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Abstract

Despite widespread acceptance of the spatial structure of ecosystems and the
spatial nature of processes acting within them, critical tests of the importance of
spatial phenomena to the structure and dynamics of ecosystems have not been
forthcoming. In most marine epibenthic communities, the single limiting resource is
space. Here I investigate the spatial dynamics of an epibenthic community in a
shallow subtidal system in Tasmania and a spatial model of this community to
examine how spatial process influences invasion resistance, stability, interactions
among species and the growth rates of individuals.
In Chapter 2 I examine the relationship between invasion resistance and species
richness in the natural community. The rate of invasion increases with local species
richness by two distinct mechanisms. Opportunistic colonisers invade species rich
patches at higher rates because speciose patches are dominated by small colonies and
mortality rates of small colonies are greater than that of large ones. Thus, mortality
provides bare space for opportunists to colonise more frequently in speciose patches.
However, some species avoid colonising free space but preferentially associate with
established colonies of particular other species. In this case, a given preferred
associate is more likely to occur in more species rich patches, and so colonisation
rates are greater in more speciose patches. In Chapter 3 the importance of spatial context on the outcomes of pair-wise
species interactions and neighbour-specific growth rates is examined. The outcomes
of competitive (overgrowth) interactions among species and neighbour-specific
growth rates in experimentally contrived pair-wise interactions are often dissimilar to
their counterparts in the non-manipulated natural community. I use a spatial model and its non-spatial equivalent to demonstrate that these differences in outcomes and
growth significantly affect predicted community dynamics.
In Chapter 4 I develop a spatial simulation model parameterised by empirical
observations of the recruitment, growth, interaction outcomes and mortality of the
natural community. I compare the model dynamics to the dynamics of manipulated
and non-manipulated natural communities. The model self-organises to form distinct
colonies and adequately captures many features of the short-term dynamics of
manipulated communities observed over a 16 month period, although some model
behaviours are not reflected in the natural community. When compared to the longerterm
dynamics of the non-manipulated communities (ca. 12 years), the model
accurately predicts the species evenness, diversity, size structure and multivariate
variance of these communities. None of these emergent features is evident from
equivalent non-spatial (mean field) models. In Chapter 5 I use the model developed and tested in chapter 3 to examine the
relationships between species richness, area, persistence stability of total cover,
resilience stability and invasion resistance. Communities occupying small areas are
less stable and less resilient than those in larger areas. While richness is positively
correlated with persistence stability in small landscapes (<900 cm 2), in larger
landscapes richness is negatively correlated with stability. Moreover, the stability of
landscapes is a strong determinant of invasibility. Thus, in landscapes .900 cm2 the
number of invasions increased with species richness. The underlying mechanisms are
emergent in the model and are the same as shown in Chapter 1. None of these features
arise in equivalent mean field models.
In conclusion, marine epibenthic communities have strong spatial dynamics and
processes. These can be represented accurately by spatial models which self-organise to form colonies. The dynamics of these models and of the natural communities are
contrary to much of established ecological theory. For example, the relationships
between richness and persistence stability, and between richness and invasion
resistance, depend on patch size, largely because patch size determines the extent of
spatial self-organising. For large patches (?_ 900 cm2) of a given size, both persistence
stability and invasion resistance decrease with species richness. This is an important
demonstration that community level properties such as stability and invasion
resistance are determined by the properties of the component species and the
emergent dynamics of each particular community, and are not an intrinsic function of
richness or any other aggregate property.

Item Type:	Thesis - PhD
Authors/Creators:	Dunstan, Piers K.(Piers Kyren)
Keywords:	Benthic animals, Spatial ecology, Marine ecology
Copyright Holders:	The Author
Copyright Information:	Copyright 2002 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Thesis (Ph.D.)--University of Tasmania, 2002. Includes bibliographical references
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