Poa arachnifera demography and sex ratio surveys

Understanding the mechanisms that generate biogeographic range limits is a long-standing goal of ecology. It is widely hypothesized that distributional limits reflect the environmental niche, but this hypothesis is complicated by widespread potential for intra-specific niche heterogeneity. In dioecious species, sexual niche differentiation may cause divergence between the sexes in their limits of environmental suitability. We studied range boundary formation in Texas bluegrass ( Poa arachnifera ), a perennial dioecious plant, testing the alternative hypotheses that range limits reflect the niche limits of females only versus the combined contributions of females and males, including their inter-dependence via mating. Common garden experiments across a longitudinal aridity gradient revealed female-biased flowering approaching eastern range limits, suggesting that mate limitation may constrain the species' distribution. However, a demographic model showed that declines in λ approaching ra...

阐明生物地理分布边界的形成机制，是生态学领域长期以来的核心研究目标之一。学界普遍认为，物种的分布边界反映其环境生态位（environmental niche），但种内生态位异质性的广泛存在，使得这一假说的验证趋于复杂。在雌雄异株物种（dioecious species）中，性生态位分化可能导致两性在环境适宜性边界上出现分化。我们以多年生雌雄异株植物得克萨斯早熟禾（Poa arachnifera）为研究对象，检验两种对立假说：其一为分布边界仅反映雌性个体的生态位极限，其二为分布边界由雌雄两性的共同贡献决定，其中包括二者通过交配形成的相互依赖关系。沿经度干旱梯度开展的同质园实验（common garden experiment）显示，在接近该物种种群东部分布边界的区域，开花个体以雌性为主，这表明配偶限制可能制约了该物种的分布范围。然而，种群统计模型显示，随着种群接近其分布边界，种群增长率λ逐渐下降，其……