Browsing by Subject "productivity"
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Item Biodiversity simultaneously enhances the production and stability of community biomass, but the effects are independent(Ecological Society of America, 2013) Cardinale, Bradley J; Gross, Kevin; Fritschie, Keith; Flombaum, Pedro; Fox, Jeremy W; Rixen, Christian; Van Ruijven, Jasper; Reich, Peter B; Scherer-Lorenzen, Michael; Wilsey, Brian JTo predict the ecological consequences of biodiversity loss, researchers have spent much time and effort quantifying how biological variation affects the magnitude and stability of ecological processes that underlie the functioning of ecosystems. Here we add to this work by looking at how biodiversity jointly impacts two aspects of ecosystem functioning at once: (1) the production of biomass at any single point in time (biomass/area or biomass/volume), and (2) the stability of biomass production through time (the CV of changes in total community biomass through time). While it is often assumed that biodiversity simultaneously enhances both of these aspects of ecosystem functioning, the joint distribution of data describing how species richness regulates productivity and stability has yet to be quantified. Furthermore, analyses have yet to examine how diversity effects on production covary with diversity effects on stability. To overcome these two gaps, we reanalyzed the data from 34 experiments that have manipulated the richness of terrestrial plants or aquatic algae and measured how this aspect of biodiversity affects community biomass at multiple time points. Our reanalysis confirms that biodiversity does indeed simultaneously enhance both the production and stability of biomass in experimental systems, and this is broadly true for terrestrial and aquatic primary producers. However, the strength of diversity effects on biomass production is independent of diversity effects on temporal stability. The independence of effect sizes leads to two important conclusions. First, while it may be generally true that biodiversity enhances both productivity and stability, it is also true that the highest levels of productivity in a diverse community are not associated with the highest levels of stability. Thus, on average, diversity does not maximize the various aspects of ecosystem functioning we might wish to achieve in conservation and management. Second, knowing how biodiversity affects productivity gives no information about how diversity affects stability (or vice versa). Therefore, to predict the ecological changes that occur in ecosystems after extinction, we will need to develop separate mechanistic models for each independent aspect of ecosystem functioning.Item Distribution, Composition and Biomass of the Crustacean Zooplankton Population in Western Lake Superior(Water Resources Research Center, University of Minnesota, 1973-08) Conway, J.B.; Odlaug, T.O.; Olson, T.A.; Ruschmeyer, O.R.Although data were collected for two years, 1970 and 1971, the major portion of this research was carried out the second year. This research took place in western Lake Superior and most of the data were collected at two stations, Larsmont and Stony Point, which were twenty miles northeast of Duluth. Each of these stations included two sites, one a half mile and the second two miles from shore. The other area where samples were collected was at the Little Marais and Sugar Loaf Cove stations, some 70 miles north of Duluth. The major purposes of this research were to study the productivity and the vertical, seasonal and horizontal distribution of the crustacean zooplankton population in western Lake Superior. A limited study of the biology of the copepod, Limnocalanus macrurus, was also conducted. Productivity at the Larsmont and Stonv Point area averaged 323 crustaceans per 100 liters of water, and 60 grams per square meter (based on a fifty meter water column). Productivity at the Little Marais and Sugar Loaf Cove area averaged 95 crustaceans per 100 liters and 37 grams per square meter. In general, productivity decreased as the depth increased from zero to 50 meters. If a thermocline was present, then both the toted number of crustaceans and the biomass became relatively scarce below twenty meters. Cladocerans were most frequent1y found in the upper ten meters of the water column whereas copepods were present at every level. Adult copepods were usually heavier than adult cladocerans and it was not unusual to find the mean weight of an organism at 50 meters ten or more times that of one at five meters. Productivity at the Larsmont and Stony Point area was bimodal during the sampling season; the first peak occurred in July and contained primarily copepods and the second, which was the seasonal maximum, occurred in September and contained both copepocls and cladocerans. Surface water temperatures were also bimodal during the sampling season; the peak recorded in July was thirteen degrces centigrade and sixteen degrees was reached in September. The cladoceran, Bosmina, became abundant after the water temperature reached five degrees in July, Another cladoceran, Dapnia, Replaced Bosmina in September when the water temperature was about eleven degrees. Ephippia, the overwintering stage of Daphnia first appeared in late August. Three copepods, Diaptomus, Limnocalanus, and Cyclops were present during most of the sampling season. Limnocalanus was present at all depths from June to early August, but was most numerous at ten meters. When the water temperature warmed above twelve degrees, the population shifted downward and was usually below the thermocline during the davlight hours. At this time, they were most abundant at 40 meters, The copepod, Epischura, was numerous in the upper lavers after the water warmed above eleven degrees. Productivity differences were found between the various sites and stations. These differences point to the lack of homogeneity in the horizontal distribution of the crustacean zooplankton population and support the phenomenon of “zooplankton patchiness". Productivity levels at the Little Marais and Sugar Loaf Cove area were from one-third to two- thirds of those at Larsmont and Stony Point. The Larsmont station was slightly more productive than Stony Point. The Stony Point inshore site was slightly more productive than the offshore site. The period of maximum productivity occurred at the Larsmont inshore site amd at both Stony Point sites in September. Maximum productivity was recorded at the Larsmont offshore site in July. A phytoplankton bloom was observed at the Stony Point station on July 20, 1971, but was not seen on the same day at the Larsmont station. Limnocalanus macrurus contrihuted to the greatest percentage of the crustacean biomass (often more than 90 percent) at depths 30, 40 and 50 meters in western Lake Superior. The male to female ratio established was 1:2. The mean lengths of mature males and females were, 2.09 and 2.16 millimeters, respectively. The length-weight correlation was: Dry weight (mg/100) = 3.31 length (mm) - 2.95. Two cladocerans, new to Lake Superior, were identified. They were: Alona guttata Sars and Holopedium gibberum Zaddach.Item Effects of Enrichment on Lake Superior Periphyton(Water Resources Research Center, University of Minnesota, 1973-05) Krogstad, B.O.; Nelson, R.R.; Odlaug, T.O.; Olson, T.A.; Ruschmeyer, O.R.The primary objective of this research as carried out in the summer and fall of 1969 and 1970 was to determine the possible changes which would take place in Lake Superior periphvton when polluting or enriching substances were added to the lake Hater. To this end, two natural rock basins were constructed at the lakeside along the north shore at Castle Danger, Minnesota for the purpose of exposing naturcll1y grown and regrowth periphyton to higher-than-normal levels of phosphate and nitrate. At weekly intervals, samples were collected and productivity was measured by enumeration of organisms, chlorophyll analysis, and weight, dry and organic. Lake Superior periphyton responds dramatical1 y to increased additions of phosphorus and nitrogen. If the near-shore area of Lake Superior ever received nutrients, such as those added to the experimental test pool at Castle Danger, a drastic change in the Lake.'s biota could occur. For example, as enrichment increased, the predominant clean-water diatom forms could eventually be replaced by the more tolerant green or blue-green algae. In addition, the very composition of the macrobenthic forms found in Lake Superior could be altered as a result of their dependence on the periphyton, which, as primary producers, form the first link in the food chain. Likewise, certain fish which depend on benthic organisms for their food may be adversely affected as an indirect result of a changing periphyton community. Having established that enrichment of Lake Superior water will drnmatically change the normal periphyton growth, another baseline has been established for future reference in the event that phosphorus and nitrogen rich wastes should be added to the 1ake. If certain types of algae appear as replacements of the normal flora now characterizing the periphyton and the productivity increases, one will have a means [or assessing the possible changes taking place in the water quality of Lake Superior.Item Essays on the Industrial Organization of Ocean Shipping(2021-05) Bailey, SamuelThis dissertation consists of two chapters on the industrial organization of ocean shipping. In the first chapter, I study the investment decisions of US ports. Transportation infrastructure is characterized by two opposing forces: economies of scale that encourage centralization, and spread-out consumers that encourage dispersion. These forces may not be correctly balanced in the United States as decisions are made by many different regional authorities which receive large federal subsidies. I study seaports during a period when those on the East Coast were making investments to prepare for the larger vessels that could navigate an expanded Panama Canal. With data on all container imports and capital costs of major US ports, I estimate a model of the investment game that port authorities play. Competing ports invest more than a social planner would, even allowing for deviations from profit maximization, because they do not internalize their business stealing effects on others. In particular, the $1.7 billion expansion of the Port of New York and New Jersey would not have been chosen by a coastal authority. Social surplus would be over a billion dollars higher with coordination, the equivalent of about one year's worth of revenue for all the East Coast ports. Lowering federal subsidies appears to lower much of the gap. In the second chapter, I show how port productivity changed after a historic labor agreement. Across many industries, employers and workers often argue over technology adoption. In 2008, the International Longshore and Warehouse Union signed a contract agreeing that all ports on the US West Coast could fully automate their terminals, recognizing there would be job losses. Using a new, ship-level dataset of the labor it takes to unload ships, I study changes in productivity after the contract was signed and after one port automated. Having the ship-level data is important, as I show more aggregate measures would produce misleading estimates. I find productivity increased about 25% as a result of the new contract and an additional 15% among the port that actually automated. I find that the effects did not completely persist through the 2015 contract, even though the automation clause did not change, and suggest possible ways employee-employer relations may alter outside the written contract.Item Financing the Future: Advancing Excellence Through Cost Reductions and Productivity, June 2011(University of Minnesota, 2011-06) Bruininks, Robert H.Following the release of the Future Financial Resources Task Force report in fall of 2009 and its presentation to the University of Minnesota’s Board of Regents, President Robert Bruininks adopted all five task force recommendations and appointed a cross-functional, University-wide team to begin implementing them.Item Fine-root biomass from Cloquet and Auclair IDENT sites(2022-03-14) Schuster, Michael J.; Williams, Laura J; Stefanski, Artur; Bermudez, Raimundo; Messier, Christian; Belluau, Michaël; Paquette, Alain; Gravel, Dominique; Reich, Peter B; schuster@umn.edu; Schuster, Michael JMean fine-root biomass data gathered from the IDENT experiments in Cloquet, MN and Auclair, Quebec.Item Nitrogen mineralization and productivity in 50 hardwood and conifer stands on diverse soils(Ecological Society of America, 1997) Reich, Peter B; Grigal, David F; Aber, John D; Gower, Stith TThe generality of relationships between soil net nitrogen (N) mineralization, aboveground N cycling, and aboveground net primary production (ANPP) for temperate forest ecosystems is unclear. It is also not known whether these variables and their relationships differ between evergreen and deciduous forests, or across soil types. To address these questions we compiled data on annual rates of in situ net N mineralization and ANPP for 16 conifer and 34 hardwood forests, including plantations and natural stands on a range of soils at six locations in Wisconsin and Minnesota, USA. For 31 natural stands, 48 stands with native species (including plantations), and all data, ANPP increased linearly with annual net N mineralization rates. Native evergreen conifer and two deciduous hardwood types (oaks and mesic hardwoods) followed similar patterns in this regression, indicating common functional relationships at the ecosystem level. The relationship of N mineralization and ANPP differed between finer textured Alfisol soils and sandier Entisols, with higher ANPP at any given N mineralization level in Alfisols. A multiple regression of N mineralization on soil texture (percentage silt plus clay), litterfall N, and mean annual temperature explained 81% of the variance in annual N mineralization for natural stands, and a multiple regression of ANPP on soil texture and annual N mineralization rate explained 83% of the variance in ANPP. Naturally regenerated forest types differed in mean annual net N mineralization, litterfall N, and ANPP, and all were greater in oaks than in mesic hardwoods or conifers, respectively. However, differences among the 50 stands and six locations were largely a result of differences in soils and stand origin. For all natural hardwood stands, ANPP and N mineralization were greater on fine-textured Alfisols than on sandy Entisols. For evergreen conifers, ANPP and N mineralization were greater in plantations on Alfisols than in natural stands on Histosols, Entisols, or Spodosols. Hardwood and evergreen conifer stands did not differ significantly in ANPP or N mineralization on comparable soils and stand origin: they differed neither as plantations on Alfisols nor as natural stands on Entisols. This suggests that observed average differences among natural forest types in ANPP and N mineralization resulted largely from variation in their distribution on differing soils, and not from feedback effects on N mineralization or differing productivity per available N. These data suggest that, at a regional scale, at least half of the variation in ANPP can be attributed to variation in annual N mineralization. Both ANPP and N mineralization differ more strongly with soil type/parent material than with forest type; ANPP at any given level of N mineralization is higher on silty/loamy Alfisols than on sandy Entisols, Histosols, or Spodosols, but not different for coniferous and broad-leaved deciduous species. There is no indication of N saturation of ANPP within the range of natural N availability in these forests.Item Response of Nearshore Periphyton in Western Lake Superior to Thermal Additions(Water Resources Research Center, University of Minnesota, 1974-10) Drown, D.B.; Odlaug, T.O.; Olson, T.A.The intent of this research was to ascertain what effects a temperature increase in the order of 10 degrees to 12 degrees C would have on the near-shore periphyton assemblage of Western Lake Superior. To this end a field station, complete with holding tanks and a hot water source, was constructed on a rock ledge of the Lake Superior shore near Castle Danger, Minnesota. During the summer and fall of 1971 and 1972 periphyton covered rocks from the local area of the lake were placed in the experimental holding tanks where they were exposed to a continuous flow of lake water. In addition, denuded rocks were included as part of a regrowth study. One system provided a flow-through of unheated lake water while in the other the temperature was raised above ambient. Growth patterns were followed under both sets of conditions. Periphyton samples were collected on a weekly basis from the ambient control and heated water tanks and were analyzed for photosynthetic pigment concentration, dray and organic weight and total cell count. A quantitative and qualitative examination of the phyletic distribution of algae from the two systems was emphasized. Some of the more important findings and conclusions were as follows: 1. Diatoms were found to be the most prevalent algal type in both heated and cold water tanks. 2. Normal populations of Lake Superior periphytic diatoms (control), in terms of percent composition of the entire assemblage, were not greatly altered by the temperature increases used during the course of this study. 3. Three of the most common algal genera; Synedra, Navicula, and Achnanthes, showed essentially no difference in maximum growth levels attained in cold or heated water other than the fact that, in heated regrowth samples, peak concentrations were reached in a shorter period of time. 4. Several of the periphytic diatoms common to Lake Superior would continue to survive at temperatures well in excess of normal seasonal maxim. 5. Lake Superior contains genera of non-filamentous green algae which have species capable of adapting to extremely high ambient water temperatures. 6. The warm water system was more favorable to green filamentous algae, such as Mougeotia and Zygnema, than was the cold water system. 7. A prevalent green alga found in Lake Superior, Ulothrix zonata, was inhibited by the warmer water conditions. 8. In general, green algae common to Lake Superior are favored by temperatures in excess of those normally found in the lake. 9. Under conditions of these experiments blue-green algae did not increase as a result of thermal addition. 10. Analysis of pheo-pigments indicated that a substantial amount of “apparent” chlorophyll a was actually pheophytin a, a degradation product. Hence, the pheophytin analysis is important to any study dealing with the chlorophyll content of periphyton. 11. Concentrations of pheo-pigments were higher in the cold water tank than in the warm water system. 12. Supplementary observations have suggested that a separate invertebrate community occupied each of the tanks. While the above findings and conclusions indicate that a great deal more needs to be learned of the effects of thermal additions on Lake Superior, this study has pointed out that, if near-shore areas of the lake were warmed to the extent that could occur as the result of a thermal-electric generating station discharge, changes in the phyletic composition of the local periphyton community could be expected. The very nature of a change from diatoms to greens could have serious repercussions on benthic grazers and indeed the entire foodweb of the affected area.