Autotomy shapes the trade-off between seeking cover and foraging in larval damselflies

Animals commonly choose between microhabitats that differ in foraging return and mortality hazard. I studied the influence of autotomy, the amputation of a body part, on the way larvae of the damselfly Lestes sponsa deal with the trade-off between foraging or seeking cover. Survival of Lestes larvae when confronted with the odonate predator Aeshna cyanea was higher in a complex than in a simple microhabitat, indicating that this more complex microhabitat was safer. Within the simple microhabitat, larvae without lamellae had a higher risk for mortality by predation than larvae with lamellae, showing a long-term cost of autotomy. When varying the foraging value (food present or absent) and predation risk (encaged predator or no predator) in the simple microhabitat, larvae with and without lamellae responded differentially to the imposed trade-off. All larvae spent more time in the simple microhabitat when food was present than when food was absent. Larvae without lamellae, however, only sporadically left the safe microhabitat, irrespective of the presence of the predator. In contrast, larvae with lamellae shifted more frequently towards the risky microhabitat than those without lamellae, and more often in the absence than in the presence of the predator. These decisions affected the foraging rates of the animals. I show for the first time that refuge use is higher after autotomy and that this is associated with the cost of reduced foraging success. The different microhabitat preferences for larvae with and without lamellae are consistent with their different vulnerabilities to predation and demonstrate the importance of intrinsic factors in establishing trade-offs. Received: 4 June 1999 / Received in revised form: 18 August 1999/ Accepted: 18 August 1999