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| Aim Although the breeding ranges of most Western Palaearctic migratory
passerines are well documented in Europe, their overwintering ranges and
patterns of species richness in Africa remain poorly understood. To illustrate
potential patterns of species richness despite severely limited data, we
extrapolated species ranges from a new and unique data bank of locality
records that documents overwintering locations of these birds in Africa.
Location Sub-Saharan Africa.
Methods We predicted potential geographical distributions of 60 species of
passerine birds based on overwintering records using bioclimatic models. We
then combined these predictions to estimate potential species richness and
explored response shapes using spatial linear regression. We also evaluated the
evidence for a mid-domain effect using a one-dimensional null model.
Results Spatial linear regression analyses of the species richness pattern revealed
non-linear relationships to seasonality in precipitation, minimum net primary
productivity, minimum average temperature, habitat heterogeneity, percentage of
tree cover, distance from the Sahara Desert and inter-annual variability in net
primary productivity. The explanatory power of these variables decreased with
geographic range size. The one-dimensional null model of species richness based
on distance from the Sahara Desert did not show evidence of a mid-domain
effect.
Main conclusions Distributions of migrants seem generally strongly determined
by distance from the Sahara Desert working in concert with climatic effects, but
this cannot adequately explain richness patterns of species with small ranges in
Africa, many of which are of substantial conservation concern. | |
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