Abstract
BackgroundThe complex network of direct and indirect relationships determines not only the species abundances but also the community characteristics such as diversity and stability. In this context, seed predation is a direct interaction that affects the reproductive success of the plant. For Acrocomia aculeata, the seed predation by Pachymerus cardo and Speciomerus revoili in post-dispersal may destroy more than 70% of the propagules and is influenced by the herbivory of the fruits during pre-dispersal. Fruits of plants with a higher level of herbivory during pre-dispersal are less attacked by predators in post-dispersal. We proposed a hypothesis that describes this interaction as an indirect defense mediated by fungi in a multitrophic interaction. As explanations, we proposed the predictions: i) injuries caused by herbivores in the fruits of A. aculeata favor fungal colonization and ii) the colonization of A. acuelata fruit by decomposing fungi reduces the selection of the egg-laying site by predator.Methodology/Principal FindingsFor prediction (i), differences in the fungal colonization in fruits with an intact or damaged epicarp were evaluated in fruits exposed in the field. For prediction (ii), we performed fruit observations in the field to determine the number of eggs of P. cardo and/or S. revoili per fruit and the amount of fungal colonization in the fruits. In another experiment, in the laboratory, we use P. cardo females in a triple-choice protocol. Each insect to choose one of the three options: healthy fruits, fruits with fungus, or an empty pot. The proposed hypothesis was corroborated. Fruits with injuries in the epicarp had a higher fungal colonization, and fruits colonized by fungi were less attractive for egg-laying by seed predators.Conclusion/SignificanceThis study emphasizes the importance of exploring the networks of interactions between multitrophic systems to understand the dynamics and maintenance of natural populations.
Highlights
Terrestrial ecosystems are characterized by high species richness and a wide range of interactions among these species
The treatment group, which consisted of fruits that were perforated to simulate herbivory in pre-dispersal, had a higher rate of fungal colonization than did the control group, which consisted of intact fruits
The treatment group had a higher rate of fungal colonization, both the treatment and the control group displayed an increasing tendency in the colonization rate until approximately 20 days of exposure
Summary
Terrestrial ecosystems are characterized by high species richness and a wide range of interactions among these species. Ecological interactions between two species can often be indirectly mediated by a third species [3,8,9,10,11] This type of interaction is described in the literature mainly regarding plant defenses against herbivores (performed by ants) [12,13,14,15,16], the attraction of parasitoids by volatile substances produced by plants under attack by herbivores [17,18], and interactions in which the presence of endophytic fungi, pathogens, or mycorrhizae defends the plants by producing secondary metabolites that have different effects on the performance of herbivores [19,20,21,22,23]. We proposed the predictions: i) injuries caused by herbivores in the fruits of A. aculeata favor fungal colonization and ii) the colonization of A. acuelata fruit by decomposing fungi reduces the selection of the egg-laying site by predator
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