Assessing the benefits of frugivory for seed germination: the importance of the deinhibition effect

1. Many studies have examined the effects of frugivores on the germination of seeds of fleshy fruited plants. However, three key issues are rarely addressed: the need to measure germination of seeds in intact fruits; the effect of germination conditions on results; and the distinction between dead vs dormant seeds. 2. A literature review including 51 plant species from 28 families found that the often-measured scarification effect (germination of bird-defecated vs hand-cleaned seeds) is significantly smaller than the rarely-measured deinhibition effect (germination of hand-cleaned seeds vs those in intact fruits). 3. Both the literature review and new experimental data show that germination conditions affect germination. In particular, seeds in intact fruits have much lower germination percentages in Petri dishes than in the field. Poor germination from intact fruits in Petri dishes may be an artefact. 4. A field experiment with three New Zealand species showed variable effects of non-removal of the fruit pericarp. The retention of the pericarp had no effect on germination in Nestegis cunninghamii; increased the proportion of seeds entering dormancy in Melicytus lanceolatus; and greatly increased seed mortality in Pennantia corymbosa. 5. Germination experiments must be designed carefully to evaluate accurately the risks for plants of frugivory mutualism failures.