Victorian Subtidal Reef Monitoring Program - Parks Victoria
Victorian Subtidal Reef Monitoring Program - Parks Victoria
Victorian Subtidal Reef Monitoring Program - Parks Victoria
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<strong>Parks</strong> <strong>Victoria</strong> Technical Series #73<br />
SRMP Merri MS<br />
2.2.2. Biodiversity<br />
Community Structure<br />
Community structure is a multivariate function of both the type of species present and the<br />
abundance of each species. The community structure between pairs of samples was<br />
compared using the Bray-Curtis dissimilarity coefficient. This index compares the abundance<br />
of each species between two samples to give a single value of the difference between the<br />
samples, expressed as a percentage (Clarke 1993; Faith et al. 1987).<br />
Following Sweatman et al. (2003), the count data were log transformed and percent cover<br />
values were transformed using the empirical logit transformation (McCullagh and Nelder<br />
1989).<br />
The hyper-dimensional information in the dissimilarity matrix was simplified and depicted<br />
using non-metric multidimensional scaling (MDS; Clarke 1993). This ordination method finds<br />
the representation in fewer dimensions that best depicts the actual patterns in the hyperdimensional<br />
data (i.e. reduces the number of dimensions while depicting the salient<br />
relationships between the samples). The MDS results were then depicted graphically to show<br />
differences between the replicates at each location. The distance between points on the<br />
MDS plot is representative of the relative difference in community structure.<br />
Kruskal stress is an indicator statistic calculated during the ordination process and indicates<br />
the degree of disparity between the reduced dimensional data set and the original hyperdimensional<br />
data set. A guide to interpreting the Kruskal stress indicator is given by Clarke<br />
(1993): (