How landscape and biotic interactions shape a Mediterranean reptile community

Context: Disentangling the effect of environment and biological interaction on community composition with observational data, within the environmental filtering framework, is challenging because the two processes produce non independent results. Objectives: Adopting community N-mixture models with symmetric interactions, we aimed at estimating differential effects of landscape structure and biotic interactions on the local abundance of a Mediterranean reptile community including four lizards (Lacerta bilineata; Podarcis siculus; P. muralis; Chalcides chalcides) and two snakes (Hierophis viridiflavus; Natrix Helvetica). Methods: We sampled reptiles for three consecutive years (2019–2021; 4 surveys/year) on 52 linear transects on a Mediterranean coastal landscape. We analyzed count data by means of a multi-species N-mixture model with symmetric interactions. Interactions within pair of species were estimated from the residual correlation of their realized abundances, after accounting for four landscape features: landscape heterogeneity calculated from land cover data, edge density of woody vegetation patches, tree cover density, net primary productivity. Results: Most species displayed very low detection probability (p ~ 0.10). All species responded with different intensity and sensitivity to landscape predictors. Two biological interactions resulted significant: L. bilineata and P. siculus showed a positive interaction, while P. muralis and C. chalcides displayed a negative interaction. Conclusions: Using community N-mixture models we demonstrated that, also with observational data obtained from a realized community, partitioning the filtering process of the landscape from the one of biotic interactions is possible.