Table 1

Summary of the metrics used to assess changes in community composition, where S  =  the number of species in a sample, N  =  the number of individuals found in a sample, ni  =  the number of individuals found of the ith species in a sample, pi = a proportional representation of ith species within a sample (whether abundance [A] or biomass [B]), and ωij  =  the distance between two species (i and j) on a Linnaean classification tree.

Metric Description Interpretation
Margalef's Richness (d)
Standardizes the number of species found by sum of the sample. Higher values represent greater species richness.
Shannon-Wiener Entropy (H)
Quantifies the uncertainty in predicting the species identity of an individual (or mass) that is taken at random from the dataset. Higher values represent greater species diversity and evenness.
Pielou's Evenness (J')
Quantifies how equal the community is numerically. Higher numbers suggest species are present in more equal amounts.
Gini-Simpson Index
Quantifies probability that two individuals (or masses) drawn at random are from the same species. Higher values suggest assemblages are dominated by a few species.
Berger-Parker Index
= max(pi)
The proportional value of the most abundant species. Higher numbers indicate that the most abundant species dominates the assemblage.
Average Taxonomic Distinctness
(presence/absence data)
The average path length (ωij) traced along Linnaean taxonomic trees between all species pairs in a sample. Higher values indicate a greater number of species from disparate taxonomic groups.
Variation in Taxonomic Distinctness
(presence/absence data)
The variance of the taxonomic distances (ωij) between each pair of species i and j, about their mean value Δ+. Increases suggests greater diversity of closely related species, thus decreases suggest higher environmental quality.
W Statistic
Quantifies the degree of separation of biomass and abundance k-dominance curves. Positive values represent non-disturbed states; Negative values represent disturbed states.
Mass per Individual
Total biomass of a sample divided by the number of individuals in the sample. Increasing mass per individual would suggest larger, older individuals are more common.
Assemblage Anomalies
Where Yi = Bray-Curtis dissimilarity between sample i and the grand mean of samples
How similar a sample is to the average of how similar all samples are to the grand mean of the assemblage. Assemblages vastly different from the mean assemblage structure will have larger (positive or negative) valu`es.

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