Medium-sized mammals carried seeds of dogwood trees farther than birds did

Different contributions of birds and mammals to seed dispersal of a fleshy-fruited tree

Yoshihiro Tsunamoto (a), Shoji Naoe (a), Takashi Masaki (b), Yuji Isagi (c)

(a) Tohoku Research Center, FFPRI, Morioka, Iwate, Japan.

(b) Principal Research Director, FFPRI, Tsukuba, Ibaraki, Japan.

(c) Kyoto University, Kyoto, Japan.

Basic and Applied Ecology 43, 66 March 2020 DOI：10.1016/j.baae.2019.07.005( External link )

Numerous birds and mammals eat the fruits of trees and disperse the seeds by excreting them, contributing to the growth of next-generation trees and the expansion of their distribution. However, it is difficult to directly study the behavior of such frugivores inside forests, and little has been known about how seeds are dispersed.

The present study examined dogwood trees, whose fruits are eaten by both birds and mammals. Using two types of genetic analysis, we successfully revealed the roles of each frugivore species. First, we identified the mother trees of seeds from the seeds' DNA sequences, and derived the seed dispersal distance from the locations of the seeds and the mother trees through SSR (simple sequence repeat) genotyping. Next, we examined the DNA sequences of the excrement which contained the seeds to identify the animal species which had dispersed the seeds (DNA barcoding).

As a result, we found that the average seed dispersal distance by all bird species (such as small and medium-sized birds like thrushes and green pigeons) was short (13m), and that many if not most of the seeds had been dropped immediately beneath tree crowns. On the other hand, the average seed dispersal distance of medium-sized mammals (such as badgers and raccoon dogs) was much longer (127m). These results suggest that small and medium-sized birds play a role in regeneration near mother trees, while medium-sized mammals help to expand the distribution of trees.

Revealing the roles of each type of such seed-dispersing animals will provide useful information for forest management, especially for warm temperate and tropical forests where seeds of numerous trees are dispersed by animals.

Figure : There is a large difference between the distances that birds and mammals carry seeds.

Photo : Traps that were set up to collect seeds