Deer diet selection is known to depend on nutrients and defense chemicals of plant leaves that provide benefits and costs to deer. On the other hand, a trade-off is expected between plant’s allocation to growth and defensive traits. Here, I focus on this trade-off and show that its seasonally deference largely determines deer preference. I conducted field experiment to determine sika deer (Cervus nippon yakushimae) preference, and quantified the amount of protein and defensive leaf traits. I constructed molecular phylogenetic tree to test correlations with the independent contrast method.

Deer preference increased with the amount of protein and decreased with the amount of tannin. In June, here was a trade-off between protein and tannin. However, the trade-off decreased in September, and the effect of protein on deer preference disappeared. In general, deer preferred deciduous tree species with larger amounts of protein, and avoided evergreen tree species with higher levels of leaf defense. While larger amount of protein enables plants to grow faster, higher levels of leaf defense result in decreasing allocation to protein. However, this relationship is weakened with phenology. This seasonal change of plant trait trade-off is considered to be behind deer preference.