Table 1.

Predicted consequences of increased phytochemical diversity based on long-standing general hypotheses or models

Predictions from hypotheses linking phytochemical diversity, plants, herbivores, and enemies	Relevant path coefficients	What support is provided by results from the Piper system?
Divergent phytochemistry hypothesis: Higher diversity of chemical defense within a plant community is associated with increased herbivore diversity and increased specialization in diet breadth (7, 8, 28, 29).	All path coefficients are relevant.	The overall results provide strong support for this general hypothesis, along with clear mechanisms for increasing herbivore diversity via increased specialization.
Screening hypothesis: Phytochemical diversity is maintained by high taxonomic and guild diversity of associated herbivores; increases in phytochemical diversity cause reduced total herbivory (2).	IA, IB	Results from this study are consistent with the screening hypothesis, with a strong effect of phytochemical diversity reducing herbivory and increasing toxicity.
Bottom-up cascade: Increases in plant diversity (including functional or phytochemical diversity) cause greater diversity at upper trophic levels through direct and indirect mechanisms (45).	IA, IB, IVA, IVB	Results provide good support for the bottom-up hypothesis and that phytochemical diversity (rather than toxicity) increases rates of parasitoid success.
Hypothesized mode of action: Phytochemical diversity of phototoxic compounds (associated with downfield NMR spectra) reduces the diversity of associated herbivores as well as overall herbivory (25, 26, 46, 47).	IC, ID, IE	Although further support for this hypothesis will require experimental work, the indirect evidence for this hypothesis is clear.
Extreme diet breadth hypothesis: Greater diversity of chemical defense is associated with more restricted diets for specialist herbivores and broader diets for generalist herbivores (19, 20).	IIA, IIB, IIC, IID	Results provide moderate support for this hypothesis. Path coefficients were not large for these specific associations, but local diet breadth is a complex variable affected by a mix of local biotic interactions and evolutionary history.
Coevolution is dead hypothesis: Specialization in herbivorous insects does not evolve in response to phytochemistry (48).	IA, IB, IIB, IIC	Results do not support the prediction of no relationship between phytochemistry, diet breadth, and herbivory (49).
Null hypothesis: Phytochemical diversity does not affect herbivory, herbivore diversity, phototoxicity, mean consumer diet breadth, or densities of upper trophic levels.	Null path model	This model is not supported by the Piper data.

The predictions are listed in order of decreasing support from the empirical data, and the key references for the major hypotheses (indicated in bold) that have generated these predictions are noted. The specific hypotheses tested were assessed with a priori path models (I, II, III, IV), and the support for these hypotheses is denoted by corresponding path coefficients (A–E).