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Abstract
The mutualistic interaction between scatter-hoarding rodents and seed plants have
a long co-evolutionary history. Plants are believed to have evolved traits that influence
the foraging behavior of rodents, thus increasing the probability of seed removal
and caching, which benefits the establishment of seedlings. Tannin and nutrient content
in seeds are considered among the most essential factors in this plant-animal interaction.
However, most previous studies used different species of plant seeds, rendering it
difficult to tease apart the relative effect of each single nutrient on rodent foraging
behavior due to confounding combinations of nutrient contents across seed species.
Hence, to further explore how tannin and different nutritional traits of seed affect
scatter-hoarding rodent foraging preferences, we manipulated tannin, fat, protein
and starch content levels, and also seed size levels by using an artificial seed system.
Our results showed that both tannin and various nutrients significantly affected rodent
foraging preferences, but were also strongly affected by seed size. In general, rodents
preferred to remove seeds with less tannin. Fat addition could counteract the negative
effect of tannin on seed removal by rodents, while the effect of protein addition
was weaker. Starch by itself had no effect, but it interacted with tannin in a complex
way. Our findings shed light on the effects of tannin and nutrient content on seed
removal by scatter-hoarding rodents. We therefore, believe that these and perhaps
other seed traits should interactively influence this important plant-rodent interaction.
However, how selection operates on seed traits to counterbalance these competing interests/factors
merits further study.