Factors affecting the characteristics of trips conducted between visits to waterholes.

<p>Distance traveled (A), maximum distance to start/end waterhole (B) and mean speed (C) were regressed against explanatory variables in linear mixed models with elephant identity as a random effect on intercept and slopes. The waterhole at the beginning of the trip is either different (commuting trip) or the same (looping trip) than the waterhole at the end of the trip. Estimates of the reference intercept (looping trips) and of deviations associated to other levels of explanatory variables are presented, with 95% confidence intervals obtained by parametric bootstrap with 10000 samples. Estimates for which the 95% confidence interval do not include zero are in bold.</p

Factors affecting elephant speed between visits to waterholes.

<p>Speed was regressed against explanatory variables in linear mixed models with elephant identity as a random effect on intercept. The 'Progression' variable was included as a quadratic predictor (i.e. the value and the square of the value ('Prediction²') was included in the model). The waterhole at the beginning of the trip is either different (commuting trip) or the same (looping trip) than the waterhole at the end of the trip. Progression in the trip was expressed as percent of the total trip duration. Estimates for the reference intercept (looping trips) and for the deviations associated to other levels of explanatory variables are presented, with 95% confidence intervals obtained by parametric bootstrap with 10000 samples. Estimates for which the 95% confidence interval do not include zero are in bold.</p

Relationship between speed and progression in the trip.

<p>(A) Speed of elephants within trips, in relation to the progression in the trip (expressed as percent of the total duration of the trip). Each line represents data for a single trip. Trips are defined as the movement between visits to waterholes, and elephants are therefore closer to water at the beginning and at the end of the trip. The waterhole at the beginning of the trip is either different (commuting trip) or the same (looping trip) than the waterhole at the end of the trip. A statistical model revealed that speed was best related to progression in the trip, trip type (commuting vs. looping) and some interactions with trip duration (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0059164#pone-0059164-t002" target="_blank">Table 2</a>). Panel (B) shows the model predictions. Note that in the wet season when elephants are not constrained by water availability mean speed is 0.33±0.52 s.d. km/h.</p

Effects of playbacks on the use of exclusive vigilance and vigilance while chewing.

<p>Mean proportions of time (± SE) spent by female impalas in (A) exclusive vigilance and (B) vigilance while chewing during the pre- and post-playback periods after their exposure to playbacks of control stimuli, lions’ roars and male impalas’ calls. *, ** and *** indicate significance at the p < 0.05, p < 0.01 and p < 0.001 levels, respectively.</p

Characteristics of trips conducted between visits to waterholes.

<p>(A) Frequency of trip durations; (B) Relationship between distance traveled and trip duration; (C) Relationship between the maximum distance to waterholes visited at the start/end of the trip and trip duration; (D) Relationship between mean travel speed and trip duration. Note that in the wet season when elephants are not constrained by water availability mean speed is 0.33±0.52 s.d. km/h. All panels show differences between commuting trips (when different waterholes are visited at the beginning and at the end of the trip; white-filled symbols, dotted lines) and looping trips (when the same waterhole is visited at the beginning and at the end of the trip; black-filled symbols, solid lines). Note that the difference between commuting and looping trips in panel (C) is not significant (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0059164#pone-0059164-t001" target="_blank">Table 1</a>).</p

Effects of playbacks on females’ behaviour.

<p>Mean (A) proportions of time spent in vigilance (± SE), (B) bite rates (± SE) (numbers of bites per minute during foraging), and (C) step rates (± SE) (numbers of steps per minute) of female impalas exposed to control stimuli, playbacks of lions’ roars and male impalas’ calls during pre- and post-playback periods. *, ** and *** indicate significance at the p < 0.05, p < 0.01 and p < 0.001 levels, respectively.</p

Map of the study area.

<p>The figure shows the locations of the waterholes surveyed (diamonds), and of artificial waterholes located outside the studied area (circles). Although waterhole size could vary from year to year, they were generally < 50 m in diameter at the time of the surveys. Rivers (dotted lines) dry up during the dry season, with only a few pools remaining. The solid line indicates the boundary of the Park.</p

Amount of variance (%) in species abundance at waterholes explained by temporal (between-year) or spatial (between-waterhole) variations, obtained from between-year and between-waterhole PCA respectively.

<p>See text for details.</p

Effect of annual rainfall on herbivore abundance at waterholes.

<p>Relationship between annual rainfall and component scores from the first axis of the between-year principal component analysis (Pearson r = 0.68, P = 0.01). This first axis represented 92.6% of the inter-annual variation in herbivore abundance at waterholes, and lower values indicated lower herbivore abundance.</p

Results of the within-year (a,b), between-waterhole (c,d), within-waterhole (e,f) and between-year (g,h) principal component analyses.

<p>Scatterplots of their results on the first two axes are shown in (a,c,e,g). Each census (black dot) is linked to the centroid of all censuses conducted (c,e) at the same waterhole or (a,g) during the same year—an ellipse encompass the closer 66% of all censuses conducted (c,e) at the same waterhole or (a,g) during the same year. Correlations of individual variables (species abundance at waterholes) with axes 1 and 2 are shown in (b,d,f,h).</p