Temporal Patterns in the Herbivorous Insects of Bracken: A Test of Community Predictability

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Abstract
Data on the abundance and seasonal phenology of herbivorous insects feeding upon bracken at Skipwith Common, in North Yorkshire [UK] in the years 1980-86 were used to determine the temporal predictability of this assemblage, both on an open site and on an adjacent woodland site. There were seventeen species on the open site, plus pooled data on two genera each with two species, and one genus with three species: twenty taxa in all. The woodland site held fifteen species, plus the same pooled genera: eighteen taxa in all. For simplicity we refer to all the taxa as species. In both habitats taxonomic composition, and relative mean peak and total seasonal abundances per frond for each species are all conserved across years. In other words, rare species have remained rare, and common species common over the 7-year study period. On the open site, slightly less complete data allow us to extend these conclusions over 15 years. Species have also tended to enter the community in a predictable sequence each year, more so on the open site than in the woodland. This assemblage conforms to the characteristics of one of the four theoretical ideal community types defined by Strong, Lawton and Southwood (1984) (type ii). Populations appear to be subject to density-dependent control, and therefore the community has a reasonably predictable structure, but it is not saturated with species and interspecific competition is unimportant.