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First published online March 28, 2008
Journal of Experimental Biology 211, 1336-1343 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.011296
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Estimating maximum performance: effects of intraindividual variation

Stephen C. Adolph* and Trevor Pickering{dagger}

Department of Biology, Harvey Mudd College, 301 Platt Boulevard, Claremont, CA 91711, USA


Figure 1
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  		Fig. 1. Sprint speed (m s–1 over 75 cm; mean ± s.e.m.; N=21) vs trial number in the western fence lizard Sceloporus occidentalis. Mean speed did not increase or decrease linearly with time at either temperature (see Results).

 

Figure 2
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  		Fig. 2. Inter- and intraindividual variation in burst sprint speeds of western fence lizards (Sceloporus occidentalis) at 35°C and 20°C. Each point represents the mean (±s.d.) of 20 trials for a single individual. The same individuals (N=21) are shown for each temperature, but some individual rankings differed between temperatures.

 

Figure 3
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  		Fig. 3. Individual mean speeds plotted against individual median speeds of S. occidentalis for 35°C and 20°C. Diagonal lines indicate 1:1 relationships (not regressions).

 

Figure 4
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  		Fig. 4. Magnitude of pairwise correlations between speeds for two different trials i and j as a function of the number of trials separating the two (|i–j|). Correlations declined significantly with separation for both 20°C and 35°C but most of the variation was unexplained (Mantel tests; see Results).

 

Figure 5
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  		Fig. 5. Effect of number of trials per individual (Ntrials) on estimated maximum speed (normalized for each individual) of western fence lizards (Sceloporus occidentalis). Data were randomly sampled from empirical distributions of sprint speeds. Symbols indicate the mean of maximum speed (normalized for each individual) obtained from 1000 random samples (from 21 individuals) for each value of Ntrials. Error bars indicate 75th and 25th percentiles. These data are for 35°C (results for 20°C are virtually identical, and are not shown).

 

Figure 6
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  		Fig. 6. Estimated correlations between individual mean speeds at 20°C and 35°C (filled circles) and individual maximum speeds at 20°C and 35°C (open circles) in the lizard Sceloporus occidentalis, as a function of the number of trials sampled per individual. Points show the mean correlation of 1000 independently drawn samples from the empirical distribution of speeds. Upper error bars indicate the 75th percentile of the distribution of correlations between means, and lower error bars indicate the 25th percentile of the distribution of correlations between maxima. The corresponding error bars are nearly symmetrical but are omitted for clarity.

 

Figure 7
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  		Fig. 7. Effect of intraindividual variability on the bias in estimating locomotor performance parameters in the lizard Sceloporus occidentalis. Original data were adjusted to achieve different degrees of intraindividual variability, then used in computer sampling experiments like those illustrated in Figs 5 and 6. (A) Mean proportion of maximum sprint speed at 35°C plotted against number of trials per individual (each point is the mean of 1000 independent samples). Data were adjusted to achieve average CV of 10% (filled squares), 20% (open circles) and 30% (filled circles). (B) Correlation coefficient between average individual speeds at 20°C and 35°C plotted against number of trials per individual (each point is the mean from 1000 independent samples). Data were adjusted to achieve repeatability (intraclass correlation coefficients) for both traits of 0.75 (filled squares), 0.50 (open circles) and 0.25 (filled circles).

 

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© The Company of Biologists Ltd 2008