Towards a unification of movement ecology and biogeography: conceptual framework and a case study on Afrotropical ducks

Aim We present elements of a new conceptual framework for the unification of biogeography and movement ecology, and demonstrate the value of the new framework using a case study of two species of Afrotropical duck (Anatidae) across a latitudinal gradient. Location Southern Africa. Methods The first part of the paper rests on logic and philosophy. For the second (case study) section, we used data from up to 3 years of satellite telemetry for 26 individuals of two species of Afrotropical duck, the Egyptian goose (Alopochen aegyptiaca) and red-billed teal (Anas erythrorhyncha), from three different populations with moulting sites spread across 17 degrees of latitude. We compared quantitative measures of movement patterns using principal components analysis and boxplots. Results We argue that unpacking the concept of dispersal into the fundamental elements of movement (internal drivers, external drivers, navigation capacity, and motion capacity) provides a more solid basis for contrasting competing hypotheses in biogeographical studies. We found, surprisingly, that red-billed teal, a highly nomadic species, moved with a relatively high degree of consistency at each of our three study latitudes, while Egyptian geese, a resident species, showed latitude-dependent variation in their movements. However, much of the latitude-related variation for Egyptian geese was driven by their annual moult migrations, rather than directly by fluctuations in resource availability. Internal factors appear to dominate movements and probably determine the species ranges of both of our study species. Main conclusions The integration of biogeography and movement ecology, through a more sophisticated view of mechanisms formerly lumped together under dispersal, offers a fertile area for further research. The biogeography of Afrotropical ducks appears to be strongly influenced by internal factors. Biogeographical patterns in this taxon may thus be best understood (and modelled) as a long-term response to environmental stochasticity, rather than as a deliberate selection of optimal habitat. Latitudinal comparisons emerge as a valuable way of gaining insights into the drivers of movement for widespread species.