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Unformatted text preview: Functional Ecology 2006 20 , 174–179 174 © 2006 The Author Journal compilation © 2006 British Ecological Society μBlackwel Publishing Ltd Does speed help you survive? A test with Collared Lizards of different ages J. F. HUSAK† Department of Zoology, Oklahoma State University, Stillwater, OK 74078, USA Summary 1. While it is generally accepted that the evolution of morphological traits is mediated by selection on whole-animal performance, few studies have examined how variation in performance explains variation in fitness. Most studies to date have studied how performance predicts survival, and these typically examine only a single age class. 2. Maximal sprint speed was measured for hatchling and adult Collared Lizards ( Crotaphytus collaris ), in addition to morphological measurements, in order to deter- mine how well annual survival could be predicted by performance and whether the relationship between performance and survival differed between age classes. 3. Logistic regression revealed that no morphological trait or sprint speed performance predicted survival in adults. However, sprint speed predicted survival in hatchlings. Further, hindlimb length differed between survivors and non-survivors and correlated with sprint speed, suggesting that the evolution of hindlimb length in hatchlings may be driven by selection on sprint speed performance. 4. Selection on sprint speed may be mediated directly by predators where hatchlings cannot attain speeds sufficient to escape predators or indirectly where slower individuals use a greater proportion of their maximal capacity than faster individuals while escaping predators, perhaps causing elevated stress levels or a higher expenditure of energy stores. Key-words : Fitness, foraging, locomotion, natural selection, performance, predation, survival, territoriality Functional Ecology (2006) 20 , 174–179 doi: 10.1111/j.1365-2435.2006.01069.x Introduction Differential survival among individuals reflects varia- tion in underlying morphological and physiological traits, but selection acts on the integrated manifesta- tion of such traits (i.e. whole-animal performance; Huey & Stevenson 1979; Arnold 1983). Since Arnold (1983) described an operational framework for linking morphology, performance and fitness, many authors have extended and refined his paradigm (e.g. Bennett & Huey 1990; Wainwright & Reilly 1994; Irschick 2002). The link between morphology and performance has received considerable attention (reviewed in Gar- land & Losos 1994; Irschick & Garland 2001), whereas the link between performance and fitness has received comparatively little (Irschick & Garland 2001). The lack of studies is probably due to the difficulty of quan- tifying both physiological performance and lifetime fitness in the same individuals. Studies attempting to do so have focused on how performance predicts sur- vival (e.g. Jayne & Bennett 1990; Miles 2004) typically within a specific age class. These studies have been instructive regarding how natural selection may act on...
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- Regression Analysis, British Ecological Society, Functional Ecology, sprint speed, Irschick, J. F. Husak