DIRICHLET TESSELLATION OF BARK BEETLE SPATIAL ATTACK POINTS

1. Algorithms for Dirichlet tessellation of spatial points are developed and implemented on personal computer. Up to 3000 tessellations of points in an area of any rectangular dimensions can be scaled appropriately and viewed on computer screen or output to laser printer. 2. The program also calculates Dirichlet cell areas and their coefficient of variation (CV) as well as the average nearest neighbour distance between points. 3. Simulations revealed the polynomial relationship between the CV and the minimum spacing between points. The relationship is used to predict the percentage of maximum spacing that is exhibited by a population. This value times the maximum spacing distance possible between objects in an area (hexagonal arrangement) yields the minimum allowed distance (MAD) that is characteristic of individuals of some territorial or 'inhibitive' species. 4. The program and relationship were used to analyse the spatial attack patterns of the bark beetles, Dendroctonus brevicomis LeConte, Tomicus piniperda (L.), and Pityogenes chalcographus (L.) and determine their MADs. All three species exhibited spacing between attack sites, in agreement with known behavioural mechanisms that are proposed for avoiding intraspecific competition for food resources.