Elevational Relationship between Functional Leaf Traits and Insect Herbivory in Two Cloud Forest Understory Species in Mexico

ABSTRACT The composition, diversity, structure, leaf characteristics and productivity of plant communities in cloud forests vary along altitudinal gradients. These changes may drive interactions with insect herbivores; however, the empirical evidence is scarce. We evaluated seven leaf traits (specific leaf area, leaf density, leaf strength, C, N and water content, and C:N ratio) and insect herbivory of two shrub species (Xylosma flexuosa, Cinnamomum psychotrioides) at two elevations (1300 and 1600 m asl) in a Mexican cloud forest. We expected higher leaf herbivory at 1300 m, associated with a higher quality of leaf tissues (high specific leaf area, water and N content). Plant traits differed between species and elevation. In X. flexuosa, leaf density and C:N ratio were higher at 1600 m, while N content, leaf strength and C content were lower. In C. psychotrioides, only leaf density was higher at 1300 m. In accordance with these traits, herbivory was higher at 1300 m, but only in X. flexuosa. Herbivory levels ranged from 1% to 4.7% and were higher in X. flexuosa than in C. psychotrioides. Variation in leaf traits determines herbivory levels in X. flexuosa; however, perceived differences may also relate to biotic or abiotic factors driving herbivore abundance.