Community
Organisation
1 . 1
The aim of this research pro ject is to test hypotheses derived from community organisation the ory. Absolute fossil pollen data from two different plant communi ties have been used to provide test data to permit the evaluation of community organisation theory in environments of differing spatial scale and resolution. Fossil pollen counts from two different study sites have been obtained with the aid of close resolution palynology. Modelling the fossil pollen field
· data required the development of a modelling framework based on dy namical systems theory.
The following chapter pro vides a more detailed description of these objectives and an introduc tion to the central topic of this re search project - the study of com munity behaviour.
1 . 2 Intro d u c t i o n
The aims and modelling objec tives of this research project are in terdependent. The development of a modelling framework is driven by the need to test theory, while limi tations of the same framework con strain to a degree the modelling process. A further objective in volves the use of fine resolution pa lynology to provide proxy test data.
The palynology objectives
s h o u l d n o t be c o n s i d ered
unimportant simply because they
are not explicitly stated in the title to this thesis. Their absence indicates an analytical emphasis; an attempt to progress from the descriptive and narrative
stages of palynology's past (Birks 1992).
The central theme of this research project is plant community organisation while the principal topic of interest is community behaviour as characterised by equilibrium and non-equilibrium theory. The testing of theory related to community organisation is one of current interest to many community ecologists. Until it is known which of the two contending equilibrium paradigms best imitates community behaviour, it will remain very difficult to prescribe
management strategies for ecological reserves (Krebs 1985) or to formulate long
term plans for sustainable resource management.
The methodology followed in this research project is common to most scientific research (Mentis 1988). An initial statement of working hypotheses was followed by experimental design, fieldwork in which samples were collected and lab-work in which the samples became data. Running concurrent with the data collection stage was the development of a modelling framework based on dynamical systems theory. This stage involved the scripting and debugging of software (Math Works Inc. 1991) in order to construct a mathematical framework (Robertson el al. 1991) that would solve and plot coupled systems of equations and estimate equation parameters based on non-linear optimisation procedures (Grace 1992). Finally, the software had to be validated, before the modelling work could begin.
The second and final stage of this project involved computer laboratory work in which the behaviour of various ecological models was tested against the behaviour of actual field data. Modifications were made to the models in order to test various hypotheses regarding the operation and behaviour of the systems under study.
In determining the layout of this thesis, the author considered it too restrictive an exercise to write from a formal scientific point of view (i.e. aims, method, results, discussion, conclusion
etc.).
To do so would be to place an unjustified emphasis on a sequence of research events at the cost of what this project is really all about - community organisation theory and its testing.For this reason, a format more common to mathematics theses has been chosen with the justification that �t provides a more natural grouping of the ideas being developed in a context of the natural stages of the project: to derive, to develop and to compare, i.e.
(a) to derive working hypotheses and models from existing theory (b) to develop a mathematical framework for testing the models (c) to compare field and model data.
1 . 2 . 1 D erive Working Hypoth eses
Chapters one, two and three develop the theory of community organisation in three natural parts. Chapter one is primarily concerned with defining community organisation and introducing the topic of community behaviour by stressing its relationship to the activity of causal agents. Chapter one also sketches a descriptive theoretical outline of the equilibrium and non equilibrium models of community behaviour. Chapters two and three develop in more detail the historical, ecological and mathematical significance of community behaviour with the objective of defining a set of testable research hypotheses.
1 . 2 . 2 D evelop a Mathematical Fram ework
Chapter four takes up a discussion of ecological modelling and the current contribution being made in this field of research by palynologists. A further objective of this chapter is to define the modelling methodology used in this project. This will introduce subjects like the computational software and its validation along with the theory of parameter estimation as used in hypothetico deductive scientific methodology.
1 . 2 . 3 Compare Actua l and Model Data
Chapters five and six contain two case studies in which the field data is introduced, modelled and evaluated. Chapter seven contains a brief summary and statement of conclusions.
1 . 3
IntroducedSimply stated, community organisation is the study of the forces or mechanisms responsible for community structure and behaviour (fig 1 .1). The problem with this definition is that it pre-supposes a knowledge of the word community - not yet defined. Attempts to develop a definition of community have a long history in ecology and involve an ongoing debate into some of the most controversial aspects of community organisation. For these two reasons, an acquaintance with the historical trends in the community definition debate is a pre-requisite to a working definition of community organisation.
1 . 3 . 1 A Working Definition of Ecological Comm u nity
A simple definition of an ecological community is: populations of living organisms in a prescribed area or habitat. Krebs (1985) suggests that there are three main ideas involved in all definitions of ecological community: species aggregation in a defined area, the idea of a fundamentalunit of community structure and the idea of homeostasis or self regulation (fig 1.2).
The second and third concepts of community listed above have been actively disputed. The extreme supporters of the third view consider that synergistic attributes belong to communities as a consequence of internal stability
maintained by homeostatic control (Clements 1916, Tansley 1920, 1935, Braun Blanquet 1932, Lovelock 1988). • 0 0 0 Biotic Abiotic · : CiJCJsp( J;ge:nts: :
The Three
Components of
Community
Organisation
Fig 1.1 The three components of community organisation: causal agents, community structure and behaviour. Community organisation is the study of the forces or mechanisms responsible for community structure and behaviour. Causal agents may work directly upon the structure of a community (arrow
1)
and in some cases are a part of the community structure itself (e.g. a predator or competing individuals). Causal agents work through the structure of a community in order to influence community behaviour (arrow2).
The second concept of a fundamentalunit of community types or classes is a further major assumption of the Clements-Tansley-Braun-Blanquet holistic school - an idea that found wide endorsement in North America, Great Britain and Europe. Gleason (1926, 1939), an ardent critic of the super-organism paradigm, argued that communities were simply collections of populations with the same environmental requirements. This view became the central tenet of the individualistic school of community ecology.
The individualistic school argued that while communities could be recognised and classified, it was for the convenience of the human observer and
not a description of the fundamental structure of nature (Krebs 1 98 5 ) .
Furthermore, communities are not of fixed composition (Whittaker 1962, 1967), vegetation change through time is continuous (Raup 1964) and thought to occur as a result of essentially two factors: plant immigration and environmental fluctuation (Gleason 1926, 1939).