Spatial plant ecology: empirical tests and development of theory

据估计，地球上有多达5000万个物种。了解是什么导致并维持了这种惊人的多样性是至关重要的。事实上，最近的研究表明，维持这种多样性可能对维持地球的生态系统很重要。因此，许多生态学家都专注于理解这个问题。生态学中最早的假设之一是“竞争排斥原则”，该原则指出，如果两个物种在很大程度上共享相同的资源，那么一个物种，即较强的竞争者，应该排斥另一个物种，即较弱的竞争者。然而，参观一公顷热带雨林，很快就会发现在同一栖息地可以出现数百种非常相似的物种。这种多样性不仅仅是热带雨林的特性；在英国德比郡的山坡上，即使是一平方米的草地也能容纳30多种不同的植物。生态学家很早就认识到，任何给定物种的个体通常都聚集在空间中。这对竞争具有潜在的重要性，因为个体只与附近的邻居互动，而且由于聚集，它们倾向于主要与自己物种的其他成员互动。我之前的研究表明，原则上，这种聚集在解释植物群落中观察到的高度多样性方面是很重要的。如果同一物种成员之间的相互作用比不同物种成员之间的相互作用距离更长，那么两个（或更多）相似的物种可以在同一栖息地共存。我们称这种机制为“异视”，因为在某种程度上，个体只在很短的距离内“看到”不同物种的成员。据推测，这些邻居相互作用尺度上的差异是由某些植物物种特有的疾病引起的，真菌也可能帮助某些物种从土壤中收集更多的资源。然而，这只在数学模型中被证明是有效的；“异视”是否在自然植物群落中起作用还有待观察。人们预计，对于树木来说，邻居大小可能至少与邻居身份（它是哪个物种）同样重要。这是因为植物经常遮挡较小的邻居，从而限制了到达它们的光线，减缓了它们的生长速度。尽管如此，大多数用来试图理解植物群落形成和维持过程的数学模型都没有包括植物大小的差异以及邻里之间的相互作用。这主要是因为能够做到这一点的数学才刚刚发展起来。我最近的大部分工作都是在开发这些技术，可以说，数学工具箱现在已经准备好应用于生态学中的这些难题。我提出的研究将有两个主要目标。首先，我将通过分析热带雨林的数据来解决类似竞争者共存的问题，看看空间结构是否重要，“异视”是否是维持多样性的一个重要过程。其次，我将构建包括植物生长在内的数学模型，看看是否会出现像“异视”这样的新假设。然后，这个新理论可以用森林数据进行测试，看看是否有任何新的预测发生在真实的植物群落中。这些目标加在一起，应该使我们能够更好地了解，面对有限资源的激烈竞争，如何保持高度的生物多样性。

It is estimated that there is up to 50million species on earth. Understanding what causes and maintains this staggering diversity is one of vital importance. Indeed recent studies have suggested that maintaining this diversity might be important in maintaining the earth's ecosystems. As a consequence many ecologists are focussed at understanding this problem. One of the earliest hypotheses in ecology, the 'competitive exclusion principle' states that if 2 species greatly share the same resources then one, the stronger competitor, should exclude the other, weaker competitor. However, visiting a single hectare of tropical rainforest will soon show that many hundreds of very similar species can occur in the same habitat. This diversity is not just a property of tropical rainforests; even a metre square of grassland on a Derbyshire hillside in the UK can hold over 30 separate species of plant. Ecologists have long recognised that individuals of any given species are often clumped in space. This is potentially important for competition because individuals interact only with their nearby neighbours, and because of the clumping they are tending to interact mainly with other members of their own species. My previous research has shown that in principle, this clumping can be important in explaining the high diversity observed in plant communities. If interactions between members of the same species are over longer distances than those between members of different species then two (or more) similar species can coexist in the same habitat. We called this mechanism 'heteromyopia' because in some way, individuals 'see' members of different species (heterospecifics) over only short distances. It is expected that these differences in scales of neighbour interactions are caused by diseases that are specific to some species of plant, and also by fungi which may help some species collect more resources from the soil. However, this has only been shown to work in a mathematical model; it remains to be seen if 'heteromyopia' works in natural plant communities. It is expected that for trees neighbour size might be at least as important as neighbour identity (which species it is). This is because plants often shade out smaller neighbours, thereby restricting the light that reaches them, and slowing their growth rate. Despite this fact, most of the mathematical models used to try and understand what processes shape and maintain plant communities do not include differences in plant size as well as neighbourhood interactions. This is primarily because the mathematics that is able to do this, has only just been developed. Much of my recent work has been in developing these techniques, and arguably the mathematical toolbox is now ready to be applied to such difficult problems in ecology. My proposed research will have two main objectives. Firstly, I will tackle the problem of coexistence of similar competitors by analysing data from tropical rainforests to see if the spatial structure is important and if 'heteromyopia' is an important process in maintaining diversity. Secondly, I will construct mathematical models that include plant growth to see if any new hypotheses like 'heteromyopia' emerge. This new theory can then be tested with the forest data to see if any of the new predictions occur in real plant communities. Together these objectives should enable a greater understanding of how high biodiversity is maintained in the face of intense competition for limiting resources.