Data from: Cascading effects of defaunation on the coexistence of two specialized insect seed predators

Identification of the mechanisms enabling stable coexistence of species
with similar resource requirements is a central challenge in ecology. Such
coexistence can be facilitated by species at higher trophic levels through
complex multi-trophic interactions, a mechanism that could be compromised
by ongoing defaunation. We investigated cascading effects of defaunation
on Pachymerus cardo and Speciomerus giganteus, the specialized insect seed
predators of the Neotropical palm Attalea butyracea, testing the
hypothesis that vertebrate frugivores and granivores facilitate their
coexistence. Laboratory experiments showed that the two seed parasitoid
species differed strongly in their reproductive ecology. Pachymerus
produced many small eggs that it deposited exclusively on the fruit
exocarp (exterior). Speciomerus produced few large eggs that it deposited
exclusively on the endocarp, which is normally exposed only after a
vertebrate handles the fruit. When eggs of the two species were deposited
on the same fruit, Pachymerus triumphed only when it had a long head
start, and the loser always succumbed to intraguild predation. We
collected field data on the fates of 6569 Attalea seeds across sites in
central Panama with contrasting degrees of defaunation and wide variation
in the abundance of vertebrate frugivores and granivores. Speciomerus
dominated where vertebrate communities were intact, whereas Pachymerus
dominated in defaunated sites. Variation in the relative abundance of
Speciomerus across all 84 sampling sites was strongly positively related
to the proportion of seeds attacked by rodents, an indicator of local
vertebrate abundance. Synthesis. We show that two species of insect seed
predators relying on the same host plant species are niche differentiated
in their reproductive strategies such that one species has the advantage
when fruits are handled promptly by vertebrates and the other when they
are not. Defaunation disrupts this mediating influence of vertebrates and
strongly favours one species at the expense of the other, providing a case
study of the cascading effects of defaunation and its potential to disrupt
coexistence of non-target species, including the hyperdiverse phytophagous
insects of tropical forests.