The time course of dark adaptation in the bee: a phototactic and electrophysiological investigation

ABSTRACT. The time course of dark adaptation in Apis melifera L. was investigated by analyses of phototactic behaviour and electroretinogram (ERG). The behavioural results give a function for dark adaptation showing that in the dark after strong light adaptation the sensitivity increases exponentially with a time constant of 3 min. The sensitivity changes c. 2.4 log units during the time span of 5–720 s. The electrophysiological results indicate a smaller change in sensitivity at the level of the photoreceptors. Within a time span between 20 and 720 s the sensitivity increases during dark adaptation by a factor of 4.3 on a linear scale.     

Development of a new piosphere in arid chenopod shrubland grazed by sheep. 2. Changes to the vegetation

The initial development of a piosphere created by stocking a new watering trough with ca. 200 sheep at a near-pristine site in arid chenopod shrubland near Whyalla, South Australia, was studied. The following variables were monitored for up to 8 years using fenced plots as controls:shrub mortality; forage biomass and defoliation of the dominant shrubs and short-lived grasses; linear dimensions of Rhagodia ulicina; the density of short-lived species; and the invasion of exotics. Patterns in these variables were looked for which reflected the attenuation of stocking pressure with distance from water; that is, ‘piosphere patterns’. Piosphere patterns were detected for many variables. Those with values increasing towards the trough were mortality of the main forage shrub Atriplex vesicaria. the density of three short-lived taxa, viz. the bassias (Sclerolaena obliquicuspis, S. patenticuspis. Maireana sclerolaenoides), Tetragonia tetragonoides, and annual Zygophyllum spp. (Z. crenatum. Z. ovatum), and growth of short-lived grass species when sheep stocking pressure was low. Variables with values decreasing towards the trough were grass biomass, percentage of A. vesicaria individuals in flower, the percentage foliation of A. vesicaria and of the forage shrub Maireana sedifolia, and shrub forage biomass of A. vesicaria and M. sedifolia. The rate at which these patterns were registered varied. After only 3 months, a piosphere pattern was evident for grass biomass. Marrubium vulgare, an introduced weed, invaded the trough site within the first 6 months. Almost no A. vesicaria shrubs had died after 2 years, but after 8 years there was a marked piosphere pattern in their mortality. The piosphere patterns in forage biomass and defoliation of A. vesicaria and M. sedifolia became more pronounced with time. Some variables did not exhibit a piosphere pattern, such as the dimensions of the shrub R. ulicina and the densities of successive cohorts of the forb Erodium spp., even though there was an overall effect of grazing in reducing their values. There was no mortality of two dominant shrubs, M. sedifolia and R. ulicina, during the first 8 years.     

The annual cycle in body weight of small mammals from the Transvaal, South Africa, as an adaptation to a subtropical seasonal environment

Seasonal breeding of non-hibernating small mammals is generally associated with a reduction in body weight during the non-breeding period. In aseasonal breeders and in exceptional situations, when winter breeding occurs, this pattern cannot be found.
The reduction in body weight is thought to be a means to reduce energy requirements during the harsh non-breeding season that can either be winter, in the Holarctic, or the dry season in the Transvaal highveld.
The controlling mechanism in the strongly seasonal subtropical environment in southern Africa seems to be photoperiod as in small mammals from the northern hemisphere.
Since a general agreement in body weight changes was found in rodents and shrews from both areas, further similarities in adaptations to strongly seasonal environments in the subtropics are expected.
For the first time it is shown that the adaptive responses of small mammals to unfavourable seasons are similar in the Holarctic and seasonal subtropical areas.     

Growth rates of western myall (Acacia papyrocarpa Benth.) during its main phase of canopy spreading

Abstract Data collected by students during a decade are examined for use in constructing growth models of western myall trees during their mid-life phase of canopy spreading. Measurements of tree canopy diameters are found to be too variable (between replicates and through time) to describe growth patterns, but measurements of trunk girth prove more reliable. Two models for growth are presented, based on the trunk girth data set. The models lead to similar estimates of the time taken for canopy spreading, viz. about 160 years, which is consistent with previous anecdotal evidence of western myall longevity.