Temporal patterns of ant diversity across a mountain with climatically contrasting aspects in the tropics of Africa

Factors that drive species richness over space and time are still poorly understood and are often context specific. Identifying these drivers for ant diversity has become particularly relevant within the context of contemporary global change events. We report on a long-term bi-annual (wet and dry seasons), standardized sampling of epigeal ants over a five year period on the mesic and arid aspects of an inselberg (Soutpansberg Mountain Range) in the tropics of Africa. We detail seasonal, annual and long-term trends of species density, test the relative contribution of geometric constraints, energy, available area, climate, local environmental variables, time, and space in explaining ant species density patterns through Generalized Linear Mixed Models (GLMM) where replicates were included as random factors to account for temporal pseudo20 replication. Seasonal patterns were very variable and we found evidence of decreased seasonal variation in species density with increased elevation. The extent and significance of a decrease in species density with increased elevation varied with season. Annual patterns point to an increase in ant diversity over time. Ant density patterns were positively correlated with mean monthly temperature but geometric constraints dominated model performance while soil characteristics were minor correlates. These drivers and correlates accounted for all the spatio-temporal variability in the database. Ant diversity was therefore mainly determined by geometric constraints and temperature while soil characteristics (clay and carbon content) accounted for smaller but significant amounts of variation. This study documents the role of season, elevation and their interaction in affecting ant species densities while highlighting the importance of neutral processes and temperature in driving these patterns.

调控物种丰富度时空分布的驱动因子目前仍未被充分认知，且往往具有情境特异性。在当代全球变化的背景下，探明蚁类多样性的这些驱动因子显得尤为重要。本研究针对非洲热带区域一座岛山（inselberg，索特潘斯贝格山脉）的湿润与干旱坡向，开展了为期5年、每半年（湿季与干季各一次）的标准化地表蚂蚁（epigeal ants）采样工作。本研究详细分析了物种密度的季节、年际及长期变化趋势，并通过广义线性混合模型（Generalized Linear Mixed Models, GLMM）检验了几何约束、能量、可用面积、气候、局地环境变量、时间与空间对蚂蚁物种密度格局的相对解释贡献；模型中将重复采样作为随机因子，以校正时间伪重复带来的偏差。季节格局具有显著异质性，研究发现物种密度的季节波动随海拔升高而减弱。物种密度随海拔升高而降低的程度及其显著性，会随季节发生变化。年际格局显示，蚁类多样性随时间推移呈上升趋势。蚂蚁物种密度格局与月均温度呈正相关，而几何约束对模型性能的贡献占主导地位，土壤特征仅为次要关联因子。上述驱动因子与关联因子可解释数据库中全部的时空变异。因此，蚁类多样性主要由几何约束与温度决定，而土壤特征（黏粒含量与碳含量）虽贡献占比更小，但仍对变异具有显著解释作用。本研究阐明了季节、海拔及其交互作用对蚂蚁物种密度的调控作用，同时强调了中性过程与温度在塑造该格局中的重要性。