Hosts as habitats: faunal similarity of phytophagous insects between host plants

1. Published lists on the phytophages recorded on 86 cabbage plant species (Brassicaceae) and 30 thistle species (Cynaroideae) were used to investigat e patterns in the faunal similarity of phytophages, This was done by calcul ating the Jaccard index and a standardised index of similarity between pair s of host species using presence/absence data. 2. The faunal similarity measured as Jaccard indices indicated that pairs o f cabbage hosts share on average 36% of phytophagous species whereas pairs of thistle hosts share only 10%. 3. The faunal similarity between two host species increased with the taxono mic affinity of hosts. This increase was more pronounced in thistles than i n cabbage plants. 4. Irrespective of the taxonomic affinity of hosts. in the cabbage plants t he faunal similarity of endophages was lower than in ectophages. In contras t, in the thistles faunal similarity differed only between endophages and e ctophages for hosts of the same genera. 5. Differences in the patterns of faunal similarity between the two host ta xa may be due to idiosyncratic characteristics of the plant taxa. e.g. the unique chemical properties of the cabbage plants and the resource-rich flow er heads of thistles.