The loss of large herbivores leads to ecological changes that can affect even the lowest trophic levels. Plant-fungi mutualism is found in over 80% of all plants and is critical for nutrient cycling and plant biomass accrual. As seed dispersers and ecosystem engineers, tapirs (Tapirus terrestris) and white-lipped peccaries (Tayassu pecari) are potential long-distance dispersers of arbuscular mycorrhizal (AM) fungal species and important for the structure of fungal and plant communities. Here we examine the hypothesis that the loss of larger herbivores reduces the density of AM fungal spores and their diversity in the Atlantic Forest. To test our predictions, we analyzed soil samples from 8 pairs of open (control) and closed plots (fenced with 1.5 m tall wire mesh to exclude medium and large mammals) in an area of Atlantic Forest in Brazil. We collected 6 soil sub-samples (10 cm deep) from each of the 16 (3 m x 5 m) plots. Soil samples were homogenized, weighted and wet sieved. Sediments and particulate organic matter were separated by density (sucrose 70%). The supernatant was analyzed under the stereomicroscope and the AM fungal spores were counted and placed on slides for identification.
Results/Conclusions
We recorded over 1,700 AM fungal spores, belonging to more than 20 taxa/morphotypes (Glomeromycotina), with potential novel records. Partial results showed the number of species is higher in open plots (11 to 16 morphotypes) compared with closed plots (7 to10). Open plots had a significant higher spore density compared with closed plots (paired t-test [1,7] = -3.39, P-value = 0.012). However, we found high variation in spore density among pair of plots that could be explained by the fact that (i) not all open plots are visited by large mammals at the same rate (based on camera trap data), (ii) soil fertility is also variable among pairs of plots (we found variations in total N, NH+ and NO3) and, (iii) there is a gradient in the abundance of the main food resource for the fauna, the palm tree Euterpe edulis, as well as in the diversity of other plants. This is the first empirical evidence for the cascading effects due to the loss of large herbivores on a below-ground organism in the Atlantic Forest. Ongoing analysis will help us elucidating such patterns and place the below-ground dynamics in the context of the eminent defaunation of the Atlantic rainforest.