Discovering interaction between oaks and carabid beetles on a local scale by point pattern analysis

The understanding of habitat demands of single species needs an explicit habitat element approach which includes both the effect of intensity of the habitat element on the species population and the spatial effect of that habitat element in a given matrix (e.g., forest or water). An established tool in ecological research for this purpose is the point pattern analysis, which yields information on relationships between organisms and habitat elements, as well as on interactions among individuals. However, the application of this tool seems to be restricted so far to locally fixed species and habitat elements. As our model system consists of carabid beetles and single old oak trees in a Scots pine forest, we needed to address the issue of fauna mobility in point pattern analysis. We adopted a random field approach to transform the lattice beetle traps data to point data. For the resulting bivariate point pattern we applied the toroidal shift test to verify the independence of tree and beetle distribution. To overcome the problem of irregular window shape, we reconstructed the oak data to obtain a point pattern in a larger rectangular window to make toroidal shifts possible. We could justify a positive spatial association between oak tree and carabid beetle distributions. By our results, specific spatial fields of oak influence on the beetle species can be derived which may allow for beetles supporting management measures like an increase of oak tree proportion and a more regular spatial distribution of single admixed oak trees. Those measures may increase the ecological effect of C. coriaceus as an antagonist for pest insects in mono-cultured Scots pine forests.