Standard deviation of carabid size in Western German forest succession - a complex picture

The large size range of carabids (Coleoptera: Carabidae) in, e.g., Western German beech and Douglas fir forests depends on the colonization of various habitats and microhabitats. These may change in the run of forest succession. Therefore, we hypothesized an increase of different microhabitats in ageing forests that is reflected by a corresponding rise in size variability within each of, e.g., two carabid species (Carabus violaceus, n = 2,853; Carabus problematicus, n = 428) in comparable forest stands of increasing age. Beetles were trapped according to Barber on 18 separate forest stands (beech: 14 sites, 1 - 165 years; Douglas fir: 4 sites, 1 - 30 years) over the vegetation period 2009. Subsequent to determining the species their elytrae were longitudinally measured. The mean values as well as standard deviations (SD) of elytrae length were calculated for the males and females in order to analyze correlations between SD of male and female beetle sizes and age of the stands by Spearman rank test statistics. In our most abundant species (C. violaceus) there was no significant correlation between elytrae-length SD of males (beech: 18.24 plus or minus 0.70mm, n = 1,560; Douglas fir: 18.23 plus or minus 0.65 mm, n= 104) and females (beech: 19.71 plus or minus 0.77, n= 1,120; Douglas fir: 19.57 plus or minus 0.85 mm, n = 69). Except for a non-significant trend indicating a positive correlation between size SD of male C. violaceus and forest age (combined beech and Douglas fir, p = 0.051) our initial hypothesis could not be confirmed, neither for C. violaceus nor for C. problematicus. In conclusion, more field-ecological data on the variety of microhabitats in forest succession should be generated in order to elucidate the complex picture of differences in carabid size.