Moutouama Jacob K, Gaoue Orou G
Department of Ecology and Evolutionary Biology University of Tennessee Knoxville Tennessee USA.
Faculty of Agronomy University of Parakou Parakou Benin.
Ecol Evol. 2022 Feb 9;12(2):e8572. doi: 10.1002/ece3.8572. eCollection 2022 Feb.
Understanding the ecological processes that govern species' range margins is a fundamental question in ecology with practical implications in conservation biology. The center-periphery hypothesis predicts that organisms have higher abundance at the center of their geographic range. However, most tests of this hypothesis often used raster data, assuming that climatic conditions are consistent across one square km. This assumption is not always justified, particularly for mountainous species for which climatic conditions can vary widely across a small spatial scale. Previous studies rarely evenly sample occurrence data across the species' distribution. In this study, we sampled an endemic perennial herb, (Acanthanceae), throughout its range in West Africa using 54 plots and collected data on (a)biotic variables, the species density, leaf mass per area, and basal diameter. We built a structural equation model to test the direct and indirect effects of distance from geographic and climatic niche centers, and altitude on density as mediated by abiotic and biotic factors, population demographic structure, and individual size. Contrary to the prediction of the center-periphery hypothesis, we found no significant effect of distance from geographic or climatic niche centers on plant density. This indicates that even the climatic center does not necessarily have optimal ecological conditions. In contrast, plant density varied with altitudinal gradient, but this was mediated by the effect of soil nitrogen and potassium which had positive effect on plant size. Surprisingly, we found no direct or mediating effect of interspecific competition on plant density. Altogether, our results highlight the role of geography, climatic, and ecological mismatch in predicting species distribution. Our study highlights that where altitudinal gradient is strong local-scale heterogeneity in abiotic factors can play important role in shaping species range limits.
了解控制物种分布范围边缘的生态过程是生态学中的一个基本问题，在保护生物学中具有实际意义。中心 - 边缘假说预测，生物在其地理分布范围的中心具有更高的丰度。然而，该假说的大多数检验通常使用栅格数据，假定一平方公里内的气候条件是一致的。这一假设并不总是合理的，特别是对于山区物种而言，其气候条件在小空间尺度上可能差异很大。以往的研究很少在物种分布范围内均匀地采样出现数据。在本研究中，我们使用54个样地在西非的整个分布范围内对一种特有多年生草本植物（爵床科）进行了采样，并收集了关于（非）生物变量、物种密度、单位面积叶质量和基部直径的数据。我们构建了一个结构方程模型，以检验距离地理和气候生态位中心的距离以及海拔高度通过非生物和生物因素、种群人口结构和个体大小对植物密度的直接和间接影响。与中心 - 边缘假说的预测相反，我们发现距离地理或气候生态位中心的距离对植物密度没有显著影响。这表明即使是气候中心也不一定具有最佳的生态条件。相比之下，植物密度随海拔梯度而变化，但这是由土壤氮和钾的影响介导的，它们对植物大小有积极影响。令人惊讶的是，我们没有发现种间竞争对植物密度有直接或介导作用。总之，我们的结果突出了地理、气候和生态不匹配在预测物种分布中的作用。我们的研究强调，在海拔梯度强烈的地方，非生物因素的局部尺度异质性在塑造物种分布范围限制方面可以发挥重要作用。
