Weed community structure in spring-seeded crops in Manitoba

1991 ◽  
Vol 71 (4) ◽  
pp. 1069-1080 ◽  
Author(s):  
A. G. Thomas ◽  
M. R. T. Dale

The phytosociological structure of weed communities in spring wheat, barley, oats, flax, and canola was investigated using data collected during a 3-yr survey of 1384 fields in Manitoba. Fields were surveyed during July and August, after the application of all herbicides. Association and cluster analysis techniques, using the presence or absence of species in a field, were employed to distinguish co-occurring groups of species. Only a small number of significant positive and negative associations were found between species and only minor clusters with a few species were formed at low similarity levels. These results indicated that the weed community was composed of species responding to conditions more or less independently of each other. A comparison of weed associations among the five crops and four geographic regions in the province indicated that the weed community structure was determined largely by climatic variables. The pattern of weed association in the four geographic regions was correlated with differences in temperature and precipitation during the spring and summer. The lack of floristic differentiation was attributed to the fact that production practices were similar for the five spring-seeded crops. Key words: Weed communities, weed ecology, cluster analysis, association analysis

2020 ◽  
Vol 9 (1) ◽  
pp. 4-25
Author(s):  
Dennis Tay

This paper illustrates an analytical approach combining LIWC, a computer text-analytic application, with cluster analysis techniques to explore ‘language styles’ in psychotherapy across sessions in time. It categorizes session transcripts into distinct clusters or styles based on linguistic (di)similarity and relates them to sessional progression, thus providing entry points for further qualitative exploration. In the first step, transcripts of four illustrative therapist-client dyads were scored under ten LIWC variables including ‘analytic thinking’, ‘clout’, ‘authenticity’, ‘emotional tone’, and pronoun types. In the next step, agglomerative hierarchical clustering uncovered distinct session clusters that are differently distributed in each dyad. The relationships between these clusters and the chronological progression of sessions were then further discussed in context as contrastive exemplars. Applications, limitations and future directions are highlighted.


Weed Science ◽  
1987 ◽  
Vol 35 (3) ◽  
pp. 348-355 ◽  
Author(s):  
Mark R. T. Dale ◽  
A. Gordon Thomas

This paper describes the communities of weeds in cereal and oilseed crops in Saskatchewan, using data collected in a 4-yr survey that sampled more than 400 fields. The survey data for the 40 most common weeds were analyzed in an attempt to distinguish natural groups of weed species and to compare the weed communities associated with the different crops and with different soils. The crops were barley (Hordeum vulgareL.), flax (Linum usitatissimumL.), oats (Avena sativaL.), rape (Brassica campestrisL.,Brassica napusL.), and wheat (Triticum aestivumL.). Phytosociological association and cluster analysis indicated that the associations of the weed species were more or less independent of the crop, although some differences existed and were determined more by soil or the associated climate. The 40 most common species were divided into three groups related to the soil and climatic subregions of the province.


2020 ◽  
Vol 1 (2) ◽  
pp. 93-97
Author(s):  
Zainal Abidin

Periphyton is a community of microorganisms that live attached to or adjacent to a substrate sink. For aquatic organisms, periphyton habitats have a relatively fixed. With it is so, the changes of water quality and substrate greatly affects the composition of his life and abundance. Periphyton composition and abundance depends on the tolerance or sensitivity to environmental changes. This study aims to determine each periphyton community in responding to changes in habitat quality by way of adjustment in community structure. The methodology used in this prektikum involves taking data from four stations along the river Coban Rondo, in each station there are 3 replicates. And take measurements of factors such environments as supportive data turbidity, flow rate, pH, and depth. Analyzed using Simpson's Dominance Index to determine the type of periphyton dominance, as well as morisita similarity indices and cluster analysis. The results showed that the diversity in each station belonging to the category of high (H more than 3.32) because the obtained value of the index H' between 3.2 to 3.48. Species that dominate from the four stations is Pinularia with an average Index Value Important (IVI) 31,5.


2011 ◽  
Vol 5 (3) ◽  
pp. 20 ◽  
Author(s):  
Pearl Tan ◽  
Hian Chye Koh ◽  
Aik Meng Low

This paper investigates the differences in the relative perceptions of auditing terms among groups of accountants, bankers and students. Perceptual models were constructed using multi-dimensional scaling and cluster analysis techniques. The models derived therefrom indicate that there are no major inter-group differences in the relative perceptions of auditing terms. This study does not therefore support the hypothesis that the expectation gap between users and preparers of the audit report are caused by semantical problems.


1984 ◽  
Vol 44 (3) ◽  
pp. 271-281 ◽  
Author(s):  
Michael F. W. Festing ◽  
Klaus Bender

SUMMARYGenetic similarities among 46 strains of rats based on published data involving 93 samples and 28 biochemical loci were assessed using principal coordinate and cluster analysis techniques. Seventeen strains were represented by more than one colony. In ten of these, nominally identical strains differed, and in four cases this was attributed to genetic contamination. A total of 52 genetically different strains were eventually identified. Strains BN and DA were most dissimilar, while strain BP was the most unusual strain over-all. The principal coordinate and cluster analysis showed three main clusters, which could be explained on the basis of linkage disequilibrium for some of the esterase loci in linkage group 5. Among six of these loci only 12 haplotypes were observed, with 24/52 strains having a single haplotype. Re-analysis of loci in linkage equilibrium failed to reveal any important clusters.


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