LARGE MOTION VISUALIZATION AND ESTIMATION FOR FLAPPING WING SYSTEMS

Studies of fluid-structure interactions associated with flexible structures such as flapping wings require the capture and quantification of large motions of bodies that may be opaque. Motion capture of a free flying insect is considered by using three synchronized high-speed cameras. A solid finite element representation is used as a reference body and successive snapshots in time of the displacement fields are reconstructed via an optimization procedure. An objective function is formulated, and various shape difference definitions are considered. The proposed methodology is first studied for a synthetic case of a flexible cantilever structure undergoing large deformations, and then applied to a Manduca Sexta (hawkmoth) in free flight. The three-dimensional motions of this flapping system are reconstructed from image date collected by using three cameras. The complete deformation geometry of this system is analyzed. Finally, a computational investigation is carried out to understand the flow physics and aerodynamic performance by prescribing the body and wing motions in a fluid-body code. This thesis work contains one of the first set of such motion visualization and deformation analyses carried out for a hawkmoth in free flight. The tools and procedures used in this work are widely applicable to the studies of other flying animals with flexible wings as well as synthetic systems with flexible body elements.

Bat-plant pollination interactions in southern Thailand

The overwhelming majority of flowering plant species depend on animals for pollination, and such pollinators are important for the reproductive success of many economically and environmentally important plant species. Yet pollinators in the Old World tropics are relatively understudied, particularly paleotropical nectarivorous bats (Pteropodidae), and much is unknown about their interactions with night-blooming plant species. To better understand these bat-plant pollination interactions, I conducted fieldwork in southern Thailand for a total of 20 months, spread across three years. I examined the foraging times of pteropodid bat species (Chapter 1), and found that strictly nectarivorous species foraged earlier, and for a shorter duration, than primarily frugivorous species. I also studied year-long foraging patterns of pteropodid bats to determine how different species track floral resources across seasons (Chapter 2). Larger species capable of flying long distances switched diets seasonally to forage on the most abundant floral species, while smaller species foraged throughout the year on nearby plant species that were low-rewarding but highly reliable. To determine which pteropodid species are potentially important pollinators, I quantified the frequency and effectiveness of their visits to six common bat-pollinated plant taxa for an entire year (Chapter 3). The three strictly nectarivorous species were responsible for almost all pollination, but pollinator importance of each bat species varied across plant species. I further examined the long-term reliability of these pollinators (Chapter 4), and found that pollinator importance values were consistent across the three study years. Lastly, I explored mechanisms that reduce interspecific pollen transfer among bat-pollinated plants, despite having shared pollinators. Using a flight cage experiment, I demonstrated that these plant species deposit pollen on different areas of the bat’s body (mechanical partitioning), resulting in greater pollen transfer between conspecific flowers than heterospecific flowers (Chapter 5). Additionally, while I observed ecological and phenological overlap among flowering plant species, pollinators exhibited high floral constancy within a night, resulting in strong ethological separation (Chapter 6). Collectively, these findings illustrate the importance of understudied Old World bat pollinators within a mixed agricultural-forest system, and their strong, interdependent interactions with bat-pollinated plant species within a night, across seasons, and across years.

FREQUENCY DOMAIN CHARACTERIZATION OF OPTIC FLOW AND VISION-BASED OCELLAR SENSING FOR ROTATIONAL MOTION

The structure of an animal’s eye is determined by the tasks it must perform. While vertebrates rely on their two eyes for all visual functions, insects have evolved a wide range of specialized visual organs to support behaviors such as prey capture, predator evasion, mate pursuit, flight stabilization, and navigation. Compound eyes and ocelli constitute the vision forming and sensing mechanisms of some flying insects. They provide signals useful for flight stabilization and navigation. In contrast to the well-studied compound eye, the ocelli, seen as the second visual system, sense fast luminance changes and allows for fast visual processing. Using a luminance-based sensor that mimics the insect ocelli and a camera-based motion detection system, a frequency-domain characterization of an ocellar sensor and optic flow (due to rotational motion) are analyzed. Inspired by the insect neurons that make use of signals from both vision sensing mechanisms, advantages, disadvantages and complementary properties of ocellar and optic flow estimates are discussed.