The geographic and seasonal dimensions of habitat use in Galerida larks: implications for species coexistence and range limits

Abstract

In this paper, we investigated the patterns of habitat use in three sibling species of larks: the Thekla lark Galerida theklae which is sympatric with either of two parapatric species of crested larks (G. macrorhyncha replacing G. cristata in arid areas of Morocco). Specifically, we addressed the following questions: 1) do species show niche conservatism in space (France vs Morocco) and time (breeding vs winter period)? 2) Does habitat use change at different interspecific densities? 3) Which factors drive the narrow range limit between G. cristata and G. macrorhyncha? We found that G. theklae was strongly associated with sloping and rocky (rugged) habitats in comparison with crested larks, but habitat use was not entirely consistent in space and time. Evidences for ecological displacement were mitigated. In the only habitat shared by G. cristata and G. theklae in France (vineyards surrounded by low shrubland), we observed a one-third increase of G. theklae from nearby garrigues in winter, which coincided with a significant decrease of G. cristata after we controlled for density changes in non-shared habitats. However, in Morocco, the use of rugged habitats by G. theklae was not affected by the prevalence of G. cristata or G. macrorhyncha in surrounding areas, at least at the spatial scales investigated. Our results suggest that interspecific competition plays a role in the parapatric distribution of G. cristata and G. macrorhyncha, because: 1) the alternative of a recent contact receives little support; 2) transition between species coincides with aridity gradients but not with topographic barriers or a sharp ecotone; 3) G. cristata also occurs in arid areas wherein G. macrorhyncha is rare or absent. Overall, our results add support to the view that a better integration of biotic interactions and spatio-temporal variations in ecological niches might increase the predictive power of ecological niche models.