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Abstract

A key question in community ecology is whether communities are a natural
level of biological organisation, with characteristic emergent properties
influenced by evolution and comprising species that have mutually influenced
each others evolution, or whether they are simply haphazard collections of
species adapted to similar physical conditions. Are they a real biological
phenomenon or merely artificial constructs to help biologists order their
thinking? If communities are real entities determined and constrained by
evolution and with distinct emergent properties, then one place to look for
evidence of this is during the assembly process. A community that displays a
broadly consistent structure regardless of the order of arrival and abundance of
taxa and thus whose structure reflects predictable post-settlement processes and
not merely the accumulation of settlers, is likely to be a real community rather
than a haphazard assemblage.
Community assembly in macrofauna communities developed in artificial kelp
holdfasts was monitored at 1-month intervals over a 13 month period using a
sampling design that used systematic patterns of temporal overlap and changes
in start and collection dates. The aim of this experiment was to study the links
between recruitment and community dynamics through the assembly process by
comparing community trajectories for substrata deployed on different dates, and
thus subject to different potential recruitment from the larval pool. The rate of
settlement is thought to be an important determinant of marine community
dynamics. The design is unique in its intensity of sampling and level of
replication, which could only be achieved through the use of artificial habitats.
The hierarchical nature of the experimental design allowed several different
approaches to analysis; by date of deployment and by date of collection of the
artificial habitats, which enabled comparison of community assembly with and
without the seasonal effects of the date of collection, and by community age to
test whether there were alternative end-states to assembly depending on season
or recruitment history.
While the process of assembly varied across the different deployment and
collection dates, community structures defining the completion of assembly,
were broadly similar. This was because the interactions between individuals
(interspecific and/or intraspecific) were an important structuring force. This was
particularly the case in older communities, and thus, the rate of supply of
recruits (relative to the frequency and intensity of disturbance) can be a key
determinant of community dynamics in macrofauna communities. Richness was
lower than expected from accumulation of monthly recruits, suggesting the
importance of pre- and/or post-settlement competitive and/or predatory
interactions. However, results were taxon specific, with evidence of settlementdriven
population dynamics (e.g. hiatellid bivalves), facilitation (e.g. serpulid
polychaetes) and competition/predation (e.g. phyllodocid polychaetes), among
the 100 families examined. The behaviours of a series of null models, which
displayed increasing levels of ecological realism and which were based on
observed data, showed that while the interactions among individuals already
established in the community influenced community dispersion, the interactions
occurring between settling individuals and the established community had the
greatest influence on community structure. Results on a subset of taxa of
sufficient abundance for further analysis suggested that the direction of these
interactions was consistent across communities of different age. These results
have implications for the way we approach the study of macrofauna
communities, because recruitment to bare space is likely to be a poor indicator
of the actual recruitment of organisms to an established community.
The overall results suggest that the collection of organisms that establish within
an artificial kelp holdfast are more than just assemblages of settling organisms,
rather they should be considered real communities. This was evident in an
analysis designed to identify and assess the performance of surrogates employed
to monitor community structure through changes in season and community age.
While surrogate performance varied depending on the surrogate examined, with
careful selection, effective surrogates of community structure could be identified.
Notably, good surrogates could be identified from as few as 10% of the total
number of families, but surrogates based on familial diversity within abundant
higher taxa did not perform any better than random selections of the same
number of families.

Item Type:	Thesis - PhD
Authors/Creators:	Magierowski, RH
Keywords:	Marine ecology, Marine biology, community assembly, kelp holdfast, biodiversity surrogate, recruitment, competition, community ecology, marine macrofauna
Copyright Holders:	The Author
Copyright Information:	Copyright 2006 the author
Additional Information:	Thesis (PhD)--University of Tasmania, 2007. Includes bibliographical references
Item Statistics:	View statistics for this item

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