When predators become prey: flight decisions in jumping spiders

Current optimal escape theory focuses on economic distance-based models that predict that animals will flee at greater distances when risk of capture is greater. Although these models have been tested extensively on vertebrate prey animals using large approaching stimuli (e.g., humans), it has never been tested on an invertebrate generalist predator with a stimulus that is in the size range of potential prey. I presented adult jumping spiders, Phidippus princeps, with a small black model to test flight decisions when physically handicapped, under different levels of threat, and on surfaces that potentially hindered escape. Predator approach speed, running surface texture, and leg autotomy had no effect on flight decisions. I also measured running distance and speed under different levels of hunger and energy state to test how these variables affect the decision to flee or to turn and defend oneself against a predator. When prodded, larger spiders fled shorter distances before switching to a defensive posture, hungry spiders fled longer distances than sated spiders, and rested spiders ran faster than tired spiders. There is likely a trade-off between body size and energy stores when deciding to flee from a threat or turning to defend oneself. These findings 1) reflect differences in how predators and prey assess risk in their environment and the distances at which they treat an approaching object as threatening and 2) suggest that future studies should focus on how animals optimize escape decisions in ways other than traditional distance-based economic models (e.g., relying absolutely on crypsis). Copyright 2009, Oxford University Press.