Niche partitioning in carabids: single-tree admixtures matter

The importance of tree mixtures to the faunal and floral biodiversity of forests has been documented on many occasions, but little is known about the relationships between single-tree effects, such as litter distribution and carabid beetles. The aim of the study was to investigate the relationship between the occurrence of carabid beetles and the locations of admixed oak trees within a Scots pine (Pinus sylvestris L.) stand. Individuals of four Carabus species were collected in dry pitfall traps in a pine forest with single admixed sessile oaks [Quercus petraea (Matt.) Liebl.]. The capture-mark-recapture technique was used to differentiate carabid beetles by species, gender (female, male), and development stage (imagines, larvae). Three zones of influence were defined according to the distribution of oak leaf litter. The beetle counts from trap data were transformed to a point pattern by means of a random-field approach where it is assumed that the beetle count per trap is representative of a specified number of single points in the square surrounding the trap. Spatial patterns specific to species, gender, and development stage were observed relative to the oak tree locations. Females and larvae of C. coriaceus and C. hortensis had a high affinity to the oaks, whereas C. violaceus revealed a negative association to the oak trees. No clear trend could be observed for C. arvensis. It was concluded that single-tree admixtures of oaks affect the spatial patterns of mobile organisms (e.g. Coleoptera) serving as ecological niches in pine forests.