of diversity measures to species addition is more suitable for many ecological questions. Building on this idea, we have introduced a typification of diversity measures based on how quickly diversity increases as species are added
Ordination based on classification: yet another solution?
No full textA new simple method of ordination is proposed. It is based on classification of relevks, or variables, and matrix multiplication. An example of application is given with data from a simulated coenocline with different noise levels.
The performance of the method may be considered as good as that of the most popular methods, or even better if the monotonous pattern is considered as an advantage
Naiveté of fuzzy system spaces in vegetation dynamics?
No full textThe application of fuzzy set theory for describing vegetation dynamics is discussed on the basis of results obtained with forest data of NE Italy
Fuzzy Sets and structural changes in forest succession: an example from broad leaved forests of N.E. Italy
No full textAs a working hypothesis, the test model used is the well-known successional sequence of Ostrya-Quercus-Fagus. Results show that fuzzy set theory allows use of a classification approach in a dynamic system perspectiv
Spatial pattern of ecological processes: the role of similarity in GIS application for landscape analysis
No full textFuzzy set system ordination of Serengeti short grasslands
No full textSpecies abundance data from 32 representative stands are used to evaluate the vegetation in the heavily grazed Serengeti short grasslands. The abundant species are: Kyllinga nervosa, Sporobolus ioclados, S. kentro-phyllus and Eustachys paspaloides, all occurring in elevated areas, and Hypoestes forskalei, which is found in the drainage areas.
Numerical classification and fuzzy set ordination revealed four main grassland communities associated with a topographic gradient. The communities are considered distinct since their niches, as computed in the community and environmental fuzzy system space are not overlapping. Leaching, erosion and animal disturbance effects correlated with the topographic gradient are found to determine species composition and overall community structure in the grasslands
An Application of "AQUAMOD" Trophic Model to the Marine Ecosystem along the Emilia-Romagna Coastal Region in the Adriatic Sea
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