Niche Partitioning at Emergence of Two Syntopic Dragonflies

We investigated the ecological requirements in the emergence phase of two congeneric species of Aeshnidae, Aeshna grandis (Linnaeus 1758) and A. juncea (Linnaeus 1758), occurring in syntopy at the southernmost limit of their range. We sampled the exuviae of the two species at the peak of their emergence in three lakes in NW Italy. In each lake we defined 30 to 50 sampling plots along the lake borders where we checked for the presence of exuviae and collected data on the microhabitat composition. By modeling the response of the exuviae presence and abundance against the environmental parameters, we could highlight a partial differentiation in the ecological requirements of the two species at emergence. In particular, A. grandis is more influenced by the structure of the aquatic vegetation than A. juncea and the niche space occupied by A. grandis is wider, almost totally encompassing the one of A. juncea. We argue that A. grandis exploits microhabitats rich in aquatic plants to avoid competition with A. juncea. We suggest the preservation of well-structured aquatic vegetation as a key management practice to preserve the three studied populations of A. grandis, a species which has been recognized as Vulnerable for Italy according to the IUCN criteria.