PREDICTING AND VERIFYING BUTTERFLY RICHNESS ON ISLANDS USING THE SPECIES AREA RELATIONSHIP: OTHONI (IONIAN ISLANDS) AS A CASE STUDY

Abstract

We used the Species Area Relationship (SAR) (modelled with the power function) to predict the butterfly richness of Othoni, the westernmost Ionian island, (Greece), by comparing two datasets: one only based on literature data, and the other including new records. Although the SAR based on literature data indicated that butterfly richness for this island was already well sampled (nine species recorded against 7.3 predicted by the model), during a four-day fieldwork in August 2023 we spotted 11 previously unrecorded butterfly species. We discussed that the evaluation of the SAR was largely affected by under sampling of small islands while faunal inventories of large islands appeared almost complete. This was also reflected by a very high slope (z ≈ 0.5) and an intercept (c ≈ 2) which appears quite low for Mediterranean butterflies. A SAR model only including large islands and those showing richness above the 95% confidence interval revealed more trustworthy c and z values (0.3 and 8, respectively). We conclude that evaluating SAR parameters using literature data which did not originate from specifically planned research in archipelagos comprising small islands could return unreliable predictions. Moreover, we documented that the current faunal list of Othoni island can be considered sufficiently accurate to reliably include this island in wider biogeographical analyses. Key Words: Butterflies, Ionian islands, Othoni, Richness, Species area relationship.