We manipulated the presence and absence of all three species in a factorial design that yielded eight treatments and comprised four levels of diversity: three consumers (crabs + snails + fungus), two consumers (crabs + snails, crabs + fungus, snails + fungus), one consumer (crabs or snails or fungus), and no consumers. Sixty-four plots were selected (mean Spartina density: 120.8 ± 6.2 stems per m2).

Ecosystem Function 1: NPP. To determine the effect of experimental consumer variety on NPP, net Spartina production was estimated by measuring change in live aboveground plant mass from the beginning to end of the experiment.

Ecosystem Function 2: Decomposition Rate. We quantified the effect of consumer variety on marsh decomposition rate by deploying a plug consisting of three dead Spartina stems zip tied to a plastic flag post.

Ecosystem Function 3: Infiltration Rate Measurement. We quantified the effect of consumer variety on marsh infiltration at the conclusion of the experiment by using a double-ring infiltrometer.

Assessing Multifunctionality. To assess whether snail, crab, and fungi consumers differed in their ability to perform all measured functions simultaneously, we calculated an average multifunctionality index for each treatment. This method is a simple technique involving averaging standardized values of multiple functions into a single index. For each of the three functions, we used a “standardization by maximum observed value” approach where we defined maximum functioning as the mean of the highest three values from all 64 plots in the experiment for each function, giving us one maximum for each function regardless of treatment. Using this maximum, plot data were recorded as the percent of that maximum for each function, creating a scaled “percent functioning” value for each individual plot.

See Hensel and Silliman 2013 for detailed methods descriptions.

Hensel, M. J. S. & Silliman, B. R. Consumer diversity across kingdoms supports multiple functions in a coastal ecosystem. Proc Natl Acad Sci USA 110, 20621–20626 (2013).
DOI: 10.1073/pnas.1312317110