Diversity and distribution of soil micro-invertebrates across an altitudinal gradient in a tropical montane rainforest of Ecuador, with focus on free-living nematodes

•Elevation affected distribution of soil micro-invertebrates in montane rainforest.•Despite moderate densities, the nematode community was diversified and equitable.•Fungivore nematodes increased with altitude following higher fungal biomass.

Here we describe the community structure of soil micro-invertebrates at three altitudes (1000, 2000, and 3000 m) and two soil layers (upper L/F layer and deeper H/Ah layer) of a tropical montane rainforest situated on the eastern slope of the Andes (southern Ecuador) with special focus on nematodes. Nematodes dominated the micro-invertebrate assemblage (average density 1.82 × 105 ind. m−2), accompanied by populations of typical aquatic invertebrates, such as harpacticoid copepods and rotifers, which increased with increasing altitude. Among 1217 nematode individuals inspected, 143 morphospecies were identified. The equitability index was remarkably high. Sample rarefaction curves suggested that up to 244 nematode species dwell in soils of the studied area. Nematode diversity was affected neither by altitude nor by layer; however, the community structure changed with altitude. Bacterial-feeding nematodes dominated throughout the altitudinal gradient whereas at higher altitude populations of plant-feeding nematodes were replaced by hyphal-feeding nematodes, presumably because of changes in habitat and resource availability. Canonical correspondence analysis identified litter C/N ratio and fungal biomass as major drivers of the changes in nematode community composition with altitude. Abundant and diverse assemblages of large predacious and omnivorous nematode species were found at each of the study sites, suggesting that omnivory and animal predation compensate for the lower abundance/quality of basal resources.