Restoring Remote Ecosystems

Indirect effects from climate‐driven changes in ecosystems that are remote from direct human activity pose challenges for ecological restoration. Significant and often indirect impacts on alpine ecosystems, the primary ecosystem under consideration in this article, threaten historical‐reference conditions and the viability of some species. The impetus for restoration is similar to projects involving more direct and proximate impacts, but the issues are more complicated in remote ecosystems. Restoration efforts in remote ecosystems might do more harm than good, and the effort required for effective restoration might be greater than easily justified given the shortfall of resources for restoring more heavily impacted ecosystems. The long duration and integration of impacts on remote landscapes pose a distinct set of challenges to restorationists. Intervening in remote ecosystems makes them less remote by definition (they are now affected by human agency). In this article, we examine scientific, technical, and moral issues and offer an initial model for assessing the appropriateness of restoring remote landscapes.     

A partially buried site in homologous HPr proteins is not optimized for stability

The energetic consequences of site-specific replacement of a residue at a partially buried site in the two homologous HPr proteins from Escherichia coli and Bacillus subtilis is described. We determined previously that the replacement of a partially buried Lys residue with Glu at position 49 in E.coli HPr increased the conformational stability of the protein substantially because the side-chain of the latter residue could act as a hydrogen-bond acceptor. Here, we extend this analysis to other side-chains with different chemical properties and abilities to form hydrogen bonds to compare the properties of this position in the backgrounds of two different homologous HPr proteins. We find that the variants with polar residues that can form a tertiary hydrogen bond with a nearby site in the protein are more stable than either hydrophobic residues or polar residues that become buried yet are incapable of forming a new hydrogen bond. Furthermore, the protein with the wild-type residue in each HPr variant is not among the most stable of the proteins studied. These results suggest a general strategy for designing variants in which the overall stability of a protein can be modulated in a defined fashion.     

Myofiber angle distributions in the ovine left ventricle do not conform to computationally optimized predictions

Recent computational models of optimized left ventricular (LV) myofiber geometry that minimize the spatial variance in sarcomere length, stress, and ATP consumption have predicted that a midwall myofiber angle of 20 degrees and transmural myofiber angle gradient of 140 degrees from epicardium to endocardium is a functionally optimal LV myofiber geometry. In order to test the extent to which actual fiber angle distributions conform to this prediction, we measured local myofiber angles at an average of nine transmural depths in each of 32 sites (4 short-axis levels, 8 circumferentially distributed blocks in each level) in five normal ovine LVs. We found: (1) a mean midwall myofiber angle of -7 degrees (SD 9), but with spatial heterogeneity (averaging 0 degrees in the posterolateral and anterolateral wall near the papillary muscles, and -9 degrees in all other regions); and (2) an average transmural gradient of 93 degrees (SD 21), but with spatial heterogeneity (averaging a low of 51 degrees in the basal posterior sector and a high of 130 degrees in the mid-equatorial anterolateral sector). We conclude that midwall myofiber angles and transmural myofiber angle gradients in the ovine heart are regionally non-uniform and differ significantly from the predictions of present-day computationally optimized LV myofiber models. Myofiber geometry in the ovine heart may differ from other species, but model assumptions also underlie the discrepancy between experimental and computational results. To test the predictive capability of the current computational model would we propose using an ovine specific LV geometry and comparing the computed myofiber orientations to those we report herein.     

Soil Nematodes in Terrestrial Ecosystems

There has been much work on plant-feeding nematodes, and less on other soil nematodes, their distribution, abundance, intrinsic properties, and interactions with biotic and abiotic factors. Seasonal variation in nematode fauna as a whole is correlated with factors such as moisture, temperature, and plant growth; at each site nematode distribution generally reflects root distribution. There is a positive correlation between average nematode abundance and primary production as controlled by moisture, temperature, nutrients, etc. Soil nematodes, whether bacterial feeders, fungivores, plant feeders, omnivores, or predators, all influence the populations of the organisms they feed on. Although soil trematodes probably contribute less than 1% to soil respiration they may play an important role in nutrient cycling in the soil through their influence on bacterial growth and plant nutrient availability.     

Primary Production in Terrestrial Ecosystems

"Primary production" refers to energy fixed by plants. The totalamount of energy fixed is usually called "gross production."A certain fraction of gross production is used in respirationby the plants; the remainder appears as new biomass or "netprimary production." Thus for a single plant or a communityof green plants: Net Primary Production = Gross Production – Respiration(of Autotrophs) Similar relationships occur in ecosystems except that the organicmatter and respiration of heterotrophs must be included. Theincrease in total organic matter is "net ecosystem production";respiration is the total respiration of the green plants (autotrophs)and the animal community and decay organisms (heterotrophs).Gross production is of course identical to that of the plantcommunity. Thus for an ecosystem: Net Ecosystem Production = Gross Production – Respiration(of Autotrophs and Heterotrophs) Study of these attributes of terrestrial ecosystems is difficult,both because of the complex interrelations of the processesinvolved, and because of the problems of working with systemsas large as whole forests. Three approaches are in use: (1)Harvest techniques measure weight increase (and caloric equivalentand chemical composition) of net production. A refinement otthis approach based on "dimension analysis" has made possibleimportant recent advances in the study of forests. Other techniquesapproach gross production and respiration through measurementof exchange of gases, especially CO₂. These include: (2) Enclosurestudies, involving measurements of CO₂ exchange in plastic enclosuresof parts of ecosystems and (3) Flux techniques based on measurementof CO₂ levels in the environment. All three approaches are beingapplied to a forest at Brookhaven National Laboratory to determinethe production equation of this ecosystem. Results to date have established general ranges of such parametersof ecosystems as total biomass, total surface area of leavesand of stems and branches, rates of decay of organic matterin soils, rates of production of roots, and rates of photosynthesisand respiration under different environmental conditions. Inthe Brookhaven forest net primary production is 1124 dry g/m²/yr(with an energy equivalent of 492 cal/cm²/yr), and gross productionis about 2550 dry g/m²/yr; the producers or green plants thusrespire 56% of their gross production. Net ecosystem productionis 422 dry g/m²/yr in this young forest. The ratio of totalrespiration to gross production is a convenient expression ofsuccessional status; a value of 0.82 for the Brookhaven forestindicates that this is a late successional community, but notin steady-state or climax condition (1.0). A leaf surface areaof 3.8 m² per m² of ground surface intercepts sunlight energy,and the ratio of net primary production to incident visiblesunlight energy gives a net efficiency of primary productionof 0.0088. These and other functional characteristics of ecosystems arecurrently important topics of research—involving understandingof communities as biological systems, evaluation of the potentialof environments to support life and man's harvest; and understandingof the fundamental meaning and consequences of man's alteration,exploitation, and pollution of ecosystems.     

Ecosystems biology of microbial metabolism

The metabolic capabilities of many environmentally and medically important microbes can be quantitatively explored using systems biology approaches to metabolic networks. Yet, as we learn more about the complex microbe-microbe and microbe-environment interactions in microbial communities, it is important to understand whether and how system-level approaches can be extended to the ecosystem level. Here we summarize recent work that addresses these challenges at multiple scales, starting from two-species natural and synthetic ecology models, up to biosphere-level approaches. Among the many fascinating open challenges in this field is whether the integration of high throughput sequencing methods and mathematical models will help us capture emerging principles of ecosystem-level metabolic organization and evolution.     

Industrial Ecosystems as Food Webs

Colocated industries exchange products and by-products in ways reminiscent of the exchange of resources in biological ecosystems. To better understand these "industrial ecosys-tems", we have applied food-web theory to a set of 19 actual and hypothetical eco-industrial parks and integrated biosys-tems. We find a linear relationship between number of industrial tenants and number of linkages among them and connectance values of 0.5 to 0.6 (typical of biological ecosystems). The results may provide initial perspective on designing eco-industrial parks to maximize the utilization of resources and minimize the generation of wastes. Increased connectance in industrial ecosystems, however, does not necessarily imply increased stability or improved environmental performance.