Testing the defence trade‐off hypothesis: how contents of nutrients and secondary compounds affect fruit removal

Abstract

Fruit removal has been attributed to the contents of nutrients and secondary compounds. We tested two alternative models of the chemical defence of fruits for the contents of nutrients, phenols, and condensed tannins and the nutrient content pypothesis stating that nutrient rich fruits are preferably removed. The defence trade‐off hypothesis assumes that the retention of deterrent secondary metabolites in ripe fruits reflects a trade‐off between defence against pests and attraction of dispersers. The removal‐rate model of this hypothesis predicts a negative relationship of nutrients and levels of secondary compounds due to short persistence and thus low infection risk of fruits. The nutrient‐toxin titration model postulates a positive relationship assuming that profitable fruits are able to afford high levels of protection due to a compensatory effect of high nutrient levels for consumers. Fruit removal by the entire frugivorous community for 33 plant species was best described by a dose–response curve, mediated by the stimulating effects of lipid, carbohydrate, and nitrogen contents, while the contents of phenols and water deterred removal. Moreover, traits that stimulated removal prevailed in ripe fruits except for nitrogen, unripe fruits had higher contents of phenols and nitrogen. Profitable fruits were quickly removed and had low phenolic contents. Thus, fruit removal was characterised by the nutrient content hypothesis and pulp contents by the removal‐rate model. The selective pressure of 84 frugivorous species integrated into an unidirectional preferential removal of nutrient rich fruits. The consistency of consumers’ preferences implies the potential for habitat shaping processes due to differential recruitment of plant species based on dispersers’ choices.