Clines in Africa: does size vary in the same way among widespread Sub-Saharan monkeys?

Aim We characterize and compare patterns of clinal size variation amongdiverse widespread sub-Saharan monkeys with the aim of identifying common-alities and differences in biogeographical variation. Thus, we accurately quan-tify nonlinear clines in representatives of the main lineages of widespread sub-Saharan terrestrial and arboreal monkeys, and provide a crude numerical esti-mate of the strength of similarities across taxonomic groups.Location Sub-Saharan Africa.Methods Variations of skull centroid size, as a proxy for body mass, were modelledover sub-Saharan Africa within two terrestrial monkey species (Papio hamadryas andChlorocebus aethiops) and two arboreal monkey taxa (Procolobus (Piliocolobus) sp.,and the superspecies Cercopithecus nictitans – mitis) using inverse distance weighting,thin-plate splines and kriging. The model with the highest cross-validated accuracywas used to produce contour plots that visualized clines and predicted size at equallyspaced localities across overlapping areas of distribution ranges. Correlations amongthese predictions were used as a similarity measure among clines.Results Irrespective of phylogenetic distances and ecological differences, allgroups showed similarities in clinal size over central Africa: large animalsmostly live in and around the tropical forest of the Congo basin; size declinesrapidly towards the Horn of Africa and the coasts of Kenya and Tanzania. Sizealso tends to decrease in western Africa but clinal patterns in this region vary,with vervets exceptionally showing a size increase.Main conclusions Similarities in patterns of size across diverse monkey groupswere found. Nonetheless, complexity in clines and a degree of heterogeneity acrossgroups were evident, which is unlikely to be compatible with the exclusive effect onsize of a single main environmental factor. Primary productivity may be most sig-nificant in relation to the consistent observation of large sizes in and adjacent tothe central African tropical forest belt. Complex clines, such as those of Africanmonkeys, are difficult to compare visually and data collection from evenly sampledsets of localities, where all species of interest may be found, is often impractical orsimply not feasible for primates and other protected animals. The development ofimproved quantitative methods for the description and comparison of clines inmammals and other organisms is required.