Weak interspecific interactions in a sagebrush steppe? Conflicting evidence from observations and experiments

Stable coexistence requires intraspecific limitations to be stronger than interspecific limitations. The greater the difference between intra- and interspecific limitations, the more stable the coexistence, and the weaker the competitive release any species should experience following removal of competitors. We conducted a removal experiment to test whether a previously estimated model, showing surprisingly weak interspecific competition for four dominant species in a sagebrush steppe, accurately predicts competitive release. Our treatments were 1) removal of all perennial grasses and 2) removal of the dominant shrub, Artemisia tripartita. We regressed survival, growth and recruitment on the locations, sizes, and species identities of neighboring plants, along with an indicator variable for removal treatment. If our ``baseline\" regression model, which accounts for local plant-plant interactions, accurately explains the observed responses to removals, then the removal coefficient should ...稳定共存要求种内限制（intraspecific limitations）强于种间限制（interspecific limitations）。种内与种间限制的差异越大，群落共存越稳定，且任一物种在移除竞争者后所经历的竞争释放（competitive release）程度也越弱。我们开展了移除实验，以验证先前估算的模型——该模型针对山艾灌丛草原（sagebrush steppe）中的4个优势物种，得出了种间竞争异常微弱的结论——能否准确预测竞争释放效应。本实验设置两组处理：1）移除所有多年生草本植物；2）移除优势灌木三齿蒿（Artemisia tripartita）。我们以邻体植物的位置、大小及物种身份，以及移除处理的指示变量作为自变量，对物种的存活、生长和种群补充更新（recruitment）进行回归分析。若我们用以解释本地植物间相互作用的“基准”回归模型，能够准确阐释观测到的移除响应，则该移除系数应当……