The population dynamics of the bushfly: the elucidation of population events in the field

At three well differentiated sites and over three seasons bushfly abundance at first increased rapidly, but then stabilized or fell slowly through the apparently favourable periods of summer and early autumn, before a rapid end of season decline. Analysis of the characteristics of flies taken regularly in a sampling programme allowed the sequence of population events involved to be elucidated. Adult flies immigrated in spring. They and their first progeny were comparatively large but in the subsequent locally bred generations a progressive decrease in fly size was associated with a gradual decline in the levels of natality and a gradual increase in the levels of mortality. Between site differences could be traced to variation in the balance of these changes. Climate may have a large role in the population dynamics of the bushfly but its effects are largely indirect. Fuller understanding of the bushfly life system requires some way of synthesizing the effects and interactions between the many factors involved.     

Low genetic variability of the koala Phascolarctos cinereus in south-eastern Australia following a severe population bottleneck

Genotyping of koalas at CA-repeat microsatellite loci has revealed significant differences in the levels of allelic diversity ( A ) and expected heterozygosity ( H¯ _E) between populations from north-eastern and south-eastern Australia. In the 10 populations studied, allelic diversity ranged from 8.0 in the Nowendoc population to 1.7 in the Kangaroo Is. population, and values of H¯ _E ranged from 0.831 in the Nowendoc population to 0.331 in the Kangaroo Is. population. Data from pooled populations revealed koalas from the north-eastern region had significantly higher levels of allelic diversity ( A = 11.5 ± 1.4) than those from south-eastern Australia ( A = 5.3 ± 1.0). Furthermore significantly higher heterozygosity levels were found in the north-eastern ( H¯ _E= 0.851) vs. the south-eastern ( H¯ _E= 0.436) regions of Australia. Following a near-extinction bottleneck in the 1920s, mainland Victorian and Kangaroo Is. koalas have been involved in an extensive program of relocations. The source populations of the relocated animals were islands in Westernport Bay, which were founded by very few individuals in the late 1800s and early 1900s. The significantly lower levels of variation between south-eastern Australian populations suggests that human intervention has had a severe effect on levels of genetic diversity in this region, and this may have long-term genetic consequences.     

渤海中华哲水蚤(Calanus sinicus)和小拟哲水蚤(Paracalanus Parvus)种群垂直移动生态适应性模型研究

用最优化适合度种群生态模型模拟研究了中华哲水蚤和小拟哲水蚤种群在渤海生态系统中的垂直移动模式。生命周期、世代时间、繁殖力和产卵量是决定这两种桡足类垂直移动的主要因素。在中华哲水蚤生活史类型中,无水平流动或水平流动速率很小时,昼夜的垂直移动能使其获得最优的生态适合度。水流的增加或方向的改变会使其在底层的停留时间增加。在小拟哲水蚤生活史类型中,随着水流的增加及其随之而来的损失率增高,其垂直移动的倾向逐步提高。     

Variation in Life History of Land-Locked Lacustrine and Riverine Populations of Galaxias maculatus (Jenyns 1842) in Western Australia

Galaxias maculatus is one of the most naturally widely distributed species in the world yet there is no published literature on the biology of Western Australian populations. Galaxias maculatus in the rivers of the south coast of Western Australia inhabit an environment that is variable and at times unpredictable. By examining trends in gonadal development, lengths at first maturity, growth and appearance and persistence of larvae of G. maculatus in two saline rivers (Jerdacuttup River and Oldfield River) and one freshwater lake (Moates Lake), the life histories of populations in contrasting environments were determined. The stable conditions that prevail in the low salinity, cool waters of Moates Lake have fostered an extremely protracted breeding and larval recruitment period (year round) in comparison to limited recruitment in the riverine environments which experience less predictable flow events and water quality (salinity). An upstream migration for breeding in the Jerdacuttup and Oldfield rivers is similar to land-locked G. maculatus in south-eastern Australia and is a reversal of the downstream migration in Moates Lake or populations with marine larval dispersal, i.e. diadromous populations. Differences in population demographics existed between these habitats, with smaller maximum sizes and significantly smaller sizes at maturation occurring in the rivers compared to the lake. In Moates Lake approximately 93, 6 and 1% were 0+, 1+ and 2+, respectively; while cohort progression in the rivers suggests that most fish do not live beyond their first year. As an adaptable opportunist, G. maculatus can modify its life history strategy at a local level to persist in varied and sometimes unpredictable environments.     

Molecular relationships within Bostrychia tenuissima (Rhodomelaceae, Rhodophyta)

Bostrychia tenuissima King and Puttock is restricted to southern Australia and New Zealand. Previous studies in Australia have revealed two distinct patterns in the presence of osmotically active polyols. Southern populations only have D-sorbitol whereas northern populations have both D-sorbitol and D-dulcitol. These polyol patterns lead to speculation on the ecotypic differentiation of these two population types. Using single-stranded confirmation polymorphism to rapidly score plastid haplotypes, plus DNA sequencing, a 100% congruence was found between polyol patterns and plastid haplotype. Analysis of 33 B. tenuissima isolates shows that the plastid relationships closely follow biogeo-graphic regions, with south-eastern Australia (southern NSW and Victoria) and South Australia and Tasmania having one haplotype and central and northern NSW having two alternate haplotypes. There is an overlap at the haplotype boundary just south of Sydney, New South Wales.     

The evolution of viviparity within the Australian scincid lizardLerista bougainvillii

The semi-fossorial scincid lizard, Lerista bougainvillii , is oviparous throughout its extensive range in south-eastern mainland Australia. However, two widely separated (by approximately 1000 km) island populations are viviparous; in these populations the eggshell is lost and females retain their offspring in utero until embryogenesis complete. One mainland population in south-eastern Victoria shows an intermediate condition, in which the eggshells are incomplete and uterine embryogenesis is prolonged.
Morphological and electrophoretic analyses confirm a high degree of morphological and genetic similarity between populations (i.e. there is no evidence for the presence of more than one species), and phenetic analyses of these data show that each of the two disjunct viviparous populations more closely resembles adjacent oviparous populations than the other viviparous group. Hence, we infer that viviparity may have arisen twice within L. bougainvillii , in both cases on offshore islands with a cold climate.     

Integrating population demography, genetics and self-incompatibility in a viability assessment of the Wee Jasper Grevillea (Grevillea iaspicula McGill., Proteaceae)

Grevillea iaspicula is an endangered shrub known from only eight small populations (<250 individuals) in south-eastern Australia. The species is threatened by combined ecological and genetic factors, e.g. land conversion, weed invasion, low recruitment and low gene flow among populations. The populations also show large variance in male fitness and limited mate availability which are thought to arise as a consequence of gametophytic self-incompatibility (GSI). This study has used an individual-based, spatially explicit simulation model to explore the interaction between GSI and mate limitation in this species, as well as its effect on long-term population viability. The model was parameterised with demographic and genetic data obtained from 2 years of population monitoring. Simulation results identified extremely low establishment rates as the most critical factor currently influencing the persistence of G. iaspicula populations and indicated that the extant populations are at serious risk of extinction in the near future unless this is altered by, at very least, an order of magnitude higher. SI was shown to affect the magnitude of variation in establishment but this effect was masked when establishment was critically low. Disassortative mating, owing to low allelic richness at the S-locus, had the negative demographic effect of restricting mating to relatively few compatible plants. Restricted mate availability imposed additional limitations to the viability of populations but, given a 20-fold increase in establishment rate, population fluctuations stabilised. The long-term viability of G. iaspicula is bleak without artificial augmentation of the populations but management planning must also consider genetic processes, including SI, to ensure such strategies optimise the benefits gained.     

Sooty Shearwater (<Emphasis Type="Italic">Puffinus griseus</Emphasis>) on Guafo Island: the largest seabird colony in the world?

Sooty Shearwater (Puffinus griseus) is the most common Procellariiform seabird along the south-eastern South American coast. In recent years the wintering population off California has declined noticeably. This decline has been confirmed on the breeding grounds in New Zealand. In Chile, knowledge of the population is limited. Investigations on Isla Guafo were carried out during two seasons (03/04 and 04/05), beginning an ongoing monitoring and evaluation of the breeding population of this species in southern South America. On Isla Guafo we estimate a population of about 4 million birds that nest above 150 m above sea level (m.a.s.l.) under a forest without understory. Sooty Shearwaters on Isla Guafo prefer north and western slopes that we hypothesise protect them from the predominantly southerly winds. Population of the species from New Zealand and Australia are compared with the Isla Guafo population and the state of its conservation is discussed.     

Modelling the spatial and temporal variability of diatoms in the River Murray

We have developed a simple mechanistic model, which simulates the temporal and spatial variability of concentrations of the diatom Aulacoseira granulata in the River Murray, NSW Australia, over large distances under different flow conditions. The model incorporates a simple growth function determined by the availabilities of silica and light, and by temperature. It also includes losses due to sinking and downstream advection. The model is tested against weekly measurements for the period 1981-1990, at three sites separated by 1100 km. The seasonal cycle of Aulacoseira concentrations along the river is well represented by the model. During times of high flow, the concentrations of Aulacoseira remain fairly uniform along the river as the diatoms have insufficient time to grow before being advected downstream.      

The use of open burrows to estimate abundances of intertidal estuarine crabs

Estimation of absolute (or true) abundances of intertidal burrowing crabs is a difficult problem in some estuarine habitats because the nature of the substratum and behaviour of crabs can restrict researchers to the use of sampling methods which at best estimate only apparent, or relative, abundances. One method that has been used is to count open burrows to estimate population densities. This paper discusses the results of a test examining the validity of using burrows to estimate apparent abundances of a temperate ocypodid crab, Heloecius cordiformis. inhabiting mangrove forests of south-eastern Australia. Under appropriate circumstances, this method may provide a quick and reliable estimate of abundance of crabs.     

High-altitude migration of the diamondback moth Plutella xylostella to the U.K.: a study using radar, aerial netting, and ground trapping

Abstract 1. The high-altitude wind-borne migration of the diamondback moth Plutella xylostella in the U.K. in 2000 was investigated (a) by direct monitoring of insect flight by vertical-looking radar and by aerial netting, and (b) through evidence of temporal variation in P. xylostella abundance deduced from a network of light traps.
2. Migrating P. xylostella were identified by a unique combination of size and shape data derived from the continuously operating vertical-looking radar.
3. Radar-detected migratory overflights correlated significantly with associated peaks in abundance of P. xylostella estimated by catches in a U.K.-wide light trap network; however the correlation was stronger when light trap catches were lagged by 1 day.
4. The first notable catches of P. xylostella in the U.K. occurred in early May, and were accompanied by migrations over the radar from the east.
5. Radar data and back-tracking indicated that a major wind-borne migration of P. xylostella from The Netherlands to southern England took place in early May, and that this was responsible for the establishment of the U.K. population.
6. The origin of early-season P. xylostella occurring in Britain is discussed.     

A radar and aerial-trapping study of an early spring migration of moths (Lepidoptera) in inland New South Wales

The migrations of a number of species ofnoctuid and pvralid moths were studied with a specialpurpose radar unit and by direct sampling with a kite-borne net at a locality in central-western New South Wales during the early spring of 1980. The observations coincided with the appearance of very large numbers of moths throughout much of south-eastern Australia, and immediately followed a major caterpillar plague in south-western New South Wales. The migrations occurred mainly at night, and were most intense during periods of warm weather. Several different directions of migration were observed, but the movements were always approximately downwind; distances of a few hundred kilometres were typically covered during a single night. A number of quantitative measures of the migration intensity have been estimated for some of the flights. The migrating population frequently exhibited a degree of mutual alignment, which was sometimes in a direction different from that of the migration. Migrants became concentrated into layers at high altitudes (up to 1900 m) on two occasions during the night. Similar high-altitude migrations were also detected during daylight. It is inferred that an early spring re-invasion of drought-affected inland areas, and of areas on the continental periphery which have a cool winter climate, by means of long-distance migrations from inland areas where autumn and winter conditions have been favourable for larval development, is an almost regular feature of the population dynamics of several moth species that are of economic importance in south-eas-tern Australia. These migrations are interpreted as an adaptation to the geographie and climatic factors that control larval development and moth flight in this region, and especially to the erratic rainfall regime of the inland source areas.     

Spread and potential distribution of Senecio madagascariensis Poir. (fireweed) in Australia

Abstract The potential distribution of the herbaceous weed Senecio madagascariensis Poir. (fireweed) in Australia was estimated using the Bioclimate Prediction System, BIOCLIM. Climate profiles for S. madagascariensis predicted that suitable areas occurred only in the south-eastern region of Australia. Its potential to spread outside these areas was assessed by comparing the present African and South American distributions of this species with that observed in Australia. The rate of spread of S. madagascariensis in New South Wales was exponential, although in some regions, such as the Gloucester River Valley, the rates had decreased because all farms had become infested. The results indicate that S. madagascariensis may spread and increase in abundance along the far south coast of New South Wales and in south-eastern Queensland. Coastal areas in eastern Victoria and as far north in Queensland as the Tropic of Capricorn may be invaded.     

Restricted distribution and limited gene flow in the model ciliate Tetrahymena thermophila

The biogeography of microbial eukaryotes has long been debated, but few phylogeographic data have been available to assess whether protists tend to have ubiquitous or endemic distributions. We addressed this issue in the ciliate Tetrahymena thermophila, a highly successful model system in cell and molecular biology. We found that this species has a distribution that is restricted to the Eastern United States, with high diversity in the northeast and low diversity across the rest of its distribution. We find high levels of population subdivision, low rates of migration and significant isolation by distance, supporting the moderate endemicity model of protist biogeography. This restricted gene flow may be a result of small population size, which would reduce the probability of migration events, or the inability to establish after migration. This work lays the foundation for T. thermophila to become a valuable model system for studying population biology.     

Effects of adding exotic dung beetles to native fauna on bush fly breeding in the field

Egg to pupal survival of bush fly,Musca vetustissima Walker, under field conditions was examined during 1987/88 in an area of south-eastern Australia that had not been colonised by exotic dung beetles. In pads of cattle dung containing only the native fauna, fly survival ranged from 0.3% to 12.5%. The addition of 2 species of exotic dung beetles,Euoniticellus fulvus (Goeze) andOnthophagus taurus (Schreber) to field pads, in numbers similar to those observed at the collection site, reduced fly survival to between 0.3% and 4.4%. Fly survival in the presence of the native and exotic dung fauna was sufficiently low to keep fly breeding below their mean replacement level of 3% for most of the season. Widespread dispersal and establishment of exotic dung beetles in south-eastern Australia, alongside the native fauna, should lead to long-term reduction of the bush fly problem.      

Thesis abstracts

Bioturbation, rainwash and texture contrast soils: An evaluation of transporting processes on soil genesis in the Sydney Basin G. S. Humphreys Some aspects of the role of bioturbation in soil formation in south-eastern Australia P. B. Mitchell Plant water relations and community water use in a Banksia woodland near Perth, Western Australia Jonathan Dodd The pre-mining assessment of a coal mining lease north of Esperance, Western Australia Paul G. van der Moezel     

Thesis abstracts

Spatial and temporal heterogeneity in the epibenthic fauna of estuarine sand and seagrass beds V. A. Wadley The ecology of Pseudomys spp. in south-eastern Australia Andrew Cockburn     

Effects of the Australian 2019–2020 megafires on a population of endangered broad-headed snakes Hoplocephalus bungaroides

The 2019–2020 Australian megafires were unprecedented in their intensity and extent. These wildfires may have caused high mortality of adult broad-headed snakes Hoplocephalus bungaroides which shelter inside tree hollows during summer. We evaluated the impacts of two high-intensity wildfires (2002 Touga Fire and 2020 Morton Fire) on a broad-headed snake population in Morton National Park, south-eastern Australia. We analysed a 29-year mark–recapture data set to estimate survival rates of adults in years with and without wildfires, and with and without human disturbance to rock outcrops. To examine the short-term effects of fire on occupancy, we analysed presence–absence data collected from 25 sites during 2019 and 2020. Estimates of occupancy were higher for 2020 (0.93 ± 0.09) than for 2019 (0.66 ± 0.14), while detection rates were constant (0.40 ± 0.06). Over the period 1992–2020, the best supported Cormack–Jolly–Seber model was one in which adult survival rates were high and stable (0.81 ± 0.04), but were 23% lower in years when humans disturbed rocks (0.63 ± 0.08). A model in which adult mortality was 20% higher in years with human disturbance and 14% higher in years with wildfires was also supported. Estimates of abundance revealed that the population declined by 34% after the Touga Fire, and 26% after the Morton Fire. Over the 29-year study, the population has declined by 60%. Our results highlight how mortality events from wildfires need to be evaluated in the context of other threatening processes. For this population, the removal of snakes and associated habitat disturbance poses a more serious threat to population viability than infrequent wildfires.     

The ecology of Helicoverpa spp. (Lepidoptera: Noctuidae) in the Riverina region of south-eastern Australia and the implications for tactical and strategic management

Decisions on the choice of appropriate tactical and strategic control techniques require an understanding of the seasonal distribution and ecology of the target species. To address this need, data were collected from 1997 to 2000 using crop surveys, field sampling and pheromone trapping to monitor the population trends of Helicoverpa armigera (Hübner) and H. punctigera (Wallengren) in the Riverina region of south-eastern Australia. The data gathered are compared to predictions from the HElicoverpa Armigera and Punctigera Simulation (HEAPS) model, that simulates Helicoverpa population dynamics to assist in identifying the drivers of regional populations and provide a framework to make informed decisions. The results highlight the contrasting seasonal dynamics of H. punctigera and H. armigera within the region. Helicoverpa punctigera populations peak in the spring, driven by large scale spring migration into the region and subsequently decline. Helicoverpa armigera populations, conversely, are characterized by a period of spring recruitment of adults from overwintering pupae within the region, followed by a within-season population increase leading to severe late season pressure. The within-season increase of H. armigera is a result of the succession of crop and non-crop hosts with the main driver being sequentially sown, unsprayed maize. Tactical and strategic management options are discussed in light of these findings.     

Genetic Bottlenecks in Time and Space: Reconstructing Invasions from Contemporary and Historical Collections

Herbarium accession data offer a useful historical botanical perspective and have been used to track the spread of plant invasions through time and space. Nevertheless, few studies have utilised this resource for genetic analysis to reconstruct a more complete picture of historical invasion dynamics, including the occurrence of separate introduction events. In this study, we combined nuclear and chloroplast microsatellite analyses of contemporary and historical collections of Senecio madagascariensis, a globally invasive weed first introduced to Australia c. 1918 from its native South Africa. Analysis of nuclear microsatellites, together with temporal spread data and simulations of herbarium voucher sampling, revealed distinct introductions to south-eastern Australia and mid-eastern Australia. Genetic diversity of the south-eastern invasive population was lower than in the native range, but higher than in the mid-eastern invasion. In the invasive range, despite its low resolution, our chloroplast microsatellite data revealed the occurrence of new haplotypes over time, probably as the result of subsequent introduction(s) to Australia from the native range during the latter half of the 20^th century. Our work demonstrates how molecular studies of contemporary and historical field collections can be combined to reconstruct a more complete picture of the invasion history of introduced taxa. Further, our study indicates that a survey of contemporary samples only (as undertaken for the majority of invasive species studies) would be insufficient to identify potential source populations and occurrence of multiple introductions.