Aim
The number of studies investigating the nestedness and turnover components of beta diversity has increased substantially, but our general understanding of the drivers of turnover and nestedness remains elusive. Here, we examined the effects of species traits, spatial extent, latitude and ecosystem type on the nestedness and turnover components of beta diversity.

Location
Global.

Time period
1968–2017.

Major taxa studied
From bacteria to mammals.

Methods
From the 99 studies that partition total beta diversity into its turnover and nestedness components, we assembled 269 and 259 data points for the pairwise and multiple site beta-diversity metrics, respectively. Our data covered a broad variation in species dispersal type, body size and trophic position. The data were from freshwater, marine and terrestrial realms, and encompassed geographical areas from the tropics to near polar regions. We used linear modelling as a meta-regression tool to analyse the data.

Results
Pairwise turnover, multiple site turnover and total beta diversity all decreased significantly with latitude. In contrast, multiple site nestedness showed a positive relationship with latitude. Beta-diversity components did not generally differ among the realms. The turnover component and total beta diversity increased with spatial extent, whereas nestedness was scale invariant for pairwise metrics. Multiple site beta-diversity components did not vary with spatial extent. Surprisingly, passively dispersed organisms had lower turnover and total beta diversity than flying organisms. Body size showed a relatively weak relationship with beta diversity but had important interactions with trophic position, thus also affecting beta diversity via interactive effects. Producers had significantly higher average pairwise turnover and total beta diversity than carnivores.

Main conclusions
The present results provide evidence that species turnover, being consistently the larger component of total beta diversity, and nestedness are related to the latitude of the study area and intrinsic organismal features. We showed that two beta-diversity components had generally opposing patterns with regard to latitude. We highlight that beta-diversity partition may give additional insights into the underlying causes of spatial variability in biotic communities compared with total beta diversity alone.

/pdf/a-meta-analysis-of-nestedness-and-turnover-components-of-52n5f8at3l.pdf

A meta-analysis of nestedness and turnover components of beta diversity across organisms and ecosystems

Intensification of fires and grazing by large herbivores has caused population declines in small vertebrates in many ecosystems worldwide. Impacts are rarely direct, and usually appear driven via indirect pathways, such as changes to predator-prey dynamics. Fire events and grazing may improve habitat and/or hunting success for the predators of small mammals, however, such impacts have not been documented. To test for such an interaction, we investigated fine-scale habitat selection by feral cats in relation to fire, grazing and small-mammal abundance. Our study was conducted in north-western Australia, where small mammal populations are sensitive to changes in fire and grazing management. We deployed GPS collars on 32 cats in landscapes with contrasting fire and grazing treatments. Fine-scale habitat selection was determined using discrete choice modelling of cat movements. We found that cats selected areas with open grass cover, including heavily-grazed areas. They strongly selected for areas recently burnt by intense fires, but only in habitats that typically support high abundance of small mammals. Intense fires and grazing by introduced herbivores created conditions that are favoured by cats, probably because their hunting success is improved. This mechanism could explain why, in northern Australia, impacts of feral cats on small mammals might have increased. Our results suggest the impact of feral cats could be reduced in most ecosystems by maximising grass cover, minimising the incidence of intense fires, and reducing grazing by large herbivores.

/pdf/landscape-management-of-fire-and-grazing-regimes-alters-the-2q3cspxftd.pdf

Landscape Management of Fire and Grazing Regimes Alters the Fine-Scale Habitat Utilisation by Feral Cats

Fire refugia are landscape elements that remain unburned or minimally affected by fire, thereby supporting postfire ecosystem function, biodiversity, and resilience to disturbances. Although fire refugia have been studied across continents, scales, and affected taxa, they have not been characterized systematically over space and time, which is crucial for understanding their role in facilitating resilience in the context of global change. We identify four dichotomies that delineate an overarching conceptual framework of fire refugia: unburned versus lower severity, species-specific versus landscape-process characteristics, predictable versus stochastic, and ephemeral versus persistent. We outline the principal concepts underlying the ecological function of fire refugia and describe both the role of fire refugia and uncertainties regarding their persistence under global change. An improved understanding of fire refugia is crucial to conservation given the role that humans play in shaping disturbance regimes across landscapes.

/pdf/fire-refugia-what-are-they-and-why-do-they-matter-for-global-rhb55txnh0.pdf

Fire Refugia: What Are They, and Why Do They Matter for Global Change?

Recent studies at some sites in northern Australia have reported severe and rapid decline of some native mammal species, notwithstanding an environmental context (small human population size, limited habitat loss, substantial reservation extent) that should provide relative conservation security. All of the more speciose taxonomic groups of mammals in northern Australia have some species for which the conservation status has been assessed as threatened, with 53% of dasyurid, 46% of macropod and potoroid, 33% of bandicoot and bilby, 33% of possum, 31% of rodent, and 24% of bat species being assessed as extinct, threatened or Near Threatened. This paper reviews disparate recent and ongoing studies that provide information on population trends across a broader geographic scope than the previously reported sites, and provides some information on the conservation status and trends for mammal groups (bats, larger macropods) not well sampled in previous monitoring studies. It describes some diverse approaches of studies seeking to document conservation status and trends, and of the factors that may be contributing to observed patterns of decline. The studies reported provide some compelling evidence that predation by feral cats is implicated in the observed decline, with those impacts likely to be exacerbated by prevailing fire regimes (frequent, extensive and intense fire), by reduction in ground vegetation cover due to livestock and, in some areas, by ‘control’ of dingoes. However the impacts of dingoes may be complex, and are not yet well resolved in this area. The relative impacts of these individual factors vary spatially (with most severe impacts in lower rainfall and less topographically rugged areas) and between different mammal species, with some species responding idiosyncratically: the most notable example is the rapid decline of the northern quoll Dasyurus hallucatus due to poisoning by the introduced cane toad Rhinella marina , which continues to spread extensively across northern Australia. The impact of disease, if any, remains unresolved. Recovery of the native mammal fauna may be impossible in some areas. However, there are now examples of rapid recovery following threat management. Priority conservation actions include: enhanced biosecurity for important islands, establishment of a network of substantial predator exclosures, intensive fire management (aimed at increasing the extent of longer-unburnt habitat and in delivering fine scale patch burning), reduction in feral stock in conservation reserves, and acquisition for conservation purposes of some pastoral lands in areas that are significant for mammal conservation.

/pdf/stemming-the-tide-progress-towards-resolving-the-causes-of-59t6fligiu.pdf

Stemming the tide: progress towards resolving the causes of decline and implementing management responses for the disappearing mammal fauna of northern Australia

Patch mosaic burning, in which fire is used to produce a mosaic of habitat patches representative of a range of fire histories (‘pyrodiversity’), has been widely advocated to promote greater biodiversity. However, the details of desired fire mosaics for prescribed burning programs are often unspecified. Threatened small to medium-sized mammals (35 g to 5.5 kg) in the fire-prone tropical savannas of Australia appear to be particularly fire-sensitive. Consequently, a clear understanding of which properties of fire mosaics are most instrumental in influencing savanna mammal populations is critical. Here we use mammal capture data, remotely sensed fire information (i.e. time since last fire, fire frequency, frequency of late dry season fires, diversity of post-fire ages in 3 km radius, and spatial extent of recently burnt, intermediate and long unburnt habitat) and structural habitat attributes (including an index of cattle disturbance) to examine which characteristics of fire mosaics most influence mammals in the north-west Kimberley. We used general linear models to examine the relationship between fire mosaic and habitat attributes on total mammal abundance and richness, and the abundance of the most commonly detected species. Strong negative associations of mammal abundance and richness with frequency of late dry season fires, the spatial extent of recently burnt habitat (post-fire age <1 year within 3 km radius) and level of cattle disturbance were observed. Shrub cover was positively related to both mammal abundance and richness, and availability of rock crevices, ground vegetation cover and spatial extent of ≥4 years unburnt habitat were all positively associated with at least some of the mammal species modelled. We found little support for diversity of post-fire age classes in the models. Our results indicate that both a high frequency of intense late dry season fires and extensive, recently burnt vegetation are likely to be detrimental to mammals in the north Kimberley. A managed fire mosaic that reduces large scale and intense fires, including the retention of ≥4 years unburnt patches, will clearly benefit savanna mammals. We also highlighted the importance of fire mosaics that retain sufficient shelter for mammals. Along with fire, it is clear that grazing by introduced herbivores also needs to be reduced so that habitat quality is maintained.

/pdf/influence-of-fire-mosaics-habitat-characteristics-and-cattle-4htaz16yq1.pdf

Influence of Fire Mosaics, Habitat Characteristics and Cattle Disturbance on Mammals in Fire-Prone Savanna Landscapes of the Northern Kimberley

We construct a state-and-transition model for mammals in tropical savannas in northern Australia to synthesize ecological knowledge and understand mammalian declines. We aimed to validate the existence of alternative mammal assemblage states similar to those in arid Australian grasslands, and to speculate on transition triggers. Based on the arid grassland model, we hypothesized that assemblages are partitioned across rainfall gradients and between substrates. We also predicted that assemblages typical of arid regions in boom periods would be prevalent in savannas with higher and more regular rainfall. Data from eight mammal surveys from the Kimberley region, Western Australia (1994 to 2011) were collated. Survey sites were partitioned across rainfall zones and habitats. Data allowed us to identify three assemblage states: State 0:- low numbers of mammals, State II:- dominated by omnivorous rodents and State III:- dominated by rodents and larger marsupials. Unlike arid grasslands, assemblage dominance by insectivorous dasyurids (State I) did not occur in savannas. Mammal assemblages were partitioned across rainfall zones and between substrates as predicted, but—unlike arid regions—were not related strongly to yearly rainfall. Mammal assemblage composition showed high regional stability, probably related to high annual rainfall and predictable wet season resource pulses. As a consequence, we speculate that perpetually booming assemblages in savannas allow top-down control of the ecosystem, with suppression of introduced cats by the dingo, the region's top predator. Under conditions of low or erratic productivity, imposed increasingly by intense fire regimes and introduced herbivore grazing, dingoes may not limit impacts of cats on native mammals. These interacting factors may explain contemporary declines of savanna mammals as well as historical declines in arid Australia. The cat-ecosystem productivity hypothesis raised here differs from the already-articulated cat-habitat structure hypothesis for mammal declines, and we suggest approaches for explicit testing of transition triggers for competing hypotheses.

/pdf/mammals-of-australia-s-tropical-savannas-a-conceptual-model-3xc2xjj679.pdf

Mammals of Australia's tropical savannas: a conceptual model of assemblage structure and regulatory factors in the Kimberley region

Patches of fire-sensitive vegetation often occur within fire-prone tropical savannas, and are indicative of localized areas where fire regimes are less severe. These may act as important fire refugia for fire-sensitive biota. The fire-sensitive tree Callitris intratropica occurs in small patches throughout the fire-prone northern Australian savannas, and is widely seen as an indicator of low-severity fire regimes and of good ecosystem health. Here, we address the question: to what extent do Callitris patches act as refuges for other fire-sensitive biota, and therefore play a broader conservation role? We contrast floral and faunal species composition between Callitris patches and surrounding eucalypt savanna, using three case studies. In the first case study, a floristic analysis of 47 Callitris patches across Western Australia's Kimberley region showed that woody species in these patches were overwhelmingly widespread, fire-tolerant savanna taxa. No species of special conservation concern occurred disproportionately within Callitris patches. Similarly, there was no concentration of fire-sensitive fauna or flora in five Callitris patches in the East Kimberley. Finally, there was no difference in ant species composition among 12 Callitris patches and surrounding eucalypt savannas in Kakadu National Park, Northern Territory, and there were no fire-sensitive ant species in Callitris patches. Our three case studies from throughout the northwestern Australia provide no evidence that Callitris patches act as important refuges for fire-sensitive flora or fauna within fire-prone eucalypt savannas. This calls into question the notion that Callitris is a strong indicator of general ecosystem health.

The Fire Refuge Value of Patches of a Fire-Sensitive Tree in Fire-prone Savannas: Callitris intratropica in Northern Australia


 Detecting and mitigating near-wellbore fines migration is important in order to avoid formation damage in many gas wells. This has bearing not only on gas production but also carbon capture through the geological storage of Carbon dioxide (CO2), in pressurised, deep saline aquifers. Fines migration may occur because of weakened electrostatic forces caused by an introduced fluid which also makes fines more prone to movement by viscous drag, or where the drag forces are sufficient to physically break or lift clay crystals from their original location and transport them through the pore network.
 Potential near-wellbore fines migration is typically assessed via coreflood tests. In an ideal scenario, such tests will be conducted using reservoir core material, with reservoir gas at rates and pressures comparable to the reservoir. However, due to practicality and cost constraints, tests are often conducted using available outcrop core and scaled down reservoir conditions. Laboratory tests reduce higher field pressures down to lab scale. In certain scenarios, simulating the total gas flux in a given near-wellbore system is achieved by increasing gas flow rates. Although, in some investigations, the need to utilise field realistic pressures in the lab is also becoming more of a requirement. This paper aims to address differences in lab protocols by examining both field realistic and scaled down conditions to aid best practice for formation damage identification and remediation. The potential utility, and challenges associated with a variety of hydrocarbon gas analogues in scenarios where increased gas density is required is also discussed.
 The fines migration potential of a clay rich (Blaxter) sandstone was demonstrated using salinity and flux related fines migration methods, demonstrating that under certain conditions, selected cores are susceptible to fines migration. Test results with CO2 at low and medium pressure conditions demonstrated that pressure and flow rate variation in the laboratory had no notable effect on the fines migration of Blaxter sandstone samples, under the conditions examined. Additional tests conducted at higher pressures of 7250 psig did not yield fines migration although a 10% permeability loss was observed. While this was the case for Blaxter sandstone, caution is advised when testing with field substrate under these conditions, as reservoir rocks may be more susceptible to damage. Field cores typically display a well-developed crystal structure and surface area/volume ratios more normally associated with kaolinite booklets and platelets of clays, which may expose them to higher drag forces. Therefore, the minimal permeability reduction effects observed at high pressure may potentially be multiplied in field cores.
 Additional core flood tests were conducted to evaluate the use of hydrocarbon gas analogues (such dodecane) as a substitute for dense gases in core flood testing. This allows lower pressures than that would be required for compressed gases. Results showed that dodecane can be used as a gas analogue under appropriate conditions. A note of caution in the use of dodecane is that results from the high-pressure tests showed that, under the conditions examined, dodecane induced a 24% permeability reduction in the core.
 The work presented in this paper aims to improve the use of coreflood tests as a tool for identifying formation damage, particularly in gas wells. This work provides useful guides and shows that while testing at atypical pressures is not prevalent, it can be performed and may be required for more robust formation damage identification programs in specific scenarios.

From Lab to Field 2 - Assessing Impact of Fluid Density, Salinity, and Injection Rate on Fines Migration Potential in Gas Wells

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

Gordon Graham

Author Tools

Chat about Author

Papers

Mammals of Australia's tropical savannas: a conceptual model of assemblage structure and regulatory factors in the Kimberley region

The Fire Refuge Value of Patches of a Fire-Sensitive Tree in Fire-prone Savannas: Callitris intratropica in Northern Australia

From Lab to Field 2 - Assessing Impact of Fluid Density, Salinity, and Injection Rate on Fines Migration Potential in Gas Wells