Edge effects on trophic cascades in tropical rainforests

: The cascading effects of biodiversity loss on ecosystem functioning within forested systems have recently become more apparent. However, how edge effects shape these processes has yet to be established. Here we assessed how edge effects alter arthropod populations and the strength of any resultant trophic cascades on herbivory rate in tropical forests of Brazil. We experimentally excluded vertebrates from seven paired edge and interior sites in habitat with a high percentage of forest cover. Understory arthropods and percentage leaf damage were sampled every four weeks to give cumulative data summed over an eleven-month experimental period. Path analysis was used to determine the strength of trophic cascades within the interior and close to the edge. Within the forest interiors, vertebrate exclusion had a positive impact both predaceous and herbivorous arthropods, with significant cascading effects on herbivory. Edge-dwelling invertebrates responded weakly to exclusion and there was no evidence of trophic cascade. Our results suggest that the vertebrate community at forest edges controls invertebrate densities to a lesser extent than that within the interior. Edge habitat is known to support vertebrate communities with a smaller contingent of insectivores. This allows arthropods to flourish and indirectly accounts for higher levels of plant damage at these sites. Increased herbivory rates may have important consequences for floristic community composition and primary productivity, as well as cascading effects on nutrient cycling. By interspersing natural forest patches with agroforests, instead of pasture, abiotic edge effects can be softened and prevented from penetrating deep into the forest. This would ensure a greater proportion of forest remains habitable for sensitive species and could help to retain ecosystem functions within edge zones. Article impact statement: Changes in vertebrate communities with edge creation leads to loss of ecosystem function in tropical forests. This article is protected by copyright. All rights reserved.