ONTOGENIC SHIFTS IN HOW GRASSHOPPERS INTERACT WITH LANDSCAPE STRUCTURE - AN ANALYSIS OF MOVEMENT PATTERNS

1. Patterns of animal movement provide a spatial record of how organis ms interact with landscape structure. 2. Although species may differ i n absolute measures of movement (e.g. net displacement), they may neve rtheless interact with landscape structure in similar ways. Fractal an alysis affords a scale-independent measure that assesses pattern struc ture across a range of spatial scales. Similarities in the fractal geo metry of movement pathways therefore indicate that species are interac ting with landscape structure in similar ways. 3. Within a species, di fferent life stages may possess different perceptions of landscape str ucture. To test this idea, I examined how developmental stages of a go mphocerine grasshopper (Orthoptera, Acrididae), Opeia obscura, interac ted with microlandscape structure in a grassland mosaic. 4. Adults mov ed two to six times farther and were more strongly influenced by micro landscape structure than were nymphs. The fractal dimensions of moveme nt pathways (an index of pattern complexity) differed significantly be tween life stages, indicating that adults and nymphs interacted with l andscape structure in different ways. 5. Nymphs traverse the landscape in a different manner to adults: nymphs leap between discrete vegetat ive structures (e.g. grass blades), whereas adults move across the pla ne of the landscape. Nymphs thus possess a finer perceptual grain of l andscape structure; nymphs move at slower rates and can resolve small- scale details. Adults move at faster rates across the mosaic, and may operate at a greater spatial extent than nymphs.