Ranging behaviours across ecological and anthropogenic disturbance gradients: a pan-African perspective of giraffe (Giraffa spp .) space use

Abstract

Animal movement behaviours are shaped by diverse factors, including resource availability and human impacts on the landscape. We generated home range estimates and daily movement rate estimates for 149 giraffe (Giraffa spp.) from all four species across Africa to evaluate the effects of environmental productivity and anthropogenic disturbance on space use. Using the continuous time movement modelling framework and a novel application of mixed effects meta-regression, we summarized overall giraffe space use and tested for the effects of resource availability and human impact on 95% autocorrelated kernel density estimate (AKDE) size and daily movement. The mean 95% AKDE was 359.9 km² and the mean daily movement was 14.2 km, both with marginally significant differences across species. We found significant negative effects of resource availability, and significant positive effects of resource heterogeneity and protected area overlap on 95% AKDE size. There were significant negative effects of overall anthropogenic disturbance and positive effects of the heterogeneity of anthropogenic disturbance on daily movements and 95% AKDE size. Our results provide unique insights into the interactive effects of resource availability and anthropogenic development on the movements of a large-bodied browser and highlight the potential impacts of rapidly changing landscapes on animal space-use patterns.

Keywords: continuous time movement modelling; daily movement; home range; mixed effects meta-regression; movements; productivity gradients.

Figure 1.

Distribution of giraffe tracking study sites across Africa. We deployed tracking units in 30 distinct populations across 11 countries over most of the known geographical range of giraffe. Black dots represent individual study sites. Outset maps represent focal giraffe trajectories from selected populations from each of the four species: (a) Giraffa camelopardalis peralta in the Giraffe Zone of Niger, (b) Giraffa reticulata in northern Kenya, (c) Giraffa tippelskirchi in the Amboseli ecosystem of Kenya and (d) Giraffa giraffa angolensis in the greater Etosha ecosystem of Namibia. The background of outset maps shows aboveground woody biomass derived from Bouvet et al. [52] and the range map is derived from O'Connor et al. [34] and Brown et al. [33].

Figure 2.

(a) Mean 95% AKDE and (b) mean daily distance travel for each giraffe species. Error bars represent upper and lower 95% confidence intervals. The solid red line represents the global mean value for all giraffe with the dashed lines representing upper and lower 95% global confidence limits.

Figure 3.

Standardized model coefficients and confidence intervals from the best supported model evaluating environmental and anthropogenic influences on home range size (95% AKDE). Coefficients indicate the influence of each covariate on giraffe space use, with larger magnitude suggesting greater importance.

Figure 4.

Standardized model coefficients and confidence intervals from the best supported model evaluating environmental and anthropogenic influences on daily movement. Coefficients indicate the influence of each covariate on giraffe space use, with larger magnitude suggesting greater importance.