Suchergebnisse

Patch-burning is frequently advocated as a management tool to enhance the biodiversity and pasture values of spinifex (Triodia) grasslands. In the northern Simpson Desert, Queensland, pastoralists use fire to reduce the likelihood of broad-scale wildfires and improve pastures for cattle. I conducted a before–after–control–impact experiment to investigate the response of small mammals to the short-term (<1 year) effects of patch-burning between August 1999 and June 2001. The experiment was replicated at three locations subject to differing rainfalls, with two 1-ha study grids remaining unburnt as controls, and two being burnt at each location. The areas burnt ranged from 1 to 3 ha. Dasycercus cristicauda and Pseudomys desertor responded negatively to the fire treatment. Notomys alexis responded positively to the fire treatment in the final trapping session but only at one location. Factors indicative of temporal and spatial variation in rainfall, time and site had a greater effect on the abundance of small mammals than the fire treatment. Heavy rainfalls in 2000 increased seed production and prompted increases in the populations of rodent species and Dasycercus cristicauda. The greatest numbers of captures were made at the sites that received the highest rainfalls. Patch-burning regimes are likely to increase the resilience of 'fire-sensitive' species dependent on dense spinifex by reducing the extent of wildfires.

Since they were declared a protected species in 1971, populations of saltwater crocodiles (Crocodylus porosus) have increased in the tidal rivers, freshwater swamps and marine waters of the Northern Territory. The recovery of the C. porosus population has been accompanied by an increase in the incidence of 'problem crocodiles' that represent a threat to people in freshwater and marine habitats. Despite the implications for human safety, little is known about C. porosus populations in the freshwater reaches of rivers, well upstream of tidal influence. In this study, we examined the density and body-size structure of C. porosus populations in three freshwater rivers using a combination of data from spotlight and helicopter surveys conducted between the 1980s and 2005, and the inland extent of C. porosus using distribution records in the Northern Territory. Since the 1980s, the density of C. porosus in upstream, freshwater reaches of the Daly and Roper rivers has increased, as has the inland extent of C. porosus on the Daly River. Although C. porosus was not detected in spotlight surveys of the Victoria River, helicopter survey and anecdotal records indicate that C. porosus was present after 1989. In all, 52.1% of the crocodiles sighted in spotlight surveys were 2.1–3.4 m long. Distribution records show that C. porosus occurs up to 235 km inland and at elevations of up to 126 m above sea level. The potential distribution of C. porosus is likely to be similar to that of barramundi (Lates calcarifer), a readily identifiable diadromous fish that must spawn in estuarine waters and occurs at elevations of up to 178 m above sea level. Because the density and inland extent of C. porosus in freshwater rivers is likely to increase, it is recommended that: (1) programs communicating crocodile awareness use the linkage between the presence of barramundi and the potential presence of C. porosus; (2) that crocodile warning signs be erected in upstream areas within the potential range of C. porosus; (3) that research be conducted on developing techniques to detect and exclude C. porosus from swimming areas; and (4) that widespread systematic surveys be undertaken to document the inland extent of C. porosus.

Context
The toxic cane toad (Rhinella marina) has invaded over 50 countries and is a serious conservation issue in Australia. Because the cane toad has taken several decades to colonise northern Australia, due to the large size of the continent and the east–west invasion axis, there is scope for making testable predictions about how toads will invade new areas. The western toad invasion front is far from linear, providing clear evidence for heterogeneity in invasion speed.

Aims
Several ad hoc hypotheses have been offered to explain this heterogeneity, including the evolution of traits that could facilitate dispersal, and spatial heterogeneity in climate patterns. Here an alternative hypothesis is offered, and a prediction generated for the spatiotemporal pattern of invasion into the Kimberley Region – the next frontier for the invading toads in Australia.

Methods
Using observations of spatiotemporal patterns of cane toad colonisation in northern Australia over the last 15 years, a conceptual model is offered, based on the orientation of wet season river flows relative to the invasion axis, as well as toad rafting and floating behaviour during the wet season.

Key results
Our model predicts that toads will invade southern areas before northern areas; an alternative model based on rainfall amounts makes the opposite prediction. The models can now be tested by monitoring the spread of invasion front over the next 5–10 years.

Conclusions
Our conceptual models present a pleuralistic approach to understanding the spatiotemporal invasion dynamics of toads; such an approach and evaluation of the models could prove useful for managing other invasive species.

Implications
Although control of cane toads has largely proved ineffective, knowledge of the spatiotemporal pattern of the toad invasion in the Kimberley could: (1) facilitate potential management tools for slowing the spread of toads; (2) inform stakeholders in the local planning for the invasion; (3) provide researchers with a temporal context for quantifying toad impacts on animal communities; and (4) reveal the mechanism(s) causing the heterogeneity in invasion speed.

Carnivore conservation and management is complex and expensive, and significant ongoing management costs may inhibit the development of new tools and any subsequent transition away from lethal control. We review and compare the economic costs and benefits of dingoes and domestic dogs in Australia and suggest that public affinity for domestic dogs may be co-opted into yielding more positive management outcomes for dingoes. Whereas Australians spend over AU$10 billion annually on purchasing and maintaining 4.2 million domestic dogs, landowners and government spend at least AU$30 million attempting to limit the density and distribution of dingoes, feral dogs, and their hybrids. These contrasting investments highlight the dual response of society towards domestic and wild members of the Canis genus. We suggest that a modest conservation levy on the sale of pet dogs or dog food, or both, could secure long-term funding to support efficacious non-lethal management of dingo impacts. A modest levy could generate AU$30 million annually, funding the development of non-lethal dingo-management tools without compromising existing management practices while new tools are investigated. Ultimately, a transition away from controlling dingoes through culling or exclusion fencing, to managing the negative impacts of dingoes could result in both more successful and sustainable management outcomes of dingoes and support the ecological, cultural and economic benefits they confer as Australia's apex predator.

This study investigated the population dynamics of three species of dasyurid
marsupials in sand ridge habitat of the Simpson Desert, western Queensland,
over a 10-year period between March 1990 and December 1999. The lesser
hairy-footed dunnart (Sminthopsis youngsoni), was
captured most consistently over the period of study, followed by the wongai
ningaui (Ningaui ridei), and the mulgara
(Dasycercus cristicauda). Rates of recapture were low
(4.5–22.2%), probably because individuals of each species are
very mobile. All species bred in late winter or early spring when animals were
aged at least 8–10 months, and independent juveniles first appeared
usually in summer. S. youngsoni reared a second litter
in late spring or early summer in 3 of the 10 years studied, when the
availability of food was likely to have been high; neither
N. ridei nor D. cristicauda were
known to attempt a second litter within a season.
To explore factors that might influence population dynamics, we compared
capture rates of each species with measures of rainfall, temperature,
vegetation cover, abundance of predators [feral cats
(Felis catus), red foxes
(Vulpes vulpes), and goannas
(Varanus spp.)], dragons, other dasyurids and
indices of food abundance. The abundance of S. youngsoni appeared to depend
primarily on the cover of spinifex 7–9 months earlier, that of
D. cristicauda was related most strongly to rainfall
7–9 months earlier, while that of N. ridei was
related to minimum temperature lagged by 1–3 months.
While the dynamics of other arid-zone mammals are driven demonstrably by
interactions between rainfall, resource availability and predation, our
findings suggest that dasyurids have limited flexibility in their life
histories and are influenced more subtly and by factors such as facilitation
that are just beginning to become apparent.

Context Over the last 230 years, the Australian terrestrial mammal fauna has suffered a very high rate of decline and extinction relative to other continents. Predation by the introduced red fox (Vulpes vulpes) and feral cat (Felis catus) is implicated in many of these extinctions, and in the ongoing decline of many extant species. Aims To assess the degree to which Australian terrestrial non-volant mammal species are susceptible at the population level to predation by the red fox and feral cat, and to allocate each species to a category of predator susceptibility. Methods We collated the available evidence and complemented this with expert opinion to categorise each Australian terrestrial non-volant mammal species (extinct and extant) into one of four classes of population-level susceptibility to introduced predators (i.e. 'extreme', 'high', 'low' or 'not susceptible'). We then compared predator susceptibility with conservation status, body size and extent of arboreality; and assessed changes in the occurrence of species in different predator-susceptibility categories between 1788 and 2017. Key results Of 246 Australian terrestrial non-volant mammal species (including extinct species), we conclude that 37 species are (or were) extremely predator-susceptible; 52 species are highly predator-susceptible; 112 species are of low susceptibility; and 42 species are not susceptible to predators. Confidence in assigning species to predator-susceptibility categories was strongest for extant threatened mammal species and for extremely predator-susceptible species. Extinct and threatened mammal species are more likely to be predator-susceptible than Least Concern species; arboreal species are less predator-susceptible than ground-dwelling species; and medium-sized species (35 g–3.5kg) are more predator-susceptible than smaller or larger species. Conclusions The effective control of foxes and cats over large areas is likely to assist the population-level recovery of ~63 species – the number of extant species with extreme or high predator susceptibility – which represents ~29% of the extant Australian terrestrial non-volant mammal fauna. Implications Categorisation of predator susceptibility is an important tool for conservation management, because the persistence of species with extreme susceptibility will require intensive management (e.g. predator-proof exclosures or predator-free islands), whereas species of lower predator susceptibility can be managed through effective landscape-level suppression of introduced predators.

Context Many Australian mammal species are highly susceptible to predation by introduced domestic cats (Felis catus) and European red foxes (Vulpes vulpes). These predators have caused many extinctions and have driven large distributional and population declines for many more species. The serendipitous occurrence of, and deliberate translocations of mammals to, 'havens' (cat- and fox-free offshore islands, and mainland fenced exclosures capable of excluding cats and foxes) has helped avoid further extinction. Aims The aim of this study was to conduct a stocktake of current island and fenced havens in Australia and assess the extent of their protection for threatened mammal taxa that are most susceptible to cat and fox predation. Methods Information was collated from diverse sources to document (1) the locations of havens and (2) the occurrence of populations of predator-susceptible threatened mammals (naturally occurring or translocated) in those havens. The list of predator-susceptible taxa (67 taxa, 52 species) was based on consensus opinion from >25 mammal experts. Key results Seventeen fenced and 101 island havens contain 188 populations of 38 predator-susceptible threatened mammal taxa (32 species). Island havens cover a larger cumulative area than fenced havens (2152km2 versus 346km2), and reach larger sizes (largest island 325km2, with another island of 628km2 becoming available from 2018; largest fence: 123km2). Islands and fenced havens contain similar numbers of taxa (27 each), because fenced havens usually contain more taxa per haven. Populations within fences are mostly translocated (43 of 49; 88%). Islands contain translocated populations (30 of 139; 22%); but also protect in situ (109) threatened mammal populations. Conclusions Havens are used increasingly to safeguard threatened predator-susceptible mammals. However, 15 such taxa occur in only one or two havens, and 29 such taxa (43%) are not represented in any havens. The taxon at greatest risk of extinction from predation, and in greatest need of a haven, is the central rock-rat (Zyzomys pedunculatus). Implications Future investment in havens should focus on locations that favour taxa with no (or low) existing haven representation. Although havens can be critical for avoiding extinctions in the short term, they cover a minute proportion of species' former ranges. Improved options for controlling the impacts of cats and foxes at landscape scales must be developed and implemented.

From the late Pleistocene to the Holocene and now the so-called Anthropocene, humans have been driving an ongoing series of species declines and extinctions (Dirzo et al. 2014). Large-bodied mammals are typically at a higher risk of extinction than smaller ones (Cardillo et al. 2005). However, in some circumstances, terrestrial megafauna populations have been able to recover some of their lost numbers because of strong conservation and political commitment, as well as human cultural changes (Chapron et al. 2014). Indeed, many would be in considerably worse predicaments in the absence of conservation action (Hoffmann et al. 2015). Nevertheless, most mammalian megafauna face dramatic range contractions and population declines. In fact, 59% of the world's largest carnivores (more than or equal to 15 kilograms, n = 27) and 60% of the world's largest herbivores (more than or equal to 100 kilograms, n = 74) are classified as threatened with extinction on the International Union for the Conservation of Nature (IUCN) Red List (supplemental tables S1 and S2). This situation is particularly dire in sub-Saharan Africa and Southeast Asia, home to the greatest diversity of extant megafauna (figure 1). Species at risk of extinction include some of the world's most iconic animals-such as gorillas, rhinos, and big cats (figure 2 top row)-and, unfortunately, they are vanishing just as science is discovering their essential ecological roles (Estes et al. 2011). Here, our objectives are to raise awareness of how these megafauna are imperiled (species in tables S1 and S2) and to stimulate broad interest in developing specific recommendations and concerted action to conserve them.

From the late Pleistocene to the Holocene and now the so-called Anthropocene, humans have been driving an ongoing series of species declines and extinctions (Dirzo et al. 2014). Large-bodied mammals are typically at a higher risk of extinction than smaller ones (Cardillo et al. 2005). However, in some circumstances, terrestrial megafauna populations have been able to recover some of their lost numbers because of strong conservation and political commitment, as well as human cultural changes (Chapron et al. 2014). Indeed, many would be in considerably worse predicaments in the absence of conservation action (Hoffmann et al. 2015). Nevertheless, most mammalian megafauna face dramatic range contractions and population declines. In fact, 59% of the world's largest carnivores (more than or equal to 15 kilograms, n = 27) and 60% of the world's largest herbivores (more than or equal to 100 kilograms, n = 74) are classified as threatened with extinction on the International Union for the Conservation of Nature (IUCN) Red List (supplemental tables S1 and S2). This situation is particularly dire in sub-Saharan Africa and Southeast Asia, home to the greatest diversity of extant megafauna (figure 1). Species at risk of extinction include some of the world's most iconic animals—such as gorillas, rhinos, and big cats (figure 2 top row)—and, unfortunately, they are vanishing just as science is discovering their essential ecological roles (Estes et al. 2011). Here, our objectives are to raise awareness of how these megafauna are imperiled (species in tables S1 and S2) and to stimulate broad interest in developing specific recommendations and concerted action to conserve them.