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，这一点至关重要。事实上，最近的研究表明，保持这种多样性对维持地球生态系统可能很重要。因此，许多生态学家都专注于了解这个问题。“竞争排斥原理”是生态学中最早的假说之一，它指出，如果两个物种极大地共享相同的资源，那么其中一个较强的竞争者应该排除另一个较弱的竞争者。然而，参观一公顷的热带雨林很快就会发现，数百种非常相似的物种可能出现在同一栖息地。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，即使是一米见方的草地也可以容纳30多种不同的植物。生态学家早就认识到，任何给定物种的个体都经常聚集在太空中。这对竞争可能很重要，因为个体只与附近的邻居互动，而且由于聚集在一起，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，这种丛生现象对于解释植物群落中观察到的高度多样性是很重要的。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远，那么两个(或更多)相似的物种可以共存于同一栖息地。我们称这种机制为“异质性近视”，因为在某种程度上，个体只能在很短的距离内“看到”不同物种(异种)的成员。据估计，这些邻居相互作用规模的差异是由某些植物特有的疾病引起的，也是由真菌引起的，这可能有助于某些物种从土壤中获得更多的资源。然而，这只在一个数学模型中被证明是有效的；“异质性近视”是否在自然植物群落中起作用还有待观察。据估计，对于树木来说，邻居的大小可能至少与邻居的身份(它是什么物种)一样重要。这是因为植物经常遮蔽较小的邻居，从而限制到达它们的光线，并减缓它们的生长速度。尽管如此，大多数用于尝试和理解什么过程塑造和维护植物群落的数学模型并不包括植物大小和邻居相互作用的差异。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困难问题。我提出的研究将有两个主要目标。首先，我将通过分析来自热带雨林的数据来解决类似竞争者共存的问题，以确定空间结构是否重要，以及异质性近视是否是维持多样性的重要过程。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“异质性近视”这样的新假说。然后，这一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出现在真实的植物群落中。综合起来，这些目标应使人们能够更好地了解，面对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.