Biodiversity dynamics across environmental gradients and under impending environmental change

我们生活在一个急剧变化和生物多样性迅速丧失的时代。为了更好地预测人为变化对世界日益减少的生物多样性的影响，关键是首先了解物种是如何自然分布的，然后评估它们的分布可能会如何变化，或者更糟糕的是，消失。生物多样性在整个地球上的分布是不均匀的，向低纬度、中低海拔和森林中树冠高度增加。这些空间梯度反映了环境变量的差异，如光度、温度和湿度，这些变量影响生理、人口和生物相互作用过程。物种对这些变量表现出不同的偏好(即生态位)，这导致生物多样性在生态位高度重叠的地区达到峰值，前提是共存机制在发挥作用。与生态位相关的变量和共存机制都正在被人类破坏。由于许多环境变量自然是共变的，对比梯度应该提供洞察力，以理清它们在不断变化的世界下的生物多样性动态中的作用。因此，该项目利用了1)新的机制模型，而不是可以模拟对比环境梯度和2)一个主要的生态重要性的生物系统-维管附生植物。维管束附生植物，包括大多数兰花和凤梨，是非寄生在树木上的植物。它们是热带森林养分循环和相互作用网络的关键，占世界植物区系的10%，占一些当地植物区系的50%。它们在垂直和海拔梯度上的分布方式各不相同，可能取决于它们的温度和湿度偏好，而且往往受到地理上的限制(即特有和受威胁)。尽管附生植物特别容易受到森林砍伐和全球变暖的影响，但由于对森林树冠进行采样存在困难，对附生植物的研究一直不足。因此，模拟实验是提高我们对该系统的生态学理解的理想方法，同时还可以：1)确定在经验研究中应优先考虑的数据收集；2)在不操纵脆弱生物多样性的情况下探索人类影响的情景。

We live in a time of radical changes and rapid biodiversity loss. To make better predictions of the impacts of anthropogenic change on the world's declining biodiversity, it is crucial to first understand how species are naturally distributed and then assess how their distribution might shift or, worse, disappear. Biodiversity is unequally distributed across the Earth, increasing towards low latitudes, low to intermediate elevations, and intermediate canopy heights within forests. These spatial gradients reflect differences in environmental variables, such as luminosity, temperature and humidity, which affect physiological, demographic, and biotic interaction processes. Species show different preferences for these variables (i.e. ecological niche), which causes biodiversity to peak in areas of high niche overlap, provided that coexistence mechanisms are at play. Both niche-related variables and coexistence mechanisms are being disrupted by humans. Because many environmental variables naturally co-vary, contrasting gradients should provide insights to disentangle their roles in biodiversity dynamics under a changing world. Therefore, this project takes advantage of 1) novel mechanistic models than can simulate contrasting environmental gradients and 2) a biological system of major ecological importance - vascular epiphytes. Vascular epiphytes, including most orchids and bromeliads, are plants growing non-parasitically on trees. They are key to nutrient cycles and interaction networks in tropical forests, accounting for 10% of world's flora and up to 50% of some local floras. They vary in how they are distributed along vertical and elevational gradients, probably following their temperature and humidity preferences and often being geographically restricted (i.e. endemic and threatened). Epiphytes have been understudied due to difficulties in sampling the forest canopy despite being particularly vulnerable to deforestation and global warming. Hence, simulation experiments are ideal to improve our ecological understanding of the system while also to i) identify the data collection that should be prioritized in empirical studies and ii) explore scenarios of human impacts without manipulating vulnerable biodiversity.