Frequency-dependent seed selection by rodents: Response to seed tannins and sizes

Abstract

Seed predation by rodents relies on the abundance of available seeds and seed traits like sizes and tannin-content. Here, by tracking the fates of 2400 tagged seeds of two sympatric tree species Quercus wutaishanica and Corylus heterophylla with varying size and tannin content, we assessed rodents’ preference for specific seed traits. Meanwhile, we set the ratio of large to small seeds within species as 9:1, 7:3, 5:5, 3:7, and 1:9, respectively, to examine rodent behavior in response to seed relative frequencies. We found that: 1) rodents preferentially hoarded C. heterophylla seeds with lower-tannins after dispersal while Q. wutaishanica seeds with higher-tannins are more often eaten in situ or after dispersal. Peeling seed coat is an adaptive strategy for rodents to avoid high tannins, particularly for Q. wutaishanica. 2) Rodents prioritize small seeds over large ones for Q. wutaishanica whereas significant differences were not observed for C. heterophylla. Rodents commonly eat small seeds after successful dispersal and prefer to hoard larger ones over long distances. 3) Positive frequency-dependent selection was observed for both seed types. Our results suggest that the selection of seeds by rodents is determined by seed tannins and sizes, and changes in seed size frequencies could alter the interaction between trees and rodents from predation towards mutualism.