Aim To compare fire behaviour and fire management practice at a site managed continuously by traditional Aboriginal owners with other sites in tropical northern Australia, including the nearby Kakadu National Park, and relate those observations to indicators of landscape condition. Location Dukaladjarranj, a clan estate in north‐central Arnhem Land, in the seasonal tropics of northern Australia. The site abuts a vast sandstone plateau that is an internationally recognized centre of plant and animal biodiversity. Methods Ecological assessments included: (1) mapping of the resource base of the estate from both traditional and ecological perspectives; (2) aerial survey of the extent of burning, distribution of the fire‐sensitive native pine Callitris intratropica, rock habitats, and a range of macropod and other fauna resources; (3) fauna inventory; (4) detailed ecological assessment of the status of fire‐sensitive vegetation; and (5) empirical assessment of the intensities of experimental fires. Ethnographic information concerning traditional fire management practice was documented in interviews with senior custodians. Results Experimental fires lit during the study were of low intensity compared with late dry season fires reported elsewhere, despite weather conditions favouring rapid combustion. In contrast to other parts of the savanna, fuel loads comprised mostly leaf litter and little grass. We found that (i) a large proportion of the estate had been burned during the year of the study (ii) burned sites attracted important animal food resources such as large macropods (iii) important plant foods remained abundant (iv) well represented in the landscape were fire sensitive vegetation types (e.g. Callitris intratropica Baker & Smith woodlands) and slow growing sandstone ‘heath’ typically dominated by myrtaceaous and proteaceous shrubs (v) diversity of vertebrate fauna was high, including rare or range‐restricted species (vi) exotic plants were all but absent. Traditional practice includes regular, smaller fires, lit throughout the year, and cooperation with neighbouring clans in planning and implementing burning regimes. Main conclusions We attribute the ecological integrity of the site to continued human occupation and maintenance of traditional fire management practice, which suppresses otherwise abundant annual grasses (Sorghum spp.) and limits accumulation of fuels in perennial grasses (Triodia spp.) or other litter. Suppression of fuels and coordination of fire use combine to greatly reduce wildfire risk and to produce and maintain diverse habitats. Aboriginal people derive clear economic benefits from this style of management, as evidenced by abundant and diverse animal and plant foods. However, the motives for the Aboriginal management system are complex and include the fulfillment of social and religious needs, a factor that remains important to Aboriginal people despite the rapid and ongoing transformation of their traditional lifestyles. The implication of this study is that the maintenance of the biodiv...

The food hypothesis of population regulation was tested using two predation—free populations of feral donkeys in tropical northern Australia. Growth, body condition, and age—specific rates of fecundity and mortality were compared between the two populations. One of the populations was roughly one—half the density of the other, following an experimental reduction 3—4 yr previously. Fecundity was high and independent of density, with >70% of mature females pregnant in both populations. Age at maturity and juvenile mortality displayed some density dependence. Populations conformed to predictions of the food hypothesis, abundance being ultimately regulated by food—related juvenile mortality. At high density, juvenile mortality was three times as great as at low density, and was associated with poorer juvenile body condition and slower growth. Differences in rates of juvenile mortality are associated with nutritional status of lactating females, which is in turn determined by density—dependent competition for quality forage. The effects of competition for forage upon juvenile mortality synchronize lactation with an annual flush of quality forage at the onset of the monsoonal wet season.

Because it achieves rapid reductions in pig density, helicopter shooting is perceived to be a cost-effective option for feral pig control. In order to evaluate the cost effectiveness of the technique and develop predictive models of variation in costs, functional response models derived from predator–prey theory were fitted to 3 data-sets describing variation in kill rates with feral pig density. The data-sets were collected during shooting programs conducted on the Mary River floodplain in northern Australia, and on the Macquarie Marshes and Paroo River floodplain in western New South Wales. Fitted models indicated that variation in kill rates with pig density took the form of a Type 3 functional response for all 3 data sets, kill rates approaching a constant maximum at high pig densities and declining toward 0 at pig densities greater than 0. While maximum kill rates were similar for the 3 shooting programs (average 60.49 kill h–1, range 49.64–76.28), densities below which no pigs would theoretically be killed varied significantly (average 2.79 pigs km–2, range 1.34–5.02). Similar maximum kill rates for the 3 shooting programs indicates that, once located, the time taken by shooting teams to dispatch pigs was relatively constant (0.023 h). Variation in threshold densities below which no more pigs would theoretically be shot, indicates that as the density of pigs was reduced, their vulnerability to shooting teams differed between the 3 shooting programs. This may have reflected differences between sites in either the capacity of resident pigs to learn to evade shooting teams or, more likely, the availability of refuge habitat. For 2 of the shooting programs, too few data were available to estimate the effect of declining pig density on kill rate, precluding detailed examination of differences in the efficiency with which pigs were found (search efficiency). Using estimates of pig density below which no pigs would theoretically be shot to set a limit to the effectiveness of shooting programs, models predicting variation in hours per kill with pig density were derived from each data set. These models demonstrated that hours per kill increased exponentially as shooting reduced pig populations below threshold densities of approximately 2–6 pigs km–2. Generalised models relating variation in cost per kill to pig density for the 3 shooting programs are described.

Summary 0[ Intrinsic variation in the availability of food to animal populations re~ects the in~uence of foraging by the animals themselves[ Intrinsic variation in food availability provides a link between population density\ subsequent food availability and variation in the rate of population increase "r#\ operating through density!dependent food shortage[ In contrast\ extrinsic variation in food availability is caused by environ! mental in~uences on food or animal abundance\ which are independent of animal foraging[ Extrinsic variation in food availability is random relative to that arising through intrinsic shortage[ Intrinsic and extrinsic variation in food availability can in~uence animal populations simultaneously[ Intrinsic variation will impart a tend! ency towards an equilibrium between animal and food abundance\ which will be progressively obscured by density!independent variation as the in~uence of extrinsic factors increases[ 1[ This study used a large!scale _eld experiment\ in which the density of food!limited feral pig "Sus scrofa L[# populations was manipulated on six sites\ to assess the relative in~uence of intrinsic and extrinsic variation in food availability[ The experiment evaluated the in~uence of pig population density on r and the abundance of food resources measured as pasture biomass[ It was predicted that if intrinsic shortages dominated variation in food availability\ pasture biomass and r would decline with increasing pig density[ If extrinsic factors dominated variation in food availability\ pig density would have no systematic e}ect on either pasture biomass or r[ If intrinsic and extrinsic sources simultaneously a}ected variation in food availability\ higher pig densities would have no systematic e}ect on r\ but would reduce pasture biomass[ The simultaneous model predicts reduced pasture biomass because\ in the absence of compensatory changes in other sources of variation\ the e}ects of intrinsic and extrinsic factors will be additive[ 2[ To examine further the degree of interdependence in pig and pasture abundance\ a series of stochastic models of the grazing system were estimated and the feedback loop comprising the functional and numerical responses of feral pigs to variation in pasture biomass was manipulated[ 3[ In the large!scale experiment\ neither pasture biomass nor r declined with increasing pig density\ suggesting that food availability was dominated by extrinsic factors[ However\ limitations of the experiment meant that a minor decline in pasture biomass may have gone undetected[ Comparison of simulation models\ which included and omitted pasture o}take by pigs\ indicated that because they were less e.cient grazers and persisted at lower average densities relative to other large herbivores\ pigs had little in~uence on variation in pasture biomass 4[ The minor in~uence pigs appear to exert on pasture biomass suggests that trophic processes\ typically invoked to explain herbivore population persistence\ have\ at best\ limited consequences for pig populations[ Despite th...