Impatto dei predatori lungo un gradiente forestale di urbanizzazione in Danimarca

Abstract

Along an urbanization gradient ranging from forest, dominated by wild Fagus, to fragments of original forest in the Sorø urban park in southern Denmark (Island Zealand), ground beetles do not show a decrease in their overall diversity, but species with a preference for forest decrease (Magura & al. 2010, Global Ecology and Biogeography). Seeking an explanation for this anomaly, predation and competition rates were analyzed in different habitats at different levels of urbanization. To this end, an innovative method was used (Howe & al. 2009, Entomol. Exp. Appl.), consisting of placing artificial lepidopteran larvae made of green plasticine and exposing them for 24 hours in different habitats. Many predators do not recognize that this is artificial prey and leave bite marks on the plasticine. For the analysis of interspecific competition, food was placed on plates, where food occupation indicates the presence of competitors. Predation rates in the first two months of spring were variable, but generally high (15-50%) in all three habitat types. Beetles, ants, small mammals, and birds were identified as the most frequent predators. The predation intensity of small mammals was highest in the suburban area. They are also predators of ground beetles, indicating that the scarcity of ground beetles in suburban habitats can be attributed to the high activity of this group. An estimate of competition primarily from ants (Formicidae) is indicated. The results underscore that the ecology of ground beetles cannot be interpreted without considering other groups that are part of the same guild (generalist predators), nor can the activity of predators of the target group (ground beetles) be ignored.