A highly resolved food web for insect seed predators in a species‐rich tropical forest

Abstract

The top‐down and indirect effects of insects on plant communities depend on patterns of host use, which are often poorly documented, particularly in species‐rich tropical forests. At Barro Colorado Island, Panama, we compiled the first food web quantifying trophic interactions between the majority of co‐occurring woody plant species and their internally feeding insect seed predators. Our study is based on more than 200 000 fruits representing 478 plant species, associated with 369 insect species. Insect host‐specificity was remarkably high: only 20% of seed predator species were associated with more than one plant species, while each tree species experienced seed predation from a median of two insect species. Phylogeny, but not plant traits, explained patterns of seed predator attack. These data suggest that seed predators are unlikely to mediate indirect interactions such as apparent competition between plant species, but are consistent with their proposed contribution to maintaining plant diversity via the Janzen–Connell mechanism.

Assessing the potential for indirect interactions between tropical tree species via shared insect seed predators

“…In contrast, phylogenetic relatedness and trait similarity between pairs of plant species had little effect on the corresponding d ij values, except for in one year (2016), when there was a significant positive association between the temporal overlap in fruit production and d ij . These host‐use patterns contrast strongly with those described by Gripenberg et al (), who found that the majority of woody plant species on Barro Colorado Island are attacked by highly host‐specific seed predators and that there is low potential for apparent competition in the wider plant community. What makes species in the Lauraceae family different from other taxa remains unclear, but the fact that many of the Lauraceae species on Barro Colorado Island have similar fruit morphologies and overlap in their fruiting phenology (supplying seed predators with a permanent food resource for much of the year) may have contributed to the high degree of overlap in seed predator–host use.…”

“…Preliminary investigations in 2011–2013 showed that insects damage a substantial proportion of Lauraceae fruits. Rearing of internally feeding seed predators revealed some overlap in the pre‐dispersal insect seed predator fauna associated with individual Lauraceae species (Gripenberg et al, ). While little is known about the biology of individual seed predator species, typically adult females lay one or several eggs on or in developing or mature fruits.…”

“…Existing studies of internally feeding insect seed predators (including post‐dispersal seed predators) suggest that these plant enemies tend to be relatively host‐specific (Gripenberg et al, ), but there are also cases where individual seed predator species are associated with multiple plant species, typically within the same genus or family (Ctvrtecka, Sam, Miller, Weiblen, & Novotny, ; Janzen, ; Sam et al, ). Such seed predator species could potentially link the regeneration dynamics of their host plant species via enemy‐mediated indirect interactions such as apparent competition (Holt, ; Lewis & Gripenberg, ).…”

“…Quantitative food webs have been used for this purpose in studies assessing the role of parasitoids in structuring communities of herbivorous insects (Morris et al, ; Tack, Gripenberg, & Roslin, ). Although existing methods (e.g., Lewis et al, ; Müller, Adriaanse, Belshaw, & Godfray, ) are directly applicable to studies of plants and their internally feeding seed predators (Lewis & Gripenberg, ), quantitative food web methods have only recently been applied in this novel context (Gripenberg et al, ; Jeffs et al ).…”

Quantifying the relative importance of competition, predation, and environmental variation for species coexistence

“…Measurements of demographic rates and food web interactions are usually made separately—often entire studies in their own rights (e.g. Dibner et al (2019); Gripenberg et al (2019)), and thus all the necessary information is difficult to obtain for many systems. As such, we encourage future work to examine both demographic rates along with trophic links and their corresponding strengths.…”