Missouri Botanical Garden, 4344 Shaw Boulevard, St. Louis, MO 63110, USA.
Department of Biology, Eastern Michigan University, Ypsilanti, MI 48197, USA.
Ann Bot. 2024 May 10;133(5-6):773-788. doi: 10.1093/aob/mcae009.
Quantifying spatial species richness is useful to describe biodiversity patterns across broad geographical areas, especially in large, poorly known plant groups. We explore patterns and predictors of species richness across Africa in one such group, the palaeotropical genus Grewia L. (Malvaceae).
Grewia species richness was quantified by extracting herbarium records from GBIF and Tropicos and creating geographical grids at varying spatial scales. We assessed predictors of species richness using spatial regression models with 30 environmental variables. We explored species co-occurrence in Madagascar at finer resolutions using Schoener's index and compared species range sizes and International Union for Conservation of Nature status among ecoregions. Lastly, we derived a trait matrix for a subset of species found in Madagascar to characterize morphological diversity across space.
Grewia species occur in 50 countries in Africa, with the highest number of species in Madagascar (93, with 80 species endemic). Species richness is highest in Madagascar, with ≤23 Grewia species in a grid cell, followed by coastal Tanzania/Kenya (≤13 species) and northern South Africa and central Angola (11 species each). Across Africa, higher species richness was predicted by variables related to aridity. In Madagascar, a greater range in environmental variables best predicted species richness, consistent with geographical grid cells of highest species richness occurring near biome/ecoregion transitions. In Madagascar, we also observe increasing dissimilarity in species composition with increasing geographical distance.
The spatial patterns and underlying environmental predictors that we uncover in Grewia represent an important step in our understanding of plant distribution and diversity patterns across Africa. Madagascar boasts nearly twice the Grewia species richness of the second most species-rich country in Africa, which might be explained by complex topography and environmental conditions across small spatial scales.
量化空间物种丰富度有助于描述广阔地理区域内的生物多样性模式，特别是在大型、了解甚少的植物群中。我们在一个这样的群组中探索了物种丰富度的模式和预测因子，该群组为古热带属番荔枝属（锦葵科）。
通过从 GBIF 和 Tropicos 提取标本记录，并创建不同空间尺度的地理网格，量化番荔枝属物种丰富度。我们使用 30 个环境变量的空间回归模型评估了物种丰富度的预测因子。我们在马达加斯加使用 Schoener 指数更精细地探索了物种共存，并比较了生态区之间的物种分布范围大小和国际自然保护联盟地位。最后，我们从在马达加斯加发现的一部分物种中得出了一个特征矩阵，以表征跨空间的形态多样性。
番荔枝属物种分布在非洲的 50 个国家，其中马达加斯加的物种数量最多（93 种，其中 80 种为特有种）。物种丰富度最高的是马达加斯加，每个网格单元有≤23 种番荔枝属物种，其次是坦桑尼亚/肯尼亚沿海地区（≤13 种）和南非北部和安哥拉中部（各 11 种）。在整个非洲，与干旱相关的变量预测了更高的物种丰富度。在马达加斯加，环境变量的更大范围最好地预测了物种丰富度，这与物种丰富度最高的地理网格单元出现在生物区/生态区过渡附近的情况一致。在马达加斯加，我们还观察到随着地理距离的增加，物种组成的相似性逐渐降低。
我们在番荔枝属中发现的空间模式和潜在的环境预测因子代表了我们对非洲植物分布和多样性模式理解的重要一步。马达加斯加的番荔枝属物种丰富度几乎是非洲第二丰富的国家的两倍，这可能是由于小空间尺度上复杂的地形和环境条件造成的。
