Does plant diversity increase top–down control of herbivorous insects in tropical forest?

Abstract

Higher trophic level interactions are key mediators of ecosystem functioning in tropical forests. A rich body of theory has been developed to predict the effects of plant diversity on communities at higher trophic levels and the mechanisms underlying such effects. The 'enemies hypothesis’ states that predators exert more effective top–down control of herbivorous insects with increasing plant diversity. Support for this hypothesis has been found in temperate forests and agroecosystems, but remains understudied in tropical forests. We compared incidence of attacks of different natural enemies using artificial caterpillars in a tropical forest landscape and investigated the role of plant community structure (i.e. species richness, composition and density), and the role of forest fragmentation (i.e. patch size, edge distance and canopy openness) on predation intensity. Plant community effects were tested with respect to three vegetation strata: trees, saplings and herbs. Observed predation was substantially due to ants. Predation rates increased with plant species richness for trees and herbs. Density of saplings, herb cover and herb species composition were important factors for predation. No significant patterns were found for fragmentation parameters, suggesting that forest fragmentation has not altered predation intensity. We conclude that in tropical forests, top–down control of herbivorous insects in the understory vegetation is affected by a combination of plant diversity, plant species composition and structural features of the plant community.

Tropical tree diversity mediates foraging and predatory effects of insectivorous birds

“…Whereas other studies have found arthropod predators to be the dominant drivers of predation rates in forested systems and tropical regions [41,52], we found that birds were responsible for the majority of attacks on the artificial caterpillars and arthropod predation was very low in comparison. Our experimental system may differ because it lacks understory vegetation and is of relatively low diversity (even in high diversity plots) compared to typical forests at this latitude.…”

Plant neighbour identity and invasive pathogen infection affect associational resistance to an invasive gall wasp

“…The ''enemies hypothesis'' (Elton 1958;Root 1973) posits that plant communities with higher species richness provide more resources and habitats and thus can shelter more diverse predator or parasitoid communities (Wilby and Thomas 2002;Schuldt et al 2011;Castagneyrol and Jactel 2012), which could in turn provide a better control of herbivore populations (Riihimäki et al 2005;Leles et al 2017). A spill-over of natural enemies from associated to target trees is expected if associated and target trees share common or alternative prey or hosts (Cappuccino et al 1998).…”

Ant assemblage composition explains high predation pressure on artificial caterpillars during early night

“…The total average predation rate in this study (18% after 6 h exposure) was higher than other studies in tropical regions [e.g. 74.6% after 5 days (Sam et al ., ); 34.5% after 24 h (Seifert et al ., ); 20.9% after 4 days (Leles et al ., )] when we standardise it to predation rate over 24 h exposure (Lövei & Ferrante, ). We attributed the relatively high predation rate in our system to: (i) the predation caused by predators which had yet to learn to avoid the artificial caterpillars; and (ii) relatively high predation by ants (91%).…”

“…In this study, invertebrates (including ants) accounted for 94% of predation events, which was similar to the previous studies not only in this area (Leles et al ., ), but also in other tropical ecosystems (Loiselle & Farji‐Brener, ; Sam et al ., ). We found no significant differences in predation by ants between the day and night, which is consistent with predation by ants found in Amazonian rainforests (Seifert et al ., ).…”