Factors Affecting Clonal Diversity and Coexistence

Recent genetic studies of asexually reproducing fishes in thegenus Poeciliopsis (Poeciliidae) revealed abundant variationin the form of multiple sympatric clones. Recurrent hybridizationsbetween sexual species provides the principal source of clonalvariation. The hybrids are spontaneously endowed with a clonalreproductive mechanism that perpetuates a high level of heterozygosity.Migration within and between river systems, and mutations, alsocontribute to clonal diversity in these fish. Coexistence amongdifferent clones and with the sexual ancestors depends in partupon specializations characteristic of individual clones. Clonalreproduction is an efficient mechanism for freezing a portionof the niche-width variation contained in the gene pool of themore broadly adapted, sexual ancestors. Multiclonal populationsachieve significantly higher densities relative to the sexualforms than do monoclonal populations. This relationship is afunction of the clonal variability upon which natural selectioncan act and upon the capacity of a multiclonal population tobetter exploit a heterogeneous environment through niche diversification.In all-female organisms such as Poeciliopsis, which are dependentupon sexual species for insemination, competitive abilitiesprobably are at a premium in the densely populated pools andarroyos of the Sonoran Desert. Competitive abilities are probablyless important for truly parthenogenetic clones which rely oncolonization abilities to escape from their sexual ancestorsand from other clones.     

An improved hexagon open‐top chamber system for stable diurnal and nocturnal warming and atmospheric carbon dioxide enrichment

The use of solar passive hexagonal open‐top chambers (POTCs) is a viable method for experimentally manipulating daytime air temperatures in low‐stature plant communities at high latitudes. Here we describe a new hexagon POTC‐based system that uses thermal inertia to increase overnight temperatures and variable chamber height to reduce overheating in summer. Field data collected in tall temperate grasslands show that the presence of thermal mass raised minimum and mean nighttime air temperatures by up to 1.5 °C while lowering chamber height, along with thermal mass, limited the development of extreme daytime chamber temperatures in summer. We also demonstrate that, by using a simple, inexpensive twin carbon dioxide (CO₂) injection system regulated by an infrared gas monitor, it is possible to generate targeted and stable atmospheric CO₂ enrichment within these chambers. These innovations significantly improve the conventional hexagon POTC design and represent a low‐cost method for assessing the effects of warming and CO₂ enrichment on low‐stature vegetation in low latitude environments.     

Will European soil-monitoring networks be able to detect changes in topsoil organic carbon content?

Within the United Nations Framework Convention on Climate Change, articles 3.3 and 3.4 stipulate that some voluntary activities leading to an additional carbon (C) sequestration in soils could be accounted as C sinks in national greenhouse gas inventories. These additional C stocks should be verifiable. In this work, we assess the feasibility of verifying the effects of changes in land use or management practice on soil organic carbon (SOC), by comparing minimum detectable changes in SOC concentration for existing European networks suitable for soil monitoring. Among the tested scenarios, the minimum detectable changes differed considerably among the soil-monitoring networks (SMNs). Considerable effort would be necessary for some member states to reach acceptable levels of minimum detectable change for C sequestration accounting. For SOC, a time interval of about 10 years would enable the detection of some simulated large changes in most European countries. In almost all cases, the minimum detectable change in SOC stocks remains greater than annual greenhouse gases emissions. Therefore, it is unlikely that SMNs could be used for annual national C accounting. However, the importance of organic C in soil functions, and as an indicator of soil condition and trends, underlines the importance of establishing effective national SMNs.     

Embryonic control of isocitrate lyase activity in the megagametophyte of ponderosa pine seeds

The intensity of the process of redistribution of the elements potassium, boron, iron, magnesium and calcium was determined by following the rate of accumulation of these elements into the fruits of apple (Malus domestica Borkh.) trees. The determination is based on the assumption that the process of primary distribution via the xylem becomes relatively unimportant with respect to supply along the phloem during the period of fruit growth. Thus a decreasing rate of accumulation for a phloem-immobile and xylem-mobile element will be seen during this period of growth, while an element which is mobile in both pathways will give a linear rate of accumulation when the supply by the root does not alter too much. In addition, the ratios of the contents in fruits and leaves were used as an indicator of the relative mobility in redistribution. In these experiments with apple, potassium and boron showed a high mobility. Magnesium and especially calcium showed a much lower mobility in redistribution than in the primary rate of supply. Iron was intermediary. The results, especially for boron and magnesium, are in contradiction to some of the data in the literature. Further studies are needed before these contrasting results can be explained.     

Role of the aquatic pathway in the carbon and greenhouse gas budgets of a peatland catchment

Peatland streams have repeatedly been shown to be highly supersaturated in both CO₂ and CH₄ with respect to the atmosphere, and in combination with dissolved (DOC) and particulate organic carbon (POC) represent a potentially important pathway for catchment greenhouse gas (GHG) and carbon (C) losses. The aim of this study was to create a complete C and GHG (CO₂, CH₄, N₂O) budget for Auchencorth Moss, an ombrotrophic peatland in southern Scotland, by combining flux tower, static chamber and aquatic flux measurements from 2 consecutive years. The sink/source strength of the catchment in terms of both C and GHGs was compared to assess the relative importance of the aquatic pathway. During the study period (2007–2008) the catchment functioned as a net sink for GHGs (352 g CO₂‐Eq m^?2 yr^?1) and C (69.5 g C m^?2 yr^?1). The greatest flux in both the GHG and C budget was net ecosystem exchange (NEE). Terrestrial emissions of CH₄ and N₂O combined returned only 4% of CO₂ equivalents captured by NEE to the atmosphere, whereas evasion of GHGs from the stream surface returned 12%. DOC represented a loss of 24% of NEE C uptake, which if processed and evaded downstream, outside of the catchment, may lead to a significant underestimation of the actual catchment‐derived GHG losses. The budgets clearly show the importance of aquatic fluxes at Auchencorth Moss and highlight the need to consider both the C and GHG budgets simultaneously.     

El Niño and dry season rainfall influence hostplant phenology and an annual butterfly migration from Neotropical wet to dry forests

We censused butterflies flying across the Panama Canal at Barro Colorado Island (BCI) for 16 years and butterfly hostplants for 8 years to address the question: What environmental factors influence the timing and magnitude of migrating Aphrissa statira butterflies? The peak migration date was earlier when the wet season began earlier and when soil moisture content in the dry season preceding the migration was higher. The peak migration date was also positively associated with peak leaf flushing of one hostplant (Callichlamys latifolia) but not another (Xylophragma seemannianum). The quantity of migrants was correlated with the El Niño Southern Oscillation, which influenced April soil moisture on BCI and total rainfall in the dry season. Both hostplant species responded to El Niño with greater leaf flushing, and the number of adults deriving from or laying eggs on those new leaves was greatest during El Niño years. The year 1993 was exceptional in that the number of butterflies migrating was lower than predicted by the El Niño event, yet the dry season was unusually wet for an El Niño year as well. Thus, dry season rainfall appears to be a primary driver of larval food production and population outbreaks for A. statira. Understanding how global climate cycles and local weather influence tropical insect migrations improves the predictability of ecological effects of climate change.