Lesley Gibson

Phytophthora cinnamomi and Australia's biodiversity : impacts, predictions and progress towards control

Phytophthora cinnamomi continues to cause devastating disease in Australian native vegetation and consequently the disease is listed by the Federal Government as a process that is threatening Australia’s biodiversity. Although several advances have been made in our understanding of how this soil-borne pathogen interacts with plants and of how we may tackle it in natural systems, our ability to control the disease is limited. The pathogen occurs widely across Australia but the severity of its impact is most evident within ecological communities of the south-west and south-east of the country. A regional impact summary for all states and territories shows the pathogen to be the cause of serious disease in numerous species, a significant number of which are rare and threatened. Many genera of endemic taxa have a high proportion of susceptible species including the iconic genera Banksia, Epacris and Xanthorrhoea. Long-term studies in Victoria have shown limited but probably unsustainable recovery of susceptible vegetation, given current management practices. Management of the disease in conservation reserves is reliant on hygiene, the use of chemicals and restriction of access, and has had only limited effectiveness and not provided complete control. The deleterious impacts of the disease on faunal habitat are reasonably well documented and demonstrate loss of individual animal species and changes in population structure and species abundance. Few plant species are known to be resistant to P. cinnamomi; however, investigations over several years have discovered the mechanisms by which some plants are able to survive infection, including the activation of defence-related genes and signalling pathways, the reinforcement of cell walls and accumulation of toxic metabolites. Manipulation of resistance and resistance-related mechanisms may provide avenues for protection against disease in otherwise susceptible species. Despite the advances made in Phytophthora research in Australia during the past 40 years, there is still much to be done to give land managers the resources to combat this disease. Recent State and Federal initiatives offer the prospect of a growing and broader awareness of the disease and its associated impacts. However, awareness must be translated into action as time is running out for the large number of susceptible, and potentially susceptible, species within vulnerable Australian ecological communities.

Modelling habitat suitability of the swamp antechinus (Antechinus minimus maritimus) in the coastal heathlands of southern Victoria, Australia

Abstract In recent years, predictive habitat distribution models, derived by combining multivariate statistical analyses with Geographic Information System (GIS) technology, have been recognised for their utility in conservation planning. The size and spatial arrangement of suitable habitat can influence the long-term persistence of some faunal species. In southwestern Victoria, Australia, populations of the rare swamp antechinus (Antechinus minimus maritimus) are threatened by further fragmentation of suitable habitat. In the current study, a spatially explicit habitat suitability model was developed for A. minimus that incorporated a measure of vegetation structure. Models were generated using logistic regression with species presence or absence as the dependent variable and landscape variables, extracted from both GIS data layers and multi-spectral digital imagery, as the predictors. The most parsimonious model, based on the Akaike Information Criterion, was spatially extrapolated in the GIS. Probability of species presence was used as an index of habitat suitability. A negative association between A. minimus presence and both elevation and habitat complexity was evidenced, suggesting a preference for relatively low altitudes and a vegetation structure of low vertical complexity. The predictive performance of the selected model was shown to be high (91%), indicating a good fit of the model to the data. The proportion of the study area predicted as suitable habitat for A. minimus (Probability of occurrence ⩾0.5) was 11.7%. Habitat suitability maps not only provide baseline information about the spatial arrangement of potentially suitable habitat for a species, but they also help to refine the search for other populations, making them an important conservation tool.

Seasonal changes in the diet, food availability and food preference of the greater bilby (Macrotis lagotis) in south-western Queensland

Diet and food availability of the greater bilby (Macrotis lagotis), was examined at two sites and over two summer and two winter seasons in Astrebla Downs National Park in south-western Queensland. The presence of both invertebrate and plant material in almost all faecal pellets (99.6% and 98.5%, respectively) indicated that bilbies in south-western Queensland are omnivorous. The plant component of the bilby diet consisted predominantly of Dactyloctenium radulans seeds (frequency of occurrence: 94.4%). The major invertebrate prey items were Isop-tera (termites, 73.1%) and Formicidae (ants, 77.6%). The frequency of occurrence of invertebrates in faecal pellets was higher during summer than winter, but the frequency of occurrence of plants was relatively constant regardless of season. Within the invertebrate categories, Isoptera and Acrididae (grasshoppers) displayed the greatest seasonal difference, with a significantly higher proportion of both categories in the diet during summer than winter at both study sites. The availability of invertebrate prey items also varied with season, and for most taxa, frequency of oc-currence was significantly higher in summer than winter. In contrast, the frequency of occurrence of seeds and bulbs (Cyperus bulbosus) varied only slightly with season. Seasonal changes in food availability were reflected by variation in dietary composition; however, relative proportions of some dietary items differed from their proportional availability. Therefore, bilbies were considered to be qualitatively opportunistic; selecting more invertebrates when their apparent availability increased, but continually exploiting the available seeds and bulbs. Additionally, although bilbies appeared to have some preferences for particular food items, several food items were selected almost randomly, and therefore bilbies were also considered to be dietary generalists. Such an opportunistic feeding strategy is advantageous to an arid-zone species as it permits the continuous exploitation of food resources that are unpredictable in their availability both spatially and temporally.

Dietary strategy of the swamp antechinus (Antechinus minimus maritimus) (Marsupialia : Dasyuridae) in coastal and inland heathland habitats

In the coastal heathlands of southern Victoria, populations of a rare dasyurid, the swamp antechinus (Antechinus minimus maritimus), are restricted to small and disjunct patches of suitable habitat. Although characteristics of their preferred habitat in terms of vegetation structure and composition have been described, little is known of their diet preferences. Diet and food availability of the species was examined at two coastal and two inland sites, during winter and spring by way of faecal analyses and pitfall trapping. Only minor differences in diet were observed between the coastal and inland habitats and this was consistent across season. There was, however, variation in food availability between the two habitat types, with generally higher frequencies of invertebrates occurring within the inland than in the coastal habitat during spring. Even so, when diet was directly compared with food availability, the differences observed within individual categories within each season were similar in magnitude and direction for both habitats, suggesting that inland and coastal populations of the swamp antechinus have similar dietary strategies. Insect larvae, Diplopoda and Coleoptera appeared to be favoured dietary items being almost consistently over-represented in the diet compared to their availability, whereas Collembola, Amphipoda, Dermaptera and Formicidae were avoided as they were never consumed in proportion to their availability. Although dietary preferences were evident, there was no clear selection of any one particular prey item, and so the swamp antechinus was considered a dietary generalist. Also, as the species sampled from most of the range of prey items available to them, it fits the qualitative criterion of opportunism. The generalist strategy of the swamp antechinus is likely to be advantageous in an environment subject to disturbance.