Insect herbivory, plant defense, and early Cenozoic climate change

Insect damage on fossil leaves from the Central Rocky Mountains, United Sta tes, documents the response of herbivores to changing regional climates and vegetation during the late Paleocene (humid. warm temperate to subtropical , predominantly deciduous). early Eocene (humid subtropical, mixed deciduou s and evergreen), and middle Eocene (seasonally dry, subtropical, mixed dec iduous and thick-leaved evergreen). During all three time periods, greater herbivory occurred on taxa considered to have shout rather than long leaf l ife spans, consistent with studies in living forests that demonstrate the i nsect resistance of long-lived, thick leaves. Variance in herbivory frequen cy and diversity was highest during the middle Eocene, indicating the incre ased representation of two distinct herbivory syndromes: one for taxa with deciduous, palatable foliage, and the other for hosts with evergreen, thick -textured, small leaves characterized by elevated insect resistance. Leaf g alling, which is negatively correlated with moisture today, apparently incr eased during the middle Eocene, whereas leaf mining decreased.