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Weighting effective number of species measures by abundance weakens detection of diversity responsesmore » « less
Abstract The effective number of species (
ENS ) has been proposed as a robust measure of species diversity that overcomes several limitations in terms of both diversity indices and species richness (SR). However, it is not yet clear ifENS improves interpretation and comparison of biodiversity monitoring data, and ultimately resource management decisions.We used simulations of five stream macroinvertebrate assemblages and spatially extensive field data of stream fishes and mussels to show (a) how different
ENS formulations respond to stress and (b) how diversity–environment relationships change with values ofq , which weightENS measures by species abundances.Values of
ENS derived from whole simulated assemblages with all species weighted equally (true SR) steadily decreased as stress increased, andENS ‐stress relationships became weaker and more different among assemblages with increased weighting.The amount of variation in
ENS across the fish and mussel assemblages that was associated with environmental gradients decreased with increasingq .Synthesis and applications . Species diversity is valued by many human societies, which often have policies designed to protect and restore it. Natural resources managers and policy makers may use species richness and diversity indices to describe the status of ecological communities. However, these traditional diversity measures are known subject to limitations that hinder their interpretation and comparability. The effective number of species (ENS ) was proposed to overcome the limitations. Unfortunately, our analyses show thatENS does not improve interpretability of how species diversity responds to either stress or natural environmental gradients. Moreover, incorporating the relative abundance of individuals in different species (evenness) into diversity measures as implemented inENS can actually weaken detection of diversity responses. Natural resources managers and policy makers therefore need to be cautious when interpreting diversity measures, includingENS , whose values are jointly influenced by richness and evenness. We suggest that both researchers and practitioners measure and report three aspects of diversity (species richness, evenness, and composition) separately when assessing and monitoring the diversity of ecological communities. -
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Abstract The development of nonfullerene acceptors has brought polymer solar cells into a new era. Maximizing the performance of nonfullerene solar cells needs appropriate polymer donors that match with the acceptors in both electrical and morphological properties. So far, the design rationales for polymer donors are mainly borrowed from fullerene‐based solar cells, which are not necessarily applicable to nonfullerene solar cells. In this work, the influence of side chain length of polymer donors based on a set of random terpolymers PTAZ‐TPD10‐C
n on the device performance of polymer solar cells is investigated with three different acceptor materials, i.e., a fullerene acceptor [70]PCBM, a polymer acceptor N2200, and a fused‐ring molecular acceptor ITIC. Shortening the side chains of polymer donors improves the device performance of [70]PCBM‐based devices, but deteriorates the N2200‐ and ITIC‐based devices. Morphology studies unveil that the miscibility between donor and acceptor in blend films depends on the side chain length of polymer donors. Upon shortening the side chains of the polymer donors, the miscibility between the donor and acceptor increases for the [70]PCBM‐based blends, but decreases for the N2200‐ and ITIC‐based blends. These findings provide new guidelines for the development of polymer donors to match with emerging nonfullerene acceptors. -
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Abstract The generation of a high‐frequency plasmaspheric hiss (HFPH) wave observed by Van Allen Probes is studied in this letter for the first time. The wave has a moderate power spectral density (∼10−6 nT2/Hz), with a frequency range extended from 2 to 10 kHz. The correlated observations of waves and particles indicate that HFPH is associated with the enhancement of electron flux during the substorm on 6 January 2014. Calculations of the wave linear growth rate driven by the fitted electron phase space density show that the electron distribution after the substorm onset is efficient for the HFPH generation. The energy of the contributing electrons is about 1–2 keV, which is consistent with the observation. These results support that the observed HFPH is likely to be generated locally inside the plasmasphere due to the instability of injected kiloelectron volt electrons.
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Abstract Two donor–acceptor (D–A) conjugated polymers composed of the same ratio of 5‐fluorobenzothiadiazole and thiophene subunits are synthesized through different routes, providing a precisely regioregular (
2TRR ) and a random (2TRA ) polymer structures. Detailed structural analyses indicate that the backbone of regioregular2TRR has only one donor segment of bithiophene, while the backbone of random2TRA consists of three different donor segments: thiophene, bithiophene, and terthiophene (in a ratio of 0.16:0.68:0.16). Synergetic contributions from these segments allow the “tetrapolymer”2TRA to achieve more favorable film morphology and a higher hole‐mobility relative to2TRR . Consequently, the random polymer2TRA achieves a substantially higher power conversion efficiency (8.8%) than the regioregular polymer2TRR (5.1%). Notably, the “tetrapolymer”2TRA is readily synthesized from two monomers, rather than through complex conventional preparation required for similar multipolymers. These findings provide a novel route toward the design and synthesis of multipolymeric materials and demonstrate their potential advantages in high‐performance organic electronic applications.
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