Interhabitat variation in diplochory: Seed dispersal effectiveness by birds and ants differs between tropical forest and savanna

Abstract

Diversified assemblages of frugivores interact with fruits/seeds in tropical environments. Species within assemblages vary largely in body size, abundance, seed treatment and places of seed deposition, with possible delayed consequences for seed dispersal and plant regeneration. The variable outputs of the interaction may be magnified when considering different habitats and diplochoric plants that include more than one agent in subsequent steps of dispersal. Here we compared the contribution of birds and ants to the seed dispersal effectiveness (SDE) of two species of Etythroxylum shrubs that grow in Atlantic forest and Cerrado savannas in Brazil. We compared the number of seeds dispersed by each one of 16 bird and 30 ant species and their delayed consequences for seed germination and seedling survival combining experimental and modeling approaches. We observed shifts in the role of different dispersal agents between habitats, with birds being more important in the forest while ants are highlighted in the savanna. Quantity and quality components of SDE were not correlated, but large body size emerged as an important trait driving the quantity (birds) and quality (ants) components of SDE. A high diversified assemblage of dispersal agents does not always result in redundant effects for SDE, with some species consistently providing better dispersal than others and several opportunities for complementary effects. Therefore, even in diversified assemblages operating in diplochoric dispersal systems, there is the opportunity for ecological specialization.