Escape Decisions by the Syntopic Congeners Sceloporus jarrovii and S. virgatus: Comparative Effects of Perch Height and of Predator Approach Speed, Persistence, and Direction of Turning

Abstract

Many predation risk factors operate similarly in closely related taxa, but ecological and other differences among prey species may expose them to different risks in similar circumstances. We compared escape responses by the syntopic lizards Sceloporus jarrovii and S. virgatus to similar risk factors: perch height, predator approach speed, predator persistence, and direction of predator turning. Flight initiation distance (predator–prey distance when escape begins) decreased as perch height increased in both species but was shorter in S. virgatus. Sceloporus jarrovii fled except when perch height was above 2 m., but S. virgatus often did not flee even at low perch heights. These differences may reflect lower detectability of S. virgatus, which is difficult to detect on shaded sides of tree trunks and typically escapes without climbing out of reach. Flight initiation distance was greater for the faster and second of two approaches in both species. Sceloporus jarrovii fled more frequently than S. virgatus when a nearby investigator turned away from, but not toward, a lizard. At low perch heights and when a nearby predator moves, the larger S. jarrovii is warier than S. virgatus, which may rely relatively more on crypsis than escape. Similarity of responses to some risks by both species might reflect retention of ancestral behaviors or convergence. Escape differences seem to occur when risk operates differently due to ecological differences, suggesting that aspects of escape may be molded by natural selection with at least partial independence, resulting in escape strategies suitable to the ecologies of each species.