Rivest Sébastien, Vellend Mark
Département de Biologie Université de Sherbrooke Sherbrooke QC Canada.
Ecol Evol. 2017 Dec 12;8(2):892-903. doi: 10.1002/ece3.3397. eCollection 2018 Jan.
Studies of species' range limits focus most often on abiotic factors, although the strength of biotic interactions might also vary along environmental gradients and have strong demographic effects. For example, pollinator abundance might decrease at range limits due to harsh environmental conditions, and reduced plant density can reduce attractiveness to pollinators and increase or decrease herbivory. We tested for variation in the strength of pollen limitation and herbivory by ungulates along a gradient leading to the upper elevational range limits of (Melanthiaceae) and (Liliaceae) in Mont Mégantic National Park, Québec, Canada. In pollen limitation was higher at the range limit, but seed set decreased only slightly with elevation and only in one of two years. In contrast, herbivory of increased from <10% at low elevations to >60% at the upper elevational range limit. In , we found no evidence of pollen limitation despite a significant decrease in seed set with elevation, and herbivory was low across the entire gradient. Overall, our results demonstrate the potential for relatively strong negative interactions (herbivory) and weak positive interactions (pollination) at plant range edges, although this was clearly species specific. To the extent that these interactions have important demographic consequences-highly likely for herbivory on , based on previous studies-such interactions might play a role in determining plant species' range limits along putatively climatic gradients.
对物种分布范围界限的研究通常聚焦于非生物因素，尽管生物相互作用的强度也可能会随着环境梯度而变化，并产生强烈的种群统计学效应。例如，由于恶劣的环境条件，传粉者的数量在分布范围界限处可能会减少，而植物密度的降低会降低对传粉者的吸引力，并增加或减少食草动物的啃食。我们在加拿大魁北克省蒙特梅甘蒂克国家公园，沿着一条通向黑藜芦科的黑藜芦属和百合科的大花延龄草属植物海拔上限范围界限的梯度，测试了花粉限制强度和有蹄类动物食草作用的变化。在黑藜芦属植物中，花粉限制在分布范围界限处更高，但结实率仅在两年中的一年随海拔略有下降。相比之下，黑藜芦属植物的食草作用从低海拔处的不到10%增加到海拔上限范围界限处的超过60%。在大花延龄草属植物中，尽管结实率随海拔显著下降，但我们没有发现花粉限制的证据，并且在整个梯度上食草作用都很低。总体而言，我们的结果表明，在植物分布范围边缘可能存在相对强烈的负相互作用（食草作用）和较弱的正相互作用（授粉作用），尽管这显然具有物种特异性。基于之前的研究，就这些相互作用具有重要的种群统计学后果而言——对黑藜芦属植物的食草作用极有可能如此——这样的相互作用可能在沿着假定的气候梯度确定植物物种的分布范围界限方面发挥作用。
