Effect of Habitat on the Life History Strategies of Some British Grasshoppers

Abstract

The effect of habitat on life history strategies was examined in 2 spp. of grasshopper (Chorthippus parallelus and Chorthippus brunneus) in 3 habitats-dry grassland, wet meadow, and heathland-listed in order of decreasing favorableness. For both species, egg eclosion commenced in the order: dry grassland, wet meadow, heathland, thus potentially shortening the breeding season on the later sites. A decrease in the nymphal developmental periods on the later sites lowers the age at 1st reproduction, counteracting this. The preoviposition period of the adult females remains unchanged between populations. The reproductive effort of C. brunneus is greatly increased both within clutches and over the breeding season in the later populations. Larger clutches of larger eggs are produced. Total egg production per female therefore increases in the later populations. C. parallelus displays similar increased reproductive effort over the whole breeding season, but produces larger eggs in more, smaller clutches. Total egg production per female does not vary between populations. The suitability for egg development appears to decrease from dry grassland to wet meadow to heathland. Egg weight may increase in response to this in both species. C. brunneus also has a corresponding increase in adult mortality. Thus, for both species there is an increase in density-independent mortality of the eggs and/or adults. These interpopulation changes in the age at 1st reproduction and reproductive effort agree with the predictions of the r-K theory, although there is some discrepancy in the size and number of offspring.