Forest fragmentation truncates a food chain based on an old‐growth forest bracket fungus

Abstract

We studied the effect of forest fragmentation on the insect community inhabiting an old‐growth forest specialist bracket fungus, Fomitopsis rosea , in eastern Finland. Samples of the fungus from large non‐isolated control areas were compared with samples from forest fragments in two isolation time classes; 2–7 yr and 12–32 yr since isolation. Fomitopsis rosea hosted a species‐rich community with relatively many specialized old‐growth forest insects. The numerically dominant food chain consisted of F. rosea , the tineid moth Agnathosia mendicella and the tachinid fly Elfia cingulata , a specialist parasitoid of A. mendicella . The frequency of F. rosea on suitable fallen spruce logs and the frequency of A. mendicella in fruiting bodies were significantly lower in the forest fragments than in the control areas. The median number of trophic levels decreased from three in the control areas to one in the fragments that had been isolated for the longest period of time. The parasitoid was completely missing from the fragments isolated for 12–32 yr. Our results show that in boreal forests habitat loss and fragmentation truncate food chains of specialized species in the course of time since isolation.