Variation of community assembly rules of a whole turtle family (Pelomedusidae) from continental to local scales in Africa

Assessing community assembly rules has been a prominent task by community ecologists. Using a turtle family (Pelomedusidae) as a study case, we analyze the structure of their communities from the continental scale to the habitat scale, by using a suite of statistical approaches: (i) GIS modeling of the most complete presence sites dataset (from IUCN/SSC TFTSG archive); (ii) niche overlap and co-occurrence null models with Monte Carlo simulations; (iii) generalized linear models. We used, after controlling for spatial autocorrelation, continental scale presence data totalling 1698 locality records belonging to 27 species of African Pelomedusidae and local scale data from 58 surveyed stations in eight different countries, totalling 1936 turtle individuals of at least five species (but several taxa are included into one of these “species”: the Pelomedusa subrufa complex). At the local scale, the number of co-occurring Pelomedusidae in Africa ranged from two to three species, although the ranges of up to five total species overlapped at various locations on the continental scale. A simulation study showed that, at the continental scale, the various species co-occurred following assembly rules that are compatible with interspecific competition by two metrics. At the habitat scale, the mean number of sympatric species was just below two and the maximum number of sympatric species per local site was three, with significant variation among habitat categories (more in forest than in any other habitat). Body size filtering may be also a mechanism that facilitates coexistence of pelomedusid species under sympatric conditions.