Data from: Interactions between soil habitat and geographic range location affect plant fitness

Populations are often found on different habitats at different geographic locations. This habitat shift may be due to biased dispersal, physiological tolerances or biotic interactions. To explore how fitness of the native plant Chamaecrista fasciculata depends on habitat within, at and beyond its range edge, we planted seeds from five populations in two soil substrates at these geographic locations. We found that with reduced competition, lifetime fitness was always greater or equivalent in one habitat type, loam soils, though early-season survival was greater on sand soils. At the range edge, natural populations are typically found on sand soil habitats, which are also less competitive environments. Early-season survival and fitness differed among source populations, and when transplanted beyond the range edge, range edge populations had greater fitness than interior populations. Our results indicate that even when the optimal soil substrate for a species does not change with geographic range location, the realized niche of a species may be restricted to sub-optimal habitats at the range edge because of the combined effects of differences in abiotic and biotic effects (e.g. competitors) between substrates.

种群常于不同地理区域内占据不同生境。此类生境偏移现象，可归因于偏向性扩散、生理耐受差异或生物交互作用。为探究本土植物短叶决明（Chamaecrista fasciculata）的适合度（fitness）如何随其分布范围内部、边缘及边缘以外生境的变化而改变，我们在上述地理区域中，将5个种群的种子种植于两种土壤基质（soil substrates）内。研究结果显示，在竞争减弱的条件下，壤土（loam soils）生境下植株的终生适合度始终更高或持平，而沙质土壤上的苗期存活率（early-season survival）则更为优异。在分布范围边缘，自然种群通常栖息于沙质土壤生境，此类生境的竞争压力也相对更低。不同源种群的苗期存活率与适合度存在显著差异；当被移植至分布范围边缘以外区域时，分布边缘种群的适合度显著高于内部种群。本研究表明，即便某一物种的最优土壤基质并不随地理分布位置发生改变，由于不同基质间非生物与生物因素（例如竞争者）差异的联合作用，该物种的现实生态位（realized niche）仍可能被限制在分布范围边缘的次优生境中。