Insects feeding on seeds and fruits at BCI, KHC and WAN

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.