Holocene forest development and maintenance on different substrates in the Klamath Mountains, northern California, USA

The influence of substrate on long-term vegetation dynamics has received little attention, and yet nutrient-limited ecosystems have some of the highest levels of endemism in the world. The diverse geology of the Klamath Mountains of northern California (USA) allows examination of the long-term influence of edaphic constraints in subalpine forests through a comparison of vegetation histories between nutrient-limited ultramafic substrates and terrain that is more fertile. Pollen and charcoal records spanning up to 15000 years from ultramafic settings reveal a distinctly different vegetation history compared to other soil types. In non-ultramafic settings, the dominant trees and shrubs shifted in elevation in response to Holocene climate variations resulting in compositional and structural changes, whereas on ultramafic substrates changes were primarily structural, not compositional. Fire activity was similar through most of the Holocene with the exception of declines over the last 4000 years on ultramafic substrates, likely due to the reduction of understory fuels and cooler wetter conditions than in the middle Holocene. These results suggest that the tree and shrub distributions were more responsive to past climate changes on non-ultramafic substrates compared to those on ultramafic substrates. The combination of these dynamics may help explain high levels of plant diversity in the Klamath Mountains and provide insights for managing these complex ecosystems.     

Composting of miscible cellulose acetate propionate-aliphatic polyester blends

A series of miscible blends consisting of cellulose acetate propionate (CAP) and poly(ethylene glutarate) (PEG) or poly(tetramethylene glutarate) (PTG) were evaluated in a static bench-scale simulated municipal compost environment. Samples were removed from the compost at different intervals, and the weight loss was determined before evaluation by gel permeation chromatography, scanning electron microscopy, and¹H NMR. The type of polyester (PEG versus PTG) in the blend made no difference in composting rates. At fixed CAP degree of substitution (DS), when the content of polyester in the blend was increased, the rate of composting and the weight loss due to composting increased. When the CAP was highly substituted, little degradation was observed within 30 days and almost all of the weight loss was ascribed to loss of polyester. Although the polyester was still observed to degrade faster, when the CAP DS was below approximately 2.0, both components are observed to degrade. The data suggests that initial degradation of the polyester is by chemical hydrolysis and the rate of this hydrolysis is very dependent upon the temperature profile of the compost and upon the DS of the CAP.     

Feeding the world's increasing population while limiting climate change impacts: linking N2O and CH4 emissions from agriculture to population growth

The global demand for agricultural products, including food, is rapidly increasing due to population growth and shifts in consumption patterns. The required increase in agricultural production is predominantly to be achieved in countries with relatively low agricultural production levels at present. These are mainly developing countries and countries in transition, the so-called non-Annex I countries of the UNFCCC. However, intensification of agricultural production systems is currently closely linked to high emissions of greenhouse gases notably nitrous oxide (N₂O) and methane (CH₄). In this paper the relations between population growth, agricultural development and emissions of N₂O and CH₄ were assessed for 10 non-Annex I countries, viz. China, India, Vietnam, Brazil, Argentina, Mexico, Mongolia, Nigeria, Tanzania and South Africa. We combined FAO data on agricultural production levels, CENSUS data on population statistics and EDGAR data on N₂O and CH₄ emissions. The projected trends in agricultural production indicate that emissions of N₂O and CH₄ are expected to increase rapidly in the coming years and will level off from 2040 onwards. The results confirm the positive relation between population increase and increased emissions from agricultural activities for most countries. However, for some countries (South Africa, China and Mexico) this relation was weak or absent. Although numerous factors (e.g. changes in international trade) may have scattered the relation and we were unable to explain this decoupling, it suggests that population growth can be possible without additional emissions. The variation between the different countries and farming systems is however large and mitigation measures at farm-level should be tailored to the wide diversity in environmental conditions, regional customs and farming systems.     

Selective herbivory on low-zinc phenotypes of the hyperaccumulator Thlaspi caerulescens (Brassicaceae)

Summary. The European plant Thlaspi caerulescens hyperaccumulates zinc in its leaves to concentrations exceeding 2 %. This may represent a defense against herbivory, as shown by reduced feeding on plants grown in high-zinc versus low-zinc substrates. However, the more evolutionarily relevant comparison involves plants whose metal content differs due to genetic rather than environmental causes. In our study, plants were grown in a uniform hydroponic solution containing 10 mg/l Zn. Foliar Zn concentrations were measured, and plants of contrasting Zn concentration were chosen for feeding trials using Pieris napi oleracea larvae. Comparisons revealed no statistically significant preferences when young larvae were used, but highly significant avoidance of high-Zn leaves by later-instar caterpillars, suggesting that hyperaccumulation could evolve in response to the selective pressures of herbivory.     

Life history correlates of alternative migratory strategies in American Dippers

Partial migration is thought to be a critical step in the evolution of avian migration, but data on the life history correlates of alternative migratory strategies are extremely limited. We have studied a partially migratory population of American Dippers since 1999. This population is composed of sedentary individuals (residents) that maintain the same territory year round and altitudinal migrants that share winter grounds with residents, but move to higher elevations to breed. We used seven years of data on individually marked birds to (1) determine if individuals consistently use the same migratory strategy, (2) determine if offspring have the same strategy as their parents, and (3) estimate reproductive and survival rates of the two migratory strategies. We evaluate hypotheses for the persistence of partial migration and discuss their implication for the evolution of migration in sedentary populations. Individual American Dippers rarely switched migratory strategy (4/169 monitored more than one year). An individual's strategy, however, was not always that of its parents, indicating that, while migratory behavior may have a genetic component, environmental or social conditions probably influence the migratory strategy that an individual adopts. Sedentary dippers consistently had higher annual productivity (approximately 1.4 more fledglings/year) than migratory dippers, but mark-recapture models suggested that migratory dippers may have slightly higher survival than residents (approximately 3.4%). Migrants were estimated to have lower lifetime reproductive success than residents because their higher survival was insufficient to offset their lower productivity. Our data suggest that alternative migratory strategies in American Dippers are unlikely to be a fixed genetic dimorphism that persists because the two strategies have equal fitness, or because the relative fitness of the two strategies fluctuates over time. Migratory strategies in American Dippers are more likely to be condition dependent, and the two strategies persist because migrants "make the best of a bad job" by moving to higher elevations to breed. Because migrants obtained no fitness benefits by moving to seasonal breeding territories, our data are consistent with the hypothesis that migration could evolve in sedentary populations if competition for limited resources forces some individuals to seek breeding opportunities outside their initial range.     

Sex differences in survival costs of reproduction in a promiscuous primate

In sexually promiscuous mammals, female reproductive effort is mainly expressed through gestation, lactation, and maternal care, whereas male reproductive effort is mainly manifested as mating effort. In this study, we investigated whether reproduction has significant survival costs for a seasonally breeding, sexually promiscuous species, the rhesus macaque, and whether these costs occur at different times of the year for females and males, namely in the birth and the mating season, respectively. The study was conducted with the rhesus macaque population on Cayo Santiago, Puerto Rico. Data on 7,402 births and 922 deaths over a 45-year period were analyzed. Births were concentrated between November and April, while conceptions occurred between May and October. As predicted, female mortality probability peaked in the birth season whereas male mortality probability peaked in the mating season. Furthermore, as the onset of the birth season gradually shifted over the years in relation to climatic changes, there was a concomitant shift in the seasonal peaks of male and female mortality. Taken together, our findings provide the first evidence of sex differences in the survival costs of reproduction in nonhuman primates and suggest that reproduction has significant fitness costs even in environments with abundant food and absence of predation.     

Green abalone, <Emphasis Type="Italic">Haliotis fulgens</Emphasis> infected with the agent of withering syndrome do not express disease signs under a temperature regime permissive for red abalone, <Emphasis Type="Italic">Haliotis rufescens</Emphasis>

All California abalone species have been shown to be susceptible to infection with the bacterial agent of abalone withering syndrome (WS), although expression of signs of the disease may vary between species and with environmental conditions. We examined thermal modulation of WS expression in green abalone Haliotis fulgens at temperatures mimicking El Niño (18.0°C) and La Niña (14.2°C) events in southern California. In contrast to results obtained from previous experiments with red abalone, H. rufescens, the higher temperature did not result in higher infection intensities of the causative agent of the disease nor increase in clinical signs of disease. These results demonstrate clear differences in thermal regulation of disease expression between abalone species, and provide further data suggesting that green abalone should be a target species of recovery efforts in southern California, where WS is endemic.     

The false limpet Siphonaria gigas, a simultaneous hermaphrodite, lives in pairs in rock fissures on the Pacific coast of Panama

The pulmonate limpet Siphonaria gigas, a simultaneous hermaphrodite, lives in the mid- to upper-intertidal zone on rocky shores in the tropical Eastern Pacific. Samples along five transects taken in June–July, 2004, on Culebra Point (8º54′N to 79º31′W), Republic of Panama, showed that 71 % of the population occurred in fissures, a significant preference for this habitat. Of 200 adults in 27 fissures, 150 lived side by side in pairs with their shells touching or nearly so, a significant deviation from the number of pairs expected given a random arrangement. Pair frequency did not increase with limpet density suggesting pairing was not an incidental consequence of crowding. Pair living was unknown in the genus Siphonaria, and is very uncommon among simultaneous hermaphrodites. Reproductive synchrony and restrictions on movement due to predation and environmental stress may limit opportunities for encountering and mating with multiple partners favoring pair living in S. gigas.     

Oxidation of Cyclic Ethers by Alkane‐Grown Mycobacterium vaccae JOB5

In this study we investigated the cometabolic oxidation of six cyclic ethers by alkane‐grown Mycobacterium vaccae JOB5. These ethers include, among others, tetrahydrofuran (THF), 1,4‐dioxane (14D), 1,3‐dioxolane (13DO), and tetrahydropyran (THP). Cells grown on propane, n‐butane, n‐pentane, isobutane, or isopentane oxidized all six ethers. Ether‐degrading activity was inhibited by acetylene in alkane‐grown cells and was largely absent from cells grown on dextrose‐containing media. Propane competitively inhibited THF oxidation. γ‐Butyrolactone (γBL) accumulated and was also further oxidized during THF oxidation by propane‐grown cells. In contrast, no products were detected during 14D oxidation. Propane‐grown cells also rapidly oxidized 3‐hydroxytertrahydrofuran and exhibited strong hemiacetal‐oxidizing activity in an assay following methyl formate production from mixtures of methanol and formaldehyde. These observations suggest γBL is likely generated during THF oxidation through further oxidation of 2‐hydroxytetrahydrofuran. Limited growth of strain JOB5 was supported by several cyclic ethers and the corresponding lactones and diols potentially derived from these compounds. However, strain JOB5 grew more readily on 4‐hydroxybutyrate, the product of γBL hydrolysis. The ability of strain JOB5 to productively assimilate THF‐derived metabolites during growth on n‐alkanes was examined in carbon‐limited batch cultures. Relative to C‐limited growth on n‐pentane alone, culture growth increased up to twofold in the presence of THF while no stimulation of growth was observed in comparable experiments conducted with n‐pentane and 14D. Our results are discussed in terms of their significance to our understanding of cyclic ether cometabolism and their potential impact on approaches for cyclic ether biodegradation in the environment. © 2013 Wiley Periodicals, Inc.