Seeds go up and down: The role of dung beetles in soil seed movement in the Southern Atlantic Forest of Argentina

The vertical movement of seeds performed by dung beetles from the soil
bank and in animal feces influences seed germination and the temporal
dynamic of forest regeneration. While this process has been explored at
the community level, the individual role of species is less understood.
Here, we investigated the role of dung beetle size and seed size in this
vertical movement under experimental conditions. We performed experiments
using a gradient of dung beetle sizes and three sizes of artificial seeds
(plastic beads) in two situations: inside feces (secondary dispersal) and
buried in the ground (soil bank). Through regression analysis, we related
dung beetle size, seed size, and the initial position of seeds on the soil
bank to the final position of seeds and their potential germination. For
seeds in the soil bank, upward movement and exhumation were mainly of
medium and large seeds, initially located at shallower depths, with larger
beetles being primarily responsible for this movement. The downward
movement was similar for all seed sizes. In dung seeds, the percentage of
small seeds buried gradually increased with beetle size, while larger
beetles made the main contribution for medium and large seeds. Besides,
all seed sizes were buried at an average maximum bury depth of nearly 4 cm
(the limit of the germination zone). The relative contribution of species
depended on the interaction between dung beetles and seed sizes. Moreover,
large dung beetles were essential for burying large seeds in the southern
Atlantic Forest.