Diversity of soil invertebrates associated to six spatially aggregated plant species in the Yasuní National Park, Amazonian Ecuador.

Abstract

Amazonian tropical rainforests harbor the largest biodiversity on Earth. Over the past decade, there has been increasing interest in understanding how such diversity can coexist in small areas. One broadly accepted explanation is the Negative Density Dependence hypothesis (NDD) that promotes species coexistence through a spacing mechanism that prevents species from becoming locally abundant. This may happen due to seedling mortality caused by intraspecific competition, or the attack of natural enemies. However, there are organisms such as particular plant tree species that are adapted to live in aggregation. How does this particular group of plants cope with the above mentioned survival constraints? A potential mechanism would be the efficient use of nutrients mainly coming from their own litter resources that are invested by plants in growing and defense. If that is so, one would expect detritivore communities within the sites of plants aggregation to be different from what is found outside these microhabitats. Here, using two different sampling methodologies, we provide a detailed description of soil fauna community diversity in areas of aggregation of six common tree species in the Yasuní National Park (Amazonian Ecuador). We hypothesized that (i) both capture methodologies used in our survey (i.e. Winkler extraction and pitfall traps) are complementary between them in terms of species composition; (ii) the ‘litter transformers’ guild represents the largest portion of the soil invertebrate fauna in both, the number of species and abundance; and (iii) soil fauna communities in areas of plants aggregation are significantly different in terms of the number of species, composition, abundance and functionality, compared to the sites where the focal plant species are absent. Agreeing with our hypotheses, our results showed that Amazonian soil fauna are predominantly represented by species included within the litter transformers functional group (65 % of total collection), and they are clustered in small-scale patches and specific to the areas of aggregation of our focal plant species. This suggests that plant species living in aggregation may create microhabitats that promote the association of particular soil fauna species that may be adapted to exploit specific combinations of nutrients in the Yasuní forest floor.