Evol Ecol Res 5: 315-327 (2003)     Full PDF if your library subscribes.

Predation-mediated selection on prey morphology: a test using snowshoe hares

Aaron J. Wirsing*

Department of Fish and Wildlife Resources, University of Idaho, Moscow, ID 83844-1136, USA

Address all correspondence to Aaron Wirsing, Behavioural Ecology Research Group, Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada.
e-mail: awirsing@sfu.ca


Predation has been implicated in the evolution of many prey characteristics. However, few studies have measured the strength and direction of predation-mediated selection on prey morphology. I tested whether predation exerted directional selective pressure on morphometric measures related to skeletal size in snowshoe hares (Lepus americanus). Hares were live-trapped at six study sites in Idaho and monitored between 1998 and 2000. Each hare was characterized using hind-foot length, snout-to-vent length and mass. All trapped individuals (n = 103) were equipped with mortality-sensitive radio-collars and predation events were identified. The force of selection on morphology was measured using both multiple linear regression and path analysis. Multiple regression furnished directional selection gradients indicating that predation exerted positive directional selection on both hind-foot length and snout-to-vent length; conversely, the path-analytic model implied that predation-mediated selection acted only on size-adjusted snout-to-vent length (i.e. shape rather than size), favouring juveniles with relatively long bodies. Based on the agreement between the two analytic procedures for snout-to-vent length, I concluded that juvenile hares with small size-adjusted snout-to-vent lengths (i.e. newly weaned individuals) were disproportionately vulnerable to predation, perhaps because this measure is positively correlated with escape speed.

Keywords: Lepus americanus, morphology, path analysis, selection, snowshoe hare, vulnerability to predation.

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