A complex landscape favours the abundance and species richness of syrphids (Diptera: Syrphidae) in olive groves

Abstract

Sustainability of agroecosystems depends on the ecosystem services, provided by beneficial organisms, such as the syrphids (Diptera: Syrphidae) acting as other-insect predators and pollinators in different crops. In the case of olive groves, syrphids are predators of important pests and are endangered by the continuous intensification of agriculture, including landscape simplification. In this work, the effect of landscape structure on the abundance and species richness of syrphids in the olive agroecosystem of central Spain is assessed. Adult syrphids were sampled in 2015 and 2016 in the centre of circular areas of 15 olive grove landscapes (from 250 to 1500 m radius) representing a gradient of landscape complexity, in the province of Madrid, central Spain. The syrphid assemblage was made up of 57 species, although Eupeodes corollae, Eristalis tenax, Eristalis similis and Chrysotoxum intermedium made up 76% of the captures. Syrphid abundance and species richness were favoured in complex landscapes, with low olive grove area (CAO). Other landscape indices showed also this trend although their effect was not as strong and consistent as that of CAO. The area of scrublands (CAS) favoured syrphids in spring, but was unfavourable in autumn. The effect of Shannon's Evenness Index (SHEI) and mean shape index (MSI) was less consistent. The effect of CAO increased with increasing buffers radii, while the effect of CAS, SHEI and MSI was detected in general at smaller radii, indicating these indices affect different processes. Redundancy analysis (RDA) detected some differences between species regarding their abundance in spring versus autumn, and their relationship with landscape indices. This work provides new evidence that maintenance of complex landscapes is essential for maintaining functional biodiversity in the olive agroecosystem.