Structural complexity of arthropod guilds is affected by the agricultural landscape heterogeneity generated by fencerows

MOLINA, GONZALO A R; POGGIO, SANTIAGO L.; GHERSA, CLAUDIO M.

ANNALS OF APPLIED BIOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2016 vol. 168 p. 173 - 184

0003-4746

Intensive farming imposes harsh conditions impeding the persistence ofmost arthropod species within crop fields. Hence, arthropods surviving theunfavourable conditions prevailing within crop fields may disperse towardsnearby uncropped margins, such as fencerows. Here, we evaluate the influenceof landscape heterogeneity on the abundance of different guilds, particularlyherbivores and their natural enemies. Said heterogeneity mostly derives fromfencerow network density. Hence, we developed an approach based on fittinglinear-mixed models to elucidate the effects of landscape heterogeneityand field position (fencerows and crop interiors) on arthropod diversity. Mixedmodels were fitted to arthropod data obtained by pitfall trap samplings in 36crop fields. Arthropod communities were structurally and functionally morecomplex along fencerows than within nearby crop interiors. Arthropods abundancewas modulated by landscape heterogeneity, increasing the abundanceof natural enemies as the landscape heterogeneity increased. On the contrary,herbivores abundance decreased as landscape heterogeneity increased. Consequently,the ratio between herbivores and natural enemies also decreasedas landscapes became more heterogeneous. Natural enemies with larger bodysizes, mostly carabid beetles, were more sensitive to landscape homogenisation.Our study reveals that, despite the coarse-grained landscapes in the RollingPampa, fencerow density appears as a key factor for structuring complex arthropodguilds in intensively farmed agriculturalmosaics. In landscapes with higherdensity of fencerows, arthropods tend to concentrate along them, thus increasingthe community structural complexity as well as the predation pressure overherbivores. This structural complexity of upper trophic levels enhances the?top-down? regulation of herbivore populations, consequently decreasing theprobability of pest outbreaks within crop fields.