Land use impacts poison frog chemical defenses through changes in leaf litter ant communities

Much of the world’s biodiversity is held within tropical rainforests,
which are increasingly fragmented by agricultural practices. In these
threatened landscapes, there are many organisms that acquire chemical
defenses from their diet and are therefore intimately connected with their
local food webs. Poison frogs (Family Dendrobatidae) are one such example,
as they acquire alkaloid-based chemical defenses from their diet of leaf
litter ants and mites. It is currently unknown how habitat fragmentation
impacts chemical defense across trophic levels, from arthropods to frogs.
We examined the chemical defenses and diets of the Diablito poison frog
(Oophaga sylvatica), and the diversity of their leaf litter ant
communities in secondary forest and reclaimed cattle pasture. Notably,
this research was performed in collaboration with two high school science
classrooms. We found that the leaf litter of forest and pasture frog
habitats differed significantly in ant community structure. We also found
that forest and pasture frogs differed significantly in diet and alkaloid
profiles, where forest frogs contained more of specific alkaloids and ate
more ants in both number and volume. Finally, ant species composition of
frog diets resembled the surrounding leaf litter, but diets were less
variable. This suggests that frogs tend to consume particular ant species
within each habitat. To better understand how ants contribute to the
alkaloid chemical profiles of frogs, we chemically profiled several ant
species and found some alkaloids to be common across many ant species
while others are restricted to a few species. Our experiments are the
first to link anthropogenic land use changes to dendrobatid poison frog
chemical defenses through variation in leaf litter communities, which has
implications for conservation management of these threatened amphibians.