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Dung beetles relocate vertebrate feces under the soil surface, and this
behavior has many ecological consequences. In tropical forests, for
example, seeds defecated by mammals that are subsequently buried by dung
beetles are less likely to suffer predation. While the effects of dung
beetles on the fate of defecated seeds have been relatively well studied,
their effect on seeds already buried in the soil has not. To contribute to
fill this gap we designed a study with three objectives: (1) Describe the
vertical re-distribution of soil seeds that occurs due to dung beetle
activity; (2) Determine if beetle activity favors establishment of
seedlings from the soil seed bank; and (3) Determine if the effect of dung
beetles is stronger in sites of recurrent mammal defecation. We carried
out three complementary field experiments, one with artificial seeds
(plastic beads) of three sizes buried at known depths, one with two
species of seeds buried at those same depths, and one with the natural
soil seed bank in sites of single vs. recurrent defecation. Buried beads
were moved by dung beetles along the vertical axis, both upwards (9.5%)
and downwards (11.5%); smaller beads were more frequently moved downwards
while the contrary occurred for larger beads. Dung beetle activity caused
an increase in seedling establishment, both from experimentally buried
seeds and from the natural seed bank. Defecation recurrence had no effect
on seedling establishment. We conclude that dung beetle activity affects
seed bank dynamics with important consequences for seedling establishment
in tropical forests.
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