Reproduction, recruitment, and genetic diversity of the threatened tree species Manilkara maxima T.D. Penn.: An economically and ecologically important tree species from the biodiversity hotspot of southern Bahia, Brazil.

摘要

Habitat fragmentation is one of the major threats to biodiversity, by negatively affecting ecological and genetic processes in many species. Tree species in small fragmented forests have an increased risk of extinction with reduced reproduction, reduced recruitment, and genetic consequences. I utilized ecological, genetic, and spatial data to examine the effects of fragmentation on the IUCN vulnerable tree species, Manilkara maxima, in the Atlantic forest of southern Bahia, Brazil, a biodiversity hotspot. I estimated flower production, fruit set, seed dispersal, sapling recruitment, genetic diversity indices, and spatial genetic structure across two large forest sites (200 and 400 ha) and one site comprising eight small fragments (25, 10, and 5 ha) for adult and sapling life stages that were established pre and post fragmentation respectively. Density of both adults and saplings were significantly lower in the small fragment site. The effect of fragment size on reproduction and dispersal is less clear. Reproduction did not vary with fragment size, but fruit set decreased with increasing tree size. Vertebrates handled a majority of the fruits, but dispersal was not different among study sites. Recruitment patterns of saplings exhibited significant negative density dependence across all sites. Fragment size accounted for 71 and 56 % of density variation in adult and sapling trees, respectively, but did not account for genetic variation. Rather, density accounted for 64 and 60 % of allelic diversity and 57 % of allelic richness in adults and saplings, respectively. The lack of relationship between genetic diversity and fragment size was driven in part by a co-variation in density and genetic diversity in 25-ha fragments. Within the study sites weak to moderate spatial genetic structure (SGS) was found for both saplings and adults established pre and post fragmentation respectively. Sapling SGS was not significantly different among the study sites suggesting SGS has not been affected by fragmentation. Overall, the results suggest long distance dispersal is important for density dependent recruitment, maintaining genetic diversity, and influences genetic structure for fragmented populations. Conservation of animal pollinator and seed disperser species will be critical for the persistence of the threatened tree species, Manilkara maxima..