Plantas raras e ameaçadas de extinção - sucesso reprodutivo, interações com polinizadores e implicações para a conservação

Abstract

Knowledge of reproductive biology is essential for the conservation of rare or endemic plants, and the definition of limiting factors for reproduction is particularly important to predict the populations’ viability of endangered species. This work investigated the relationships between the reproductive strategy and the rarity of three endangered species: Eriocnema fulva and Solanum graveolens, endemic to the Brazilian Atlantic Forest and Legrandia concinna, endemic to the andean Forest Deciduous of Chile. Illegitimate flower visitors reduce the reproductive success of E. fulva (Melastomataceae). In a population with about 50 individuals, bees of six species visited their flowers, but only three species collected pollen by vibration. The frequency of pollinating bees was negligible while worker bees of Trigona fulviventris (Apidae), which damage flowers, accounted for 70% of visits. During lengthy visits, they cut anthers to access the pollen, and often styles as well. The low fruit set (6.9%) of E. fulva is a direct negative consequence of flowers damage by Trigona bees, as well as their indirect impact by making the flowers unattractive for effective pollinators. Considering the rareness of this plant species, these negative effects endanger the maintenance of the E. fulva populations. Solanum graveolens is an andromonoecious species, the plants have hermaphrodite and staminate flowers, and the female function is expressed in flowers with a long style that grows gradually from the fourth to the sixth day in 73% of the flowers. In a population with about 30 individuals, females of seventeen species of bees visited the flowers to collect pollen: thirteen vibrated the anthers (79% of visits) and four did not vibrate (21%). Solanum graveolens is a self-incompatible species and shows limited pollination. The andromonoecius system presented by S. graveolens could work well if the population was larger, with greater possibility of crossing, however the number of plants in the population is reduced and causes a low fruit set. Thus, to protect and conserve this species, strategies such as increasing population size, promoting connectivity among them and preserving their habitat, including pollinating bees, should be implemented. Flowers of L. concinna (Myrtaceae) are important for the reproduction of Manuelia postica (Apidae), which feed their larvae with 82% of pollen of this species and to provisioning the cell breeding uses an average of 19 flowers of this plant. In a population with 20 individuals, bees of three species visited L. concinna flowers: Manuelia postica (53%), Bombus terrestris (39%) and Apis mellifera (8%), with a low visitation rate. Manuelia postica, the only native species that visited L. concinna, are small bees with low potential for pollen loading, lengthy flower visits, do not fly among individuals because they complete their scopa in few flowers of the same individual and by visiting few flowers, it contributes little for cross-pollination. While B. terrestris, less frequently than M. postica, can be considered the most efficient pollinator of L. concinna because it performs short visits, has a great capacity of pollen load, flies between individuals and visits numerous flowers, generally contacting the stigma. The reintroduction of L. concinna individuals would be recommended to increase their populations and the pollen resources for bees, since this plant is the source of a large amount of these resources. Manuelia postica and possibly other native bees, with more pollen resources, and more frequently, could potentiate the chances of pollination, improving the fitness of this critical threatened species.