Micro-hotspots for conservation: an umbrella tree species for the unique Socotran reptile fauna

Abstract

Umbrella species are defined as species that can be rare and sensitive to human disturbance, whose protection may confer the protection of other co-occurring species. The dragon's blood tree Dracaena cinnabari Balf.f. was already considered an umbrella species on Socotra Island (Indic Ocean, Yemen) due to its ecological importance for some native biota. We studied the reptile community living on D. cinnabari from Socotra Island. We sampled reptiles on trees across most D. cinnabari populations and applied co-occurrence and network partition analyses to check if the presence of reptiles on D. cinnabari populations was random or structured. Regardless of its patched and scarce actual distribution, we report the use of this tree as a habitat by more than half of the reptile community (12 endemic reptiles). Co-occurrence and network partition analyses demonstrate that this community is structured across the distribution of dragon's blood trees, reflecting complex allopatric, vicariant, and biotic interaction processes. Hence, these trees act as micro-hotspots for reptiles, that is, as areas where endemic and rare species that are under threat at the landscape scale co-occur. This Socotra endemic tree is currently threatened by overgrazing, overmaturity, and climate change. Its protection and declaration as an umbrella species are expected to benefit the reptile community and to protect evolutionary processes that are partially driven by the ecological links between reptiles and this tree. To our knowledge, no tree species has been proposed as an umbrella species for island vertebrate endemics so far, highlighting the ecological uniqueness of Socotra Island.