The role of rainforest dung beetles as secondary dispersers of seeds found in mammal defecations is well known, but other effects of their activity on rainforest plants are little known. During dung relocation, these insects also move seeds that are buried in the seed bank; when buried seeds are moved upward, seedling establishment may increase. Dung beetle activity also causes changes in soil properties that may benefit seedling performance. To assess these little known ecological functions of rainforest dung beetles we performed two field experiments in the Los Tuxtlas Biological Station, Mexico. To assess the effect of dung beetles on seed bank dynamics and seedling establishment, we manipulated the presence and recurrence of dung and the presence of dung beetles in an experiment with five treatments: dung with beetles, recurrent dung with beetles, dung with no beetles, recurrent dung with no beetles, no dung or beetles. We registered seedling establishment of woody plant species during eight months. To assess the effect of dung beetles on seedling performance we measured seedling growth, survival, and the concentration of foliar nitrogen and phosphorous, on experimental seedlings of two tree species under three treatments: dung with beetles, dung without beetles, no dung or beetles.
Results/Conclusions
Seedling establishment was affected by treatment; more seedlings established in plots with dung beetle activity, but dung recurrence had no significant effect. Contrary to expectations, dung beetle activity had no effect on seedling growth, seedling survival or the foliar concentration of nitrogen and phosphorus. For one of the seedling species we found higher phosphorus concentration in the ‘dung with beetles’ compared to the ‘dung without beetles’ treatment, but not compared to seedlings with no dung or beetles. Our results show that the activity of rainforest dung beetles can affect plant regeneration through at least one other mechanism besides secondary seed dispersal, namely, through their effects on seed bank dynamics. Although one previous study found increased foliar nutrient concentration in seedlings of a tropical tree species as a consequence of dung beetle activity, we did not find evidence of this effect or other effect on seedling performance (growth, survival). More studies in different forests (e.g., with different soil fertility) and including a larger number of plant species will be necessary before we can draw conclusions on the effects that dung beetle activity has on rainforest plants via increased nutrient availability.