Habitat age increases reproduction and nutritional condition in a generalist arthropod predator

We studied the nutritional and reproductive response of Poecilus cupreus (synonymous with Pterostichus cupreus), one of the most abundant carabid beetles in arable land, to the succession in sixteen 1- to 4-year-old wildflower areas. A total of 390 male and 373 female beetles was examined. Each female was dissected and the number of ripe eggs counted. The nutritional state was expressed by a condition factor, which was calculated for each individual based on the observed weight and elytra length of male and female P. cupreus. Carabids in the 1-year-old wildflower areas contained significantly less ripe eggs than those from the 4-year-old areas. The condition factor of female and male beetles was significantly lower in 1- than 2- to 4-year-old areas. We examined the influence of habitat parameters (vegetation cover, soil water content, coarse and fine sand, pore volume, habitat size and age, surrounding landscape structure) on the reproductive success and nutritional state of P. cupreus in the 16 wildflower areas. The number of eggs was best explained by habitat age, accounting for 53.4% of the variability. The variation in the condition factor of female and male beetles was best explained by habitat age, which accounted for 73% and 71% of the variation, respectively. Moreover, the beetles' reproductive potential and nutritional condition were significantly associated with vegetation cover, and occasionally also with soil water content. The potential of wildflower areas as a reservoir for the generalist predator P. cupreus was shown to increase with successional age.