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- Creators: College of Liberal Arts and Sciences
- Creators: Marine Biological Laboratory (Woods Hole, Mass.)
Aim
To establish a chronology for late Quaternary avian extinction, extirpation and persistence in the Bahamas, thereby testing the relative roles of climate change and human impact as causes of extinction.
Location
Great Abaco Island (Abaco), Bahamas, West Indies.
Methods
We analysed the resident bird community as sampled by Pleistocene (> 11.7 ka) and Holocene (< 11.7 ka) fossils. Each species was classified as extinct (lost globally), extirpated (gone from Abaco but persists elsewhere), or extant (still resident on Abaco). We compared patterns of extinction, extirpation and persistence to independent estimates of climate and sea level for glacial (late Pleistocene) and interglacial (Holocene) times.
Results
Of 45 bird species identified in Pleistocene fossils, 25 (56%) no longer occur on Abaco (21 extirpated, 4 extinct). Of 37 species recorded in Holocene deposits, 15 (14 extirpated, 1 extinct; total 41%) no longer exist on Abaco. Of the 30 extant species, 12 were recovered as both Pleistocene and Holocene fossils, as were 9 of the 30 extirpated or extinct species. Most of the extinct or extirpated species that were only recorded from Pleistocene contexts are characteristic of open habitats (pine woodlands or grasslands); several of the extirpated species are currently found only where winters are cooler than in the modern or Pleistocene Bahamas. In contrast, most of the extinct or extirpated species recorded from Holocene contexts are habitat generalists.
Main conclusions
The fossil evidence suggests two main times of late Quaternary avian extirpation and extinction in the Bahamas. The first was during the Pleistocene–Holocene transition (PHT; 15–9 ka) and was fuelled by climate change and associated changes in sea level and island area. The second took place during the late Holocene (< 4 ka, perhaps primarily < 1 ka) and can be attributed to human impact. Although some species lost during the PHT are currently found where climates are cooler and drier than in the Bahamas today, a taxonomically and ecologically diverse set of species persisted through that major climate change but did not survive the past millennium of human presence.
Here, focusing on calcium, phosphorus and nitrogen, we used nutritional geometry to analyse individual-based data on foraging and extraction efficiencies, and combined these with data on reproduction and migratory behaviour to understand how a large herbivorous carnivore can complete its life cycle on a narrow and seemingly low quality bamboo diet.
Behavioural results showed that pandas during the year switched between four main food categories involving the leaves and shoots of two bamboo species available. Nutritional analysis suggests that these diet shifts are related to the concentrations and balances of calcium, phosphorus and nitrogen. Notably, successive shifts in range use and food type corresponded with a transition to higher concentrations and/or a more balanced intake of these multiple key constituents.
Our study suggests that pandas obligatorily synchronize their seasonal migration and reproduction with the disjunct nutritional phenologies of two bamboo species. This finding has potentially important implications for habitat conservation for this species and, more generally, draws attention to the need for understanding the nutritional basis of food selection in devising management plans for endangered species.
We present an analysis of the stellar populations of 102 visually selected early-type galaxies (ETGs) with spectroscopic redshifts (0.35 ≲ z ≲ 1.5) from observations in the Early Release Science program with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). We fit one- and two-component synthetic stellar models to the ETGs UV-optical-near-IR spectral energy distributions and find that a large fraction (∼40%) are likely to have experienced a minor (fYC ≲ 10% of stellar mass) burst of recent (tYC ≲ 1 Gyr) star formation. The measured age and mass fraction of the young stellar populations do not strongly trend with measurements of galaxy morphology. We note that massive (M > 1010.5M☼) recent star-forming ETGs appear to have larger sizes. Furthermore, high-mass, quiescent ETGs identified with likely companions populate a distinct region in the size-mass parameter space, in comparison with the distribution of massive ETGs with evidence of recent star formation (RSF). We conclude that both mechanisms of quenching star formation in disk-like ETGs and (gas-rich, minor) merger activity contribute to the formation of young stars and the size-mass evolution of intermediate redshift ETGs. The number of ETGs for which we have both HST WFC3 panchromatic (especially UV) imaging and spectroscopically confirmed redshifts is relatively small, therefore, a conclusion about the relative roles of both of these mechanisms remains an open question.
Serial femtosecond crystallography requires reliable and efficient delivery of fresh crystals across the beam of an X-ray free-electron laser over the course of an experiment. We introduce a double-flow focusing nozzle to meet this challenge, with significantly reduced sample consumption, while improving jet stability over previous generations of nozzles. We demonstrate its use to determine the first room-temperature structure of RNA polymerase II at high resolution, revealing new structural details. Moreover, the double flow-focusing nozzles were successfully tested with three other protein samples and the first room temperature structure of an extradiol ring-cleaving dioxygenase was solved by utilizing the improved operation and characteristics of these devices.
X-ray free-electron lasers provide novel opportunities to conduct single particle analysis on nanoscale particles. Coherent diffractive imaging experiments were performed at the Linac Coherent Light Source (LCLS), SLAC National Laboratory, exposing single inorganic core-shell nanoparticles to femtosecond hard-X-ray pulses. Each facetted nanoparticle consisted of a crystalline gold core and a differently shaped palladium shell. Scattered intensities were observed up to about 7 nm resolution. Analysis of the scattering patterns revealed the size distribution of the samples, which is consistent with that obtained from direct real-space imaging by electron microscopy. Scattering patterns resulting from single particles were selected and compiled into a dataset which can be valuable for algorithm developments in single particle scattering research.
Single particle diffractive imaging data from Rice Dwarf Virus (RDV) were recorded using the Coherent X-ray Imaging (CXI) instrument at the Linac Coherent Light Source (LCLS). RDV was chosen as it is a well-characterized model system, useful for proof-of-principle experiments, system optimization and algorithm development. RDV, an icosahedral virus of about 70 nm in diameter, was aerosolized and injected into the approximately 0.1 μm diameter focused hard X-ray beam at the CXI instrument of LCLS. Diffraction patterns from RDV with signal to 5.9 Ångström were recorded. The diffraction data are available through the Coherent X-ray Imaging Data Bank (CXIDB) as a resource for algorithm development, the contents of which are described here.
