Ant body size mediates functional performance and species interactions in carrion decomposer communities

Growing concern over rapid species declines and extinctions has led to
considerable interest in the role of biodiversity for maintaining
ecological processes. However, the loss of particular species has more
pronounced effects on ecosystem services than others, highlighting the
importance of key functional species traits and their relationships to
ecosystem functioning. Human induced disturbances, such as species
invasions, land use changes or abiotic changes, appear to
disproportionally impact larger species rather than smaller ones. The loss
of large-bodied species in the community diminishes key ecosystem services
like seed dispersal, pest control, pollination and decomposition. Here we
use carrion, a nutrient-rich ephemeral resource, to test the hypotheses
that ants positively affect decomposition rates and that their role in the
necrophilous community – as predator or decomposer – is mediated by body
size. We further investigate the relative contribution of maggots vs. ants
to biomass decomposition. Our results show that ants contributed
positively to the decomposition process. Moreover, decomposition was
shaped by an intricate interplay between competition and predation among
the guild of decomposer insects. As predicted, larger ants show a double
action in increasing decomposition rate and predating on maggots, while
small ants are rather inefficient decomposers and did not act as predators
on other decomposer species. Our study shows that differentiating key
taxonomic groups in function of their body size is key to untangle the
diversity and directions of the various roles they play within complex
ecological processes.