Capturing the Commons: Devising Institutions to Manage the Maine Lobster Industry

Capturing the Commons: Devising Institutions to Manage the Maine Lobster Industry . James M. Acheson. Lebanon, NH: University Press of New England, 2003. 264 pp.     

Adaptive Significance of a Small Heat Shock/{alpha}-Crystallin Protein (p26) in Encysted Embryos of the Brine Shrimp, Artemia franciscana

Encysted embryos of the primitive crustacean, Artemia franciscana,are among the most resistant of all animal life history stagesto extremes of environmental stress. This resistance has likelybeen acquired during evolutionary adaptation to their harshecological setting. In the laboratory, for example, some ofthese embryos survive more than 6 years of continuous anoxiawhile fully hydrated and at room temperature, a phenomenal capabilitythat can easily be related to their frequent encounters withanoxic conditions in nature. A small heat shock protein belongingto the -crystallin family of proteins, referred to as p26, appearsto play a central role in the stress resistance of these embryos.Our evidence shows that this protein is an important componentin their adaptive repertoire, and vital for the survival ofArtemia in nature.     

Electron transfer of dissolved organic matter and its potential significance for anaerobic respiration in a northern bog

We investigated electron transfer processes of dissolved organic matter (DOM) and their potential importance for anaerobic heterotrophic respiration in a northern peatland. Electron accepting and donating capacities (EAC, EDC) of DOM were quantified using dissolved H₂S and ferric iron as reactants. Carbon turnover rates were obtained from porewater profiles (CO₂, CH₄) and inverse modeling. Carbon dioxide was released at rates of 0.2–5.9 mmol m⁻² day⁻¹ below the water table. Methane (CH₄) formation contributed <10%, and oxygen consumption 2% to 40%, leaving a major fraction of CO₂ production unexplained. DOM oxidized H₂S to thiosulfate and was reduced by dissolved ferric iron. Reduction with H₂S increased the subsequently determined EDC compared to untreated controls, indicating a reversibility of the electron transfer. In situ redox capacities of DOM ranged from 0.2 to 6.1 mEq g⁻¹ C (EAC) and from 0.0 to 1.4 mEq g⁻¹ C (EDC), respectively. EAC generally decreased with depth and changed after a water table drawdown and rebound by 20 and −45 mEq m⁻², respectively. The change in EAC during the water table fluctuation was similar to CH₄ formation rates. In peatlands, electron transfer of DOM may thus significantly contribute to the oxidation of reduced organic substrates by anaerobic heterotrophic respiration, or by maintaining the respiratory activity of sulfate reducers via provision of thiosulfate. Part of the anaerobic electron flow in peat soils is thus potentially diverted from methanogenesis, decreasing its contribution to the total carbon emitted to the atmosphere.     

Winter herbivory by voles during a population peak: the relative importance of local factors and landscape pattern

1. We studied the relative role of local habitat variables and landscape pattern on vole–plant interactions in a system with grey-sided voles ( Clethrionomys rufocanus (Sund.)) and their favourite winter food plant, bilberry ( Vaccinium myrtillus L.). The study was conducted during a vole peak year (1992–93) in a tundra area in northern Norway.
2. Using Mantel statistics we were able to separate the direct effects of the spatial patterning of habitats and the indirect effects due to spatial aggregations of similar habitats.
3. Results indicate that knowledge about the explicit spatial patterning of patches does not improve our understanding of the system. Instead, two local factors, vegetation height and bilberry biomass, explained more than 50% of the variation in cutting intensity in winter (defined as the proportion of above-ground shoots cut). Increasing vegetation height increased, and increasing bilberry biomass decreased, the cutting intensity.
4. The conclusion that grey-sided voles are able to distribute themselves relative to habitat quality was also partially supported by our estimated over-winter persistence by voles in the various habitats. Vole persistence was uncorrelated with vegetation height, the important predictor of autumn vole density, but tended to correlate with the deviation from the relation between vegetation height and autumn vole density. This conforms to the expectations from the theory of ideal-free habitat distribution.
5. The cue for vole habitat choice, i.e. vegetation height, indicates that either predation or freezing risk is important for voles when selecting over-wintering habitat.     

Xylem water transport: is the available evidence consistent with the cohesion theory?

Since its introduction in the late 19th century, the so-called cohesion theory has become widely accepted as explaining the mechanism of the ascent of sap. According to the cohesion theory, the minimum standing vertical xylem tension gradient should be 0·01 MPa m⁻¹. When transpiration is occurring, frictional resistances are expected to make this gradient considerably steeper. The results of numerous pressure chamber measurements reported in the literature are generally regarded as corroborating the cohesion theory. Nevertheless, several reports of pressure chamber measurements in tall trees appear to be incompatible with predictions of the cohesion theory. Furthermore, the pressure chamber is an indirect method for inferring xylem pressure, which, until recently, has not been validated by comparison against a direct method. The xylem pressure probe provides a means of testing the validity of the pressure chamber and other indirect techniques for estimating xylem pressure. We discuss here the results of concurrent measurements made with the pressure chamber and the xylem pressure probe, particularly recent measurements made at the top of a tall tropical tree during the rainy season. These measurements indicate that the pressure chamber often substantially overestimates the tension previously existing in the xylem, especially in the partially dehydrated tissue of droughted plants. We also discuss other evidence obtained from classical and recent approaches for studying water transport. We conclude that the available evidence derived from a wide range of independent approaches warrants a critical reappraisal of tension-driven water transport as the exclusive mechanism of long-distance water transport in plants.     

The changing ecosystem of a shallow, brackish lake, Hickling Broad, Norfolk, U.K. II. Long-term trends in water chemistry and ecology and their implications for restoration of the lake

• 1 Hickling Broad underwent major changes from a clear water, charophyte-dominated state in the decades previous to 1970 to a turbid, phytoplankton-dominated state by the mid 1970s. These changes were complexly linked with increasing eutrophication by black-headed gulls and increased salinity due to agricultural changes in the catchment.
• 2 At the turn of the 1970s, the lake began to change again and during the 1980s a submerged plant community, of tall, vigorously growing species (e.g. Myriophyllum spicatum, Patamogeton pectinatus) had recovered, despite a major reduction in the roosting gull population, no change in salinity, and only small reductions in phytoplankton biomass and total phosphorus concentration.
• 3 Recovery of the plants may be linked to grazing of periphyton on them by an increased population of a mysid Neomysis integer which had been suppressed by toxicity from an alga, Prymnesium parvum formerly stimulated by the ingress of gull guano.
• 4 A cladoceran community present in the clear-water phase has not recovered and may be suppressed by continued high salinities. Further restoration of the lake requires displacement of the large phytoplankton biomass and this might best be contemplated by land use changes leading to lowered salinity and predicted recovery of grazing Cladocera.
• 5 Models are given which summarize the likely workings of the system in the early twentieth century, the mid-twentieth century, the 1970s and the late 1980s.