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The ecology of phytal animal communities


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Edgar, Graham 1982 , 'The ecology of phytal animal communities', PhD thesis, University of Tasmania.

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The factors influencing the motile macrofauna associated with marine
algae were investigated on spatial and temporal scales in order to determine
how these assemblages are organised. Results from these phytal studies were
also used to assess mathematical and biological aspects of the theory of

Water depth had the greatest influence on the distribution of the phytal
fauna within a localised area. Within a depth zone, animal species ranged
widely over most algal species, but there were quantitative differences in the
abundances of the faunas on different algae. These differences partly resulted
from a close correspondence between algal shape and faunal size structure.
Monthly sampling of the phytal assemblages associated with five algal
species showed that the abundances of almost all animal species peaked at the
time of a seasonal epiphyte bloom in late summer-early autumn, and faunistic
differences between the erect algae were obscured at this time. These results,
in conjunction with observed seasonal changes in the size-frequency histograms
of four ampithoid amphipod species, and motility, predation and algal-selection
experiments, provided evidence that cyclic fluctuations in phytal
amphipod populations were directly influenced by epiphytic biomass and
predation pressure. The ampithoid guild was probably also structured by
competitive constraints.

Widely-used diversity indices were calculated for the phytal samples and
compared. it was found that these indices could be grouped into those
primarily influenced by dominance, those primarily influenced by species
density, and those, such as the Shannon-Wiener Index, which were intermediate between the other two groups. Evenness indices were also investigated but were
found to be highly dependent on sample size and consequently difficult to

Environmental correlates of dominance and species density indicated that
these two community parameters were relatively independent. Dominance and
animal abundance both appeared to be monotonically increasing functions of the
level of food resources. Species density was dependent on the weight of
sampled algae but was also strongly influenced by wave exposure and habitat
complexity (sensu number of habitats, rather than rugosity). Neither species
density nor dominance were found to be greatly influenced over a 28 ° range of

Diversity parameters were considered to be helpful in the interpretation
of the effects of external factors on communities. However, the lack of
discrimination between dominance and the alpha and gamma components of species
density in the past has resulted in much confusion on the causes of diversity.

Item Type: Thesis - PhD
Authors/Creators:Edgar, Graham
Keywords: Animal communities, Animal ecology, Marine algae
Copyright Holders: The Author
Copyright Information:

Copyright 1982 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, 1983. Bibliography: p. 173-189

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