Using Next Generation Sequencing to assess the effects of livestock on arthropod biodiversity in Iberian holm oak savannas

In this study we performed a landscape-scale sampling to assess the richness and diversity of ground arthropod communities after livestock exclusion. In three dehesa farms, we randomly chose several oaks and built livestock exclosures around them. Paired to each experimental tree, another close by oak was selected as control. We sampled arthropods under both trees one year later. In addition, we monitored trees in three abandoned oak savannas from which livestock had been absent for at least 10 years. We followed this approach to assess the potential negative effects of using intraguild predation by livestock as biological control of acorn pests. The differences between treatments would show what the consequences of increasing grazing pressure could be. Additionally, the results would reveal the speed of the changes in arthropod communities once livestock grazing stopped. According to the intermediate disturbance hypothesis, we predict that species richness will peak shortly after livestock exclosure. Our concrete objectives were: i) to compare the success of the two genetic markers (COI and 16S) used for species detection by DNA metabarcoding, ii) to assess changes in vegetation structure after livestock exclusion, and iii) to compare arthropod species richness and community species composition among control oaks and those in which livestock had been excluded for one year or more than 10.