University of Cape Town and the National Research

The copyright of this thesis vests in the author. No quotation from it or information derived from it is to be published without full acknowledgementTown of the source. The thesis is to be used for private study or non- commercial research purposes only. Cape Published by the University ofof Cape Town (UCT) in terms of the non-exclusive license granted to UCT by the author. University University of Ca pe Town THE DEFENSIVE ROLE OF ULTRASONIC MOTH CLICKS AGAINST BAT PREDATION: A MATHEMATICAL MODELING APPROACH Daniel De Lemos Ribeiro Town A THESIS SUBMITTED TO THE FCapeACULTY OF SCIENCE IN FULFI LL MEN T OF THEof REQUIREMENTS FOR THE DE GREE OF MASTER OF SCI ENCE February 2007 University Su pervisors A. Prof D. S. Jacobs ZoolOgy DepJrtrnent Abstract Some moths emit ultrasonic clicks in response to bat echolocation calls. These clicks are believed to serve as a defence mechanism against bat predation by means of jamming, aposematism or startle. By assessing the characteristics and variation of the ultrasonic moth clicks it was possible to define the most likely function of the ultrasonic clicks by moths from sites in South Africa. Additionally, this study used Schaefer based mathematical models informed by field data on moth diversity and abundance, moth click parameters and bat population numbers and diversity, from these same sites in South Africa, to gainTown insight into the conditions that are required for each of these functions to work. The Jamming hypothesis proposes that moth clicks function by interferingCape with the bat's perceptual system, which is believed to be most effectiveof in the terminal phase of the bat's attack were the clicks have been shown to be the most similar to the bats echolocation calls. This would place functional constraints on the clicks, decreasing the variation in the clicks. This was shown not to be the case, as a high level of variation was found between species' clicking parameters (e.g. peak frequency, inter pulse interval and intensity). A highUniversity level of individual moth variation was also found, with numerous patterns being produced by the same moths. Clicking variation was created both by manipulation of individual tymbals (e.g. changes in modulation cycle rate and durations) and between tymbals (e.g. timing of tymbal alternation). Furthermore the moth clicks are too different to bat echolocation calls to allow them to be mistaken by the bat as echoes from its own calls. The aposematic hypothesis suggests that the ii clicks function as a warning signal to inform the predator of the prey's unpalatability. As in visual based aposematism, the cost of. predator learning on the prey population would exert selective pressure towards higher densities of clicking moths and convergence in warning signals. This would allow one species to benefit from the predator learning induced by another species. This strategy is thus density dependent and would require a minimum proportion of clicking moths to work. Both the data from the ultrasonic moth clicks and mathematical modelling does not support this hypothesis as there is no signs of convergence and the mathematical modelling suggests that the low proportion of clicking moths (2.3%) in the natural moth population does not allow bats to form the associationTown between moth clicks and noxiousness of the moth. In the case of jamming, the low proportion of clicking moths also does not reflect the competitiveCape advantage supposedly gained from jamming. The startle hypothesis proposesof that moth clicks confuse the bat by altering the normal sequence of expected events during the bat's attack. However, bats will habituate to these sounds if they are encountered regularly. Both the low proportions of clicking moths and the extreme variability of the click patterns hinder habituation and are consistent with the startle hypothesis, which suggest that the most likelyUniversity function of ultrasonic moth clicks in these South African sites is startle. On the other hand, the aposematic and startle models do suggest that the existence of both noxiousness and clicking create the initial conditions for the evolution of an aposematic function for moth clicks. If the clicking moth is noxious the startle effect of the clicking could allow the population to grow to high enough numbers to make the aposematic function of the clicks viable. iii Acknowledgements I would like to start by thanking my parents for their support. This masters would have not been possible without them. A very special thanks Corrie Schoeman, David Gwynne-Evans, Dinko Basich, Geeta Eick, Erika Mendes, Jua Marques, Lyndal Pottier, Maryalice Walker, Uno Parriera and Verity Shandler for the assistance in my masters. I thank my co-supervisor Anesh Govender for the many hours of assistance on the mathematical component of the thesis. Without his extensive mathematical lessons and overall advice this masters would have been muchTown weaker than it is at present. More importantly his support as a friend kept me motivated during some of the problems that occurred during the masters. I thank my supervisor David Jacobs for his input and editing that wentCape into the thesis, especially towards the end. Having English as my ofsecond language the first drafts were scary confusions. I thank Simon Perkins for the programming lessons and helping with the development of theUniversity program. I thank David Gwynne-Evans for his botanical help in identification and biomass calculations. I thank Dr. Jongens from University of Cape Town's acoustics department for allowing access to the acoustic chamber and sound metering equipment, vital for the calculation of true intensities of the moth clicks. Very special thanks to Martin KrOger from the Lepidoptera Department at the Transvaal Museum. His knowledge on the Lithosiinae iv subfamily was crucial for the identification and description of the new species. I also thank Dr. Picker from the Department of Zoology at the University of Cape Town and Dr. Van Noort from the Iziko Natural History Museum in Cape Town for helping with identification of problematic moths. I also thank the Algeria Forestry Station and the Western Cape Nature Conservation Board for permission to work in the area. This study was funded by DLR and grants to DSJ from the University Research Committee of the University of Cape Town and the National Research Foundation of South Africa. Town Cape of University v Table of Contents Abstract .................................................................. :.............................................. ii Acknowledgements ............................................................................................. .iv Table of Contents ..................................................................................................vi List of Tables .........................................................................................................ix List of Figures ....................................................................................................... ix Chapter One: Bats, Moths and Mathematical Models Introduction ........................................................................................................... 1 Jamming ...............................................................................................................Town 3 Aposematism .........................................................................................................5 Startle .....................................................................................................................8 Mathematical Modelling .......................................................................................Cape 10 Aims .....................................................................................................................of 11 Chapter Two: Variation in ultrasonic moth clicks in the context of bat predation University Introduction ......................................................................................................... 14 Jamming ................................................................................................... 14 Aposematism ............................................................................................ 15 Startle ........................................................................................................ 18 Aims ..........................................................................................................18 Materials and Methods ......................................................................................... 19 Moth capture .............................................................................................20 vi Clicking moths and sound recordings ......................................................22 Data analysis .............................................................................................23 Result. ...................................................................................................................26 Moth population diversity ..........................................................................26 Clicking diversity .......................................................................................28 Clicking patterns ........................................................................................36 Discussion ............................................................................................................52 Proportions of clicking moths ...................................................................

Load more