Fruit‐quality tradeoffs generate asymmetry in plant reliance on mutualistic frugivores

Seed dispersal is a fundamental ecological process influencing the evolution of plant life‐history strategies. In fleshy‐fruited plants dispersed by mutualistic frugivores, variation in fruit traits among closely related species may shape the temporal and spatial dynamics of dispersal events critical to population success. Here, we test a tradeoff model for dispersal strategies, inspired by Grime's triangle of life‐history tradeoffs, that links fruit quality and seed traits (e.g. nutrients, chemical defenses, seed dormancy) to plant reliance on frugivore‐mediated dispersal. The model predicts that species producing nutrient‐rich, rewarding fruits benefit from frequent frugivory interactions, leading to enhanced seed deposition and seedling recruitment across broader spatial and temporal scales. Conversely, species investing in chemically defended fruits or seed dormancy are expected to rely less on frugivores and more on vegetative reproduction or persistent seed banks. We experimentally evaluated this model using three Solanum species (Solanaceae) with distinct fruit traits and seed dormancy levels. For each species, we documented frugivory interactions and conducted a seed‐addition experiment in the field mimicking frugivore dispersal to assess how the spatial and temporal patterns of seed deposition by frugivores affect seedling emergence. Our results show that the Solanum species with sugar‐rich fruits experienced higher frugivory rates and greater seedling emergence under seed‐addition treatments mimicking frugivore dispersal. In contrast, species investing more in pulp defenses or seed dormancy engaged in fewer frugivory interactions and had lower seedling emergence in seed addition treatments mimicking dispersal by frugivores. Altogether, our findings show that differences in fruit traits and quality can mediate tradeoffs among dispersal strategies, leading to interspecific variation in how strongly plant species may rely on frugivory mutualisms for recruitment.