Changes in understorey plant species richness following logging and prescribed burning in shrubby dry sclerophyll forests of south‐eastern Australia

Abstract The impacts of prescribed burning and timber harvesting on species diversity have been the subject of considerable debate. The temporal and spatial scale of these disturbances often presents major limitations to many studies. Here we present the medium‐term results of a planned long‐term study examining the impacts of logging and prescribed burning on the understorey floristic richness in shrubby dry sclerophyll forest in the south‐east of New South Wales, Australia. Generalized estimating equations were used to model the effect of environmental factors and disturbance variables on species richness at the coupe (～30 ha) and plot (～0.01 ha) scale. At the plot scale, fire effects on separate components of the vegetation were broadly consistent with other studies, with frequent fire resulting in a relative increase of species richness for species less than 1 m in height and a decline of larger species taller than this height. At the coupe scale, there was no decline in richness of larger shrub species, possibly owing to the spatial heterogeneity of fire frequency at this scale. Logging resulted in significantly greater species richness in the shrub layer, but had no significant effect on species richness in the ground layer. During the study period, there was a general decline in plant species richness at both coupe and plot scales which occurred independently of imposed management regimes. This is thought to be related to a natural succession following wildfire, and may be due to the absence of high‐intensity fire in the study area since 1973, or to an effect related to season of burning.     

Studies on the Mechanism of Action of Estradiol in Regulating Follicular Progesterone Levels: Effects on cAMP Mediated Events and 3β-Hydroxysteroid Dehydrogenase

Previous studies demonstrated that estradiol interferes with pituitary-induced progesterone production and oocyte maturation in cultured amphibian ( Rana pipiens ) ovarian follicles. To elucidate the mode of action of estradiol in modulating follicular progesterone accumulation we have examined its effects on cAMP-induced progesterone production and enzymatic conversion of pregnenolone to progesterone by 3β-hydroxysteroid dehydrogenase (3β-HSD). Follicular cAMP levels were manipulated with forskolin (an adenylate cyclase activator), isobutyl methyl xanthine (IBMX-phosphodiesterase inhibitor) and exogenously added cAMP. Progesterone production induced by forskolin alone or forskolin in combination with frog pituitary homogenate (FPH) was inhibited by estrogen. Addition of estradiol to culture medium markedly inhibited follicular progesterone accumulation following treatment of follicles with cAMP and IBMX. In the presence of exogenous pregnenolone, non-FPH stimulated ovarian follicles effectively converted the 3β-HSD substrate to progesterone. Treatment of follicles with estradiol inhibited conversion of pregnenolone to progesterone. The results indicate that estradiol acts, following FPH stimulation, at one or more steps subsequent to elevation of cAMP levels to regulate intrafollicular progesterone accumulation and oocyte maturation. Estrogen appears to directly influence the enzymatic (3β-HSD) conversion of pregnenolone to progesterone.     

醇母PHO81基因的克隆和表达

从酵母染色体ＤＮＡ中获得１个约３．０ｋｂ的ＢａｍＨＩ的克隆片段和１个约５．０ｋｂ的ＰｓｔＩ片段,前者包含１７４５ｂｐ的ＰＨＯ８１基因编码序列及１２４４ｂｐ的上游序列,后者包含２２３６ｂｐ的编码序列及约２．８ｋｂ的下游序列,经拼接得到完整的ＰＨＯ８１基因。以ＵＲＡ３基因取代部分ＰＨＯ８１的编码序列,通过体内同源重组,获得ＰＨＯ８１基因缺陷的酵母细胞株。构建ＰＨＯ８１－ＬａｃＺ融合基因,以β－半乳糖苷酶的活力表示ＰＨＯ８１基因的表达水平,研究了它的表达作用。ＰＨＯ８１基因为阻遏型表达,受无机磷浓度的控制,高磷使基因表达阻遏,低磷去阻遏。ＰＨＯ８１对其自身的表达有正调控作用,它与ＰＨＯ５和ＰＨＯ１１基因的调控模式相似,但ＰＨＯ８１上游调控序列和ＰＨＯ５及ＰＨＯ１１的同源性很低。     

Selection by humans searching for computer- generated prey images: the effect of prey density

We investigated the effect of 'prey' density on frequency-dependent selection by human 'predators'. Eighty subjects were presented with computer-generated populations of two cryptically coloured characters on the screen of a colour monitor. Each subject was given the prey at a single combination of one of two frequencies and one of five densities, and was instructed to delete the prey as fast as possible with a light-pen. The results suggested that the degree of selection was inversely proportional to prey density, but there was no evidence that any frequency-dependent component of selection was affected.     

Thinking with Animals: New Perspectives on Anthropomorphism

Thinking with Animals: New Perspectives on Anthropomorphism. Lorraine Daston and Gregg Mitman, eds. New York: Columbia University Press, 2005. 230 pp.     

Rethinking Commodification: Cases and Readings in Law and Culture

Rethinking Commodification: Cases and Readings in Law and Culture . Martha M. Ertmanand Joan C. Williams, eds. New York. New York University Press, 2005. 450 pp.