Niche overlap and breadth are fundamental characteristics of ecological niches that have been hypothesized to relate both to environmental conditions and to biotic interactions within a community. Abiotic factors and interspecific competition may have opposing effects on those niche characteristics by respectively filtering out species from the niche space and limiting among-species similarity. Here we set out to assess niche overlap and breadth of ant assemblages in Mediterranean grasslands along a 1668-m elevational gradient in the Guadarrama range (Central Spain). We carried out an outdoor cafeteria experiment considering two niche dimensions on resource acquisition: food type and period of aboveground activity. We compared metrics describing niche overlap and breadth to null models and related the metrics to elevation, temperature at ground level and a proxy of interspecific competition (species richness) with general linear models. Pianka's niche overlap indexes were higher than those calculated with random assemblages, but differences among observed and random assemblages were only significant at mid-elevations and were unrelated to the explanatory variables. Overlap along elevation seemed more due to overlap in period of activity. Niche breadth at the assemblage level was significatively smaller than null expectations and was related to elevation (negatively) and to species richness (positively). These were significantly larger than estimates for the species level. These results show that ant assemblages exploit a subset of available conditions, in a pattern only partially coincident with a scenario of abiotic control. Moreover, their constituent species share time of activity and, to a lesser extent, food resources, in spite of the interspecific competition structuring communities that is often assumed. Overall, the patterns we recorded suggest that other mechanisms should be acting to promote species coexistence, such as trade-offs among ecological functions.

生态位的重叠和广度是生态位的基本特征，被认为与环境条件和社区内的生物相互作用有关。非生物因素和种间竞争可能通过分别从生态位空间中过滤掉物种并限制物种间的相似性而对那些生态位特征产生相反的影响。在这里，我们着手评估瓜达拉马山脉（西班牙中部）沿1668米高程梯度在地中海草原上的生态位重叠和蚂蚁组合的广度。我们进行了一个户外自助餐厅实验，考虑了资源获取的两个利基维度：食物类型和地面活动时间。我们将描述利基重叠和广度的指标与空模型进行了比较，并将指标与海拔高度相关联，地面温度和种间竞争（物种丰富度）的代用一般线性模型。Pianka的生态位重叠指数高于使用随机组合计算的那些，但观察到的组合和随机组合之间的差异仅在中海拔时才有意义，并且与解释变量无关。沿海拔的重叠似乎更多是由于活动期间的重叠。组合水平的生态位宽度显着小于零期望值，并且与海拔（负向）和物种丰富度（正向）相关。这些大大超过了物种水平的估计。这些结果表明，蚂蚁组合利用了一部分可用条件，其模式与非生物控制场景仅部分重合。此外，尽管人们通常认为种间竞争构成社区，但它们的组成物种共享活动时间，并在较小程度上共享食物资源。总体而言，我们记录的模式表明，其他机制应该起到促进物种共存的作用，例如生态功能之间的权衡。