Spatial plant ecology: empirical tests and development of theory

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.