The tortoise and the hare: reducing resource availability shifts competitive balance between plant species

1.Determining how changes in abiotic conditions influence community interactions is a fundamental challenge in ecology. Meeting this challenge is increasingly imperative in the Anthropocene where climate change and exotic species introductions alter abiotic context and biotic composition to reshuffle natural systems. 2.We created plant assemblages consisting of monocultures or equal abundance of the native community dominant bluebunch wheatgrass (Pseudoroegneria spicata) and the exotic spotted knapweed (Centaurea stoebe), a co-occurring invasive forb that has overtaken grasslands across the western United States. We subjected these composition treatments to drought (20% of average precipitation vs average) and herbivory on C. stoebe by its biocontrol agent Cyphocleonus achates to explore how reduced precipitation might influence the effects of competition and biocontrol herbivory on C. stoebe's abundance. 3.At the end of seven years, C. stoebe dominated mixed-species plots under n...探明非生物条件（abiotic conditions）变化对群落互作（community interactions）的影响机制，是生态学领域的核心研究难题。在人类世（Anthropocene）背景下，气候变化与外来物种引入正持续改变非生物环境与生物组成，重塑自然生态系统的结构与功能，因此攻克这一难题的紧迫性日益凸显。 本研究构建了两类植物群落组合（plant assemblages）：其一为单作群落（monocultures），其二为本地群落优势种蓝茎冰草（Pseudoroegneria spicata）与外来入侵杂类草异株矢车菊（Centaurea stoebe）以等丰度配比形成的混合群落——异株矢车菊是一种伴生入侵物种，已成功入侵美国西部大片草原生态系统。我们为上述群落组成处理组设置两种实验胁迫处理：一是干旱胁迫，即降水量仅为正常水平的20%，对照组维持正常降水量；二是利用其生防天敌（biocontrol agent）尖喙象甲（Cyphocleonus achates）对异株矢车菊施加植食作用，以此探究降水减少如何调控种间竞争与生物防治植食作用对异株矢车菊种群丰度的影响效应。 实验开展七年后，异株矢车菊在以“n”起始的处理条件下的混合物种样地中占据优势地位。