Land-cover change and effects at the local scale on pre-dispersal seed predation by Pachymerus nucleorum (Bruchinae) in the tropical palm Syagrus coronata (Arecaceae)

Abstract

Seed predation is a major seed event in palms and affects seedling recruitment and the economic value of fruits. We investigated variations in the vegetative and reproductive traits, demography, habitat structure (tree richness), and pre-dispersal seed predation in the palm Syagrus coronata (Martius) Beccari (Arecaceae) by Pachymerus nucleorum (Fabricius) (Bruchinae) in habitats with different management intensities in the Brazilian semiarid region. In addition, we also assessed whether these plant variables affect seed predation. The palm tree known as licuri is widely used in extractivism and its cutting is prohibited by the Brazilian law. It is common to find isolated individuals in landscapes managed for agriculture and pasture. We predicted that more homogeneous microhabitats (with lower diversity of woody plants and higher density of licuri) with little fruiting synchrony would have higher levels of seed predation. Moreover, at the plant level, licuri individuals whose bunch are taller from the ground and with a larger number of fruits would sustain a lower proportion of pre-dispersal seed predation. The study was carried out in 13 sites, distributed between managed (pasture) and natural (Caatinga vegetation) habitats. Overall, 3,120 fruits were assessed, out of which 25.6% were preyed by P. nucleorum. We found that habitats with natural vegetation supported a higher density of adult licuri individuals and richness of woody plants, lower licuri fruiting synchrony, and greater seed predation. In addition, seed predation was positively affected by both total licuri abundance and tree richness, and negatively by the abundance of licuri fruiting at a micro-habitat level. This palm has unseasonal fruiting throughout all months of the year, and we suggested that the fruit harvest could be concentrated in the months of fruiting peak and the managed areas. Such measures could result in the harvest of healthier fruits by extractive populations and in seeds free from predation for use in habitat restoration through direct seeding.