RESUMEN
Foragers make decisions based on cues, information collected from their environment, processed into strategic behaviours. This information, processed in multiple regions of the brain, ultimately result in the production of stress hormones and visible changes in behaviour of animals - both reflexively to avoid depredation and strategically to avoid an encounter with the predator. In a common-garden experiment we tested how imperfect information from visual cues of a predator impacts foraging and apprehension of a desert rodent, the Egyptian gerbil (Gerbillus pyramidum). The gerbils were exposed to predation by barn owls (Tyto alba), one camouflaged on dark nights using black dye. Gerbils' response to the owls was measured using patch-use measured in giving-up densities (GUDs) and time spent in vigilance activity. Owl lethality was extrapolated from mean times spent in attacks and number of attempted strikes. Dyed owls attack-rate was lower and attack duration greater than those of the white owls. During the full moon, when dyed owls were visible, gerbils responded with extreme vigilance and minimal foraging (high GUDs). During the new moon when the owls were most stealthy, the gerbils showed low vigilance coupled with a similar high GUD. The inconsistency between gerbils' foraging and vigilance behaviours, suggest a likely mismatch between perceived risk and actual measurement of predator lethality gathered by the gerbils' observations in real time.
Asunto(s)
Gerbillinae , Animales , Conducta PredatoriaRESUMEN
Desert communities world-wide are used as natural laboratories for the study of convergent evolution, yet inferences drawn from such studies are necessarily indirect. Here, we brought desert organisms together (rodents and vipers) from two deserts (Mojave and Negev). Both predators and prey in the Mojave have adaptations that give them competitive advantage compared to their middle-eastern counterparts. Heteromyid rodents of the Mojave, kangaroo rats and pocket mice, have fur-lined cheek pouches that allow them to carry larger loads of seeds under predation risk compared to gerbilline rodents of the Negev Deserts. Sidewinder rattlesnakes have heat-sensing pits, allowing them to hunt better on moonless nights when their Negev sidewinding counterpart, the Saharan horned vipers, are visually impaired. In behavioral-assays, we used giving-up density (GUD) to gauge how each species of rodent perceived risk posed by known and novel snakes. We repeated this for the same set of rodents at first encounter and again two months later following intensive "natural" exposure to both snake species. Pre-exposure, all rodents identified their evolutionarily familiar snake as a greater risk than the novel one. However, post-exposure all identified the heat-sensing sidewinder rattlesnake as a greater risk. The heteromyids were more likely to avoid encounters with, and discern the behavioral difference among, snakes than their gerbilline counterparts.