Chapter 1 - Núria BONADA

Chapter 7
Seasonal changes in caddisfly assemblages
To check the effect of seasonality and study changes in caddisfly community along year, a
CCA analysis was performed for all samples using seasons as dummy variables. Rare species
were down weighted. Canonical axes were tested for significance using a Monte Carlo test with
199 runs.
Variance partition of spatial and temporal patterns
To determine the proportion of all caddisfly variability explained by measured variables and
seasonality and their interaction, a Variance Partition was performed (Bocard et al., 1992). To
carry out this analysis, two CCA and two pCCA were performed: (1) with environmental
variables, (2) with seasonality variables, (3) with environmental variables and seasonality
covariables and (4) with seasonality variables and environmental covariables. (3) and (4) steps
(pCCA) allow us to separate what is purely environment or seasonality and what is a result of
the interaction. The sum of canonical eigenvalues of each analysis respect the sum of all
eigenvalues (i.e., inertia) gives the percentage of variation explained by each group of variables.
Non-explained variability was also calculated. Moreover, the percentage explained by
environmental variables was partitioned to detect the proportion attributed to geomorphologic,
temporality, physical-chemical and biological parameters. To perform that, successive CCA
analysis using each subgroup of variables were done, and sum of all canonical eigenvalues
were kept to calculate percentages.
RESULTS
Taxa distribution
A high and significant correlation was obtained comparing caddis-max with caddis-mod
matrix (rM=0.9822 and p-value=0.0101) indicating that similar information is provided using
both matrixes. We decided to use the caddis-mod matrix to simplify the analysis and the
interpretation of final results. A total of 71 taxa (including species and genus) were obtained
(Annex 3). Taxonomical notes of these taxa are found in Bonada et al. (Chapter 6). Number of
taxa is variable between basins (Figure 2). Segura basin presents the highest value of taxa
whereas in Aguas and Mijares less than 20 taxa have been found. The rest of basins present
intermediate values between 20 and 35 taxa. Some of collected taxa are ubiquitous whereas
other are exclusive from one o more basins.
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