Ecological Archives E093-008-A4

Moisés A. Aguilera and Sergio A. Navarrete. 2012. Functional identity and functional structure change through succession in a rocky intertidal marine herbivore assemblage. Ecology 93:75–89.

Appendix D. Herbivores diet analyses.

Fig. D1. Dendrogram of diet similarity (Pianka's niche overlap index) obtained from cluster analysis for the four focal herbivores considered in the experiments. The broken vertical line at 50.8% represents the criterion of significant similarity (P = 0.05) set by bootstrapping the diet similarity matrix.

Niche overlap through diet analysis

Diets of all focal grazer species were analyzed through gut content analyses of individuals collected at the study site of Pelancura. Every month from March through September 2008, we collected 10, 8, 12 and 5 individuals of C. granosus, S. araucana, S. lessoni, and F. crassa, respectively, from areas adjacent to the experimental platform. Previous sampling allowed us to construct rarefaction curves (Gotelli and Colwell 2001) to estimate sample size to characterize grazers' diet. Animals were collected after foraging excursions (day or night), and were immediately injected with 1ml formalin 10% to stop digestion. Animals were then stored frozen, dissected and gut contents analyzed under a microscope at ECIM laboratories.

Diet similarity or overlap was calculated between all species pairs based on the average percentage of each item observed in the gut for each species. A niche overlap index (Pianka 1973) was calculated; which ranges between 0 and 1. The diet similarity matrix was analyzed with UPGMA clustering (using arithmetic averages) in order to generate a diet similarity dendrogram. We use a bootstrapping procedure to determine the threshold against which observed overlap similarity was compared. The method involves calculating the 95% confidence interval from reshuffling the trophic data 1000 times and recalculating the overlap values each time. The randomization algorithm used was RA4 (Lawlor 1980).


Literature Cited

Gotelli, N., and R. Colwell. 2001. Quantifying biodiversity: procedures and pitfalls in the measurement and comparison of species richness. Ecology Letters 4:379–391.

Lawlor, L. 1980. Structure and stability in natural and randomly constructed competitive communities. The American Naturalist 116:394–408.

Pianka, E. 1973. The structure of lizard communities. Annual Review of Ecology and Systematics 4:53–74.


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