Department of Biology, California State University, Northridge, CA 91330-8303, USA.
Proc Biol Sci. 2011 Jun 22;278(1713):1804-13. doi: 10.1098/rspb.2010.2246. Epub 2010 Nov 24.
Quantifying species interaction strengths enhances prediction of community dynamics, but variability in the strength of species interactions in space and time complicates accurate prediction. Interaction strengths can vary in response to density, indirect effects, priority effects or a changing environment, but the mechanism(s) causing direction and magnitudes of change are often unclear. We designed an experiment to characterize how environmental factors influence the direction and the strength of priority effects between sessile species. We estimated per capita non-trophic effects of barnacles (Semibalanus balanoides) on newly settled germlings of the fucoid, Ascophyllum nodosum, in the presence and absence of consumers in experiments on rocky shores throughout the Gulf of Maine, USA. Per capita effects on germlings varied among environments and barnacle life stages, and these interaction strengths were largely unaltered by changing consumer abundance. Whereas previous evidence shows adult barnacles facilitate fucoids, here, we show that recent settlers and established juveniles initially compete with germlings. As barnacles mature, they switch to become facilitators of fucoids. Consumers caused variable mortality of germlings through time comparable to that from competition. Temporally variable effects of interactors (e.g. S. balanoides), or spatial variation in their population structure, in different regions differentially affect target populations (e.g. A. nodosum). This may affect abundance of critical stages and the resilience of target species to environmental change in different geographical regions.
量化物种相互作用强度可以增强对群落动态的预测，但物种相互作用在时空上的可变性使得准确预测变得复杂。相互作用强度可以响应密度、间接效应、优先效应或不断变化的环境而变化，但导致变化方向和幅度的机制往往不清楚。我们设计了一项实验，以表征环境因素如何影响固着物种之间优先效应的方向和强度。我们在美国缅因湾的岩石海岸上进行了实验，估计了藤壶（Semibalanus balanoides）对新定居的紫菜（Ascophyllum nodosum）幼苗的非营养个体效应，同时存在和不存在消费者。在不同的环境和藤壶生命阶段，幼苗的个体效应存在差异，而且这些相互作用强度在消费者丰度变化时基本不变。虽然先前的证据表明成年藤壶有利于紫菜的生长，但在这里，我们发现最近的定居者和已建立的幼体最初与幼苗竞争。随着藤壶的成熟，它们转变为紫菜的促进者。消费者通过时间导致了与竞争相似的幼苗可变死亡率。相互作用者（如 S. balanoides）的时间变化效应，或其在不同区域的种群结构的空间变化，会以不同的方式影响目标种群（如 A. nodosum）。这可能会影响关键阶段的丰度以及目标物种对不同地理区域环境变化的恢复力。
