Diversity of regenerating plants and seed dispersal in two canopy trees from Colombian Amazon forests with different hunting pressure

Victoria Andrea Barrera Zambrano,Pablo R. Stevenson,Jenny Zambrano Moncada

doi:10.15517/rbt.v56i3.5727

Abstract

Hunting may have drastic effects on some populations of frugivores and seed dispersal agents, which in turn may affect patterns of forest regeneration and plant diversity. However, when a species disappears, it is possible that the population of other species increases due to competition release, compensating or not, their ecological roles. The main aim of this study was to measure density compensation in primate communities, their possible effects on seedling and sapling diversity, and compensation of seed removal rates in two canopy trees (Apeiba aspera and Hymenaea oblongifolia). The study site was Amacayacu National Park (Colombian Amazon), where we carried out a census of mammal species using line transect methods in two forests with different levels of hunting pressure. Vegetation plots were used to quantify plant diversity for seedlings and saplings (4 m2 and 25 m2 respectively), and fruit traps were set up to estimate seed removal of A. aspera and H. oblongifolia. Large primates were less frequently encountered near human settlements, while small primates exhibited the opposite pattern, suggesting a density compensation effect. The diversity of regenerating plants was higher in the forest where large primates occur. Seed removal was higher in forests with large primates for A. aspera, but not for H. oblongifolia. Overall, the results support the hypothesis of density compensation on the primate community; however, there is no strong evidence of ecological compensation in terms of seed dispersal and regeneration in the species studied. Finally, the presence of large seed dispersers (e.g. Lagothrix lagothricha) was associated with higher plant diversity.

Highlights

Central and western Amazonia tropical rain forests have been considered mega-diversity areas (Gentry 1988, Ter Steege et al 2003), and several hypothesis have tried to explain this fact (Tuomisto et al 1995, Wills et al 1997, Schupp et al 2002, Terborgh et al 2002)
Some plant species are known to have a limited number of seed dispersal agents
When large primates are heavily hunted and the population size of smaller primates increases, it is possible that some plant species will not reach an ecological compensation in terms of seed dispersal, because small animals might not fulfill the role of larger animals (e.g. Peres and Roosmalen 2002, Stevenson et al 2005a, Nuñez and Howe 2007)

Summary

Introduction

Central and western Amazonia tropical rain forests have been considered mega-diversity areas (Gentry 1988, Ter Steege et al 2003), and several hypothesis have tried to explain this fact (Tuomisto et al 1995, Wills et al 1997, Schupp et al 2002, Terborgh et al 2002). Plants may experience negative density and distance-dependent effects, caused by pathogens and seed predators, as well as intra-specific competition. According to this theory, in the absence of dispersal mechanisms, some species such as large seeded animal dispersed plants would not be. Large seeded endozoochorus plants rely on a few large frugivore species for dispersal (Janson 1983, Peres and van Roosmalen 2002, Stevenson 2007) Even in these plant species it is difficult to predict the effect of a population decrease in large dispersers due to the likelihood of concurrent compensation processes taking place. When large primates are heavily hunted and the population size of smaller primates increases, it is possible that some plant species will not reach an ecological compensation in terms of seed dispersal, because small animals might not fulfill the role of larger animals (e.g. Peres and Roosmalen 2002, Stevenson et al 2005a, Nuñez and Howe 2007)

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Results

Conclusion