Insects feeding on seeds and fruits at BCI, KHC and WAN
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Unlike mutualistic pollination and seed dispersal networks, antagonistic seed predation networks have not been well studied in the tropics. We tested whether the structure of antagonistic tripartite networks composed of host plants, insects breeding in seeds and fruits and their insect parasitoids at three representative rainforest locations (Panama, Thailand, Papua New Guinea) can be predicted from plant phylogeny and plant traits. We considered subsets of the networks at each location, either based on insect families, plant families or plant functional groups. We reported 3,197 interactions and observed a low percentage of realized interactions, especially at the Panamanian site, where insect host specificity was higher than at the other two sites. Seed-eaters were more host-specific than pulp-eaters and insects feeding on dry fruits were more host specific than those feeding on fleshy fruits. Local plant richness did not influence insect host specificity, but other site characteristics may be important in this regard. Most networks were extremely specialized, such as those including Tortricidae and Bruchinae at the Panamanian site. Apart from sampling effort, plant phylogeny had an important effect on network structure, but this effect was not overwhelming, as variables related to plant resource (basal area) or plant traits (number of seeds per fruit) were also important, particularly for networks based on plant functional groups. Path analyses revealed no direct correlation between the number of compartments in plant-herbivore networks and those in plant-parasitoid networks, indicating limited support for the nasty host hypothesis. Our study emphasizes the duality between seed dispersal and seed predation networks in the tropics, as the former are not very specific while the latter are far more specialized and may include different keystone plant species. This underlines the need to study both types of networks including a variety of potential keystone plant species for sound practices of forest regeneration.