Planning for a long-term monitoring program for island forest mountain spiders and beetles: A simplified COBRA Protocol for monitoring beta diversity

Abstract

Current island native forest habitats are particularly important repositories of threatened endemic arthropods that are frequently restricted to higher elevations. As a consequence of the ongoing deleterious impacts of invasive species, land-use changes and climatic changes, the long-term conservation of island forest mountain invertebrates is considered a priority. During the project NETBIOME –ISLANDBIODIV a modified version of COBRA protocol was used to inventory alpha diversity of spiders and beetles on pristine native forest of three islands, Terceira (Azores), Tenerife (Canaries) and La Réunion (Mascarenes). The modified COBRA protocol incorporated the following standardized methods that totaled 28 samples: AAS - active aerial searching during the night (4 hours); BLM - searching under bark, lichens and mosses during the day (2 hours); TWS - searching in decaying trunks, dead wood on the ground, and under stones during the day (2 hours); FBD - foliage beating during the day (2 hours); FBN - foliage beating during the night (2 hours); FSD - foliage sweeping during the day (2 hours); FSN - Foliage sweeping during the night (2 hours); PIT- Pitfall traps (12 samples). Monitoring is essentially different from inventorying, that was the main objective of the original COBRA protocol. Here we will describe a new optimized and standardized COBRA protocol designed to respond to long-term changes of spider and beetle diversity, i.e., designed to measure beta diversity. Using data collected in the above mentioned islands and using simulation methods the new COBRA protocol was optimized to only six samples using: AAS - active aerial searching during the night (four hours); FBN - foliage beating during the night (two hours). With this new solution it is possible to quantify and monitor long-term changes in communities with minimal effort and using a method that proved to be suitable, efficient, feasible, flexible, transparent and accountable.