Avian succession along ecological gradients： Insight from species-poor and species-rich communities of Sylvia warblers

The mechanisms responsible for species replacement during ecological successions is a long-standing and open debate. In this study, we examined the distribution of the Sardinian warbler Sylvia melanocephala along two grassland-to-forest gradients, one in a high-diversity area （Albera-Aspres chain in Catalonia： eight Sylvia warbler species） and one in a low-diversity area （Mount Hymittos in Greece： four species）. In Catalonia, distribution models suggested that the apparent exclusion of S. melanocephala from the open and forest ends of the gradient may be explained entirely by the preference of S. melanocephala for mid-successional shrublands. However, a joint analysis of both data sets revealed that： 1） S. melanocephala was more evenly dis- tributed along the vegetation gradient in Greece, suggesting ecological release in the low-diversity area; and 2） a distribution model assuming interspecific competition （based on the distribution of Sylvia species showing a negative co-occurrence pattern with S. melanocephala） had a significantly higher predictive ability than a distribution model based on habitat variables alone. Our study supports the view that species turnover along ecological gradients generally results from a combination of intrinsic preferences and interspecific competition [Current Zoology 57 （3）： 307-317, 2011].

Annoying neighbors： Multi-scale distribution determinants of two sympatric sibling species of birds

We tested the role of interspecific competition in driving species distribution at multiple spatial scales using two sibl- ing species of Galerida larks （G cristata and G. theklae） in Morocco （sympatry）, Balearic islands （G theklae only） and Israel （G cristata only）. We first investigated regional-scale determinants by contrasting allopatric versus sympatric patterns in five distinct habitat types. We next focused on a single habitat used by both species, the coastal sand dunes. Dune quadrats were established along the Moroccan coast and completed by a quadrat in the nearest distinct landscape habitat. Poisson regressions were used to model Galerida counts together with ecological predictors as concerns the climate, topography, vegetation structure and soil gra- nulometry. At the local scale, both species preferred grey dunes over white sand dunes, and both were negatively affected by the abundance of the congeneric species in the dune. However, we found that G theklae tended to replace G. cristata in more arid sand dunes, even if the transition was not strictly clinal. Instead, the transition occurred when the surrounding landscape changed from coastal wetlands to bathas （grasslands with shrubs）, highlighting the importance of habitat composition at the landscape scale. The fact that G cristata used bathas in allopatry, but not in sympatry, suggested that the competitive environment contri- buted to determine sand dune occupancy. We suggest that landscape-level effects may be pivotal in explaining species distribu- tion not only at the local scale, by affecting the pool of potential immigrants, but also at the regional scale, by contributing to species＇ range limit [Current Zoology 61 （1）： 10-22, 2015].