Habitat fragmentation and habitat quality interact synergistically and can drastically affect survival and fitness of insect herbivores. Here, we perform a case study to assess the effect of habitat quality and fragmentation on the morphology of a large, mobile, generalist insect herbivore, the bird locust, Ornithacris cyanea (Orthoptera: Acrididae). Four isolated, semi-natural grassland fragments within an exotic timber plantation matrix were ranked in terms of their habitat quality on the basis of vegetation surveys, management actions, and habitat context surrounding the fragments. Mark-release-recapture was used to estimate bird locust population size. Bird locusts from each fragment were measured for nine morphological characters: four length characters and five asymmetry and phenodeviation characters expected to be indicative of developmental instability. The highest density of individuals was found in an intermediate-quality fragment. Individuals from the poorest quality fragment had significantly shorter hind femurs than those from the best-quality fragment. Females from the poorest quality fragment also had significantly shorter forewings and more forewing pattern phenodeviation than females from other fragments. Morphological differences among the four populations indicated that they were distinct and that the population at the poorest quality site displayed adaptation for reduced mobility and increased developmental instability. Although we cannot determine whether populations were distinct due to inherent preferences of the species or as a result of reduced movement because of the inhospitable matrix, the correlation of morphological differences with habitat quality indicates that even highly mobile, generalist species can undergo rapid adaptations within isolated fragments and in response to varying habitat quality.
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Vol. 22 • No. 4