Plant-herbivore interactions influence tropical rainforest biodiversity across time and space, yet a clear signature of such interactions requires finding consistent patterns across myriad host-specific interactions and disentangling complex biotic and abiotic processes. Recent studies have shown that multivariate plant defense traits among co-occurring species collapse into defense syndromes, distinct strategies for mitigating fitness losses. Plant defense syndromes may indicate a role for plant-herbivore interactions in shaping community assembly, yet they may also be linked to overall resource allocation strategies or simply reflect inherited defense traits that are not actively selected for in the extant community. We combined foliar measurements of defense, growth, and longevity traits with a DNA barcode community phylogeny to evaluate the existence and independence of plant defense syndromes within a tropical canopy tree community in Panama. We found two lines of evidence for the existence and independence of plant defense syndromes within this tropical canopy tree community. First, defense traits do not follow simple patterns of bivariate trade-off, nor do they contrast uniformly with growth or longevity traits. Instead, patterns of allocation to growth, chemical defense, or physical resistance/longevity collapse into three distinct defense syndromes, which are well-aligned with the plant defense syndrome triangle described by Agrawal and Fishbein (2006). Secondly, defense traits show markedly less phylogenetic conservatism than traits related to growth and longevity. Phylogenetic signal, expressed by Blomberg’s K, was lower and generally less significant for defense traits compared to traits related to growth and longevity. Phylogenetic autocorrelograms revealed the recent divergence of all defense traits, in sharp contrast with an increase in similarity for growth and longevity traits among closely related species. These findings suggest that plant defense has contributed to the overdispersion of niches among related species and the emergence of several functionally-distinct defense syndromes operating within the canopy community, and supports the role of plant-herbivore interactions in shaping community assembly
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