Density dependence in flower visitation rates of cockroach-pollinatedClusia blattophilaon the Nouragues inselberg, French Guiana

Abstract

Abstract:The effective floral neighbourhood is the radius around a plant where the density of flowering plants and other factors affect visitation rates and pollination success of plants. This study aims to determine this radius and focuses on the effects of conspecific plant density, plant sex and the amount of shrub vegetation on visitation rates ofClusia blattophila, a dioecious bush pollinated byAmazonina platystylatacockroaches. The number of visits did not differ between flower sexes but cockroaches spent less time on the rewardless female flowers. The density effect was scale dependent. The distribution of flowering individuals within the 15-m radius had a significant positive effect on flower visitation rates. At a larger scale (35–45-m radius), an increase in density of male plants led to a decrease in visitation rates, indicating competition for pollinators. Within the smaller radius, the facilitative effect was probably induced by elevated floral advertisement and high mobility of cockroaches at this scale. Within the larger radii, the results indicated that cockroach mobility was restricted and population density was stable at this scale. Density of male plants affected visitation rates because only male plants reward pollinators. Hence, male plants were the true competitors.