Northern Bettong Bettongia Tropica Research Articles

Nice weather for bettongs: using weather events, not climate means, in species distribution models

Current applications of species distribution models (SDM) are typically static, in that they are based on correlations between where a species has been observed (ignoring the date of the observation) and environmental features, such as long‐term climate means, that are assumed to be constant for each site. Because of this SDMs do not account for temporal variation in the distribution of suitable habitat across the range of a species. Here, we demonstrate the temporal variability in the potential geographic distributions of an endangered marsupial, the northern bettong Bettongia tropica as a case study. Models of the species distribution using temporally matched observations of the species with weather data (including extreme weather events) at the time of species observations, were better able to define habitat suitability, identify range edges and uncover competitive interactions than models based on static long‐term climate means. Droughts and variable temperature are implicated in low densities and local extinctions of northern bettong populations close to range edges. Further, we show how variable weather can influence the results of competition with the common rufous bettong Aepyprymnus rufescens. Because traditional SDMs do not account for temporal variability of suitable habitat, static SDMs may underestimate the impacts of climate change particularly as the incidence of extreme weather events is likely to rise.

Capture success and population density of the northern bettong Bettongia tropica in northeastern Queensland.

The population density of the northern bettong (Bettongia tropica), an endangered potoroid restricted to northeastern Australia, was estimated using minimum known-to-be-alive (MKTBA) and Jolly-Seber estimates derived from mark-recapture data. At Davies Creek in the north of the bettong's current range, bettong population densities were significantly lower in Allocasuarina forest (1.5 bettongs km-2) that in Eucalyptus woodland (3.7 - 7.5 bettongs km-2). At Eucalyptus woodland sites south and west of Davies Creek, population density was up to twice as great as it was at Davies Creek, while at sites north of Davies Creek, population densities were very low. Capture success was variable, ranging between 5 and 21%. Our data support previous research that suggested B. tropica density on the Lamb Range was correlated with latitude and moisture. Despite the restricted distribution of the northern bettong, our data indicate that populations on the Lamb Range, the species' stronghold, are generally healthy.

Effects of season and fire on the diversity of hypogeous fungi consumed by a tropical mycophagous marsupial

Summary Despite the importance of fire in many natural systems, knowledge of how fire affects the relationship between hypogeous fungi and mycophagous mammals in fire‐prone environments is limited. Using experimental fires, we examined consumption of hypogeous ectomycorrhizal fruit‐bodies by an endangered tropical mycophagist, the northern bettong Bettongia tropica Wakefield, in north‐eastern Australia. Fungus was the major dietary component (56%) throughout all seasons, both before and after fire. At least 35 hypogeous taxa were consumed. Number of taxa consumed during different seasons was similar, but was significantly higher on unburnt sites than on burnt sites. Similarly, diversity of taxa per faecal sample was significantly greater on unburnt sites, but also increased irrespective of fire from wet season to dry season. Cluster and principal component analyses were used to examine patterns in consumption of fungal taxa. The greatest differences in dietary composition were between the period immediately after fire on burnt sites (early wet season) and all other season and treatment combinations. This difference was due to increased consumption of taxa in the fire‐adapted family Mesophelliaceae and reduced consumption of the genus Elaphomyces. Principal component analysis revealed two major gradients in consumption. The first accounted for 32% of total variance and described change in consumption of taxa with season. The second accounted for 24% of total variance and described change in consumption of taxa before and after fire. Despite taxon‐specific changes in consumption of hypogeous fungi, the body condition of bettongs did not change significantly between seasons or in relation to fire, suggesting that bettongs were never compromised in their optimal fungal intake. Our data show that the northern bettong has a flexible response to fire and could be best thought of as a fire‐adapted marsupial. We therefore propose a precautionary approach to fire management of bettong habitat; at the present time this would include maintaining the recent fire regime of low to moderately intense fires every 3–4 years.

The contribution of fungus to the diets of three mycophagous marsupials in Eucalyptus forests, revealed by stable isotope analysis

1. Many field studies have shown that small herbivorous mammals include fungus (usually hypogeous sporocarps of ectomycorrhizal fungi) in their diets. However, the dietary importance of fungus relative to other foods is generally unclear because of limitations on the power of conventional techniques of diet analysis. Stable isotope analysis in conjunction with faecal analysis was used in an attempt to overcome these limitations. 2. Two foregut‐fermenting marsupials (the Northern Bettong Bettongia tropica and Rufous Bettong Aepyprymnus rufescens) and a hindgut fermenter (the Northern Brown Bandicoot Isoodon macrourus) were studied. The Northern Bettong and Northern Brown Bandicoot are of similar body size (around 1 kg); the Rufous Bettong is significantly larger at 3 kg. Faecal analysis showed that the two bettongs ate a variety of grasses, lilies and fungi; the bandicoot ate these foods and also invertebrates. 3. Ratios of 15N/14N and 13C/12C differed in major food types collected in the field (fungus, grass, lily and invertebrates). Grass was clearly separated from the other food types by its low 13C/12C ratio, while fungus was separated from the other types by its high 15N/14N ratio. Invertebrates and lilies differed slightly in 13C/12C ratios. 4. Isotope ratios in body tissue (sampled in hair) of the three mammals were also discrete, showing that the species differed in the predominant sources of their C and N. Estimates of the proportion of C assimilated in body tissue that was derived from grass were 80% for the Rufous Bettong, 40% for the Northern Bettong and 45% for the Northern Brown Bandicoot. Analysis of 15N/14N ratios suggested that the Northern Bettong derived almost all its N from fungus, the Northern Brown Bandicoot derived practically no N from fungus, and the Rufous Bettong was intermediate. 5. The results confirm that for the Northern Bettong, fungus is a predominant source of N and C assimilated into body tissue. Differences between the use of fungi by the Northern Bettong and the Northern Brown Bandicoot strengthen conclusions from other studies that foregut fermentation confers on small mammals a greater ability to utilize fungus than does hindgut fermentation. It is hypothesized that the limited use of fungus by the Rufous Bettong is due to the patchy distribution of hypogeous sporocarps, which would result in a high energy cost of foraging for this larger‐bodied species with a higher absolute food requirement.

A distributional survey and habitat model for the endangered northern bettong Bettongia tropica in tropical Queensland

The northern bettong Bettongia tropica is an endangered rat-kangaroo that occurs only in certain dry and mesic forests in tropical Queensland, Australia. In 1994 and 1995 I conducted a live-trapping survey at 152 sites throughout its potential geographic range. Detailed floristic, physiognomic, topographic and geology data from each site were used to develop a predictive model of bettong habitat requirements, using generalized linear modeling. Data from 62 spotlighting censuses and opportunistic observations were also used to assess potential threats to northern bettongs posed by introduced foxes Vulpes vulpes, while trapping and habitat data were employed to evaluate possible effects of rooting-damage from feral pigs and competition from rufous bettongs Aepyprymnus rufescens on northern bettong populations. The northern bettong was detected in only one area, the Lamb Range, where it was present at nearly half ( 33 70 ) of the sites surveyed. Sparse populations recorded previously at several other localities in north Queensland may have declined or disappeared. A multiple Poisson regression model indicated that northern bettongs were strongly associated with certain types of wet and mesic sclerophyll forests and woodlands, while rainforest and rainforest-invaded wet sclerophyll forests were avoided. Northern bettongs occurred only on infertile metamorphic and granitic substrates, and were never detected on richer basaltic or alluvial soils. This probably occurs because fruit-bodies of ectomycorrhizal fungi, which are a key food resource of northern bettongs, are most abundant on infertile soils. Foxes were never detected during the survey, and are unlikely to threaten northern bettong populations at present. Circumstantial evidence suggests that interspecific competition from rufous bettongs is also of minimal importance. Rooting damage by feral pigs, however, may be more significant; northern bettongs were rarely detected at sites with heavy pig damage, and this may be because pigs are also feeding on fungal fruit-bodies. At present, the greatest threat to northern bettongs is probably encroaching land development, especially in the crucial Lamb Range area. Northern Queensland is experiencing rapid population growth, and local shires are attempting to shunt residential development onto areas with infertile soils to avoid the loss of productive agricultural land. While normally a laudable practice, this is precisely the wrong policy in this specific region. A re-evaluation of the strategic development plans of local shires is urgently needed to protect remaining habitats of the northern bettong. Habitat management, especially regular burning, is also required in key bettong habitats. Burning will prevent further invasion of wet sclerophyll forests by rainforest vegetation, which renders the habitat unsuitable for bettongs, and also is likely to promote the local production of fungal fruit-bodies upon which the northern bettong is highly dependent.