The importance of threatened host plants for arthropod diversity: the fauna associated with dendroid Euphorbia plants endemic to the Canary and Madeira archipelagos

The arthropod fauna associated with seven endemic dendroid Euphorbia was sampled and studied in the Canary and Madeira archipelagos. The stem-diameter of the plants was considered, along with their genetic affinity, habitat and number of localities and islands where present. The arthropod assemblages and richness found on each Euphorbia species were statistically analysed, to determine which variables influenced the survey results. A total of 179 arthropod species were found, identified, and classified into characteristic or accompanying fauna, according to their relationship with the plants and their types of diet. Faunal assemblages and arthropod species richness differed among the Euphorbia species, each thus showing a strong and almost unique host relationship. Species richness increased with the architectural complexity of the host-plant species and number of localities and islands where present. The similarity of faunal assemblages was mainly related to stem diameter. Among diet types, a great number of exclusive and/or endemic taxa associated with this plant genus were xylophages. Our survey revealed that rich arthropod communities are associated with the genus Euphorbia, especially on its rare endangered species, and highlights the need to protect their host plants. This in turn will contribute to the conservation of their arthropod communities and their ecosystem functions.