UCLA

Tropical rainforests are among the most structurally complex environments on earth. In these ecosystems, animals disperse the seeds of up to 90% of tree species, a process that influences vegetation structure in turn. In this dissertation, I use animal tracking and remote sensing to reveal elements of a feedback loop between 3D rainforest structure and movements of seed-dispersing birds and bats in southern Cameroon. In Chapter 1, I synthesize current research in a literature review that describes the feedback between vegetation structure and animal ecological roles. This chapter provides a worked example for applying the feedback loop concept to conservation problems. In Chapter 2, I assess how 3D rainforest structure can shape seed dispersal patterns by influencing movements and habitat selection of black-casqued (Ceratogymna atrata) and white-thighed hornbills (Bycanistes albotibialis). The seed dispersal model in this chapter incorporates hornbill selection for canopy height, vertical complexity, and distance to canopy gaps in a framework that maps spatial probabilities of seed dispersal. In addition, the results show that white-thighed hornbills tend to avoid swamp habitats, while black-casqued increase their preference for swamps during the hottest temperatures—a key niche difference between the species. In Chapter 3, I use recent advances in spaceborne remote sensing to show how 3D vegetation structure influences hammer-headed bat (Hypsignathus monstrosus) habitat selection over their full movement trajectories. Hammer-headed bats prefer swamp habitats, intermediate canopy height, and areas closer to canopy gaps. Chapter 4 combines approaches from Chapters 2 and 3 to show how seed dispersal patterns by hornbills arise from diversity in both movement behavior and landscape-scale habitat selection. Black-casqued and white-thighed hornbills clustered into three “movement syndromes” based on variation in movement distances and home range size. Seed dispersal models involving hornbills from all three movement syndromes yielded the greatest diversity in both distances and directions of seed dispersal routes. The results of this dissertation show the importance of movement behavioral diversity for seed dispersal and provide further evidence for a feedback loop between vegetation structure and animal ecological roles.