Ordinal abundance and richness of millipedes (Arthropoda: Diplopoda) in a subtropical wet forest in Puerto Rico
Millipedes, among other soil fauna, are important components of ecosystems because of their role in nutrient cycling. In this study, we quantified the density, biomass, and richness (in terms of order) of millipedes along a toposequence (ridges, slopes, and valleys) and different ground layers (litter, humus, 0-5 cm soil depth, and 5-2010 cm soil depth) in a subtropical wet forest in Puerto Rico. Millipedes were surveyed from twelve 50 x 50 cm plots (3 topographic positions x 4 replicates) by hand sorting. Four orders of millipedes were found in El Verde tabonuco forest: Stemmiulida (the most abundant), Glomeridesmida, Spirostreptida, and Polydesmida (the least abundant). The density of millipedes and the richness of Orders varied depending on the topographic position, with ridges having significantly less of both. The ground layer also significantly affected millipede richness but not density, with the humus being the richest layer. The biomass of millipedes did not significantly differ among the different topographic positions or layers. There was a significant positive correlation between the soil pH and millipede richness. The number of millipede orders was also significantly and positively correlated with the amount of wood and fruit found in the litter and humus layers. In conclusion, millipedes have higher density and richness in slope and valley topographic positions than in ridges, and in less acidic soils in this tabonuco forest.