224 research outputs found
Entirely as expected? What the voting data tells us about Corbyn’s re-election
When Jeremy Corbyn was elected Labour leader in 2015, the result astonished many; his re-election surprised no-one. Analysing the 2016 voting data, Peter Dorey and Andrew Denham find a few surprises amidst the details
The election of an ‘outsider’ as Labour leader is linked to new selection rules and the ideological alternative on offer
Conventional wisdom has it that rank outsiders do not become leaders of ‘mainstream’ British parties, yet Jeremy Corbyn now presides over the Labour Party. Pete Dorey and Andrew Denham reflect on the criteria which have fed into leadership selection before now and argue it was changes to the selection rules and the offer of a clear ideological alternative to recent leaders that allowed Corbyn to win such an unexpected and decisive victory
Herbicide impacts on exotic grasses and a population of the critically endangered herb "Calystegia affinis" (Convolvulaceae) on Lord Howe Island
Introduced perennial grasses are capable of altering the habitat of native species, causing reductions in population size and vigour, and potentially affecting life-history processes such as survival, pollination and seedling recruitment. We examined the utility of herbicide treatment on two exotic grasses, Pennisetum clandestinum (Kikuyu) and Stenotaphrum secundatum (Buffalo grass) to restore the habitat of Calystegia affinis, a critically endangered species endemic to Lord Howe and Norfolk Islands. Using two herbicides, Asset (designed to affect only grasses) and Glyphosate (a general herbicide), we compared effectiveness in reducing grass cover on a population of Calystegia affinis. We protected Calystegia plants from the herbicides by ensuring their leaves were covered by plastic bags during herbicide application. Both herbicides were similarly effective in reducing grass cover after four weeks and had no noticeable adverse affect on Calystegia (suggesting the plastic bag protection was effective). After 26 weeks, Glyphosate was more effective in maintaining a reduced grass cover. Plots treated with either herbicide had a greater relative increase in abundance of Calystegia stems compared to untreated controls. The Glyphosate treatment resulted in the greatest relative increase in stem abundance, but this was not significantly greater than in the Asset treatment. We consider that spraying with Glyphosate treatment, with follow-up monitoring and spot-spraying, will assist the recovery of the Calystegia affinis population. Ultimately, the maintenance of a weed-free zone at the forest edge will provide suitable habitat for additional recruitment of this and other native species
Relict and contemporary influences on the postglacial geomorphology and evolution of a current swept shelf: the Eastern Cape Coast, South Africa
Disruption of recruitment in two endemic palms on Lord Howe Island by invasive rats
Invasive species may have negative impacts on many narrow range endemics and species restricted to oceanic islands. Predicting recent impacts of invasive species on long-lived trees is difficult because the presence of adult plants may mask population changes. We examined the impact of introduced black rats (Rattus rattus) on two palm species restricted to cloud forests and endemic to Lord Howe Island, a small oceanic island in the southern Pacific. We combined estimates of the standing size distribution of these palms with the proximal impacts of rats on fruit survival in areas baited to control rats and in unbaited areas. The size distribution of palms with trunks was comparable across baited and unbaited sites. Small juvenile palms lacking a trunk (\50 cm tall) were abundant in baited areas, but rare in unbaited sites for Lepidorrhachis mooreana, and rare or absent in 3 out of 4 unbaited Hedyscepe canterburyana sites. All ripe fruits were lost to rats in the small fruited L. mooreana. Fruitremoval was widespread but less (20–54%) in H. canterburyana. Both palms showed evidence of a reduced capacity to maintain a juvenile bank of palms through regular recruitment as a consequence of over 90 years of rat impact. This will limit the ability of these species to take advantage of episodic canopy gaps. Baiting for rat control reduced fruit losses and resulted in the re-establishment of a juvenile palm bank. Conservation of both endemic palms necessitates control (or eradication) of rat populations on the unique cloud forest summits of the island
Varying levels of clonality and ploidy create barriers to gene flow and challenges for conservation of an Australian arid-zone ecosystem engineer, Acacia loderi
Acacia loderi, the ecosystem engineer of the endangered Acacia loderi Shrublands in arid eastern Australia, spans a persistent (\u3e 15 000 year) but poorly studied landscape feature, the Darling River. We investigated the genetic structure of 19 stands of eight to \u3e 1000 plants separated by \u3c 300 km to test for variation in life histories between semi-arid and arid stands to the east and west of the Darling River, respectively. Eight of nine stands east of the Darling were exclusively sexual, whereas most of those to the west were clonal. Three western stands were monoclonal, two were polyploid, and one was a diverse mix of diploid and triploid phenotypes. Bayesian analysis revealed a complex genetic structure within the western stands, whereas the eastern stands formed only two genetic clusters. Conservation of small stands may require augmentation of genotypic diversity. However, most genotypic diversity resides within the eastern stands. Although arid zone stands of A. loderi are not always clonal, clonality and polyploidy are more common in the arid west. Clear demarcation of life histories either side of the Darling River may reflect ancient or contemporary effects of physical disturbance associated with the river channel, or cryptic environmental differences, with sexual and asexual reproduction, respectively, at a selective premium in the semi-arid east and arid west. The restricted distribution of clones and variation in clonality and polyploidy suggests that smaller stands may be vulnerable and warrant individual management
The role of perceived source location in auditory stream segregation: separation affects sound organization, common fate does not
The human auditory system is capable of grouping sounds originating from different sound sources into coherent auditory streams, a process termed auditory stream segregation. Several cues can influence auditory stream segregation, but the full set of cues and the way in which they are integrated is still unknown. In the current study, we tested whether auditory motion can serve as a cue for segregating sequences of tones. Our hypothesis was that, following the principle of common fate, sounds emitted by sources moving together in space along similar trajectories will be more likely to be grouped into a single auditory stream, while sounds emitted by independently moving sources will more often be heard as two streams. Stimuli were derived from sound recordings in which the sound source motion was induced by walking humans. Although the results showed a clear effect of spatial separation, auditory motion had a negligible influence on stream segregation. Hence, auditory motion may not be used as a primitive cue in auditory stream segregation
Population Ecology of Waratahs, Telopea speciosissima (Proteaceae): Implications for Management of Fire-prone Habitats
Waratah (Telopea speciosissima) post-fire floral displays are a prominent feature of the landscape in Royal National Park and elsewhere in southeastern Australia, but factors governing the persistence of the species are poorly known. We examined long term patterns of fecundity, recruitment and survival of waratahs in Royal NP in relation to two major wildfires. Flowering occurred mainly over 3 years following both the 1994 and 2001 fi res, but fewer plants flowered, fewer seeds were produced and fewer seedlings established after the 2001 fi re. After the 1994 fire, limited seed dispersal resulted in most seedlings establishing near fruiting individuals. Only 14% of the plants that established as seedlings after the 1994 fire survived the 2001 fire. At the time of the 2001 fi re, these plants were 4-6 years old and post-fire survival was highest in older plants. A logistic model predicts that it would take 5.9 (95% CI 5.4-7.5) years of growth after germination for plants to have greater than 25% survival probability if burnt (equivalent to a fire return period of about 9 years). Waratahs are long lived, have long primary juvenile periods and occasional opportunities for recruitment. Each fire may not lead to successful recruitment. While recruitment failure after one or more fires may not be significant, understanding the proximate factors that limit recruitment is important to predict the impact of long term changes such as altered fire regimes under a changing climate
Tree Resin Flow Dynamics during an Experimentally Induced Attack by Ips avulsus, I. calligraphus, and I. grandicollis
The success of tree colonization by bark beetles depends on their ability to overcome host tree defenses, including resin exudation and toxic chemicals, which deter bark beetle colonization. Resin defenses during insect outbreaks are challenging to study in situ, as outbreaks are stochastic events that progress quickly and thus preclude the establishment of baseline observations of non-infested controls. We use synthetic aggregation pheromones to demonstrate that confined Ips bark beetle herbivory can be successfully initiated to provide opportunities for studying interactions between bark beetles and their hosts, including the dynamics of constitutive and induced resin exudation. In Pinus taeda L. plantations between 12 and 19 years old in North and South Carolina, U.S., trees were affixed with pheromone lures, monitored for evidence of bark beetle attacks, and resin samples were collected throughout the growing season. Baiting increased beetle herbivory to an extent sufficient to produce an induced resin response. Attacked trees exuded about three times more resin at some time than control trees. This supports previous work that demonstrated that information on constitutive resin dynamics alone provides an incomplete view of a host tree's resistance to bark beetle attack.Peer reviewe
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