Invertebrate community
Aquatic and terrestrial invertebrates (size > 500 μm)
present in each coarse-mesh bag were picked, identified under the
microscope and counted in the lab. More than 15,000 individuals were
found, of which 86% and 14% were dominantly aquatic and terrestrial,
respectively. Taxa were mostly identified at genus and family taxonomic
levels (Table S1). We calculated taxa richness in each site and campaign
as the sum of taxa identified.
We used a fuzzy-coding approach to determine aquatic and terrestrial
taxa feeding habits from different bibliographic sources (Table S1).
Values of 1 to 3 were given to indicate weak to strong affinity with
each feeding category (e.g. leaf-shredder or grazer, Tachet et al. 2010)
to account for variability in feeding preferences within taxa (e.g.
feeding habits may change during taxon life cycles) and among species
within the same taxon. We then transformed this information into
percentage affinity for each feeding category. To calculate the
abundance of leaf-shredders in each sample we summed the products of
each taxon’s percentage affinity to the “leaf-shredder” category with
its abundance. Trait information was missing for 39 taxa representing
0.2% and 9.1% of the total aquatic and terrestrial individuals,
respectively, which were thus not taken into account when calculating
leaf-shredder abundances. Most of those individuals (55.7%) were ants,
which have very diverse feeding habits and little impact on leaf litter
decomposition. Total taxa richness and leaf-shredder abundances were
divided by the number of coarse-mesh bags retrieved in each habitat and
campaign to account for bag losses. One site, affected by a scouring
flood, was not sampled in summer.