ABSTRACT
Assessing the role of local populations in a landscape context has become increasingly important in the fields of conservation biology and ecology. A growing number of studies attempt to ...determine the source–sink status of local populations. As the source–sink concept is commonly used for management decisions in nature conservation, accurate assessment approaches are crucial. Based on a systematic literature review of studies published between 2002 and 2013, we evaluated a priori predictions on methodological and biological factors that may influence the occurrence of source or sink populations. The review yielded 90 assessments from 73 publications that included qualitative and quantitative evidence for either source or sink population(s) for one or multiple species. Overall, sink populations tended to occur more often than source populations. Moreover, the occurrence of source or sink populations differed among taxonomic classes. Sinks were more often found than sources in mammals, while there was a non‐significant trend for the opposite to be true for amphibians. Univariate and multivariate analyses showed that the occurrence of sources was positively related to connectivity of local populations. Our review furthermore highlights that more than 25 years after Pulliam's widely cited publication on ‘sources, sinks, and population regulation’, in‐depth assessments of the source–sink status of populations based on combined consideration of demographic parameters such as fecundity, survival, emigration and immigration are still scarce. To increase our understanding of source–sink systems from ecological, evolutionary and conservation‐related perspectives, we recommend that forthcoming studies on source–sink dynamics should pay more attention to the study design (i.e. connectivity of study populations) and that the assessment of the source–sink status of local populations is based on λ values calculated from demographic rates.
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Pastoralism is spreading in Central Africa, where many protected areas are under consideration to be opened for grazing, in particular hunting zones. Here we document the loss of ...biodiversity followed by an influx of transhumant pastoralism into previously uninhabited and virtually pristine habitat in the Central African Republic. Our track count and camera trap surveys of 2012, 2016 and 2017 evidence a reduction of apex predators, particularly Northern lions (Panthera leo leo) and African wild dogs (Lycaon pictus), of which about 95% and 80% were lost, respectively. While some large herbivores such as Western African buffalo (Syncerus caffer nanus) or Eastern giant eland (Tragelaphus derbianus gigas) were also strongly reduced, most herbivores remain at significant densities. Apex predator populations did thus not crash due to a lack of prey, but rather due to targeted killing by herders and accompanying merchants, as interviews confirmed. Our call-up survey suggests that lions were attracted by livestock outside of actively protected areas, were they got poisoned or shot. These findings exemplify the potential negative effects of pastoralism on wildlife even in large areas with intact habitat. We thus caution against the transformation of protected areas or hunting zones into pasture land, unless such a land-use change can be carefully managed and strictly controlled.
Atomically precise graphene nanoribbons (GNRs) are a promising emerging class of designer quantum materials with electronic properties that are tunable by chemical design. However, many challenges ...remain in the device integration of these materials, especially regarding contacting strategies. We report on the device integration of uniaxially aligned and non-aligned 9-atom wide armchair graphene nanoribbons (9-AGNRs) in a field-effect transistor geometry using electron beam lithography-defined graphene electrodes. This approach yields controlled electrode geometries and enables higher fabrication throughput compared to previous approaches using an electrical breakdown technique. Thermal annealing is found to be a crucial step for successful device operation resulting in electronic transport characteristics showing a strong gate dependence. Raman spectroscopy confirms the integrity of the graphene electrodes after patterning and of the GNRs after device integration. Our results demonstrate the importance of the GNR-graphene electrode interface and pave the way for GNR device integration with structurally well-defined electrodes.
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A major evolutionary force driving functionally referential alarm calls is the need for different strategies to escape various predator types in complex structured habitats. In contrast, a single ...escape strategy appears to be sufficient in less‐structured open habitats, and under such conditions urgency‐dependent alarm calls may be favored. Nevertheless, some species, such as meerkats (Suricata suricatta), have evolved functionally referential alarm calls despite living in open areas, using only bolt‐holes for retreat. To understand the evolution of different alarm call systems, we investigated the calls of sympatric Cape ground squirrels (Xerus inauris) and compared their antipredator and foraging behavior with that of meerkats. Cape ground squirrels emitted urgency‐dependent alarm calls and responded to playbacks depending on urgency, not predator type. Vigilance behavior and habitat use differed between the two species. Meerkats roam widely to find prey and for efficient foraging depend on coordinated predator vigilance and escape behavior. As herbivores with smaller territories, Cape ground squirrels depend less on coordinated antipredator behavior, and urgency‐dependent alarm calls encode all essential information. We conclude that habitat complexity does not explain the evolution of functionally referential alarm calls in all species, and other constraints, such as the need to coordinate group movements to maintain foraging efficiency, could be more relevant.
Medical ultrasonic arrays are typically characterized in controlled water baths using measurements by a hydrophone, which can be translated with a positioning stage. Characterization of 3D acoustic ...fields conventionally requires measurements at each spatial location, which is tedious and time-consuming, and may be prohibitive given limitations of experimental setup (e.g., the bath and stage) and measurement equipment (i.e., the hydrophone). Moreover, with the development of new ultrasound sequences and modalities, multiple measurements are often required to characterize each imaging mode to ensure performance and clinical safety. Acoustic holography allows efficient characterization of source transducer fields based on single plane measurements. In this work, we explore the applicability of a re-radiation method based on the Rayleigh⁻Sommerfeld integral to medical imaging array characterization. We show that source fields can be reconstructed at single crystal level at wavelength resolution, based on far-field measurements. This is herein presented for three practical application scenarios: for identifying faulty transducer elements; for characterizing acoustic safety parameters in focused ultrasound sequences from 2D planar measurements; and for estimating arbitrary focused fields based on calibration from an unfocused sound field and software beamforming. The results experimentally show that the acquired pressure fields closely match those estimated using our technique.
This work reports on a method to open nanoscale gaps in h-shaped graphene nano-constrictions by electrical breakdown at room temperature and pressure below 10−5 mbar. The method was validated on 275 ...devices, fabricated on eight different chips, using Chemical Vapor Deposition (CVD)-grown graphene from in-house production and from two commercial sources. The gap width was estimated by fitting the I–V traces after electrical breakdown with the Simmons model for the intermediate-voltage range. The statistics on the collected data demonstrates that the method results in normally distributed nanoscale gaps in h-shaped graphene nano-constrictions, with an estimated average width centered around 1 nm and a gap fabrication yield of 95%.
Wireless medical sensors typically utilize electromagnetic coupling or ultrasound for energy transfer and sensor interrogation. Energy transfer and management is a complex aspect that often limits ...the applicability of implantable sensor systems. In this work, we report a new passive temperature sensing scheme based on an acoustic metamaterial made of silicon embedded in a polydimethylsiloxane matrix. Compared to other approaches, this concept is implemented without additional electrical components in situ or the need for a customized receiving unit. A standard ultrasonic transducer is used for this demonstration to directly excite and collect the reflected signal. The metamaterial resonates at a frequency close to a typical medical value (5 MHz) and exhibits a high-quality factor. Combining the design features of the metamaterial with the high-temperature sensitivity of the polydimethylsiloxane matrix, we achieve a temperature resolution of 30 mK. This value is below the current standard resolution required in infrared thermometry for monitoring postoperative complications (0.1 K). We fabricated, simulated, in vitro tested, and compared three acoustic sensor designs in the 29-43 °C (~302-316 K) temperature range. With this concept, we demonstrate how our passive metamaterial sensor can open the way toward new zero-power smart medical implant concepts based on acoustic interrogation.
In social species that cooperatively defend territories the decision to retreat or attack in contests between groups is likely to depend on ecological and social factors. Previous studies have ...emphasized the importance of the encounter location or the size of competing groups on the outcome. In addition, the identity of the intruder, whether familiar or stranger, may also play a role. To test whether the same factors affect the resident group's decisions already at the beginning of contests, we simulated intergroup encounters in banded mongooses (Mungos mungo). When spotting rival groups banded mongooses emit "screeching calls" which lead group members to bunch up. With playbacks of these calls, we tested how the groups' response was affected by the following factors: 1) the location of the playback in relation to their territory (exclusive use vs. overlap); 2) the number of resident individuals; and 3) the origin of calls (neighbor vs. stranger) used. Subjects were more likely to approach the loudspeakers and arrive within 1 m of the speakers in the exclusive use zone than in the overlap zone. Moreover, larger groups tended to be more likely to move toward the loudspeakers and were also more likely to arrive there. The origin of calls used in the playbacks did not affect the groups' responses. These findings exemplify the importance of the combined effect of location and group size on group decisions during impending intergroup contest.
Atomically precise graphene nanoribbons (GNRs) are increasingly attracting interest due to their largely modifiable electronic properties, which can be tailored by controlling their width and edge ...structure during chemical synthesis. In recent years, the exploitation of GNR properties for electronic devices has focused on GNR integration into field‐effect‐transistor (FET) geometries. However, such FET devices have limited electrostatic tunability due to the presence of a single gate. Here, on the device integration of 9‐atom wide armchair graphene nanoribbons (9‐AGNRs) into a multi‐gate FET geometry, consisting of an ultra‐narrow finger gate and two side gates is reported. High‐resolution electron‐beam lithography (EBL) is used for defining finger gates as narrow as 12 nm and combine them with graphene electrodes for contacting the GNRs. Low‐temperature transport spectroscopy measurements reveal quantum dot (QD) behavior with rich Coulomb diamond patterns, suggesting that the GNRs form QDs that are connected both in series and in parallel. Moreover, it is shown that the additional gates enable differential tuning of the QDs in the nanojunction, providing the first step toward multi‐gate control of GNR‐based multi‐dot systems.
The device integration of 9‐atom wide armchair graphene nanoribbons (GNR) into a multi‐gate field‐effect transistor geometry is reported. Low‐temperature transport spectroscopy measurements reveal quantum dot (QD) behavior with rich Coulomb diamond pattern. It is shown that the additional gates enable differential tuning of the QDs in the nanojunction, providing the first step toward multi‐gate control of GNR‐based multi‐dot systems.
Graphene is an excellent 2D material for vertical organic transistors electrodes due to its weak electrostatic screening and field-tunable work function, in addition to its high conductivity, ...flexibility and optical transparency. Nevertheless, the interaction between graphene and other carbon-based materials, including small organic molecules, can affect the graphene electrical properties and therefore, the device performances. This work investigates the effects of thermally evaporated C60 (n-type) and Pentacene (p-type) thin films on the in-plane charge transport properties of large area CVD graphene under vacuum. This study was performed on a population of 300 graphene field effect transistors. The output characteristic of the transistors revealed that a C60 thin film adsorbate increased the graphene hole density by (1.65 ± 0.36) × 1012 cm−2, whereas a Pentacene thin film increased the graphene electron density by (0.55 ± 0.54) × 1012 cm−2. Hence, C60 induced a graphene Fermi energy downshift of about 100 meV, while Pentacene induced a Fermi energy upshift of about 120 meV. In both cases, the increase in charge carriers was accompanied by a reduced charge mobility, which resulted in a larger graphene sheet resistance of about 3 kΩ at the Dirac point. Interestingly, the contact resistance, which varied in the range 200 Ω–1 kΩ, was not significantly affected by the deposition of the organic molecules.
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