Experimental evaluation of how biological invasions and climate change interact to alter the vertical assembly of an amphibian community

While biotic-abiotic interactions are increasingly documented in nature, a process-based understanding of how such interactions influence community assembly is lacking in the ecological literature. Perhaps the most emblematic and pervasive example of such interactions is the synergistic threat to biodiversity posed by climate change and invasive species. Invasive species often out-compete or prey on native species. Despite this long-standing and widespread issue, little is known about how abiotic conditions, such as climate change, will influence the frequency and severity of negative biotic interactions that threaten the persistence of native fauna.

Treefrogs are a globally diverse group of amphibians that climb to complete life-cycle processes, such as foraging and reproduction, as well as to evade predators and competitors, resulting in frog communities that are vertically partitioned. Furthermore, treefrogs adjust their vertical position to maintain optimal body temperature and hydration in response to environmental change. Here, utilizing this model group, we designed a novel experiment to determine how extrinsic abiotic and biotic factors (changes to water availability and an introduced predator, respectively) interact with intrinsic biological traits, such as individual physiology and behavior, to influence treefrogs’ vertical niche.  

Our study found that treefrogs adjusted their vertical niche through displacement behaviors in accordance with abiotic resources. However, biotic interactions resulted in native treefrogs distancing themselves from abiotic resources to avoid the non-native species. Importantly, under altered abiotic conditions, both native species avoided the non-native species  –  more than they avoided their native counterpart. Additionally, exposure to the non-native species resulted in native species altering their tree climbing behaviors by  and becoming more vertically dynamic to avoid the non-native antagonist.

Our experiment determined that vertical niche selection and community interactions were most accurately represented by a biotic-abiotic interaction model, rather than a model that considers these factors to operate in an isolated (singular) or even additive manner. Our study provides evidence that native species may be resilient to interacting disturbances via physiological adaptations to local climate and plasticity in space-use behaviors that mediate the impact of the introduced predator.

尽管生物-非生物相互作用（biotic-abiotic interaction）在自然界中的记录日益增多，但生态学领域现有文献仍缺乏基于过程的认知，以阐明这类相互作用如何影响群落组装（community assembly）。这类相互作用中，最具标志性且普遍存在的案例，便是气候变化与外来入侵物种（invasive species）对生物多样性（biodiversity）构成的协同威胁。外来入侵物种通常会通过竞争排除或捕食作用危害本土物种（native species）。尽管这一问题长期存在且分布广泛，但学界仍不甚明晰气候变化这类非生物条件，将如何影响那些威胁本土动物群（fauna）存续的负面生物相互作用的发生频率与严重程度。
树蛙（treefrogs）是一类全球分布广泛、物种多样性丰富的两栖动物（amphibians），它们通过攀爬来完成觅食、繁殖等生活史环节，同时借此躲避天敌与竞争者，由此形成了垂直分层的蛙类群落。此外，树蛙会通过调整自身垂直位置，以响应环境变化，维持适宜的体温与体内水分状态。本研究以树蛙作为模式类群，设计了一项全新实验，旨在探明外在非生物与生物因子——分别为水分可利用性变化与引入的捕食者——如何与个体生理、行为等内在生物学性状相互作用，进而影响树蛙的垂直生态位（vertical niche）。
本研究结果显示，树蛙会依据非生物资源的分布，通过移动行为调整自身的垂直生态位。但当存在生物相互作用时，本土树蛙会主动远离非生物资源，以躲避外来捕食者。值得注意的是，在非生物条件发生改变的情境下，本土树蛙对入侵捕食者的躲避程度，显著高于对本土同类的躲避。此外，当本土树蛙接触到外来捕食者后，其攀树行为会发生改变，表现出更强的垂直活动动态，以此躲避该外来天敌。
本实验证实，相较于将这些因子视为独立（单一）甚至累加作用的模型，生物-非生物相互作用模型能够最精准地刻画树蛙的垂直生态位选择与群落相互作用模式。本研究表明，本土物种可通过对当地气候的生理适应以及空间利用行为的可塑性，调节外来捕食者所带来的影响，从而对多重干扰的共同作用具备抗逆能力。