The influence of habitat quality on populations: a plea for an amended approach in the conservation of Agonum ericeti

We investigate the catching rate of the stenotopic peat bog ground beetle Agonum ericeti by reanalysing seven earlier studies from peat bogs in north-west Germany in order to investigate the relationship of the abundance of the species and parameters of habitat quality. The multiple regression analysis revealed that the cover of peat moss species of hummocks and the cover of other moss species was positively related with the trapping numbers of A. ericeti whilst an increasing cover of grass led to a decrease in beetle numbers. The relationships found show the preference of A. ericeti for natural or near-natural peat bogs, as an increasing amount of grass in peat bogs is seen to be linked with a deterioration of these habitat types. Our results underline the importance not only of the size and isolation of habitats harbouring endangered species but also of improving the habitat quality which turns out to be a crucial factor for the long-term-persistence of populations. The potential of A. ericeti as a target species for monitoring in peat bogs is discussed.