The Ecological Separation of Deer and Domestic, Feral and Native Mammals in Tropical Northern Australia-A Review

We explored the ecological and historical factors that led to formation of the unique guild of native and introduced mammalian herbivores between 5 and 1000 kg in northern Australia. Following the disappearance of large native herbivores about 46 kya, and until the arrival of Europeans and their livestock, the only herbivorous mammals were mid-sized endemic marsupial macropods, which continued to utilise the same vegetation as their much larger former neighbours. Only one species of contemporary native herbivore has an adult bodyweight approaching 100 kg, and for the past 150-200 years, the total biomass of introduced domestic and wild vertebrate herbivores has massively exceeded that of native herbivorous species. We conclude that the current guild of native and introduced mammalian herbivores differentially utilises the landscape ecologically. However, climate- and anthropogenically related changes due to fire, drought, flooding, predation and introduced weeds are likely to have significant impacts on the trajectory of their relative ecological roles and populations. Given their differing ecological and dietary characteristics, against this backdrop, it is unclear what the potential impact of the dispersal of deer species could have in northern Australia. We hence focus on whether sufficient knowledge exists against which the potential impacts of the range expansion of three deer species can be adequately assessed and have found a dearth of supporting evidence to inform appropriate sustainable management. We identify suitable research required to fill the identified knowledge gaps.

Ecological forecasts to inform near-term management of threats to biodiversity

Ecosystems are being altered by rapid and interacting changes in natural processes and anthropogenic threats to biodiversity. Uncertainty in historical, current and future effectiveness of actions hampers decisions about how to mitigate changes to prevent biodiversity loss and species extinctions. Research in resource management, agriculture and health indicates that forecasts predicting the effects of near-term or seasonal environmental conditions on management greatly improve outcomes. Such forecasts help resolve uncertainties about when and how to operationalize management. We reviewed the scientific literature on environmental management to investigate whether near-term forecasts are developed to inform biodiversity decisions in Australia, a nation with one of the highest recent extinction rates across the globe. We found that forecasts focused on economic objectives (e.g. fisheries management) predict on significantly shorter timelines and answer a broader range of management questions than forecasts focused on biodiversity conservation. We then evaluated scientific literature on the effectiveness of 484 actions to manage seven major terrestrial threats in Australia, to identify opportunities for near-term forecasts to inform operational conservation decisions. Depending on the action, between 30% and 80% threat management operations experienced near-term weather impacts on outcomes before, during or after management. Disease control, species translocation/reintroduction and habitat restoration actions were most frequently impacted, and negative impacts such as increased species mortality and reduced recruitment were more likely than positive impacts. Drought or dry conditions, and rainfall, were the most frequently reported weather impacts, indicating that near-term forecasts predicting the effects of low or excessive rainfall on management outcomes are likely to have the greatest benefits. Across the world, many regions are, like Australia, becoming warmer and drier, or experiencing more extreme rainfall events. Informing conservation decisions with near-term and seasonal ecological forecasting will be critical to harness uncertainties and lower the risk of threat management failure under global change.

The response of an arboreal mammal to livestock grazing is habitat dependant

Inappropriate livestock grazing is implicated in the decline of vertebrate fauna species globally. Faunal responses to grazing can interact with the vegetation community in which they occur. We measured the response of an arboreal marsupial, the common brushtail possum (Trichosurus vulpecula vulpecula) to different cattle grazing strategies and vegetation types, and examined whether micro-habitat selection is driving this response. We hypothesised that where arboreal habitat is intact, brushtail possums would be resistant to the impacts of heavy grazing. We conducted a mark-recapture survey among four grazing treatments and in two vegetation types (Box and Ironbark), at a 20-year grazing trial in northern Australia. We found that brushtail possums were resistant to the impact of heavy grazing in both vegetation types, but preferred the heavy grazing treatment in the Box vegetation type. Complex arboreal habitat and low ground cover was preferred, and high grass cover and low tree species richness avoided. Most individuals exclusively used one vegetation type, with few using both, suggesting a ‘matrix’ vegetation between the Box and Ironbark may be creating a movement barrier. Vegetation type should provide a context for determining the benefits to arboreal wildlife of adopting a particular grazing management strategy.

Exploring relationships between native vertebrate biodiversity and grazing land condition

Although commercial grazing can degrade natural habitats, sustainably grazed land may be effective for wildlife conservation. Thus, land condition frameworks that assess the landscape quality of grazed land may also be useful for assessment of habitat quality for wildlife. However, the relationship between the condition of grazed land and native biodiversity is mostly unknown, and this knowledge gap must be addressed to adequately balance commercial production and conservation. In the present case study we determined the relevance of a widely used grazing land condition scale to understanding native vertebrate species richness and abundance (birds, reptiles, amphibians, mammals and all these vertebrate classes grouped) in grazed rangelands in northern Australia (~24–13°S; annual rainfall ranging from >1200 to <400 mm), sampled over approximately 10 years from 17 unique sites, containing 381 1-ha study plots. We defined the land condition scale relative to climate and comprehensive assessment of habitat attributes, and then described the relationships between land condition, habitat and biodiversity. The land condition scale partially explained richness and abundance patterns only for mammals (especially rodents), which tended to be higher in better-condition pasture. For other vertebrate groups, the scale was a very poor descriptor of richness and abundance. The land condition scale was not useful to assess wildlife diversity primarily because ‘woody thickening’ (increases in woody vegetation on grazed land, including shrubs and trees) lowers the ‘grazing value’ of land while also generally promoting vertebrate diversity. In line with this, biodiversity decreased with increasing bare ground and erosion, together with, and in the absence of, vegetation cover (i.e. desertification), consistent with grazing land degradation. The present study supports observations that land clearing and reductions in woody vegetation on grazed rangelands are particularly detrimental to native vertebrates.

The database of the PREDICTS (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems) project

The PREDICTS project-Projecting Responses of Ecological Diversity In Changing Terrestrial Systems (www.predicts.org.uk)-has collated from published studies a large, reasonably representative database of comparable samples of biodiversity from multiple sites that differ in the nature or intensity of human impacts relating to land use. We have used this evidence base to develop global and regional statistical models of how local biodiversity responds to these measures. We describe and make freely available this 2016 release of the database, containing more than 3.2 million records sampled at over 26,000 locations and representing over 47,000 species. We outline how the database can help in answering a range of questions in ecology and conservation biology. To our knowledge, this is the largest and most geographically and taxonomically representative database of spatial comparisons of biodiversity that has been collated to date; it will be useful to researchers and international efforts wishing to model and understand the global status of biodiversity.

Has land use pushed terrestrial biodiversity beyond the planetary boundary? A global assessment

Land use and related pressures have reduced local terrestrial biodiversity, but it is unclear how the magnitude of change relates to the recently proposed planetary boundary ("safe limit"). We estimate that land use and related pressures have already reduced local biodiversity intactness--the average proportion of natural biodiversity remaining in local ecosystems--beyond its recently proposed planetary boundary across 58.1% of the world's land surface, where 71.4% of the human population live. Biodiversity intactness within most biomes (especially grassland biomes), most biodiversity hotspots, and even some wilderness areas is inferred to be beyond the boundary. Such widespread transgression of safe limits suggests that biodiversity loss, if unchecked, will undermine efforts toward long-term sustainable development.

More famine than feast: pattern and variation in a potentially degenerating mammal fauna on Cape York Peninsula

Context Global mammal populations continue to be threatened by environmental change, and recent decadal monitoring in northern Australia suggests a collapse in mammal abundance in key locations. Cape York Peninsula has globally significant natural values but there is very little published about the status and distribution of mammals in this region. Aims Following an extensive field survey we investigated two key questions: (i) what is the composition, spatial variation and change from previous regional surveys in the mid to late 1900s in the native terrestrial and arboreal mammal fauna recorded; and (ii) which landscape and site factors best predict mammal richness and abundance. Methods We sampled 202 one-hectare sites across seven locations from 2009 to 2012 in woodlands, closed forestand dune scrub and tussock grasslands. We collected landscape and site-based environmental data for each location, representing fire, weather and vegetation factors. We used generalised linear mixed models to examine the relationship between mammals and these factors. Key results Mammals were generally scarce across the sites and were more abundant and species rich in wet coastal grasslands or closed forests then tropical savanna woodlands. Fire frequency data and the surrounding vegetation complexity were consistent landscape-scale predictors of mammals; ground cover and woody complexity were significant at the site scale. Conclusions Notwithstanding interpretational constraints related to the limited evidence base of historic sampling, the mammal fauna recorded in this study for Cape York Peninsula was similar in composition to the mammal fauna described from 1948–1980 and surveys in 1985, with some species seemingly declining (e.g. Melomys burtoni, Dasyurus hallucatus, Sminthopsis virginiae) and others stable (e.g. Rattus sordidus) or more common (e.g. Rattus tunneyi); however, across all sites abundance was low, and many sites had few or no mammals. Implications In the absence of consistent long-term systematic monitoring it is difficult to determine if this survey and historical surveys represent pre-European patterns for mammals. The absence or low abundance of mammals in most sites suggest that cotemporary patterns may not represent an intact mammal fauna. Due to the equivocal nature of these findings a critical next step is to establish robust monitoring and experimental work to reveal the response of mammals to management interventions.

A comparison of stocking methods for beef production in northern Australia: pasture and soil surface condition responses

Historical stocking methods of continuous, season-long grazing of pastures with little account of growing conditions have caused some degradation within grazed landscapes in northern Australia. Alternative stocking methods have been implemented to address this degradation and raise the productivity and profitability of the principal livestock, cattle. Because information comparing stocking methods is limited, an evaluation was undertaken to quantify the effects of stocking methods on pastures, soils and grazing capacity. The approach was to monitor existing stocking methods on nine commercial beef properties in north and south Queensland. Environments included native and exotic pastures and eucalypt (lighter soil) and brigalow (heavier soil) land types. Breeding and growing cattle were grazed under each method. The owners/managers, formally trained in pasture and grazing management, made all management decisions affecting the study sites. Three stocking methods were compared: continuous (with rest), extensive rotation and intensive rotation (commonly referred to as ‘cell grazing’). There were two or three stocking methods examined on each property: in total 21 methods (seven continuous, six extensive rotations and eight intensive rotations) were monitored over 74 paddocks, between 2006 and 2009. Pasture and soil surface measurements were made in the autumns of 2006, 2007 and 2009, while the paddock grazing was analysed from property records for the period from 2006 to 2009. The first 2 years had drought conditions (rainfall average 3.4 decile) but were followed by 2 years of above-average rainfall. There were no consistent differences between stocking methods across all sites over the 4 years for herbage mass, plant species composition, total and litter cover, or landscape function analysis (LFA) indices. There were large responses to rainfall in the last 2 years with mean herbage mass in the autumn increasing from 1970 kg DM ha–1 in 2006–07 to 3830 kg DM ha–1 in 2009. Over the same period, ground and litter cover and LFA indices increased. Across all sites and 4 years, mean grazing capacity was similar for the three stocking methods. There were, however, significant differences in grazing capacity between stocking methods at four sites but these differences were not consistent between stocking methods or sites. Both the continuous and intensive rotation methods supported the highest average annual grazing capacity at different sites. The results suggest that cattle producers can obtain similar ecological responses and carry similar numbers of livestock under any of the three stocking methods.

Disentangling how landscape spatial and temporal heterogeneity affects Savanna birds

In highly seasonal tropical environments, temporal changes in habitat and resources are a significant determinant of the spatial distribution of species. This study disentangles the effects of spatial and mid to long-term temporal heterogeneity in habitat on the diversity and abundance of savanna birds by testing four competing conceptual models of varying complexity. Focussing on sites in northeast Australia over a 20 year time period, we used ground cover and foliage projected cover surfaces derived from a time series of Landsat Thematic Mapper imagery, rainfall data and site-level vegetation surveys to derive measures of habitat structure at local (1-100 ha) and landscape (100-1000s ha) scales. We used generalised linear models and an information theoretic approach to test the independent effects of spatial and temporal influences on savanna bird diversity and the abundance of eight species with different life-history behaviours. Of four competing models defining influences on assemblages of savanna birds, the most parsimonious included temporal and spatial variability in vegetation cover and site-scale vegetation structure, suggesting savanna bird species respond to spatial and temporal habitat heterogeneity at both the broader landscape scale and at the fine-scale. The relative weight, strength and direction of the explanatory variables changed with each of the eight species, reflecting their different ecology and behavioural traits. This study demonstrates that variations in the spatial pattern of savanna vegetation over periods of 10 to 20 years at the local and landscape scale strongly affect bird diversity and abundance. Thus, it is essential to monitor and manage both spatial and temporal variability in avian habitat to achieve long-term biodiversity outcomes.