Effects of dung beetles on seedling emergence from herbaceous seeds in the dung of sika deer (Cervus nippon) in a temperate Japanese grassland ecosystem

Abstract

The effects of dung form and condition and of dung beetles on the emergence of seedlings from herbaceous seeds in sika deer dung were examined in a temperate grassland ecosystem dominated by Zoysia japonica and Hydrocotyle maritima. I conducted field experiments to compare seedling emergence between dung exposed to dung beetles and intact dung using both dung pellets and pats during a typical rainy month (June) and the hottest, drier month (August), when large numbers of seeds of the dominant species were present in the dung. The exposed dung was immediately attacked and broken up by dung beetles, whereas dung protected from the beetles remained intact. In June, at least 12 herbaceous species, including Z. japonica, H. maritima, Mazus pumilus, and Plantago asiatica, emerged from the dung, versus at least six species in August. Decomposition rates of the pellets in June and decomposition scores of the pats in June and August were positively correlated with the number of emerging seedlings, suggesting that the acceleration of decomposition by dung beetles can positively affect seed germination. In this system of interactions among sika deer, herbaceous plants, and dung beetles, sika deer dung prevented seeds from germinating, and beetles had an indirect positive effect on seedling emergence by accelerating decomposition of the dung, although the extent of the effect may depend on the dung type, plant species, and environmental factors.

Increasing sika deer population density may change resource use by larval dung beetles

“…The feces of raccoon dogs and badgers have a high nitrogen content and contain the berry tree seeds of many species [45]. On the other hand, deer feces include grass seeds, and most tunneller dung beetles work as secondary dispersers of these seeds [46]. Therefore, an overabundance of sika deer may also affect the diverse ecological functions of dung beetles through a change in their diet, impacting on their material cycle functions and secondary seed dispersal.…”

Seed contents of sika deer (Cervus nippon) dung and the fate of seeds in a temperate short grassland in an urban park in Japan

“…In the same study area, seedlings of nine of the 26 species (five graminoids and four forbs) and an additional four forb species (Duchesnea chrysantha [Zoll. et Moritzi] (Ishikawa 2011). Thus, viable seeds of 13 herbaceous species, including Z. japonica (Kitagawa 1988, Takatsuki 2006, were excreted by sika deer at the study site.…”

“…Such approaches may underestimate both species and seed numbers (Couvreur et al 2004). The dung of herbivores may also contain many seeds that cannot germinate as a result of differences in germination conditions among plant species (Grime et al 1988, Ishikawa 2011 and/or in seed conditions such as immaturity, death, or dormancy. Grazing of immature seeds (including flower buds and flowers) or death of seeds by passing through the digestive tract may preclude the next generation.…”

“…This study was conducted in the Tobihino area (approximately 1.9 ha), which is a flat part of southeastern Nara Park (Ishikawa 2010(Ishikawa , 2011. The deer density is particularly high (between 430 and 5,500 individuals/km 2 ) (Foundation for the Protection of Deer in Nara Park unpublished data) in the Tobihino area.…”

Importance of restoration of dung beetles in the maintenance of ecosystem services

“…Plants respond to higher moisture in soils due to dung beetle activity through increases in plant growth (280%), leaf emergence (30%) and plant height (200%) under drought conditions in humid subtropical native pasture (Johnson et al, 2016) (Ishikawa, 2011).…”