Hoarding of acorns by granivorous mice and its role in the population processes of Pasania edulis (Makino) Makino

Abstract

In order to evaluate the role of granivorous mice, Apodemus speciosus Temminck and Apodemus argenteus Temminck, in the regeneration of Pasania edulis (Makino) Makino, an evergreen tree, we conducted field studies examining acorn crops, the population dynamics and hoarding behavior of mice and pre‐ and postdispersal acorn predation in an evergreen broad‐leaved forest dominated by P. edulis in Kagoshima, southern Japan. The study was conducted from 1994 to 2000. Apodemus mice selected sound acorns and hoarded them in the soil after transporting them for distances ranging from 5.4 to 19.9 m. This behavior appeared to be beneficial to the establishment of seedlings of P. edulis. However, the positive effects were negated by a high rate of recovery of the acorns hoarded by the mice. A life‐table analysis of five cohorts of P. edulis indicated that postdispersal predation of acorns by Apodemus mice was a major contributor to annual variation in the number of new seedlings. A considerable number of acorns germinated only in years with a good acorn crop and a low level of resident mice. These results suggest that Apodemus mice are serious acorn predators rather than important dispersers. After germination, acorns were attacked by the acorn borer at a high rate. From these results, we can conclude that acorn production probably makes a smaller contribution to the regeneration of P. edulis than coppice shoot production at the study site.

Determinant factors in the seedling establishment of Pasania edulis (Makino) Makino

“…The feeding scar of P. leucogenys was recorded in a few occasions (Sone et al 2002). The Japanese monkey (Macaca fuscata), the Japanese squirrel (Sciurus lis), and Sika deer (Cervus nippon Nippon) also eats acorns, but we did not observe them during the study period.…”

“…However, seeds are also a food resource for many granivorous and omnivorous animals. Many seeds produced by trees do not establish as seedlings, because they are subject to mortality from a range of sources, namely, predation by mammals and insects on the tree (e.g., Tanaka et al 1989;Maeto 1995;Sone et al 2002), predation by mammals after dropping to the ground (e.g., Shaw 1968;Watts 1968;Zemanek 1972;Sato 2000;Shimada 2001;Sone et al 2002), and attacks on germinated acorns by mammals, insects, and microbes (e.g., Ueda et al 1993;Sone et al 2002). Therefore, seed predation and other forms of seed mortality during the early stages of the population process (i.e., the period from seed production to seedling establishment) may have a serious impact on the regeneration of tree species.…”

“…P. edulis trees show major year-to-year variation in acorn production (Sone et al 2002). Because of their large size (2-4 g: 5-10 cal acorn À1 ) and low tannin content (0.5 %), P. edulis acorns are the primary food resource of Apodemus mice during autumn and winter.…”

“…Furthermore, dropped acorns are fed on by large or medium-sized omnivorous mammals such as wild boar (Sus scrofa leucomystax), badger (Meles meles anakuma), and raccoon dog (Nyctereutes procyonoides viverrinus), as well as the acorn borer (Coccotrypes graniceps) until seedling establishment (Sone et al 2002). Among these predators, the two species of Apodemus mice not only feed on but also hoard acorns of P. edulis less than 5 cm in the soil Kohno 1996, 1999;Sone et al 2002), and their hoarding activity facilitates germination if not recovered or pilfered as Vander Wall (1990) pointed out. Consequently, it is possible that these mice not only interfere with but also facilitate the regeneration of P. edulis trees.…”

“…Consequently, it is possible that these mice not only interfere with but also facilitate the regeneration of P. edulis trees. Sone et al (2002) speculated on the conditions required for the regeneration of P. edulis and the role of Apodemus mice during the early stages of its population process. This work was accomplished through the life table analysis, using the data of P. edulis acorn crops from five cohorts, in parallel to a survey of the hoarding behavior of Apodemus mice.…”