A. Kruess et T. Tscharntke, Species richness and parasitism in a fragmented landscape: experiments andfield studies with insects on Vicia sepium, OECOLOGIA, 122(1), 2000, pp. 129-137
Effects of habitat fragmentation on species diversity and herbivore-parasit
oid interactions were analyzed using the insect community of seed feeders a
nd their parasitoids in the pods of the bush vetch (Vicia sepium L.). Field
studies were carried out on 18 old meadows differing in area and isolation
. The area of these meadows was found to be the major determinant of specie
s diversity and population abundance of endophagous insects. Effects of iso
lation were further analyzed experimentally mentally using 16 small plots w
ith potted vetch plants isolated by 100-500 m from vetch populations on lar
ge old meadows. The results showed that colonization success greatly decrea
sed with increasing isolation. In both cases, insect species were not equal
ly affected. Parasitoids suffered more from habitat loss and isolation than
their phytophagous hosts. Minimum area requirements, calculated from logis
tic regressions, were higher for parasitoids than for herbivores. In additi
on, percent parasitism of the herbivores significantly decreased with area
loss and increasing isolation of Vicia sepium plots, supporting the trophic
-level hypothesis of island biogeography. Species with high rates of absenc
e on meadows and isolated plant plots were not only characterized by their
high trophic level, but also by low abundance and high spatial population v
ariability. Thus conservation of large and less isolated habitat remnants e
nhances species diversity and parasitism of potential pest insects, i.e., t
he stability of ecosystem functions.