The scale-dependence of population density–body mass allometry: Statistical artefact or biological mechanism?

The relation between population density and body mass has vexed ecologists for nearly 30 years as a consequence of high variability in the observed slope of the relation: No single generalisation of the relation has been accepted as universally representative. Here, we use a simple computational approach to examine how observational scale (the body mass range considered) determines variation in the density–mass pattern. Our model relies on two assumptions: (1) resources are partitioned in an unbiased manner among species with different masses; (2) the number of individuals that can be supported by a given quantity of resources is related to their metabolic rate (which is a function of their mass raised to the power of a scaling coefficient, b). We show that density (1) scales as a function of body mass raised to the power of ?b on average, but (2) the slope of the relation varies considerably at smaller scales of observation (over narrow ranges of body mass) as a consequence of details of species’ ecology associated with resource procurement. Historically, the effect of body mass range on the slope of the density–mass relation has been unfailingly attributed to a statistical effect. Here we show that the effect of body mass range on the slope of the density–mass relation may equally result from a biological mechanism, though we find it impossible to distinguish between the two. We observe that many of the explanations that have been offered to account for the variability in the slope of the relation invoke mechanisms associated with differences in body mass and we therefore suggest that body mass range itself might be the most important explanatory factor. Notably, our results imply that the energetic equivalence rule should not be expected to hold at smaller scales of observation, which suggests that it may not be possible to scale the mass- and temperature-dependence of organism metabolism to predict patterns at higher levels of biological organisation at smaller scales of observation.     

Modeling of Environmental Effects in Genome-Wide Association Studies Identifies SLC2A2 and HP as Novel Loci Influencing Serum Cholesterol Levels

Genome-wide association studies (GWAS) have identified 38 larger genetic regions affecting classical blood lipid levels without adjusting for important environmental influences. We modeled diet and physical activity in a GWAS in order to identify novel loci affecting total cholesterol, LDL cholesterol, HDL cholesterol, and triglyceride levels. The Swedish (SE) EUROSPAN cohort (N _SE = 656) was screened for candidate genes and the non-Swedish (NS) EUROSPAN cohorts (N _NS = 3,282) were used for replication. In total, 3 SNPs were associated in the Swedish sample and were replicated in the non-Swedish cohorts. While SNP rs1532624 was a replication of the previously published association between CETP and HDL cholesterol, the other two were novel findings. For the latter SNPs, the p-value for association was substantially improved by inclusion of environmental covariates: SNP rs5400 (p _{SE,unadjusted} = 3.6×10⁻⁵, p _SE,adjusted = 2.2×10⁻⁶, p _{NS,unadjusted} = 0.047) in the SLC2A2 (Glucose transporter type 2) and rs2000999 (p _{SE,unadjusted} = 1.1×10⁻³, p _SE,adjusted = 3.8×10⁻⁴, p _{NS,unadjusted} = 0.035) in the HP gene (Haptoglobin-related protein precursor). Both showed evidence of association with total cholesterol. These results demonstrate that inclusion of important environmental factors in the analysis model can reveal new genetic susceptibility loci.     

Applications of microwave dielectric heating in environment-related heterogeneous gas-phase catalytic systems

The application of microwave dielectric heating in a range of environment-related heterogeneous catalytic reaction systems has been reviewed. The reactions investigated include the decomposition of hydrogen sulfide, the reduction of sulfur dioxide with methane, the reformation of methane by carbon dioxide, the hydrodesulfurization of thiophene, and the oxidative coupling of methane. The interaction of microwave irradiation with heterogeneous catalytic systems and its consequence for the microwave heating behaviour of catalysts have been examined. The effect/mechanism of microwave dielectric heating on heterogeneous catalytic reaction systems has also been discussed.     

Temperature preferences of the mite, Alaskozetes antarcticus, and the collembolan, Cryptopygus antarcticus from the maritime Antarctic

Abstract. The thermal preferences of Alaskozetes antarcticus (Acari, Cryptostigmata) and Cryptopygus antarcticus (Collembola, Isotomidae) were investigated over 6 h within a temperature gradient (?3 to +13 °C), under 100% relative humidity (RH) conditions. After 10 days of acclimation at ?2 or +11 °C, individual supercooling points (SCP) and thermopreferences were assessed, and compared with animals maintained for 10 days under fluctuating field conditions (?6 to +7 °C). Acclimation at ?2 °C lowered the mean SCP of both A. antarcticus (?24.2 ± 9.1) and C. antarcticus (?14.7 ± 7.7) compared to field samples (?19.0 ± 9.0 and ?10.7 ± 5.2, respectively). Acclimation at +11 °C increased A. antarcticus mean SCP values (?13.0 ± 8.5) relative to field samples, whereas those of C. antarcticus again decreased (?16.7 ± 9.1). Mites acclimated under field conditions or at +11 °C selected temperatures between ?3 and +1 °C. After acclimation at ?2 °C, both species preferred +1 to +5 °C. Cryptopygus antarcticus maintained under field conditions preferred +5 to +9 °C, whereas individuals acclimated at +11 °C selected +9 to +13 °C. For A. antarcticus, thermopreference was not influenced by its cold hardened state. The distribution of field specimens was further assessed within two combined temperature and humidity gradient systems: (i) 0–3 °C/12% RH, 3–6 °C/33% RH, 6–9 °C/75% RH and 9–12 °C/100% RH and (ii) 0–3 °C/100% RH, 3–6 °C/75% RH, 6–9 °C/33% RH and 9–12 °C/12% RH. In gradient (i), C. antarcticus distributed homogeneously, but, in gradient (ii), C. antarcticus preferred 0–3 °C/100% RH. Alaskozetes antarcticus selected temperatures between 0 and +6 °C regardless of RH conditions. Cryptopygus antarcticus appears better able than A. antarcticus to opportunistically utilize developmentally favourable thermal microclimates, when moisture availability is not restricted. The distribution of A. antarcticus appears more influenced by temperature, especially during regular freeze‐thaw transitions, when this species may select low temperature microhabitats to maintain a cold‐hardened state.     

Effects of an Introduced Piscivore on Native Trout: Insights from a Demographic Model

Introductions of exotic species pose a significant threat to the persistence of many native populations, including many inland fishes. In 1994, piscivorous lake trout (Salvelinus namaycush) were discovered in Yellowstone Lake, Yellowstone National Park, Wyoming, USA, one of the last strongholds of the native Yellowstone cutthroat trout (Oncorhynchus clarki bouvieri). Predation by lake trout is expected to lead to a substantial decline in the native cutthroat trout population, which may have significant negative consequences for terrestrial predators that depend on cutthroat trout for prey and for the recreational fishery of the Park. We developed a matrix demographic model for the cutthroat trout population in Yellowstone Lake to identify the life stages that are most critical for understanding population dynamics. Parameter estimates (vital rates) were manipulated to explore the possible consequences of lake trout invasion. Comparisons of our results with current estimates of population trend and age structure suggested that our model reflected current conditions of the system. Elasticity analysis of the model revealed that population growth was most sensitive to annual survival of young trout, the group that is expected to be most vulnerable to lake trout predation. Projection of our deterministic model suggested that, in addition to a decline in abundance of cutthroat trout, the effects of lake trout may be manifest as changes in age and breeding structure of the population. Simulations of a stochastic version of the model indicated that a 60% or greater decline in the cutthroat trout population could be expected within 100 years if the lake trout population were permitted to grow uncontrolled. However, an effective control strategy that prevented the establishment of a large population of lake trout substantially reduced population decline, although the reduction in the availability of adult trout to terrestrial predators and anglers may be still be substantial (20–40%). In addition to current control activities in place in the Park, we recommend a renewed emphasis on understanding and monitoring juvenile life stages of cutthroat trout. Our results demonstrate the value of existing data sets for developing models to estimate the potential impact of biological invasions on the management and conservation of native populations, especially when opportunities and resources for additional empirical studies are limited.     

Challenges and science-based implications for modern management and conservation of European ungulate populations

Wildlife management systems face growing challenges to cope with increasingly complex interactions between wildlife populations, the environment and human activities. In this position statement, we address the most important issues characterising current ungulate conservation and management in Europe. We present some key points arising from ecological research that may be critical for a reassessment of ungulate management in the future.     

Spiritual Struggles and Interleukin-6: Assessing Potential Benefits and Potential Risks

The purpose of this study is to evaluate the relationship between spiritual struggles and levels of interleukin-6 (IL-6) with a subsample (N = 943) of participants who took part in a nationwide survey. This study, which was completed in 2014, was conducted in the United States. Spiritual struggles refer to difficulties that a person may encounter with his or her faith and include having a troubled relationship with God, encountering difficulties with religious others, and being unable to find a sense of ultimate meaning in life. Based on the notion that spiritual struggles may be associated with personal growth as well physical health problems, it was hypothesized that there is a nonlinear relationship between the two: levels of IL-6 will decline at relatively low levels of spiritual struggles, but levels of IL-6 will increase as spiritual struggles become more severe. The findings support this hypothesis and suggest there is a quadratic relationship between spiritual struggles and IL-6. The clinical implications of these findings are discussed.     

Parasite‐associated mortality in a long‐lived mammal: Variation with host age,sex, and reproduction

Parasites can cause severe host morbidity and threaten survival. As parasites are generally aggregated within certain host demographics, they are likely to affect a small proportion of the entire population, with specific hosts being at particular risk. However, little is known as to whether increased host mortality from parasitic causes is experienced by specific host demographics. Outside of theoretical studies, there is a paucity of literature concerning dynamics of parasite‐associated host mortality. Empirical evidence mainly focuses on short‐lived hosts or model systems, with data lacking from long‐lived wild or semi‐wild vertebrate populations. We investigated parasite‐associated mortality utilizing a multigenerational database of mortality, health, and reproductive data for over 4,000 semi‐captive timber elephants (Elephas maximus), with known causes of death for mortality events. We determined variation in mortality according to a number of host traits that are commonly associated with variation in parasitism within mammals: age, sex, and reproductive investment in females. We found that potentially parasite‐associated mortality varied significantly across elephant ages, with individuals at extremes of lifespan (young and old) at highest risk. Mortality probability was significantly higher for males across all ages. Female reproducers experienced a lower probability of potentially parasite‐associated mortality than females who did not reproduce at any investigated time frame. Our results demonstrate increased potentially parasite‐associated mortality within particular demographic groups. These groups (males, juveniles, elderly adults) have been identified in other studies as susceptible to parasitism, stressing the need for further work investigating links between infection and mortality. Furthermore, we show variation between reproductive and non‐reproductive females, with mothers being less at risk of potentially parasite mortality than nonreproducers.