Effects of urban development and habitat alterations on the distribution and abundance of native and exotic freshwater fish in the Brisbane region,Queensland

The distribution of freshwater fish in creeks throughout the Brisbane region was determined by a survey carried out in 1977–78. Seventeen native and six exotic species were recorded in 55 creeks. Sixteen native and four exotic species were collected in a more restricted survey of central Brisbane in 1981. Urban development and the establishment of exotic plants have resulted in substantial changes to the aquatic environment in many of the creeks surveyed. Exotic grasses, especially para grass (Brachiaria mutica) have reduced the extent of free water by growing partly into stream channels. Floating exotic plants blanketed some stream reaches. Native aquatic macrophytes have declined, apparently due to dredging, siltation and other disturbances. These changes have affected the distribution and abundance of native and exotic fish. Native species with a preference for open water and beds of aquatic plants have declined in creeks overgrown by para grass and floating plants. Melanotaenia fluviatilis, Retropinna semoni, Pseudomugil signifer, Craterocephalus stercusmuscarum and Ambassis nigripinnis have been affected. Para grass and floating plants have not affected the range or abundance of Hypseleotris galii, H. compressus and Mogurnda adspersa. Gambusia affinis and Xiphophorus helleri have been advantaged by expansion of their preferred habitat type - the edges of pools where exotic grasses have grown partly into the water. The effect of exotic fish on native species is unclear. There was a correlation between large numbers of G. affinis and small numbers of H. galii and M. fluviatilis. Correlations could result from predatory or competitive interactions between species. Alternatively, correlations could be due entirely to the effects of habitat alterations on exotic and native species. However, H. galii was evidently not disadvantaged by the habitat alterations studied. Thus there may be a complex interaction between this species and G. affinis. There was no evidence that X. helleri had affected the range or abundance of native species.     

Disturbance and demography of Phylica arborea (Rhamnaceae) on the Tristan-Gough group of islands

Populations of Phylica arborea Thouars, an evergreen tree endemic to six southern oceanic islands, have been depleted by wood gathering and browsing on Amsterdam Island and Tristan da Cunha, and it was feared that introduced rodents were destroying seed and reducing regeneration on uninhabited Gough Island. A comparison of the demography of this species on four islands in the Tristan-Gough group suggests that rodents have little effect on seedling numberS. Regeneration seldom occurs in undisturbed P. Arborea groves: germination and seedling survival appears to be dependent on periodical removal of established trees and understorey vegetation by soil-slips and occasional fireS. Climatic and vegetation differences problably account for the less frequent regeneration at Gough Island relative to that at the Tristan islands.     

Photosynthate Unloading from Seed Coats of Phaseolus vulgaris L.--Nature and Cellular Location of Turgor-Sensitive Unloading

Patrick, J. W., Jacobs, E., Offler, C. E. and Cram, W. J. 1986.Photosynthate unloading from seed coats of Phaseolus vulgarisL.—Nature and cellular location of turgor-sensitive unloading—J.exp. Bot. 37: 1006–1019. Unloading rates of ¹⁴C-Photosynthates from excised seed-coathalves of Phaseolus vulgaris L. plants were sharply increasedat cell turgor potentials in excess of 5 ? 10⁵ Pa. Turgor-sensitiveunloading occurred in the absence of any change in the passivepermeability of, and active sucrose influx across, the plasmalemmaand tonoplast membranes. The proton ionophore CCCP, and lowtemperature significantly slowed turgor-sensitive unloadingwhile PCMBS, a non-permeating sulphydryl-modifying compound,was without effect. Turgor-sensitive unloading significantlydepressed the ¹⁴C-Photosynthate content of the ground and branchparenchyma, but had no effect on the ¹⁴C-Photosynthate levelsin the vascular tissues. Cycling of cell turgor potentials aboveand below 5 ? 10⁵ Pa elicited reproducible responses in theunloading rate of ¹⁴C-Photosynthates. Increasing turgor above5 ? 10⁵ Pa resulted in a burst of ¹⁴C-Photosynthate unloading.Reversal to turgors less than 5 ? 10⁵ Pa caused a rapid depressionin unloading rate. It is proposed that turgor-sensitive unloadingis facilitated by a specific turgor-sensitive porter locatedon the plasmalemma of the ground and/or branch parenchyma cellsof bean seed coats. Key words: Bean, seed coat, turgor-sensitive unloading, phloem