| Popis: |
Prey of different ages may exhibit differences in escape behavior, including flight initiation distance (FID – predator-prey distance when escape begins) and distance fled before stopping (DF). Escape theory predicts FID and, in some circumstance, DF, based on trade-offs between conflicting cost of not fleeing (predation risk) and cost of fleeing (primarily opportunities to enhance fitness lost by fleeing). The prey’s expected lifetime fitness when an encounter begins also affects escape decisions. Because hatchling and adult lizards may differ in ways that affect all three of these factors, a priori prediction of age differences is not possible without measurements of all three. In a field study I found that hatchling zebra-tailed lizards (Callisaurs draconoides) had much shorter FID and DF than adults. These relationships were not affected by distance to refuge, which did not differ between ages, and refuge use was infrequent. The findings agree with those of all but one previous study of age differences, suggesting that hatchling lizards typically have shorter FID and DF than adults because they 1) assess risk as being lower due to lower attractiveness to or detectability by predators, lack of experience or greater maneuverability, 2) have greater opportunity cost due to the need for rapid growth and good body condition before winter, and possibly 3) have lower residual reproductive value due to higher mortality rate than adults. Effects of age and size are confounded, and smaller size may be the major reason for the shorter FID and distance fled of hatchlings. |
