Effects of gut passage on seed germination: do experiments answer the questions they ask?

Abstract

Summary Frugivorous vertebrates may affect plant fitness by dispersing seeds to sites favourable for establishment and by passing seeds through their gut, thereby altering germination patterns. Although gut passage can inhibit germination, most studies have found that it improves germination rate and/or success. However, studies that compare seeds passed through a gut to seeds directly removed from a fruit cannot quantify the overall effect of gut passage on seed germination. They address the ecologically narrow question of whether mechanical and/or chemical action in the gut affects germination. They do not address the germination potential of seeds in unconsumed fruits and therefore ignore a common seed fate, deposition in a fruit. We surveyed 99 studies that included the effect of vertebrate gut passage on germination and found that only 22 included germination from intact fruits. We suggest that the strongest experimental design to evaluate the impact of gut passage should include intact fruits, since release from germination inhibitors and high osmotic pressure are mechanisms that can alter germination.