The Philippine Sea Plate in the West Pacific is a unique natural laboratory to study subduction dynamics and the evolution of upper plate magmatism following subduction initiation. To investigate ...these processes, International Ocean Discovery Program Expedition 351 recovered at Site U1438, located in a rear‐arc position, a complete sedimentary sequence from recent age to the early Eocene and the top of the underlying volcanic basement. The recovered cores offered the opportunity to study for the first time and in unprecedented detail the styles, products, and timing of the volcanic events that marked the emplacement, growth, and demise of the Kyushu‐Palau volcanic arc following the inception of the Izu‐Bonin‐Mariana subduction. Here, we report a magnetostratigraphy for Site U1438 based on ∼60,000 remanence directions isolated from 1,063 archive half core sections and 429 discrete specimens. We identified 142 magnetic reversals and correlated 115 of them with the geomagnetic polarity timescale. When combined with additional biostratigraphic and geochronological constraints, our magnetostratigraphy allowed construction of a high‐resolution age model for Site U1438 and the determination of changes in sedimentation rates. We show that following subduction initiation at 52–50 Ma and the emplacement of basalts in the rear‐arc at 48.7 Ma, a diffuse volcanism in the rear‐arc (48.4–45.6 Ma) preceded the true emplacement of the Kyushu‐Palau arc at 40.2 Ma, which then grew through four compositionally distinct eruptive phases until 28.8 Ma. Subsequent rollback of the Pacific slab triggered rifting of the arc (28.8–24.3 Ma) and ultimately back‐arc spreading in the Shikoku and Parece Vela basins.
Plain Language Summary
During 2014 International Ocean Discovery Program Expedition 351 recovered a unique ∼1,200‐m‐thick sedimentary and volcanic sequence at Site U1438 within the Philippine Sea Plate, which forms the upper plate of the famous Izu‐Bonin‐Mariana (IBM) subduction system of West Pacific. The recovered rocks recorded the beginning of the subduction, and the emplacement, growth, and death of the Kyushu‐Palau volcanic arc that developed upon initiation of the IBM subduction, and may therefore hold the key to unravel the complex geological evolution of the entire West Pacific region. In this study, we reconstructed the polarity reversals of the geomagnetic field recorded at Site U1438 and produced a detailed magnetostratigraphy for this sedimentary sequence. We correlated 115 out of 142 identified magnetic reversals from our magnetostratigraphy to the reference geomagnetic polarity timescale to build a high‐resolution age model of Site U1438. This age model helped us to constrain in unprecedented detail the timing of the tectonic and magmatic events that followed IBM subduction initiation at 52–50 Ma. We show that the Kyushu‐Palau volcanic arc established in the upper plate 40.2 Ma, approximately 10–12 million years after the beginning of the Izu‐Bonin‐Mariana subduction, and then required another ∼11 million years until 28.8 Ma to grew to a full size through four compositionally distinct eruptive phases. Subsequent change in the subduction dynamics at 28.8 Ma yielded extension in the upper plate, causing the volcanic arc to split and ultimately shut down at 24.3 Ma and a new ocean basin (Shikoku and Parece Vela basins) to form within the Philippine Sea Plate.
Key Points
A magnetostratigraphy for the 1,600‐m‐thick sedimentary and volcanic sequence at International Ocean Discovery Program Site U1438 is presented
We produced a high‐resolution age model and sedimentation rates for Site U1438
We reconstructed the ages of the emplacement, rise, and death of the Kyushu‐Palau arc in the Philippine Sea Plate
Agri‐environment schemes (AES) are the primary policy mechanism for addressing farmland biodiversity declines across Europe. Despite previous studies on the impacts of AES on biodiversity, there is ...little empirical evidence on the scale of provision required to reverse declines.
Across three regions of lowland England with contrasting farm systems (arable, pastoral, mixed), we estimated avian population growth rates (PGRs) on farmland with high AES provision (‘higher‐tier’: average bird‐friendly option cover = 7.4%), low AES provision (‘lower‐tier’: 2.3%) and no bird‐friendly AES (‘no AES’). Ten‐year PGRs were derived for 24 species and three multi‐species groups comprising farmland‐associated species (‘farmland birds’), species of conservation concern (‘priority birds’) and species restricted to farmland (‘specialist birds’). We used PGRs to simulate the proportion of the regional farmland landscape that would have to be assigned to higher‐ and lower‐tier agreements to stabilise or increase populations.
In the arable and pastoral regions, 13/23 and 13/22 species, respectively, had more positive PGRs under higher‐tier AES than on no AES farmland (none had more negative PGRs), compared to 4/22 (positive) and 1/22 (negative) in the mixed region. Only two to four species per region exhibited more positive PGRs under lower‐tier AES compared to no AES farmland.
Multi‐species PGRs in the arable and pastoral regions increased from no AES (strong decline), to lower‐tier (decline or stability) to higher‐tier (moderate or strong increase). There was no overall AES effect in the mixed region.
To increase regional farmland bird populations by 10% over 10 years, 47% and 26% of the farmed landscape would need to be devoted to higher‐tier agreements in arable and pastoral landscapes respectively. This falls to 34% and 17% when higher‐tier is targeted at localities supporting higher abundances of target species, and to 29% and 10% when 30% of the farmed landscape is also devoted to lower‐tier. Priority and specialist birds require higher provision levels.
Policy implications. Where farmland bird recovery is an AES objective, farms should prioritise higher‐tier agreement delivery over lower‐tier. Farmland bird responses to AES provision are likely to vary regionally, but careful targeting will reduce the amount needed in the landscape.
Where farmland bird recovery is an AES objective, farms should prioritise higher‐tier agreement delivery over lower‐tier. Farmland bird responses to AES provision are likely to vary regionally, but careful targeting will reduce the amount needed in the landscape.
Subduction initiation is a critical link in the plate tectonic cycle. Intraoceanic subduction zones can form along transform faults and fracture zones, but how subduction nucleates parallel to ...mid‐ocean ridges, as in e.g., the Neotethys Ocean during the Jurassic, remains a matter of debate. In recent years, extensional detachment faults have been widely documented adjacent to slow‐spreading and ultraslow‐spreading ridges where they cut across the oceanic lithosphere. These structures are extremely weak due to widespread occurrence of serpentine and talc resulting from hydrothermal alteration, and can therefore effectively localize deformation. Here, we show geochemical, tectonic, and paleomagnetic evidence from the Jurassic ophiolites of Albania and Greece for a subduction zone formed in the western Neotethys parallel to a spreading ridge along an oceanic detachment fault. With 2‐D numerical modeling exploring the evolution of a detachment‐ridge system experiencing compression, we show that serpentinized detachments are always weaker than spreading ridges. We conclude that, owing to their extreme weakness, oceanic detachments can effectively localize deformation under perpendicular far‐field forcing, providing ideal conditions to nucleate new subduction zones parallel and close to (or at) spreading ridges. Direct implication of this, is that resumed magmatic activity in the forearc during subduction initiation can yield widespread accretion of suprasubduction zone ophiolites at or close to the paleoridge. Our new model casts the enigmatic origin of regionally extensive ophiolite belts in a novel geodynamic context, and calls for future research on three‐dimensional modeling of subduction initiation and how upper plate extension is associated with that.
Key Points:
Oceanic detachment faults provide ideal locus for subduction initiation
Balkans ophiolites preserve evidence for subduction initiation at detachments
Large ophiolite belts can form upon subduction initiation at detachment faults
Understanding the frequency, spatiotemporal dynamics and impacts of parasite coinfections is fundamental to developing control measures and predicting disease impacts. The European turtle dove ...(Streptopelia turtur) is one of Europe's most threatened bird species. High prevalence of infection by the protozoan parasite Trichomonas gallinae has previously been identified, but the role of this and other coinfecting parasites in turtle dove declines remains unclear. Using a high‐throughput sequencing approach, we identified seven strains of T. gallinae, including two novel strains, from ITS1/5.8S/ITS2 ribosomal sequences in turtle doves on breeding and wintering grounds, with further intrastrain variation and four novel subtypes revealed by the iron‐hydrogenase gene. High spatiotemporal turnover was observed in T. gallinae strain composition, and infection was prevalent in all populations (89%–100%). Coinfection by multiple Trichomonas strains was rarer than expected (1% observed compared to 38.6% expected), suggesting either within‐host competition, or high mortality of coinfected individuals. In contrast, coinfection by multiple haemosporidians was common (43%), as was coinfection by haemosporidians and T. gallinae (90%), with positive associations between strains of T. gallinae and Leucocytozoon suggesting a mechanism such as parasite‐induced immune modulation. We found no evidence for negative associations between coinfections and host body condition. We suggest that longitudinal studies involving the recapture and investigation of infection status of individuals over their lifespan are crucial to understand the epidemiology of coinfections in natural populations.
Dietary changes linked to the availability of anthropogenic food resources can have complex implications for species and ecosystems, especially when species are in decline. Here, we use recently ...developed primers targeting the ITS2 region of plants to characterize diet from faecal samples of four UK columbids, with particular focus on the European turtle dove (Streptopelia turtur), a rapidly declining obligate granivore. We examine dietary overlap between species (potential competition), associations with body condition in turtle doves and spatiotemporal variation in diet. We identified 143 taxonomic units, of which we classified 55% to species, another 34% to genus and the remaining 11% to family. We found significant dietary overlap between all columbid species, with the highest between turtle doves and stock doves (Columba oenas), then between turtle doves and woodpigeons (Columba palumbus). The lowest overlap was between woodpigeons and collared doves (Streptopelia decaocto). We show considerable change in columbid diets compared to previous studies, probably reflecting opportunistic foraging behaviour by columbids within a highly anthropogenically modified landscape, although our data for nonturtle doves should be considered preliminary. Nestling turtle doves in better condition had a higher dietary proportion of taxonomic units from natural arable plant species and a lower proportion of taxonomic units from anthropogenic food resources such as garden bird seed mixes and brassicas. This suggests that breeding ground conservation strategies for turtle doves should include provision of anthropogenic seeds for adults early in the breeding season, coupled with habitat rich in accessible seeds from arable plants once chicks have hatched.
Agri‐environment schemes (AES) have been criticized for being inadequately monitored and for not delivering the expected benefits to nature. Consequently, the Welsh Government funded a comprehensive ...programme of monitoring of AES between 2009 and 2012. The AES assessment focused on Tir Gofal (which translates as “Land in Care”) but also included the Organic Farming Scheme, and monitoring focused on a range of taxa of conservation importance: arable plants, grassland fungi, bats (six species), butterflies (three species), birds (five species), water vole and brown hare.
Field surveys were carried out on matched farms and fields within and outside of AES. Response variables were spatial trends of abundance, occurrence and species richness, and were modelled against AES status. Existing data were also available for two bird species.
Few differences were observed between AES and non‐AES farms and fields. Those that were observed were for species that use arable habitats (which are uncommon in Wales): arable plants, yellowhammers and brown hares. The lack of differences in non‐arable habitats may reflect the smaller contrast between AES and non‐AES management in these habitats. It may also reflect the original condition of habitat entered into AES prescriptions, as most non‐arable prescriptions were defined by mandatory management of existing habitats, rather than optional habitat creation or restoration, which is the case for most arable prescriptions.
Despite the lack of differences observed, AES may help to maintain populations of species, making it more likely that they will persist in the landscape. There is evidence, from this monitoring programme and elsewhere, that AES can increase the populations of species, when well targeted and implemented.
Policy implications. Our results indicate that Welsh Agri‐environment schemes (AES) have been only partly successful in achieving their stated aim of “maintaining and enhancing species abundance”. They can be used to improve AES design and management, both in Wales and more widely, by identifying and promoting effective management interventions, and by identifying ineffective management interventions and seeking alternatives. Comprehensive monitoring of AES, combined with specific targets regarding expected outcomes, is essential to determine whether AES are providing value for money.
Capsule Turtle Doves continue to show a strong population decline; territories were more likely to be retained in areas with more nesting habitat, and more suitable foraging habitat.Aim To determine ...which features of farmland in England are important for retaining Turtle Dove territoriesMethods Fifty-eight grid squares with recent records of territorial Turtle Doves were resurveyed, and squares retaining Turtle Dove territories compared with those from which Turtle Doves had been lost.Results Turtle Dove territories were detected in 48% of squares resurveyed. When correcting for the 70% detection rate of the survey methodology, territories were present in 66% of squares surveyed suggesting a 34% decline over a 2-year period. Established scrub and hedgerows > 4 m tall positively influenced Turtle Dove presence and abundance, as did standing water. Bare ground and fallow had positive effects on Turtle Dove abundance whereas grazed land negatively impacted abundance.Conclusion The positive effects of area of established scrub and volume of large hedgerows are likely to represent a declining density of birds selecting the best quality nest sites. We suggest instead that foraging habitat may be limiting distribution.
Studies incorporating the ecology of clinical and sub-clinical disease in wild populations of conservation concern are rare. Here we examine sub-clinical infection by Trichomonas gallinae in a ...declining population of free-living European Turtle Doves and suggest caseous lesions cause mortality in adults and nestlings through subsequent starvation and/or suffocation. We found a 100% infection rate by T. gallinae in adult and nestling Turtle Doves (n = 25) and observed clinical signs in three adults and four nestlings (28%). Adults with clinical signs displayed no differences in any skeletal measures of size but had a mean 3.7% reduction in wing length, with no overlap compared to those without clinical signs. We also identified T. gallinae as the suggested cause of mortality in one Red-legged Partridge although disease presentation was different. A minimum of four strains of T. gallinae, characterized at the ITS/5.8S/ITS2 ribosomal region, were isolated from Turtle Doves. However, all birds with clinical signs (Turtle Doves and the Red-legged Partridge) carried a single strain of T. gallinae, suggesting that parasite spill over between Columbidae and Galliformes is a possibility that should be further investigated. Overall, we highlight the importance of monitoring populations for sub-clinical infection rather than just clinical disease.
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