Guiliano Stefanie M, Karr Cerina M, Sommer Nathalie R, Buchkowski Robert W
Northeastern University, Boston, MA, United States of America.
School of Forestry & Environmental Studies, Yale University, New Haven, CT, United States of America.
PeerJ. 2020 Jun 1;8:e9184. doi: 10.7717/peerj.9184. eCollection 2020.
In old field systems, the common woodlouse may have an indirect effect on a nursery web spider. Woodlice and nursery web spiders feed in different food chains, yet previous work demonstrated that the presence of woodlice is correlated with higher predation success by nursery web spiders upon their grasshopper prey. This finding suggested a new hypothesis which links two seemingly disparate food chains: when woodlice are present, the spider predator or the grasshopper prey changes their location in the vegetative canopy in a way that increases their spatial overlap and therefore predation rate. However, warming temperatures may complicate this phenomenon. The spider cannot tolerate thermal stress, meaning warming temperatures may cause the spider to move downwards in the vegetative canopy or otherwise alter its response to woodlice. Therefore, we would expect warming and woodlice presence to have an interactive effect on predation rate.
We conducted behavioral experiments in 2015, 2017, and 2018 to track habitat domains-the use of the vegetative canopy space by grasshoppers and spiders-in experimental cages. Then, we used three models of spider movement to try to explain the response of spiders to woodlice: expected net energy gain, signal detection theory, and individual-based modelling.
Habitat domain observations revealed that spiders shift upward in the canopy when woodlice are present, but the corresponding effect on grasshopper prey survival was variable over the different years of study. Under warming conditions, spiders remained lower in the canopy regardless of the presence of woodlice, suggesting that thermal stress is more important than the effect of woodlice. Our modelling results suggest that spiders do not need to move away from woodlice to maximize net energy gain (expected net energy gain and signal detection theory models). Instead spider behavior is consistent with the null hypothesis that they move away from unsuccessful encounters with woodlice (individual-based simulation). We conclude that mapping how predator behavior changes across biotic (e.g. woodlouse presence) abiotic conditions (e.g. temperature) may be critical to anticipate changes in ecosystem dynamics.
在旧耕地系统中，普通潮虫可能会对育幼网蜘蛛产生间接影响。潮虫和育幼网蜘蛛处于不同的食物链，但先前的研究表明，潮虫的存在与育幼网蜘蛛对其蚱蜢猎物的更高捕食成功率相关。这一发现提出了一个新的假设，该假设将两条看似不同的食物链联系起来：当潮虫存在时，蜘蛛捕食者或蚱蜢猎物会改变它们在植被冠层中的位置，从而增加它们的空间重叠，进而提高捕食率。然而，气温升高可能会使这一现象变得复杂。蜘蛛无法耐受热应激，这意味着气温升高可能会导致蜘蛛向植被冠层下方移动，或者以其他方式改变其对潮虫的反应。因此，我们预计气温升高和潮虫的存在会对捕食率产生交互作用。
我们在2015年、2017年和2018年进行了行为实验，以追踪实验笼中蚱蜢和蜘蛛对植被冠层空间的利用情况，即栖息地领域。然后，我们使用三种蜘蛛运动模型来试图解释蜘蛛对潮虫的反应：预期净能量增益、信号检测理论和基于个体的建模。
栖息地领域观察表明，当潮虫存在时，蜘蛛会在冠层中向上移动，但在不同的研究年份中，对蚱蜢猎物存活的相应影响有所不同。在变暖条件下，无论潮虫是否存在，蜘蛛都停留在冠层较低位置，这表明热应激比潮虫的影响更为重要。我们的建模结果表明，蜘蛛不需要为了使净能量增益最大化而远离潮虫（预期净能量增益和信号检测理论模型）。相反，蜘蛛的行为与零假设一致，即它们会远离与潮虫的不成功遭遇（基于个体的模拟）。我们得出结论，描绘捕食者行为如何在生物条件（如潮虫的存在）和非生物条件（如温度）下发生变化，对于预测生态系统动态变化可能至关重要。
