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Variation in speed, gait characteristics and microhabitat use in lacertid lizards

Bieke Vanhooydonck^*, Raoul Van Damme and Peter Aerts

University of Antwerp (U.I.A.), Department of Biology, Universiteitsplein 1, B-2610 Wilrijk, Belgium

View larger version (17K): [in a new window]   Fig. 1. Speeds at which the lizards ran on the treadmill for each species. Each dot represents a digitised sequence. Full species names are given in Table 1.

View larger version (18K): [in a new window]   Fig. 2. Hypothesised phylogenetic relationships among the 11 lacertid lizard species under study. The phylogeny is incompletely resolved, and this tree should be considered a best approximation. Polytomies are treated as `hard' for the purposes of phylogenetic analyses (see text).

View larger version (17K): [in a new window]   Fig. 3. Graphical representations of the multiple regression analyses we performed on the morphological, gait characteristics and performance data in the 11 lacertid lizard species. (A) All potential relationships. Each arrow represents one analysis. Independent variables introduced into the same multiple regression are boxed. Arrows are drawn from the independent variables box to the dependent variable box. We performed two series of analyses: one that included the (contrasts of the) values for the four gait characteristics at maximal sprint speed, and the second on the (contrasts of the) slopes of each of the four gait characteristics against speed. (B) Significant relationships in the multiple regression analyses including the contrasts of the estimated values of the four gait characteristics at maximal sprint speed. (C) Significant relationships in the multiple regression analyses including the contrasts of the slopes of each gait characteristic against speed. By definition, the contrasts of the slopes of stride length and stride frequency against speed are inversely related so we never introduced them simultaneously into the analyses. Instead, we included only the contrasts of the slopes of stride frequency against speed in the analysis; including the contrasts of the slopes of stride length against speed gives the opposite result (r=0.56; P=0.075).

View larger version (17K): [in a new window]   Fig. 4. Bivariate correlations between the contrasts of microhabitat use and the contrasts of the slopes of stride frequency against speed (forced through the origin). (A) Relationship between the contrasts of time spent in the open microhabitat and the contrasts of the slopes of stride frequency against speed. (B) Correlation between the contrasts of time spent in the vegetated microhabitat and the contrasts of the slopes of stride frequency against speed. In both cases, including the contrasts of the slopes of stride length against speed gives the opposite result (r=0.76, P=0.017; r=-0.62, P=0.074, respectively).