Australian corticolous myxomycetes: models of distribution and development

Abstract

This paper presents an integrated model of the variation over a continental landmass of myxomycetes, a single-celled organism in the phylum Amoebozoa. Bark samples were collected on long traverses across Australia, and cultivated in Petri dishes by the moist chamber technique to obtain large assemblages of common species. The results of this survey and previous surveys are consistent with there being four major myxomycete assemblages: Tropical, Northern Arid, Southern Arid and Temperate. Where mapped, these species assemblage regions are consistent with the Australian phytogeographical regions. The myxomycetes differ between arid and non-arid areas; the arid areas have slightly higher productivity per wetting event, with members of the Physarales and Liceales relatively important and the Stemonitidales, Trichiales and Cribrariales less important. When the bark samples are placed in a moist culture there is a myxomycete growth cycle and then the population declines to resting phases. The population increase during a growth phase can be modelled by a linear plot of log(abundance) against species rank, where abundance is total harvested spore volume of a species. The population decline appears to be linear from two weeks after watering, declining to negligible activity 4 weeks after watering.

Controls on myxomycete species and species assemblages

“…The curve is consistent with most samples giving a harvest forming a broad peak with a mode at about a 0.9 mm 3 , with about one-quarter of the samples giving low harvests due, it is thought, to the stems being unsuitable for bacterial growth. The histogram is very similar to that of bark samples from Western Australia (Wellman 2019) shown in Fig. 2a.…”

“…2 have a similar shape, the origin of the highest volumes is different. Wellman (2019) showed for the bark survey the samples with the highest productivity have an abnormally big difference between the total spore volumes of the species with the highest volume and the next highest volume. This is thought to be due to carry over of mass between feeding events, leading to a large 'swarm' event giving the highest volume.…”

“…1. A survey of myxomycetes found on bark on several traverses across Australia (Wellman 2019). This survey is of much wider extent than other surveys, consequently the mean pH of sections of the traverses changes along the traverses.…”

“…There have been many comparisons of species assemblages using measures of diversity. Previous papers by Wellman (2016Wellman ( , 2019 have tackled some general topics using Australian data from the bark substrate: the number of species associations over Australia; the nature of the species association boundaries; the effects of pH on the productivity; the variation over Australia of productivity and family dominance; and the typical growth and decay over four weeks of a large mixed myxomycete 'population'. This paper uses both Australian and overseas data to investigate other general myxomycete ecological topics which affect myxomycete species.…”