Trade-off between seed defensive traits and impacts on interaction patterns between seeds and rodents in forest ecosystems

Plants often have two kinds of defensive traits against animal predation: physical and chemical defenses, but the trade-off between them is heavily debated, and their impacts on relationship between plants and animals are largely unknown. We investigated seed traits of 23 tree species and their impacts on seed fates or hoarding behaviors under predation from 16 rodent species in four forest types in China. We provide clear evidence that there is a strong nonlinear trade-off between physical (as measured by seed coat thickness) and chemical (as measured by tannin content) defensive traits in seeds. This trade-off was closely associated with nutritional traits, resulting in coordinated defense syndromes in seeds. The seed fate and hoarding behavior patterns were largely determined by the trade-off-related seed traits and the body mass of rodents, respectively, not by the phylogenetic relations of species. Tree species showed more conservative evolution in seed traits of high starch content, high tannin content, and thin seed coat, but they showed more convergent/divergent evolution in seed traits of high protein content, high fat content, and thick seed coat under rodent predation. Our results suggest that trade-off-related seed traits may play a predominant role in shaping the relationship between plants and animals.