Pollination is an essential biotic interaction to ecosystem functioning and ecosystem services provisioning, on which food security for humanity depends. Around 90% of angiosperms in natural habitats and 75% of agricultural crops depend on this interaction for fruit production and genetic diversity maintenance. Efforts towards pollinator conservation based on informed studies are a priority before the current global pollinator crisis.
We studied plant-pollinator interactions comparing natural and human modified environments in a tropical dry forest of the Pacific coast of Mexico: a) at the community level; b) focusing on the dioecious Spondias purpurea, the main managed species of this forest, grown for its edible fruits and also harvested from the wild; c) in animal pollinated agricultural crops, and focusing pollinator efficiency on the cultivated squash Cucurbita moschata. The study was carried out in the Chamela Cuixmala Biosphere Reserve and its surrounding area of influence.
Results/Conclusions
The results indicate a great diversity of plant-pollinator interactions in the tropical dry forest, with more generalized interactions under early secondary succession, where availability of floral resources was higher. The most abundant pollinators were three social bee species that are active all year around: Apis mellifera, Trigona fulviventris, and T. nigra. These species were also the main pollinators of S. purpurea accounting for almost 50% of the visits. Populations of natural and altered habitats did not differ in visitation rates, nor in sex ratios (1:1); however, fruit set was higher in conserved forest. Trees from altered habitats flowered earlier and produced more flowers (male and female individuals) than trees from conserved forests, though the number of pollen grains per flower were higher at the conserved forest. In agricultural landscapes, we recorded 22 pollinator species on seven animal pollinated crops, Apis mellifera accounting for 70% of the visits. For C. moschata, the main visitors in the rainy season were Peponapis spp. Exclusion experiments show that one visit to female flowers provides enough pollen to set fruit. We found seasonal changes in the pollinator assemblage of this species, A. mellifera attaining greater importance during the dry season. Most animal pollinated crops provide floral resources to pollinators only during a few months of the dry season, while their three main pollinator species are the same social bees that are active all year around, and therefore are highly dependent on forest floral resources to survive.