Master's Thesis
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MASTER’S THESIS ‘Megabats’ Stephen Turnbull Department of Biological Sciences Faculty of Science Aarhus University, Denmark [email protected] Supervisor: Associate Professor Jens M. Olesen Cover photograph: Dorte Nyhagen Introduction Why megabats? A brief explanation of my experiences with megabats. I first came across megabats when studying for my honours project at Aberdeen University under the supervision of Professor Paul Racey – an intimidating yet extremely likeable giant of the bat world. I was to study Pteropus rodricensis, the famed golden fruit bat, endemic to the island of Rodrigues; a tiny far-flung speck in the Indian Ocean, politically aligned with Mauritius. I had some idea of what to expect, but no firm plans of how to carry out my studies, relying instead on my confident ability to improvise. Upon arrival, the island presented itself as a catalogue of environmental short-sightedness and ecological collapse, yet the fruit bats clung on to their perilous existence, saved from extinction by the irregular topography of some parts of the island. In a near- vertical and densely vegetated gorge, the bats could roost in peace during the day, flying to their feeding sites each evening at dusk, their destinations presumably carefully planned the previous night. I quickly came to realise a number of problems inherently linked with the study of fruit-bats. Firstly, they’re nocturnal. This presents a whole host of difficulties, not least of which being the absence of daylight. Secondly, there was no way in which to access their roost site, and even if I could, my clumsy approach would disturb them. Thirdly, they are pretty mobile. Not only could they easily fly the breadth of the island, something that took hours in a vehicle, they also flew above the canopy, accessing flowers and fruits beyond my reach (and again, mainly at night). What were accessible, however, were their excretions: ‘splats’ and ‘ejecta’ – the bread and butter of field biologists. In the end, and after a lot of watching the bats from cliff-tops at dusk and laying out plastic ‘splat-traps’ on the forest floor, I had to give up on the bat study and instead turned to plants, a somewhat less arresting but much more acquiescent group. Despite my failure to return any data, I had gotten a taste for megabats, and not long afterwards found myself back in the Indian Ocean, this time on Mauritius, studying the Mauritian fruit bat, Pteropus niger. This study was successful, and the data collected was used for the paper that forms part of this MSc project; ‘An investigation into the role of the flying fox, Pteropus niger, in forest regeneration’. Second only to working with the project coordinator, Dorte Nyhagen (who is now my wife), the most rewarding part of this study was our successful attempt to capture the bats in mist- nets, something that we were told could not be done. By granting us much closer contact with the bats, this brought the project to life in my mind, and gave me a deeper understanding of the animals themselves. My next and possibly most rewarding bat project was conducted in American Samoa under the knowledgeable gaze of Dr Ruth Utzurrum and her husband Dr Joshua Seamon. Ruth is another giant of the bat world and has amassed a great deal of experience and a host of publications and was a pleasure to work alongside. With funding provided by the American Samoan Government via US Federal Grants, we were able to conduct a thorough investigation into the movements of the two species of Pteropus on the main island of Tutuila using radio telemetry, the results of which form the second part of this MSc project. This required teamwork, and I was lucky enough to be working with the most uplifting group of Samoans you could meet; Chey, Visa, Ailao, and Saifoi (a.k.a. the ‘Brown Panther’). My experiences during this time were both deeply insightful and a great deal of fun, and my interest and understanding of megabats was firmly cemented. Some of the most memorable experiences include; raising orphaned bats to adulthood, witnessing the en-mass exit of roosting P. tonganus, seeing bats’ pupils dilate whilst feeding them sugared fruit-juice, learning to raise high mist nets to catch the uncatchable P. samoensis, and of course homing in on the signals of errant bats. Also during this time I travelled to New Caledonia where we captured and did blood work on the New Caledonia Blossom Bat, Notopteris neocaledonica, and the bear-like Pteropus vetulus, the New Caledonian flying fox. Upon my return to Denmark following the birth of my daughter, Nina, I continued to work with bats, although they were of course of the ‘micro’ variety. I was also fortunate enough to enter into the MSc programme at Aarhus University under the wise and friendly supervision of Professor Jens Olesen and the subsequent research project forms the final part of this MSc project. In a departure from my previous experiences, it is based upon a search of readily available literature and data from libraries and the internet. Whilst it would be absurd to directly compare field work with desk work, this experience has been of great personal benefit, having broadened my knowledge of megabats and helped further my career in the world of science. Stephen Turnbull Contents Part 1. ‘Megabats: Macroecology and Conservation Status’. Part 2. ‘Home Range and Core Area of the Flying Foxes Pteropus samoensis and P. tonganus on Tutuila, American Samoa’. Part 3. ‘An investigation into the role of the Mauritian flying fox, Pteropus niger, in forest regeneration’. Part 1. ‘Megabats: Macroecology and conservation status’. Megabats: Macroecology and conservation status Stephen Turnbull Department of Biological Sciences Faculty of Science Aarhus University, Denmark [email protected] Supervisor: Associate Professor Jens M. Olesen Table of Contents 1 Introduction ................................................................................................................................... 4 1.1 Definition of Megabats ............................................................................................................ 4 1.2 Megabat Classification ............................................................................................................. 4 1.3 Macroecology .......................................................................................................................... 5 1.4 Body Mass ............................................................................................................................... 5 1.5 Nectarivory .............................................................................................................................. 6 1.6 Isolation ................................................................................................................................... 6 1.7 Range ...................................................................................................................................... 7 1.8 Biogeographical ‘Rules’ and trends .......................................................................................... 7 1.8.1 ‘The Island Rule’ and Optimal Body Size ............................................................................ 7 1.8.2 Bergmann’s rule ................................................................................................................ 7 1.8.3 Rapoport’s rule ................................................................................................................. 7 1.8.4 Latitudinal Diversity Gradient (LDG) .................................................................................. 8 2 Methods ......................................................................................................................................... 8 2.1 Database construction ............................................................................................................. 8 2.2 Megabat Phylogeny ................................................................................................................. 9 2.3 Data analysis ............................................................................................................................ 9 3 Results and Discussion .................................................................................................................. 10 3.1 Limitations of data and data analysis ..................................................................................... 10 3.2 Genera and species ................................................................................................................ 10 3.3 Phylogenetic modelling .......................................................................................................... 10 3.4 Body mass ............................................................................................................................. 12 3.5 Nectarivory specialisation ...................................................................................................... 13 3.6 Geographic distribution of species ......................................................................................... 14 3.7 The Latitudinal Diversity Gradient (LDG) ................................................................................ 14 3.8 Isolation, ‘The Island Rule’, and an ‘ideal’ body size................................................................ 15 3.8.1 Geographical distribution of body masses ......................................................................