Proximate cues for predator searching: a quantitative analysis of hunger and encounter rate in the ladybird beetle, Coccinella septempunctata

Many mobile predators use different foraging behaviours depending on whether prey are clumped or uniformly distributed in space. It is believed that predators can increase foraging efficiency on patchily distributed prey if they alternate intensive searching (slow speeds and frequent, acute turns) with extensive searching (high speeds and infrequent, shallow turns). We used Fourier transforms, fractal dimension analysis and traditional single-value measures of movement to determine which proximate cue caused these changes in behaviour: frequency of encounter or degree of satiation. Over a range of encounter rates and levels of hunger, we found that larval ladybird beetles showed intensive search behaviour for varying levels of encounter frequency, but did not alter their behaviour when hunger level was manipulated. We provide a conceptual model that explains why encounter frequency is more likely than hunger level to determine search behaviour. We discuss the relative merits of Fourier transforms in relation to fractal dimension and single-value measures.