Trophic diversity, niche breadth and generation times of exopterygote insects in a secondary succession.

Various ecological characteristics have been determined for the exopterygote insect fauna of three sites in a secondary succession, with successional ages zero-two years (ruderal and early successional - Young Field), seven to eight years (mid successional - Old Field) and around 60 years (late successional - Woodland). The taxonomic diversity of the group as a whole (Table 1) and the trophic diversity (major types of feeding habits) (Table 2) increased with successional age. A comparison of the numbers of individuals and species of insect with the abundance and species of plant of each of the main life forms (annuals, biennials, perennials, trees, grasses (and rushes), ferns and lower plants) showed that at the start of secondary succession there was a good correlation between the number of species of insect and number of species of plant. In the second year and later the correlation is between plant abundance and insect abundance (the number of individuals) (Table 3). The sap-feeding insects may be divided into three specialised guilds: phloem feeders, xylem feeders and mesophyll feeders. The proportion of species in each guild was similar in all four successional stages (Table 4). Niche breadth (determined from host plant records) in the sap feeding herbivores was inversely related to the successional age of their habitat (Table 6). Herbivore species colonising the stages early in succession had, on average, shorter generation times than those of later stages (Table 7).