Impacts of invasive species are often difficult to quantify, meaning that many invaders are prioritised for management without robust, contextual evidence of impact. Most impact studies for invasive ...plants compare heavily invaded with non-invaded sites, revealing little about abundance-impact relationships. We examined effects of increasing cover and volume of the non-native herbaceous groundcover Tradescantia fluminensis on a temperate rainforest community of southern Australia. We hypothesised that there would be critical thresholds in T. fluminensis abundance, below which the native plant community would not be significantly impacted, but above which the community's condition would degrade markedly. We modelled the abundance-impact relationship from 83 plots that varied in T. fluminensis abundance and landscape context and found the responses of almost all native plant indicators to invasion were non-linear. Native species richness, abundance and diversity exhibited negative exponential relationships with increasing T. fluminensis volume, but negative threshold relationships with increasing T. fluminensis cover. In the latter case, all metrics were relatively stable until cover reached between 20 and 30%, after which each decreased linearly, with a 50% decline occurring at 75-80% invader cover. Few growth forms (notably shrubs and climbers) exhibited such thresholds, with most exhibiting negative exponential relationships. Tradescantia fluminensis biomass increased dramatically at > 80% cover, with few native species able to persist at such high levels of invasion. Landscape context had almost no influence on native communities, or the abundance-impact relationships between T. fluminensis and the plant community metrics. Our results suggest that the diversity of native rainforest community can be maintained where T. fluminensis is present at moderate-to-low cover levels.
Some studies examining the impacts of invasive plant species in native plant communities have demonstrated non-linear damage functions, whereby community components, such as species richness, are ...seemingly unaffected by the presence of an invader until it has attained relatively high levels of abundance, whereupon there is a marked decrease with further increases in abundance. Given chronic limitations in the resources available for managing invasive species, it has been argued that the most damaging invaders would be controlled most efficiently by maintaining their abundances below such threshold levels. Because many impact studies do not involve sampling over a wide range of invader abundances it is not possible to estimate the prevalence of threshold relationships. Furthermore, studies that have employed appropriate sampling methods have shown that different life forms exhibit different threshold responses, indicating that maintenance management for biodiversity values should be designed to protect the most sensitive species or groups of species. Since control costs increase with invader abundance, economic and ecological considerations are aligned when invaders are sustainably maintained at relatively low abundances. Adopting such an approach should also minimise negative impacts where damage functions are linear.
Hedge cactus (Cereus uruguayanus R. Kiesling; syn.: Cereus hildmannianus K. Schum.) is a columnar cactus that was introduced to Australia as an ornamental plant and has since become invasive in ...subhumid regions of Queensland and New South Wales. Compared with its congener, queen of the night (Cereus jamacaru DC.), which is currently invasive in both eastern and southern Africa, information on seed biology of C. uruguayanus is lacking. Experiments were conducted to study the effects of alternating day/night temperature, salt stress, water stress, and burial depth on germination and seedling emergence of four seed accessions of C. uruguayanus. Seeds were also subjected to a controlled aging test (CAT) to obtain an estimate of potential persistence under field conditions. The optimum temperature regime for germination of all accessions was 30/20 C. Germination decreased with an increase in sodium chloride (NaCl) concentration, but germination of all accessions (range 26% to 81%) occurred at 160 mM NaCl, indicating very high salt tolerance. Seed germination gradually decreased with an increase in water stress, but germination in all accessions (range 19% to 47%) occurred at −0.8 MPa. Seed viability and dormancy status were unaffected by exposure to salt level (320 mM NaCl) and water (−1.6 MPa) stress under which germination did not occur. Germination responses to all three factors were generally similar to those documented for C. jamacaru. The emergence of C. uruguayanus decreased with an increase in seed burial depth. The highest emergence (43%) was recorded for surface-sown seeds, and emergence was reduced to 0 at a burial depth of 2 cm. CAT results for two seed accessions indicated that seeds of C. uruguayanus are likely to demonstrate extended (>3 yr) persistence under field conditions, a prediction that is supported by evidence that germination of its small (2-mm) seeds is markedly reduced by burial.
Abstract Following spinal cord injury, axons fail to regenerate without exogenous intervention. In this study we report that aligned microfiber-based grafts foster robust regeneration of vascularized ...CNS tissue. Film, random, and aligned microfiber-based conduits were grafted into a 3 mm thoracic rat spinal cord gap created by complete transection. Over the course of 4 weeks, microtopography presented by aligned or random poly- l -lactic acid microfibers facilitated infiltration of host tissue, and the initial 3 mm gap was closed by endogenous cell populations. This bulk tissue response was composed of regenerating axons accompanied by morphologically aligned astrocytes. Aligned fibers promoted long distance (2055 ± 150 μm), rostrocaudal axonal regeneration, significantly greater than random fiber (1162 ± 87 μm) and film (413 ± 199 μm) controls. Retrograde tracing indicated that regenerating axons originated from propriospinal neurons of the rostral spinal cord, and supraspinal neurons of the reticular formation, red nucleus, raphe and vestibular nuclei. Our findings outline a form of regeneration within the central nervous system that holds important implications for regeneration biology.
The interplay between predator and prey has catalyzed the evolution of venom systems, with predators honing their venoms in response to the evolving resistance of prey. A previous study showed that ...the African varanid species
has heightened resistance to snake venoms compared to the Australian species
,
, and
, likely due to increased predation by sympatric venomous snakes on
. To understand venom resistance among varanid lizards, we analyzed the receptor site targeted by venoms in 27 varanid lizards, including 25 Australian varanids. The results indicate an active evolutionary arms race between Australian varanid lizards and sympatric neurotoxic elapid snakes. Large species preying on venomous snakes exhibit inherited neurotoxin resistance, a trait potentially linked to their predatory habits. Consistent with the 'use it or lose it' aspect of venom resistance, this trait was secondarily reduced in two lineages that had convergently evolved gigantism (
and the
/
clade), suggestive of increased predatory success accompanying extreme size and also increased mechanical protection against envenomation due to larger scale osteoderms. Resistance was completely lost in the mangrove monitor
, consistent with venomous snakes not being common in their arboreal and aquatic niche. Conversely, dwarf varanids demonstrate a secondary loss at the base of the clade, with resistance subsequently re-evolving in the burrowing
/
clade, suggesting an ongoing battle with neurotoxic predators. Intriguingly, within the
/
clade, resistance was lost again in
, which is morphologically and ecologically distinct from other members of this clade. Resistance was also re-evolved in
which is terrestrial in contrast to the arboreal/cliff dwelling niches occupied by the other members of its clade (
,
,
,
). This 'Russian doll' pattern of venom resistance underscores the dynamic interaction between dwarf varanids and Australian neurotoxic elapid snakes. Our research, which included testing
(death adder) venoms against varanid receptors as models for alpha-neurotoxic interactions, uncovered a fascinating instance of the Red Queen Hypothesis: some death adders have developed more potent toxins specifically targeting resistant varanids, a clear sign of the relentless predator-prey arms race. These results offer new insight into the complex dynamics of venom resistance and highlight the intricate ecological interactions that shape the natural world.
Foraging modes (ambush vs. active foraging) are often correlated with a suite of morphological, physiological, behavioural and ecological traits known as the "adaptive syndrome" or "syndrome ...hypothesis." In snakes, an ecological correlate often reported in the literature is that ambush‐hunting snakes have a higher relative meal size compared to actively foraging snakes which feed on smaller prey items. This “large meal versus small meal” feeding hypothesis between ambush and active foragers has become a widely accepted paradigm of snake feeding ecology, despite the fact that no rigorous meta‐analysis has been conducted to support this generalization.
We conducted a phylogenetically explicit meta‐analysis, which included ca. 100 species, to test this paradigm of snake feeding ecology.
We gathered data on prey size by inducing regurgitation by palpation in free‐ranging snakes and by examining the stomach contents of preserved museum specimens. When we found prey, we recorded both snake and prey mass to estimate relative prey mass (prey mass/snake mass). We also reviewed published studies of snake feeding ecology to gather similar information for other species.
Ambush and active foragers did not differ in minimum or average meal size but the maximum meal sizes consumed by ambush‐foraging snakes were larger than the maximum meal sizes eaten by active foragers. This results in ambush‐foraging snakes consuming a significantly wider range of meal sizes, rather than being large meal specialists compared to active foragers. We argue that ambush foragers evolved to be more opportunistic predators because they encounter prey less frequently compared to active foragers. This hypothesis is further supported by the fact that ambush foragers also exhibited marginally wider diet breadths, consuming a broader range of prey types in comparison with active foragers.
Our study challenges aspects of the foraging syndrome as it is currently conceived, and our results have important implications for our understanding of how foraging mode has shaped the behaviour and physiology of ambush‐foraging snakes.
Ambush‐foraging snakes are generally assumed to specialize on relatively larger prey compared to active foragers. This study shows that, rather than being large meal specialists, ambush‐foraging snakes consume a significantly wider range of meals sizes in comparison with active foragers.
Docetaxel/cisplatin/infusional 5-fluorouracil (5-FU; DCF) is a standard chemotherapy regimen for patients with advanced gastric cancer (GC). This phase II study evaluated docetaxel/oxaliplatin (TE), ...docetaxel/oxaliplatin/5-FU (TEF), and docetaxel/oxaliplatin/capecitabine (TEX) in patients with advanced GC.
Patients with metastatic or locally recurrent gastric adenocarcinoma (including carcinoma of the gastro-oesophageal junction) were randomly assigned (1 : 1 : 1) to TE, TEF, or TEX. Each regimen was tested at two doses before full evaluation at optimized dose levels. The primary end point was progression-free survival (PFS). Overall survival (OS), tumour response, and safety were also assessed. A therapeutic index (median PFS relative to the incidence of febrile neutropenia) was calculated for each regimen and compared with DCF (historical data).
Overall, 248 patients were randomly assigned to receive optimized dose treatment. Median PFS was longer with TEF (7.66 95% confidence interval (CI): 6.97–9.40 months) versus TE (4.50 3.68–5.32 months) and TEX (5.55 4.30–6.37 months). Median OS was 14.59 (95% CI: 11.70–21.78) months for TEF versus 8.97 (7.79–10.87) months for TE and 11.30 (8.08–14.03) months for TEX. The rate of tumour response (complete or partial) was 46.6% (95% CI 35.9–57.5) for TEF versus 23.1% (14.3–34.0) for TE and 25.6% (16.6–36.4) for TEX. The frequency and type of adverse events (AEs) were similar across the three arms. Common grade 3/4 AEs were fatigue (21%), sensory neuropathy (14%), and diarrhoea (13%). Febrile neutropenia was reported in 2% (TEF), 14% (TE), and 9% (TEX) of patients. The therapeutic index was improved with TEF versus TEX, TE, or DCF.
These results suggest that TEF is worthy of evaluation as an arm in a phase III trial or as a backbone regimen for new targeted agents in advanced GC.
Trial registration number: NCT00382720.
A new modeling method for representing distributed scattering centers in wide-angle synthetic aperture radar (SAR) is presented. The proposed multipeak model approximates amplitudes of localized ...image peaks that typically appear at a single pixel or as an in-line set of pixels in a SAR image. In this way, the multipeak model is an improvement over existing peak models which poorly represent distributed canonical scatterers, such as the common dihedral with a fold line oriented parallel to the imaging plane. The model is derived from a wide-angle approximation of the well-known attributed scattering center or parametric models when under the action of a linear imaging operator. It is shown that, under typical imaging conditions of 10 ^{ \circ} or more in the synthetic aperture, the multipeak model approximates the image peak amplitudes due to distributed canonical scatterers as if they are due to an equivalent point scatterer with an azimuth-independent dispersive amplitude function in the spectral domain. This improves parameter estimation and scatterer classification, and it is also shown that the imaging relative error due to the approximation is less than 2% for other common image processing conditions such as tapered windowing in azimuth and when the canonical scatterer is at least ten wavelengths in size. A distinct advantage of the multipeak model over point scatterer models is that parameter estimation and scatterer classification can be performed solely in the spatial domain on a pixel-by-pixel basis and efficiently integrated within a linear SAR imaging process. To illustrate the benefits and limitations of the approach, parameter estimation and scatterer classification experiments are presented using simulated SAR data.
Much confusion exists in the English-language literature on plant invasions concerning the terms 'naturalized' and 'invasive' and their associated concepts. Several authors have used these terms in ...proposing schemes for conceptualizing the sequence of events from introduction to invasion, but often imprecisely, erroneously or in contradictory ways. This greatly complicates the formulation of robust generalizations in invasion ecology. Based on an extensive and critical survey of the literature we defined a minimum set of key terms related to a graphic scheme which conceptualizes the naturalization/invasion process. Introduction means that the plant (or its propagule) has been transported by humans across a major geographical barrier. Naturalization starts when abiotic and biotic barriers to survival are surmounted and when various barriers to regular reproduction are overcome. Invasion further requires that introduced plants produce reproductive off-spring in areas distant from sites of introduction (approximate scales: > 100 m over < 50 years for taxa spreading by seeds and other propagules; > 6 m/3 years for taxa spreading by roots, rhizomes, stolons or creeping stems). Taxa that can cope with the abiotic environment and biota in the general area may invade disturbed, seminatural communities. Invasion of successionally mature, undisturbed communities usually requires that the alien taxon overcomes a different category of barriers. We propose that the term `invasive' should be used without any inference to environmental or economic impact. Terms like 'pests' and 'weeds' are suitable labels for the 50-80% of invaders that have harmful effects. About 10% of invasive plants that change the character, condition, form, or nature of ecosystems over substantial areas may be termed 'transformers'
1. Eradication is often the preferred strategy in the management of new weed invasions, but recent research has shown that the circumstances under which eradication can be achieved are highly ...constrained. Containment is a component of an eradication strategy and also a management objective in its own right. Just as for eradication, containment of a weed invasion should be attempted only if it is considered feasible. However, very little guidance exists for the assessment of containment feasibility for weeds. 2. Numerous factors have been proposed as influencing feasibility of containment, but those that relate to the potential for management of dispersal pathways and timely detection of new foci of infestation appear to be critical. Theory suggests that the rate of spread is largely driven by long‐distance dispersal (LDD). However, LDD is generally unpredictable and often occurs for species that do not appear to be adapted for it. Furthermore, many (if not most) LDD events fail to give rise to new infestations. 3. As the probability of colonisation is related to the numbers of propagules immigrating (‘propagule pressure’) at a point in the landscape, dispersal pathways that move relatively large numbers of propagules simultaneously and/or repeatedly should most enhance weed spread. It is these pathways whose potential for management has the greatest bearing upon containment feasibility. A key impediment to containment is undetected spread; this need not occur through LDD and is more likely to occur through dispersal to lesser distances. 4. Synthesis and applications. Feasibility of containment should be viewed in terms of the effort required to reduce weed spread rate, as well as the effectiveness of relevant management actions. Where dispersal vectors are not readily manageable and the probability of detection via structured and/or unstructured surveillance is low, a much greater reliance upon fecundity control will be needed to contain a weed. A combination of empirical and theoretical approaches should be used to develop and refine estimates of containment feasibility. Such estimates will aid decision‐making with regard to whether to attempt to reduce weed spread and assist in prioritisation of different weeds for containment.
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