Adult facilitation becomes competition as juvenile soapberry bugs age

Intraspecific interactions can change from facilitative to competitive depending on the organism’s ontogeny. In plant-feeding insects, host plant defenses can be strengthened or weakened by insect feeding, and can therefore be important for determining whether two insects feeding on the same plant help or harm each other’s fitness. Here I conducted two experiments looking at the direct effect of a physical seed defense and the role of intraspecific facilitation in reducing the effects of that defense for juveniles of the red-shouldered soapberry bug. I demonstrate that juveniles are severely inhibited by the tough seed coat of their host plant, leading to high mortality early in development. Adults, in contrast, can create holes through which younger individuals could potentially feed. I manipulated whether or not seeds were fed on by adults on two host plant species: a well-defended native host and a poorly defended introduced host. Survival in the first week of development was dramati...种内相互作用可随生物的个体发育（ontogeny）从促进型转向竞争型。在植食性昆虫中，寄主植物的防御机制可因昆虫取食而增强或减弱，因此对于判断取食同一植株的两只昆虫是彼此促进还是损害对方的适合度（fitness）至关重要。本研究针对红肩皂荚蝽（red-shouldered soapberry bug）若虫开展了两项实验，探究物理性种子防御的直接效应，以及种内促进作用在减轻该防御机制对若虫负面影响方面所发挥的作用。研究表明，若虫会受到寄主植物坚硬种皮的严重抑制，导致发育早期死亡率居高不下。与之相对，成虫可钻出孔洞，供年幼个体取食。本研究在两种寄主植物（防御能力较强的本土寄主与防御能力较弱的外来寄主）上设置了成虫是否取食种子的处理组。发育第一周的存活率显著……