Assessing the relationship between fire and grazing on soil characteristics and mite communities in a semi-arid savanna of northern Australia

Northern Australian tropical savannas are subjected to pressures from both grazing and planned and unplanned burning. We know little about the effects of these processes on the below-ground environment. The aim of this study was to investigate the effects of fire, grazing and season on environmental and biological properties of the soil at the base of grass tussocks in a semi-arid savanna rangeland of north Australia. A long-term fire and grazing exclusion experiment was used to test the effects of season, fire and grazing on soil physicochemical factors (soil organic carbon, total nitrogen, ammonium, nitrate levels and bulk density) and soil mite abundance and diversity. Grazed plots were associated with small but significant reductions in total soil nitrogen and organic carbon when compared to 30 year old plots where grazing and fire had been excluded. This suggests slow, long-term losses of nitrogen and soil carbon from an ecosystem with limited available nutrients. Fire had a limited impact on soil properties, but this may reflect the modest experimental fire intensity resulting from fuel reduction due to grazing. Treatment effects on soil bulk density were also negligible. Season had a significant impact on total soil mite abundance and diversity, whereas burning and grazing treatments had no impact on soil mites. Only two morpho-species, one each from the families Cunaxidae and Stigmaeidae, decreased in abundance as a result of grazing. Increased moisture levels in the wet season were associated with increased total nitrogen and the highly mobile nitrate. Changes in mite abundance and diversity reflected these changes in levels of nitrogen and it is possible that increasing total nitrogen availability and soil moisture, is a determinant of mite abundance.     

The utility of transient sensitivity for wildlife management and conservation: Bison as a case study

Developing effective management strategies is essential to conservation biology. Population models and sensitivity analyses on model parameters have provided a means to quantitatively compare different management strategies, allowing managers to objectively assess the resulting impacts. Inference from traditional sensitivity analyses (i.e., eigenvalue sensitivity methods) is only valid for a population at its stable age distribution, while more recent methods have relaxed this assumption and instead focused on transient population dynamics. However, very few case studies, especially in long-lived vertebrates where transient dynamics are potentially most relevant, have applied these transient sensitivity methods and compared them to eigenvalue sensitivity methods. We use bison (Bison bison) at Badlands National Park as a case study to demonstrate the benefits of transient methods in a practical management scenario involving culling strategies. Using an age and stage-structured population model that incorporates culling decisions, we find that culling strategies over short time-scales (e.g., 1–5 years) are driven largely by the standing population distribution. However, over longer time-scales (e.g., 25 years), culling strategies are governed by reproductive output. In addition, after 25 years, the strategies predicted by transient methods qualitatively coincide with those predicted by traditional eigenvalue sensitivity. Thus, transient sensitivity analyses provide managers with information over multiple time-scales in contrast to the long time-scales associated with eigenvalue sensitivity analyses. This flexibility is ideal for adaptive management schemes and allows managers to balance short-term goals with long-term viability.     

Effects of artemisinin and Artemisia extracts on Haemonchus contortus in gerbils (Meriones unguiculatus)

Anthelmintic resistance is a worldwide concern in small ruminant industry and new plant-derived compounds are being studied for their potential use against gastrointestinal nematodes. Mentha piperita, Cymbopogon martinii and Cymbopogon schoenanthus essential oils were evaluated against developmental stages of trichostrongylids from sheep naturally infected (95% Haemonchus contortus and 5% Trichostrogylus spp.) through the egg hatch assay (EHA), larval development assay (LDA), larval feeding inhibition assay (LFIA), and the larval exsheathment assay (LEA). The major constituent of the essential oils, quantified by gas chromatography for M. piperita oil was menthol (42.5%), while for C. martinii and C. schoenanthus the main component was geraniol (81.4% and 62.5%, respectively). In all in vitro tests C. schoenanthus essential oil had the best activity against ovine trichostrongylids followed by C. martini, while M. piperita presented the least activity. Cymbopogon schoenanthus essential oil had LC(50) value of 0.045 mg/ml in EHA, 0.063 mg/ml in LDA, 0.009 mg/ml in LFIA, and 24.66 mg/ml in LEA. The anthelmintic activity of essential oils followed the same pattern in all in vitro tests, suggesting C. schoenanthus essential oil could be an interesting candidate for nematode control, although in vivo studies are necessary to validate the anthelmintic properties of this oil.     

Patterns and processes of carbon, water and energy cycles across northern Australian landscapes: From point to region

Savannas comprise a large proportion of the terrestrial land surface and are highly varied in their composition, structure and function. These characteristics alter land-atmosphere exchanges of heat, water, carbon dioxide and other trace gases, which feed back to the climate at multiple scales. Australian savannas provide significant ecosystem services and further systematic scientific study is needed to sustainably manage these ecosystems. We undertook an interdisciplinary research effort to understand the patterns and processes of carbon, water and energy cycles across northern Australian landscapes across scales from point to region. We quantified the land surface-atmosphere exchanges across the vast region of Australian savannas using a hierarchical, integrated measurement and modelling approach to determine regional greenhouse gas and water budgets. The research team comprised groups from seven institutions and four countries. The research effort comprised of a multi- year measurement and modelling endeavour and culminated in an intensive field program held in September 2008 (late dry season). The program aimed to improve our knowledge of the spatial and temporal variability of land-atmosphere exchanges and the processes driving them as well as our ability to remotely sense them and simulate them using land surface models, which are crucial components of Global Climate Models. We attempted to robustly integrate small scale processes, such as leaf photosynthesis to larger scales applicable to modelling and remote sensing for the savanna region. In this paper we provide the scientific background and our overall approach to the program with reference to the papers in this “Savanna Patterns of Energy and Carbon Integrated Across the Landscape” (SPECIAL) issue.     

Dynamics of Moraxella bovis infection and humoral immune response to bovine herpes virus type 1 during a natural outbreak of infectious bovine keratoconjunctivitis in beef calves

Infectious bovine keratoconjunctivitis (IBK) is an acute disease caused by Moraxella bovis (Mb). Several factors may predispose animals to an IBK outbreak; one commonly observed is infection with bovine herpes virus type 1 (BHV-1). The aim of this study was to investigate the dynamics of BHV-1 virus infection and its relation with clinical cases of IBK in weaned calves from a beef herd with a high prevalence of lesions caused by Mb. Sampling was carried out in six stages and included conjunctival swabs for isolating Mb as well as blood samples for identifying antibodies specific for BHV-1. A score for IBK lesions after observing each eye was determined. The findings of this study showed a high prevalence of BHV-1 virus infection (100% of animals were infected at the end of the trial); 67% of animals were culture-positive for Mb, but low rates of clinical IBK (19% of calves affected) were detected at the end of the trial. These results suggest that infection with BHV-1 did not predispose these animals to IBK, and that Mb infection produced clinical and subclinical disease in the absence of BHV-1 co-infection.     

The Immunological Response of South African Bulinus Natalensis Antigens to Diploid and Polyploid Bulinus Antisera

Foot muscle antigens of the diploid Bulinus natalensis from Lake Sibayi showed complete immunological correspondence with antiserum prepared from foot muscle tissues of the diploid B. tropicus. On the other hand, strong “non-identity” reactions occurred when B. natalensis antigens were tested with the antiserum prepared from foot muscle of the tetraploid B. coulboisi. It is therefore concluded that B. natalensis is indeed a member of the “tropicusspecies group”, as its chromosome number would imply, and not a diploid member of the more northern polyploid “truncatus species group”, as several morphological characters might suggest.