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The geometric and electronic structure of [Hg(o‐C6F4)]3 (1) in the gas phase, i. e. free of intermolecular interactions, was determined by a synchronous gas‐phase electron diffraction/mass spectrometry experiment (GED/MS), complemented by quantum chemical calculations. 1 is stable up to 498 K and the gas phase contains a single molecular form: the trimer [Hg(o‐C6F4)]3. It has a planar structure of D3h symmetry with a Hg–C distance of 2.075(5) Å and a Hg–Hg distance of 3.614(7) Å (both rh1). Structural differences between the crystalline and gaseous state have been analyzed. Different DFT functional‐basis combinations were tested, demonstrating the importance to consider the relativistic effects of the mercury atoms. The combination PBE0/MWB(Hg),cc‐pVTZ(C,F) turned out to be the most appropriate for the geometry optimization of such organomercurials. The electronic structure of 1, the nature of the chemical bonding in C−Hg−C fragments and the nature of the Hg⋅⋅⋅Hg interactions have been analyzed in terms of the Natural Bond Orbital (NBO) and Quantum Theory of Atoms in Molecules (QTAIM) approaches. The influence of the nature of halogen substitution on the structure of the molecules in the series [Hg(o‐C6H4)]3, [Hg(o‐C6F4)]3, [Hg(o‐C6Cl4)]3, [Hg(o‐C6Br4)]3 was also analyzed. [ABSTRACT FROM AUTHOR]

Alloying is a general strategy for modulating the electronic structures of catalyst materials. Compared to more common solid–solution alloys, intermetallic alloys feature well‐defined atomic arrangements and provide the unique platform for studying the structure‐performance correlations. It is, unfortunately, synthetically challenging to prepare the nanostructures of intermetallic alloys for catalysis research. In this contribution, we prepare intermetallic Pd3Bi nanocrystals of a uniform size via a facile solvothermal method. These nanocrystals can phase‐transform into solid solution alloy via thermal annealing while retaining a similar composition and size. In 0.1 M KHCO3 aqueous solution, the intermetallic Pd3Bi can selectively reduce CO2 to formate with high selectivity (≈100 %) and stability even at <‐0.35 V versus reversible hydrogen electrode, whereas the solid solution alloy has limited formate selectivity of <60 %. Such unique phase‐dependence is understood via theoretical simulations showing that the crystallographic ordering of Pd and Bi atoms within intermetallic alloys can suppress CO poisoning and enhance the *OCHO adsorption during electrochemical CO2 reduction to formate. [ABSTRACT FROM AUTHOR]

Rodent population cycles have fascinated scientists for a long time. Among various hypotheses, an interaction of an extrinsic factor (predation) with intrinsic factors (e.g., sociality and dispersal) was suggested to lead to the generation of population cycles. Here, we tested this hypothesis with an individual-based model fully parameterized with an exceptionally rich empirical database on vole life histories. We employed a full factorial design that included models with the following factors: predation only, predation and sociality, predation and dispersal, and predation and both sociality and dispersal. A comprehensive set of metrics was used to compare results of these four models with the long-term population dynamics of natural vole populations. Only the full model, which included both intrinsic factors and predation, yielded cycle periods, amplitudes, and autumn population sizes closest to those observed in nature. Our approach allows to model, as emergent properties of individual life histories, the sort of nonlinear density- and phase-dependence that is expected to destabilize population dynamics. We suggest that the individual-based approach is useful for addressing the effects of other mechanisms on rodent populations that operate at finer temporal and spatial scales than have been explored with models so far. [ABSTRACT FROM AUTHOR]

The rates and causes of juvenile mortality are central features of the dynamics and conservation of large mammals, like woodland caribou ( Rangifer tarandus caribou (Gmelin, 1788)), but intrinsic and extrinsic factors may be modified by variations in animal abundance. We tested the influences of population size, climate, calf weight and sex on survival to 6 months of age of 1241 radio-collared caribou calves over three decades, spanning periods of population growth (1979-1997) and decline (2003-2012) in Newfoundland, Canada. Daily survival rates were higher and rose more quickly with calf age during the population growth period compared to the decline. Population size (negatively) and calf weight (positively) affected survival during the decline but neither had a detectable influence during the growth phase. Sex, climate and plant productivity (the latter two derived from the North Atlantic Oscillation and Normalized Difference Vegetation Index, respectively) exerted minimal influence during either phase. Predation was the dominant source of mortality. The mean percentage of calves killed by predators was 30 % higher during the decline compared to the growth phase. Black bears ( Ursus americanus) and lynx ( Lynx canadensis) were the major predators during the population increase but this changed during the decrease to black bears and coyotes ( Canis latrans). Our findings are consistent with the hypothesis that Newfoundland caribou experienced phase-dependent survival mediated proximally by predation and competition for food. [ABSTRACT FROM AUTHOR]

Nonlinear and irregular population dynamics may arise as a result of phase dependence and coexistence of multiple attractors. Here we explore effects of climate and density in the dynamics of a highly fluctuating population of wild reindeer (Rangifer tarandus plalyrhynchus) on Svalbard observed over a period of 29 years. Time series analyses revealed that density dependence and the effects of local climate (measured as the degree of ablation [melting] of snow during winter) on numbers were both highly nonlinear: direct negative density dependence was found when the population was growing (Rt > 0) and during phases of the North Atlantic Oscillation (NAO) characterized by winters with generally high (1979-1995) and low (1996-2007) indices, respectively. A growth-phase-dependent model explained the dynamics of the population best and revealed the influence of density-independent processes on numbers that a linear autoregressive model missed altogether. In particular, the abundance of reindeer was enhanced by ablation during phases of growth (Rt > 0), an observation that contrasts with the view that periods of mild weather in winter are normally deleterious for reindeer owing to icing of the snowpack. Analyses of vital rates corroborated the nonlinearity described in the population time series and showed that both starvation mortality in winter and fecundity were nonlinearly related to fluctuations in density and the level of ablation. The erratic pattern of growth of the population of reindeer in Adventdalen seems, therefore, to result from a combination of the effects of nonlinear density dependence, strong density-dependent mortality, and variable density independence related to ablation in winter. [ABSTRACT FROM AUTHOR]

Climate can affect population dynamics in indirect ways via nonadditive forcing by external variables on internal demographic rates. Current analytical techniques, employed in population ecology, fail to explicitly include nonadditive interactions between internal and external variables, and therefore cannot efficiently address indirect climate effects. Here, we present the results of an analysis, employing specifically developed statistical methodology, on density-dependent survival of walleye pollock (Theragra chalcograinma) prerecruitment stages in relation to background environmental variables in the Gulf of Alaska. We found that spring winds and water temperature mediate the intensity of density-dependent survival from the eggs to the age-0 stage. Fall water temperature and juvenile pollock predator abundance mediate density dependence from the age-0 to the age- 1 stage. The inclusion of such nonadditive and nonlinear effects in a population dynamics model improved our ability to simulate pollock recruitment. Our results point to the importance of understanding nonadditive and nonlinear interactions between external (climate) and internal factors in the presence of underlying environmental variation. These topics are discussed in the context of current research priorities in population ecology and conservation biology. [ABSTRACT FROM AUTHOR]