Warren J. Müller

Temporal and Spatial Changes in a Metapopulation of the Rust Pathogen Triphragmium Ulmariae and its Host, Filipendula Ulmaria

1 The numerical dynamics of a rust disease caused by the pathogen Triphragmium ulmariae was studied in a metapopulation of 129 discrete populations of the host plant Filipendula ulmaria. 2 Over the four years 1990-1993, 37% of the populations were consistently infected by the pathogen while 43% were always healthy. In the remaining 20% of populations, the presence of disease fluctuated from year-to-year. 3 In each of the four years the incidence of disease was strongly positively correlated with the logarithm of host population size (P < 0.001). Disease incidence was also weakly affected by the type of shore on which host populations grew but not by their degree of exposure. 4 The severity of disease occurring in infected populations was weakly positively correlated with the logarithm of population size (P < 0.05). However, the relationship between the density of individuals within populations and disease prevalence showed no density-dependence. 5 The distribution of disease among populations of the metapopulation had a significant spatial component in two of the years, with infected populations being closer together than would be expected by chance.

Ecologically based management of rodents in the real world: applied to a mixed agroecosystem in Vietnam.

Rodents cause significant damage to lowland irrigated rice crops in the Red River Delta of Vietnam. A four-year study was conducted in 1999-2002 to examine the effectiveness of applying rodent control practices using the principles of ecologically based pest management. Four 100-150 ha study sites adjacent to villages were selected and farmers on two treated sites were asked to follow a set of rodent management practices, while farmers on the untreated sites were asked not to change their typical practices. Farmers on the treated sites were encouraged to use trap-barrier systems (TBSs; 0.065-ha early planted crop surrounded by a plastic fence with multiple capture traps; one TBS for every 10-15 ha), to work together over large areas by destroying burrows in refuge habitats soon after planting (before the rats reestablish in the fields and before the onset of breeding), synchronizing planting and harvesting of the their rice crops, cleaning up weeds and piles of straw, and keeping bund (embankment) size small (<30 cm) to prevent burrowing. A 75% reduction in the use of rodenticides and plastic barrier fences (without traps or an early crop) was achieved on treated sites. The abundance of rodents was low after implementation of the management practices across all sites. There was no evidence for an effect of treatment on the abundance of rodents captured each month using live-capture traps, and no difference in damage between treatments or in yields obtained from the rice crops. Therefore, ecologically based rodent management was equally effective as typical practices for rodent management. Farmers on the treated sites spent considerably less money applying rodent control practices, which was reflected in the comparative increase in the partial benefit:cost of applying ecologically based rodent management from 3:1 on treated sites and untreated sites prior to the implementation of treatments to 17:1 on treated sites in the final year of the project.

Edges in Agricultural Landscapes: Species Interactions and Movement of Natural Enemies

Agricultural landscapes can be characterized as a mosaic of habitat patches interspersed with hostile matrix, or as a gradient of patches ranging from suitable to unsuitable for different species. Arthropods moving through these landscapes encounter a range of edges, with different permeability. Patches of native vegetation in these landscapes may support natural enemies of crop pests by providing alternate hosts for parasitic wasps and/or acting as a source for predatory insects. We test this by quantifying species interactions and measuring movement across different edge-types. A high diversity of parasitoid species used hosts in the native vegetation patches, however we recorded few instances of the same parasitoid species using hosts in both the native vegetation and the crop (canola). However, we did find overall greater densities of parasitoids moving from native vegetation into the crop. Of the parasitoid groups examined, parasitoids of aphids (Braconidae: Aphidiinae) frequently moved from native vegetation into canola. In contrast, parasitoids of caterpillars (Braconidae: Microgastrinae) moved commonly from cereal fields into canola. Late season samples showed both aphids and parasitoids moving frequently out of native vegetation, in contrast predators moved less commonly from native vegetation (across the whole season). The season-long net advantage or disadvantage of native vegetation for pest control services is therefore difficult to evaluate. It appears that the different edge-types alter movement patterns of natural enemies more so than herbivorous pest species, and this may impact pest control services.

Antibody-mediated improved resistance to ClYVV and PVY infections in transgenic tobacco plants expressing a single-chain variable region antibody

Transgenic Nicotiana tabacum plants expressing a single-chain variable region antibody fragment derived from a broad-spectrum monoclonal antibody 3-17 showed suppression of virus infection following challenge by two distinct potyviruses: potato virus Y strain D, and clover yellow vein virus strain 300. Monoclonal antibody 3-17, which was raised against the potyvirus Johnsongrass mosaic virus, was shown to react strongly with 14 potyvirus species. Two different single-chain antibody constructs were used to produce chimeric genes encoding recombinant proteins designed to be targeted either to the apoplasm or to the cytoplasm. Transgenic plant lines showed reduced numbers of local lesions and systemic symptoms when challenged with potato virus Y, strain D and reduced local lesions following challenge with clover yellow vein virus, strain 300. The level of suppression conferred by the transgene when plants were challenged under laboratory conditions with high concentrations of virus, together with the ability of the transgene to partially protect plants against distinct viruses suggest that one single-chain gene construct might be used to protect plants from distinct potyviruses.

Home ranges of feral cats (Felis catus) in central-western New South Wales, Australia

Twenty-one feral cats were radio-tracked using direct sighting and triangulation techniques (amassing 730 location fixes) during winter in an agricultural landscape in central-western New South Wales. Factors affecting home-range size, home-range overlap and habitat use were assessed. Mean home-range size was 248 ha (s.e. = 34.9, n = 15 cats, 598 location fixes). Home-range size and habitat use were not influenced by sex or age of adult cats, prey abundance or time of day. However, cat weight significantly influenced range size, with heavier cats having larger ranges than smaller cats. Although the cats are apparently solitary, their home ranges overlapped considerably, particularly between young adults and old adult cats. Cats were active both by day and night and did not occupy permanent dens. Home ranges encompassed mixed habitat types that provided both shelter and prey. Open woodland and open forest were the main habitat types covered by home ranges, but within these areas cats showed a preference for grassland, where rabbits were more abundant. The results recorded in this study indicate that cat-control programs should concentrate in mixed habitat areas, where both shelter and food are available, and over widely dispersed areas. The absence of group living suggests that the effectiveness of virally vectored fertility or biological control agents would be limited.

Density-dependent mortality in Pinus sylvestris caused by the snow blight pathogen Phacidium infestans

SummaryRelationships between disease incidence and the density of host plant populations were investigated in the Pinus sylvestris-Phacidium infestans host-fungal pathogen association, in which the season of death of plants killed up to 3 years previously could be accurately determined. Significant (P<0.05), positive density-dependent relationships between the proportion of plants dying in the winters of 1987–1988, 1988–1989 or 1989–1990 and the original stand density were detected in 12 of 26 comparisons. Of the remaining comparisons, all but three had positive regression coefficients for the same association. Plants killed up to 2 years previously contributed to inoculum production. The use of “standing dead” as a predictor in the analyses showed that the proportion of plants dying in the winters of 1988–1989 or 1989–1990 was generally better correlated with standing dead in the previous summer than with the density of the original population. Significant (P<0.05), positive density-dependent associations were also found between the proportion of living plants in 1990 infected with P. infestans and the number of standing dead plants in all nine comparisons. In contrast, only four of the nine associations between these proportions of infected plants and population density were significant. The strength of the density-dependent relationships varied substantially within and between sites. Much of this variation appears to be due to differences in the stage of development of the epidemics occurring at different sites.

Is exchangeable sodium content a better index of soil sodicity than exchangeable sodium percentage ? : A reassessment of published data

The Exchangeable Sodium Percentage (ESP) is the most widely used index of sodicity for the investigation of soil structural stability and for soil classification. However, sensitivity to levels of ESP varies across soil types. An alternative index is the Exchangeable Sodium Content (ESC), in which levels of sodium are expressed on an oven-dried soil basis rather than relative to the cation exchange capacity. Early workers suggested that the ESC may prove a better index of sodicity across soil types than the ESP. This contention has not been tested in the literature. We compared the abilities of ESP and ESC to explain variation in soil structural stability across soil types using data from 15 published data sets. The logarithm of soil structural stability was correlated significantly with the logarithm of ESP in only seven data sets, compared with 14 data sets that had significant correlations with the logarithm of ESC. In 10 of the data sets, between 15 and 60% more of the variation in structural stability was explained by ESC than ESP. In three of four combined data sets where common methodologies were used, ESC explained variation better than ESP, and there was no difference in the fourth. Therefore, we conclude that ESC is generally a better index of soil sodium levels than ESP and should be used more widely.

An experimental study of the impact of feral swamp buffalo Bubalus bubalis on the breeding habitat and nesting success of magpie geese Anseranas semipalmata in Kakadu National Park

The impact of buffalo Bubalus bubalis grazing and trampling on magpie goose Anseranas semipalmata breeding habitat and nest numbers was studied over nine wet seasons (1980–1988) at Kapalga within Kakadu National Park. Aerial photographs provided data to compare nest densities within six vegetation types in an area where buffalo grazed throughout the study with an area where buffalo were removed midway through. Buffalo had no significant effect on the abundance or distribution of vegetation types important to geese for breeding. However, high densities of buffalo suppressed the growth of several other species, particularly the grass Hymenachne acutigluma which increasingly displaced the deep water spike-rush Eleocharis sphacelata after buffalo were removed. The annual number of nests fluctuated between 7 and 2028, apparently in response to rain. Most nests were built in the spike-rush/wildrice Eleocharis spp./Oryza rufipogon association (71%) and in E. sphacelata (20%). Buffalo trampling and grazing influenced the location of nests but not number. After buffalo were removed, more nests were built in deep water areas at the forest edge of the floodplain.

Population Fluctuations and Range Community Preference of Red Kangaroos in Central Australia

(1) The distribution of red kangaroos, Megaleia rufa, was determined from aerial surveys at approximately 3-weekly intervals over a 41 year period, during which climatic conditions varied from drought to the wettest on record. The study area in the arid rangelands of central Australia was approximately 158 km2 and contained a complex diversity of grassland, Mulga shrubland and woodland communities. (2) Numbers of kangaroos on the paddock ranged up to 564, seven times the long-term mean of 81, during the drought period, and fluctuated between 9 and 204 at other times. These smaller changes in numbers occurred frequently between surveys as kangaroos moved into and out of the paddock in response to changes in forage conditions due to sporadic rains or fire. (3) The Mulga-annual grass community received the greatest average use by kangaroos, followed by Mulga-perennial grass and Open woodland. Less use was made of Flood plains, Gilgaied plains, Foothill fans, and several minor communities. The Treeless Plains communities and Open woodland were used by kangaroos as a refuge during drought and were little used during good forage conditions, while Mulga-perennial grass community showed an opposite trend in relative use. The Mulga-annual grass community, however, did not show any consistent trend with changes in forage conditions. (4) Results indicate that kangaroos are nomadic in response to changing forage conditions and their home range greatly exceeds the area of the study site.

Performance improvement with haptic assistance: A quantitative assessment

We measure the performance improvement that force feedback can provide in a virtual environment, through three experiments with, and without the assistance of haptic guidance. Performance measurements were undertaken with haptic, visual and auditory feedback alternatives. The first task investigated the use of haptic guidance mimicking reality, in the form of a simulated touchable surface of an object. The second investigated haptic guidance which waxed and waned as the user violated program rules by varying amounts. The third experiment investigated whether this latter artificial guidance would inhibit the users free will by taking control out of their hands. The results showed that a significant improvement in both accuracy and speed was achieved by the introduction of haptics in all experiments. It also found that the haptic guidance did not take control away from the user and that they had significantly more control than with conventional warning methods. These experiments were not aimed at learning, or retention of skill, but on using haptics as an aid to improve performance during a task.