|Institution:||University of Tasmania|
|Keywords:||Animal communities; Animal ecology; Marine algae|
|Full text PDF:||http://eprints.utas.edu.au/19931/1/whole_EdgarGraham1983_thesis.pdf|
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 diversity. 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 interpret. 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 latitude. 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.