Interactions between a high-mountain shrub, Genista versicolor (Fabaceae), and its seed predators

Abstract

:For three years we studied the interaction between Genista versicolor (Fabaceae) and three seed-predator species, one moth (Coleophora brunneosignata; Coleophoridae) and two weevil species (Exapion compactum and Exapion nov. sp.; Apionidae), to assess the impact of the insects on seed production and the reciprocal effect of the plant reproductive strategies on the insect’s survival. Plants experienced three predispersal mortality factors of ovules: early death of ovules, seed abortion and seed predation. Each fruit bore an average of 5.4 ovules, of which 4.0 ovules died early in their development and 0.1 aborted. Each fruit sets an average of 1.3 mature seeds. Seed predators invariably infested more than 65% of the fruits every year, killing 87% of the seeds ripened by the plants. More than 90% of the seeds predators were weevils. However, including the other two predispersal mortality factors, we found that the main loss was to ovule death (74% of the initial number of ovules), whereas seed predation destroyed 19% of the ovules. The effect of the plant on the seed-predator survival is somewhat different. Although weevils were parasitized by a wasp, the main mortality factor during the larval stage within the fruits was starvation. Of weevil larvae, 68% died before completing the life cycle because eggs were not laid on mature seed and were unable to enter a seed. As the plant capacity for filling seeds was not correlated with herbivory, the mortality of weevil larvae depended mostly on external predispersal events.