The potential impacts of species colonization on the structure and functioning of ecosystems are poorly understood. We propose a novel approach for understanding the consequences of habitat colonization, highlighting the influence of colonists on the availability of limiting resources to resident species. We studied how colonization of dry oak woodlands by pines ( Pinus halepensis ) is affecting water stress of resident oaks ( Quercus calliprinos ). We monitored predawn leaf water potential (PLWP) of oaks monthly for 2 years. Using maximum likelihood and multi-model inference, we evaluated how the PLWP of oaks was affected by pine colonists. The influence of colonizing pines on PLWP of resident oaks varied in time and space from negative to positive depending on season, oak size, pine size, and proximity to pines presence. The water stress of oaks increased along the dry season (− 1.5 to − 4.5 MPa), with small oaks becoming more severely stressed than large ones (up to 60% difference). During the dry season, neighboring pine colonists increased the water stress of oaks (up to − 0.4 MPa difference), but during the wet season, they reduced the water stress mainly for large oaks. Our findings indicate that pine colonization differentially affects water limitation for resident oaks with implications for future development and regeneration. The influence of pine colonists shifted from positive to negative along an increasing water stress gradient, contrary to predictions by the stress gradient hypothesis. Our work demonstrates how colonization by non-resident species can influence key ecosystem processes through the redistribution of limiting resources. Identifying these processes is fundamental for understanding the consequences of colonization, mitigating these influences, and predicting future change in the structure and function of ecosystems.

中文翻译：

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干橡树林地松树定植的后果：对水分胁迫的影响

物种定殖对生态系统结构和功能的潜在影响知之甚少。我们提出了一种理解栖息地殖民化后果的新方法，强调了殖民者对居民物种有限资源可用性的影响。我们研究了松树（Pinus halepensis）对干燥橡树林地的殖民如何影响常驻橡树（Quercus calliprinos）的水分胁迫。我们每月监测橡树的黎明前叶水势 (PLWP)，持续 2 年。使用最大似然和多模型推理，我们评估了松树殖民者如何影响橡树的 PLWP。定植松树对常驻橡树 PLWP 的影响在时间和空间上从负到正变化，具体取决于季节、橡树大小、松树大小和与松树的接近程度。橡树的水分胁迫随着旱季增加（- 1.5 到- 4.5 MPa），小橡树比大橡树受到的压力更严重（差异高达 60%）。在旱季，邻近的松树殖民者增加了橡树的水分胁迫（高达 − 0.4 MPa 的差异），但在雨季，他们主要减少了大型橡树的水分胁迫。我们的研究结果表明，松树定植对常驻橡树的水分限制有不同的影响，对未来的发展和再生有影响。松树殖民者的影响随着水分胁迫梯度的增加而从正面转变为负面，这与压力梯度假设的预测相反。我们的工作展示了非居民物种的殖民如何通过有限资源的重新分配来影响关键的生态系统过程。