Reproductive Potential Within the Landscape: a Spatially-Explicit, Agent-Based Model of Asynchrony
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ABSTRACT Title: REPRODUCTIVE POTENTIAL WITHIN THE LANDSCAPE: A SPATIALLY-EXPLICIT, AGENT-BASED MODEL OF ASYNCHRONY Christopher Roland Guenther, Master of Science, 2005 Directed By: Professor William F. Fagan, Department of Biology Reproductive asynchrony, which can be a beneficial life-history strategy in healthy insect populations, may contribute to an Allee effect at small population densities. A spatially explicit, agent-based model is used to investigate quantitative effects of asynchrony on reproductive potential. Temporal and spatial isolation effects are treated independently and together. Three behaviors are explored: clustered emergence from host plants, hilltopping, and mating discretion by females. The magnitude of the reduction in overall spatial overlap within the simulated population is shown to be governed by the radius of circular, random-walk movement and potential interaction distance. Hilltopping behavior and clustered emergence partially alleviate detrimental effects of spatial isolation; female selectivity in mating can exacerbate the loss of reproductive potential. Among these three behaviors, hilltopping produced the largest differential in spatial/temporal overlap. REPRODUCTIVE POTENTIAL WITHIN THE LANDSCAPE: A SPATIALLY- EXPLICIT, AGENT-BASED MODEL OF ASYNCHRONY By Christopher Roland Guenther Thesis submitted to the Faculty of the Graduate School of the University of Maryland, College Park, in partial fulfillment of the requirements for the degree of Master of Science 2005 Advisory Committee: Professor William F. Fagan, Chair/Advisor Professor David Levermore Professor James Reggia Table of Contents Table of Contents.......................................................................................................... ii List of Figures.............................................................................................................. iv Chapter 1: Introduction................................................................................................. 1 1.1 Reproductive Asynchrony .................................................................................. 1 1.2 The Allee Effect.................................................................................................. 2 1.3 Agent-Based Models........................................................................................... 4 Chapter 2: Simulation ................................................................................................... 5 2.1 Behaviors ............................................................................................................ 6 2.1.1 Hilltopping................................................................................................... 6 2.1.2 Host Plants and Clustered Emergence ......................................................... 6 2.1.3 Female Mate Selectivity .............................................................................. 7 2.2 Emergence Location and Clustered Emergence ................................................. 7 2.3 Emergence Time ................................................................................................. 8 2.4 Time Iteration Actions ........................................................................................ 8 2.4.1 Overlap......................................................................................................... 8 2.4.2 Movement - Explicit versus Implicit ........................................................... 9 2.4.3 Movement - Algorithm .............................................................................. 11 2.5 Boundaries ........................................................................................................ 13 2.6 Female Selectivity and Attractiveness Rank..................................................... 13 2.7 Statistics............................................................................................................ 14 2.8 Implementation and Runtime............................................................................ 15 2.8.1 Pseudocode ................................................................................................ 15 2.8.2 Sorting and Bookmarks.............................................................................. 17 Chapter 3: Results....................................................................................................... 21 3.1 Default Parameters............................................................................................ 21 3.2 Isolating Temporal Effects................................................................................ 21 3.3 Random Movement, Random Emergence ........................................................ 25 3.3.1 Isolating Spatial Effects ............................................................................. 25 3.3.2 Temporal and Spatial Effects Combined ................................................... 27 3.4 Female Selectivity............................................................................................. 29 3.4.1 Selective Days versus Population Size ...................................................... 29 3.4.2 Selective Days versus Ratio Accepted....................................................... 31 3.5 Host Plant Emergence....................................................................................... 32 3.5.1 Number of Clusters versus Population Size............................................... 32 3.5.2 Number of Clusters versus Maximum Movement Distance...................... 35 3.6 Hilltopping........................................................................................................ 36 3.6.1 Movement Bias versus Population Size..................................................... 37 3.6.2 Movement Bias versus Maximum Movement Distance............................ 39 ii 3.7 Combinations of Life History Behaviors.......................................................... 40 3.7.1 Hilltopping versus Host Plant Emergence ................................................. 40 3.7.2 Hilltopping versus Female Selectivity....................................................... 41 3.7.3 Host Plant Emergence versus Female Selectivity...................................... 42 Chapter 4: Discussion ................................................................................................. 44 4.1 Temporal Effects............................................................................................... 44 4.2 Intrinsically Spatial Effects............................................................................... 45 4.3 Female Selectivity............................................................................................. 45 4.4 Host Plant Emergence....................................................................................... 46 4.5 Hilltopping........................................................................................................ 47 4.6 Combination of Behaviors ................................................................................ 48 4.7 Further Study .................................................................................................... 48 4.7.1 Real-World Data ........................................................................................ 50 4.8 Conclusion ........................................................................................................ 51 Bibliography ............................................................................................................... 53 iii List of Figures Figure 1: Allee Effect.................................................................................................... 4 Figure 2: Time Overlap Metric..................................................................................... 9 Figure 3: Mate Overlap Metric ..................................................................................... 9 Figure 4: Explicit Movement...................................................................................... 10 Figure 5: Implicit Movement...................................................................................... 11 Figure 6: Random Movement ..................................................................................... 12 Figure 7: Distribution of Population During Hilltopping ........................................... 12 Figure 8: Several Possible States of the Bookmarking Algorithm ............................. 20 Figure 9: Mate Overlap Ratio vs. Population Size for different values of w/W; Movement = 500; MID = 1500................................................................................... 23 Figure 10: Time Overlap Ratio vs. Population Size for different values of w/W; Movement = 500; MID = 1500................................................................................... 23 Figure 11: Ratio Unisolated vs. Population Size for different values of w/W; Movement = 500; MID = 1500................................................................................... 24 Figure 12: Ratio Mated vs. Population Size for different values of w/W; Movement = 500; MID = 1500................................................................................... 24 Figure 13: Time Overlap Ratio vs. w/W for different values of Population Size; Movement = 500; MID = 1500................................................................................... 25 Figure 14: Time Overlap Ratio vs. Population Size for different values of MID; Movement = 500;